PB-243 028
A STUDY OF THE FEASIBILITY OF REQUIRING THE FEDERAL
GOVERNMENT TO USE RETREADED TIRES
SMITHERS SCIENTIFIC SERVICE, INCORPORATED
PREPARED FOR
ENVIRONMENTAL PROTECTION AGENCY
MAY 1975
DISTRIBUTED BY:
KJQl
National Technical Information Service
U. S. DEPARTMENT OF COMMERCE
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A STUDY OF THE FEASIBILITY
OF REQUIRING THE FEDERAL GOVERNMENT
TO USE RETREADED TIRES
This final report (SW-105c) describes work performed
for the Federal solid waste management programs under contract No. 68-01-2906
to SMITHERS SCIENTIFIC SERVICE, INC.
and is reproduced as received from the contractor
U.S. ENVIRONMENTAL PROTECTION AGENCY
1975
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BIBLIOGRAPHIC DATA 1. Report No. 2.
SHEET EPA/SW-105C
4. Title and Subtitle
A Study of the Feasibility of Requiring the Federal Government
to Use Retreaded Tires
7, Author(s)
William A Rainc^ Dawirl F Ulilli^mt;
9. Performing Organization Name and Address
Smithers Scientific Service, Inc.
Akron, Ohio 44303
12. Sponsoring Organization Name and Address
Environmental Protection Agency
Office of Solid Waste Management Programs
Washington, D.C. 20460
3. Recipient's Accession No.
5. Report Datepreparation
5/75 Datp
6.
8. Performing Organization Rept.
No.
10. Project/Task/Work Unit No.
11. ContractAjfanrNo".-
68-01-2906
13. Type of Report & Period
Covered
14.
15. Supplementary Notes
16. Abstract^
Tires, which represent only 1.5 percent of municipal solid waste, pose
a special solid waste problem because tires are difficult to dispose of by
conventional methods. A partial solution to this problem can be achieved through
the reduction of tire waste. One waste reduction option suitable for this
is retreading.
Thrs report reviews the topic areas pertinent to retreading including the
mechanics of tire retreading, the performance of retreaded tires, improving
retreadability, and the economics of retreading. Based on these topics the
report evaluates the feasibility of requiring the Federal Government to use
retreaded passenger tires. The report also examines the solid waste and
energy benefits that would be derived by both the Federal Government and the
general public through the use of retreaded passenger tires. ,
17. Key Words and Document Analysis. 17o. Descriptors
Waste reduction, tires, retreading
7b. Identificrs/Open-Ended Terms
7e. COSAT! Field 'Group
8. Availability Statement
19.. Security Class (This
Report)
UNCLASSIFIED
121. No. of Pages
20. Security Class (This
Page
UNCLASSIFIED
FORM NTis-35 (REV. 10-73) ENDORSED BY ANSI AND UNESCO.
THIS FORM MAY BE REPRODUCED
USCOMM-DC 8265-P74
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This report as subrnftted by the grantee or contractor ‘as not beer
technically reviewed by the U.S. Environr ental Protection Agency (EP ).
Publication does not signify that the contents necessarily reflect the
views and policies of EPA, nor does mention of ccrii ercial products
constitute endorsement or reconinendation for use by the U.S. Government.
An environmental protection publication (SW—105c) in the solid waste
management series.
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CONTENTS
Introduction 1
Summary 4
Conciusions 11
Recomendatioris 13
Tire Retreading 14
Tire Retreading Process 15
Tire Retreading Problems 18
Performance of Retreaded Tires 22
Tire Testing 23
Retreaded Passenger Tire Failures 50
Interstate Highway Roadside Survey 54
Non-Passenger Tire Retreads 56
Improving Retreadability 60
Tire Design 60
Reasons For Casing Rejection 63
Tire Maintenance 69
Improved Retreadability by Tire Design 69
Economics of Retreading 73
Passenger Tire Retreading Cost Factors 73
The Feasibility of Requiring the Federal 76
Government to Use Retreaded Tires
Costs and Benefits to the Federal Government 77
Using Retreaded Passenger Tires
Appendix 98
(. Iossary ot erms £U9
References 116
LIST OF PHOTOGRAPHS
Photograph 1 Bias Construction 99
Photograph 2 Belted Bias Construction 100
Photograph 3 Radial Ply Construction 101
Photograph 4 Bead Damage 102
Photograph 5 Excess Treathiear 103
Photograph 6 Exposed Belt Edge 104
Photograph 7 Broken Belt 105
Photograph B Belt Edge Separation 106
Photograph 9 Sidewall WeatherCheckirig 107
Photograph 10 Tread Cut 108
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LIST OF FIGURES
Figure 1 Collection and Distribution of Used 64
Tire Casings to the Retreader
Figure 2 Design Considerations to Reduce Belt 72
Edge Separations
FIgure 3 Dollar Savings Rel-ated to Percent of Federal 83
Retreads
Figure 4 Federal Government Discarded Tires Related 85
to Percent Retreads
Figure 5 U.S. Discarded Tires Related to Percent 86
Retreads
Figure 6 Solid Waste Generated Annually Related 90
to Federal Government Passenger Tire Retreads
Figure 7 Solid Waste Generated Annually Related 91
to U.S. Passenger Tire Retreads
Figure 8 Annual Material Requirements Related to 93
Federal Government Passenger Tire Retreads
Figure 9 Annual Material Requirements Related to 96
U.S. Passenger Tire Retreads
LIST OF TABLES
Table 1 DOT-ARA Tests-Bias Ply Tires 27
Table 2 DOT-ARA Tests-Belted Bias Tires 28
laule Tire Faiiure vs. Type of Construction
Use of Holography
Table 4 DOT-TSC Tire Failure by Retreader 34
Table 5 DOT Testing of Retreaded Tires to FMVSS 109 35
(By Retreader)
Table 6 DOT Testing of Retreaded Tires to FMVSS 109 37
(By Construction)
Table .7 GSA Retreaded Tire Test (Motor Pool) 39
Table 8 GSA Motor Pool Test (Failure by Contractor) 41
Table 9 QPL Phase—GSA Test 42
Table 10 QPL-GSA Test (Failure Modes) 44
Table 11 GSA Test (Control and Non-Control) 47
Table 12 GSA-QPL New Tire Test 48
Table 13 Retread Adjustment Factors 51
Table 14 Interstate Highway Roadside Survey 55
Table 15, Reason for Passenger Tire Casing Rejection 66
Table 16 Reasons for Casing Rejection 80
Table 17 Effect of Retreading on Number of Tires 87
Discarded Annually by Federal Governcterit
Table 18 Effect of Retreading on Number of Tires 88
Discarded Annually by U.S.
Table 19 Effect of Retreading on Crude Ofl 94
Requirements for Federal Government Passenger
Tire anufacture
Table 20 Effect of Retreading on Crude Oil 97.
Requirements for U.S. Passenger Tire
1anufacture
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INTRODUCTION
More than five billion pounds of discarded tires end up as solid municipal
waste every year. This represents about 1.5 percent of the total municipal solid
waste disposed of annually, but it is an especially troublesome part of the solid
waste disposal problem. These 180 million tires are extremely difficult to dispose
of by conventional methods such as incineration or landfills *
It is estimated that about 45 million tires per year are recycled by means of
retreading. Retreaded passenger tires currently represent less than 20 percent
of the total of new and retreaded tires sold as replacements. For truck and bus
tires the percentage is over 30 percent. Obviously, one way to reduce this solid
waste problem is to increase the percentage of tires being retreaded.
A second benefit to be derived from the increased recycling of tires by retread-
ing, will be a reduction in petroleum consumption. Industry sources have estimat-
ed that it requires seven gallons of crude oil to make the average passenger tire.
Five gallons as raw material feed stock, and two gallons to supply the required
energy. If this estimate is correct, then more than two billion gallons of crude oil
were consumed in 1973 to manufacture 200 million passenger tires and 37 million
truck and bus tires. Nearly two-thirds of the crude oil was required for the
manufacture of passenger car tires.
Truck and bus operators have long accepted the economic advantages of using
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quality retreaded tires and there is little room for improvement in this area. How-
ever, passenger tires account for two-thirds of the tire disposal problem
and two-thirds o the crude oil consumption, and the potential does exist for a
major increase in the number of passenger tires presently b&ng retreaded.
Any strategy for significantly increasing the demand for retreaded tires will
have to be based on sound evidence that properly retreaded tires will meet the
same safety criteria as new tires.
If it can be estEblished that a properly designed new tire, properly main-
tained, and then properly retreaded, will continue to perform in such a manner
as to meet new tire performance standards, or the equivalent, the first step
toward increasing the acceptance of retreaded tires will have been taken.
However, barring reaction to any outside forces, such as drastically
increased new tire prices or shortages as a result of the energy crisis, simple
performance tests and standards alone will not make a major impact on the
average consumer. Only extensive operating data from actual on-the-road
experience can be expected to have any influence.
The Federal Government operates more than 400,000 vehicles, including
90,000 sedans and station wagons. Not only is this a source of all types of
vehicles, traveling all kinds of terrain, but government purchasing and maint-
enance procedures lend themselves to a well controlled and documented test fleet.
As a first step toward investigating the increased use of passenger tire
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retreading as a means of resource recovery and reducing solid waste, this
contract (EPA No. 68-01-2906) was awarded to study the feasibility of requiring
the Federal Government to use retreaded tires 4
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SUMMARY
Tire Retreading
The tire retreading industry is more than 60 years old, but retreading did not
make a serious impact in the tire market until the 19 40’s and World War II. At the
peak of the war years, 20 million new passenger tires were produced and 30 million
passenger tires were retreaded. , in post-war 1948 nearly 70 million new
passenger tires were produced while retreads plummeted to 5 million. Passenger
tire retreading gradually recovered through the fifties and has stabilized at
approximately 35 million units per year for the last 10 years. This represents less
than 20 percent of the replacement market. Truck and bus retreading also matured
during the war years, but after stabilizing at 7 1/2 million units per year through
the early 1960’s, a steady growth started about 1966 and truck and bus retreads
now exceed 10 million units per year and represent over 30 percent of the
replacement market
The American retreading industry is basically one of small shops. There are
more than 5,000 retread manufacturers with 50 percent having an annual sales
volume of less than $250 ,000 while less than 4 percent have a sales volume in excess
of $1,000,000 per year.
Performance of Retreaded Tires
The overall performance of a tire is generally measured in terms of its perfor-
mance in respect to high speed, tread wear, traction, endurance, and strength.
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Available test data on the performance of retreaded passenger tires is very
limited and inconclusive. Independent performance tests on retreaded tires have
been conducted by The Department of Transportation (DOT) and The General
Services Administration (GSA) in an effort to determine the performance of
retreaded passenger tires currently marketed. These tests show extreme quality
variations between retreaders. These quality variations are such that the “average”
retreaded passenger tire has a performance level significantly below that of a new
tire. However, there are instances where retreaded passenger tires have been
shown to have performance properties approaching or equaling that of new tires.
Also, the trucking and airline industries have had exceptionally good experience
with retreaded tires. All of this Indicates that quality retreads can be made.
Unfortunately, the only significant, independent test programs conducted to date
on retreaded passenger tires have been oriented toward an evaluation of existing
retreaded tires available on the open market. There have been no independent
tests, conducted c’n a statistically significant size sample, to determine the
performance of retreaded passenger tires manufactured under optimum and
controlled conditions of casing selection, inspection and retread processing.
There is little reliable operating or fleet data available for passenger tire
retreads such as is available for truck or aircraft retreaded tires. Retreaded
passenger tires are occasionally used for in—city fleet operation by taxi cabs or
utilities, but this experience is totally unrelated to the typical high speed and
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endurance levels to which the average passenger tire is subjected.
Although there is an absence of both test data and fleet operating experience,
it is highly probable that retreaded passenger tires can meet the same performance
criteria as a new tire.
The cost for retreaded tires having performance characteristics equivalent to
new tires could be quite high. This cost will be in proportion to the degree of
confidence and reliability desired. The largest single unknown factor influencing
this cost is casing inspection. Presently available non—destructive test (NDT)
methods are expensive to install and require skilled operators.
The only independent tread-wear test data available for oassenger retreads is
that from GSA. In 1974, GSA conducted an extensive test series on retreaded
passenger tires manufactured according to existing Federal specifications. The
tread-wear varied from less than 10,000 miles to more than 25,000 miles. Again,
the data is obscured by the extreme variations in quality. Certainly the potential
exists for all, or at least most, of the retreaded tires to meet the 25,000 mile
performance under GSA test conditions.
Improving Retreadability
Maintenance . Improved maintenance of tires could make an additional 10 to 15
percent of presently discarded tires suitable for retreading. This increase in
casings available for retreading would permit a 50 percent increase in the number of
passenger tires reb.’eaded. Improved maintenance practices include: (1) exercise
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care in mounting and demounting tires; (2) remove tire when 2/32 inch tread
remains; (3) maintain proper alignment, balance, inflation and rotate as recom-
mended. These are simple precautions, readily put into effect by Federal
Government agencies. Current GSA practices require that every car be serviced
at 3,000 mile intervals, and that servicing includes inspecting the tires and taking
any remedial action indicated--such as balancing or realignment. Getting the
general public to implement these practices will be considerably more difficult.
New Tire Construction . Careful control of tire size and selected design para-
meters could make an additional 15 percent to 20 percent of discarded casings
suitable for retreading. Approximately 11 percent of the inspected tire casings are
rejected because they are of a size no longer popular. This results from continuing
changes in automobile styling and sizes as well as from changes in tire technology.
Improvements in tire design will be required before the steel belted radial will
lend itself to retreading. At the present time a high percentage of inspected steel
belt radials are rejected for retreading because of belt edge separation. It is
expected that this problem will be resolved either by design changes in the steel
belt construction or by replacing the steel belts with textile belts. Textile belted
radials are less susceptable to belt edge separation.
Sidewall damage accounts for 12 percent of casing rejections. A large part of
this is due to sidewall aging or weather checking and will require improvements in
sidewall compounds.
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Bead damage accounts for 7 percent of casing rejections. Most of this can be
eliminated by the use of more care in mounting and demounting tires, but
additional improvement can be achieved by the increased use of fabric chafer
strips in the bead area.
Federal Government agency purchasing procedures could make a significant
contribution to reducing casing rejections due to tire size and design features and
at no additional cost.
Economics of Retreading
The trucking industry has long recognized the economic advantages of
retreading. The average retreaded truck tire will wear as well as a new tire 1
arid for only one-third the cost.
Civilian and military aircraft also make extensive use of retreads for economic
reasons. Most aircraft tires are retreaded 7 to 9 times.
Federal Government agencies are rapidly increasing their use of retreaded
tires. rn fiscal 1974, GSA retreaded 240,000 tires for an estimated savings of
$7,000,000. These were primarily truck tires with passenger tires accounting
for less than 20 percent of the total.
The economics of tire retreading are heavily dependent upon the initial cost
of the tire. In general, the higher the cost of a new tire, the lower the percent
of new tire cost for the retread (i.e., a $500 airplane tire may be retreaded for
20 percent of the new tire cost, a $150 truck tire for 33, arid a $20
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passenger tire for 50 percent.)
The increased use of radial piy passenger tires, with their higher initial cost,
will tend to make the retreading of passenger tires more economically attractive.
The Feasibility of Requiring The Federal Government
To Use Retreaded Tires
At this point in time it is not feasible to require the Federal Government
to use retreaded passenger tires. Federal agencies are making good progress
in the use of retreaded truck tires with several agencies now having goals of
70 percent or more of replacement tires being retreads.
The benefits to be derived from the increased use of retreaded passenger
tires must be delayed until; (1) independent, definitive performance tests have
been completed to determine the performance of high quality retreads as compared
to new tires, (2) new standards or specifications are developed to insure that only
high quality retreaded tires are manufactured, (3) a highly reliable, but inex-
pensive method for casing inspection is developed, (4) radial tire belt edge
separation probi ms are solved.
Once the above conditions have been successfully met, the benefits can be
realized. By changing to radial ply passenger tires with 40 percent being retreaded,
the potential exists for the Federal Government to:
(1) Save $1,000,000 per year (25 percent of present passenger tire costs),
(2) Reduce tire disposal by 75 , 000 tires (50 percent of present level),
(3) Save 1 .7 million pounds per year in solid waste, (46 percent of present
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discarded Federal passenger tire solid waste contribution),
(4) Save 9,000 barrels of crude oil per year (39 percent of present material
and energy requirements for Federal passenger tire manufacture).
Changing the United States passenger tire utilization from belted/bias tires
with 20 percent being retreaded, to radial tires with 30 percent being retreaded
could potentially:
(1) Reduce scrap tire disposal by 58 million tires per year (a 40 percent
reduction),
(2) Save 1.1 billion pounds per year of solid waste (33 percent of present
discardec passenger tire solid waste),
(3) 8 million barrels per year of crude oil (33 percent of present crude oil
requirements for passenger tire manufacture).
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CONCLUSIONS
(1) There is tin extremely wide variation in the quality of commercially
available retreaded passenger tires.
(2) There is insufficient test data to conclusively determine the performance of
high quality passenger fire retreads in comparison with new passenger
tires.
(3) The successful use of retreaded tires by the trucking and airline industries
confirms that high quality retreaded tires can be made. Experience in these
industries shows performance comparable to that of new tires, and with
major economic advantages.
(4) Tire scraps along Interstate highways result from both new and retreaded
tire failures. The approximate split is 60 percent from retreaded and 40
percent from new fires.
(5) Improved maintenance procedures can make an additional 10 percent to
15 percent of discarded fires suitable for retreading. This could result in
a 50 percent increase in the number of fires retreaded.
(6) Careful control of fire size and selected design parameters could make an
additional 15 percent to 20 percent of discarded casings suitable for
retreading.
(7) Federal Government agencies can implement maintenance procedures to
increase casing availability at no apparent additional cost.
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(8) Government agency purchasing procedures can make significant progress
in reducing casing rejections due to tire size and design features. Again,
at no apparent increase in cost.
(9) The major barriers to increased use of retreaded passenger tires are the
uncertain quality and the emotional connotations connected to a ?!used t l
product.
(10) Radial tires offer the greatest opportunity for major improvements in
reducing s 1id waste resulting from tire disposal. Radial tires also offer
the greatest potential for reducing energy and material requirements for
tire manufacture.
(11) The present generation of steel belted tires is posing serious problems
for the retreader. However, these problems are expected to be resolved
in the near fuhire.
(12) Until it can be established that a properly retreaded passenger tire can
meet new tire performance criteria, it is not feasible to require the Federal
Government to use retreaded passenger tires.
(13) If equivalent performance can be demonstrated, significant savings can
be realized in terms of dollars, energy, raw material, snd solid waste.
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RECOMMENDATIONS
On the basis of the conclusions reached during the course of this study, it is
recommended that: (1) The Federal Government undertake a test program design-
ed to determine the performance of retreaded passenger tires manufactured under
optimum and controlled conditions of casing selection, inspection, and retread
processing. The program should include enough tires to be statistically signifi-
cant, and should start with new tires. The new tires should be thoroughly
inspected, both visually and by various NDT methods. Tread wear should be
under actual highway driving conditions. Before retreading the casings should
again be inspected both visually and by NDT methods. Retreading should be done
under carefully controlled conditions and in some instances tires should be
retreaded more than once. (2) The Federal Government increase the use of
retreaded passenger tires by GSA. The initial program should involve selected
motor pools as pilot operations representing the geographic and climatic regions
of the United States. Retreading should be performed only by high quality retread
shops, under tight Government specifications, subject to frequent inspection by
well trained inspectors, and contracted for under financial incentive contracts-
not necessarily the lowest bid.
Strict tire maintenance procedures should be practiced arid tire performance
records maintained.
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TIRE RETREADING
The tire retreading industry is more than 60 years old, but until World War II
its impact on the tire market was negligable. From 1942 to 1944 virtually all
civilian passenger tire needs were met by the retreading industry which expanded
500 percent from its 1941 base. At the peak of the war years, 20 million new
passenger tires were produced and 30 million passenger tires were retreaded.
But, in post-war 1948, when nearly 70 million new tires were produced, retreads
plummeted to 5 million. Passenger tire retreading gradually recovered through
the fifties and has stabilized at approximately 35 million units per year for the
last 10 years represe:iting less than 20 percent of the replacement market. Mud
and snow tires are a major factor in the passenger retread industry, accounting
for nearly 32 percent of all production as compared to only 14 percent for new
passenger tires.
Truck and bus retreading also matured during the war years, but after
stabilizing at 7 1/2 million units per year through the early 1960’s, a steady growth
started about 1966 and truck and bus retreads now exceed 10 million units per
year and represent over 30 percent of the replacement market.
The retreading industry has always been oriented toward the small businessman
and in 1960 it was estimated that there were 9,000 to 10,000 retread shops. In
recent years there has been a trend toward larger shops, but fewer of them.
Department of Transportation records indicate about 5,000 retread shops in 1974,
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but a recent review of this listing indicates that there may be considerably less
than 5,000 retread shops actually operating. The National Tire Dealer and
Retreader’s Association estimates that in 1974, only 4 percent of the retreaders
have a sales volume in excess of $1,000,000 per year, while 50 percent have annual
sales of less than $250,000.
The Tire Retreading Process
The retreading of a tire involves a series of five steps, beginning with a
careful inspection of the casing and ending with a final inspection of the completed
product.
Primary Casing Inspection . A visual inspection is necessary to determine if
the tire is acceptable for retreading. The inspection should be carried out in a
well lighted work area, and the inspector should use a spreader to spread the
tire beads sufficiently to expose all surfaces for potential defects.
Casings having any of the following conditions are not suitable for retreading:
(1) Exposed fabric in tread area
(2) Ply separation
(3) Oxidation or heavy weather checking
(4) Irreparable surface cuts
(5) Broken or kinked beads
(6) Damaged beads exposing cords
(7) Radial cracking
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(8) Flex breaks
(9) Loose or porous liners
(10) Defective inner splices.
(11) Injury to ply cord fabric in bead area
(12) Temporary plugs in sidewall
(13) Previous section repairs
(14) Severe punctures
(15) Blisters in sidewall or carcass
(16) Severe groove cracking
(17) Broken ply or breaker cords
Following the casing inspection, the casing is measured to determine the
proper matrix or mold size. The casing should not be retreaded unless the proper
size equipment is available.
Buffing . Following inspection and measuring, the tire is buffed to remove the
remaining tread rubber and to prepare a surface texture which will insure
maximum adhesion of the new tread to the casing. It is very important that a retread
has a buffed radius and tread width which conforms to the shape in which a casing
will be cured. Until recently this precise shaping depended upon the skill of the
buffing machine opr rator. At most shops the buffing is now accomplished by the
use of automated buffers which inflate the tire to its normal running contour and
buff the tire to a precise template.
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Surface scorching of the tire must be avoided and racks or dollies should be
used to store the buffed tires to prevent contamination.
After buffing a second inspection should be made to locate any cuts, nail holes
or ply separations that were not detected during the first inspection. Also, a
second bead to bead and diameter measurement should be taken to verify correct
carcass matrix match-up.
Tread Application . Rubber cement is applied evenly over the buffed surface
either by brush application or by a spray gun to promote adhesion between the
casing and the tread rubber. Care must be taken to prevent the cement from
becoming contaminated by foreign substances. After the cement has dried, the
tread rubber for the hot cap process can be applied manuaiiy or with an extruder
device.
The manual method uses a die size rubber of predetermined dimensions which
will fill out the matrix design. The die sized strip of rubber is wound circumferen-
tially around the tire. The operator must be careful to be certain that the tread
rubber is applied di:ectly to the center of the casing. In some cases a cushion gum
has been pre-applied to the bottom of the die sized rubber to obtain optimum adhesion
of the tread rubber and the casing.
The extruded ribbon method was pioneered by the Orbitread machines of AMF.
The Orbitread machine is a cold feed extruder which develops its extrusion temp-
erature primarily through frictional temperature in the barrel and at the extrusion
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head. The tires are built on an expandable inflated hub. The extruded strip of hot
rubber is wound around the tire based on a pre-set card program which is set up on
the control console.
After the tread rubber has been applied, the tire is transferred to a curing mold
or matrix where the tread rubber is cured and a tread design molded into the rubber.
A more recent development is the precured tread process. In this case, the tread
rubber is purchased as a partially cured strip of rubber with the tread design already
formed. After cementing, an uncured cushion gum is applied to the casing or to the
bottom of the pre cured tread and the tread is then applied to the casing.
Curing . The hot cap retreads are cured in individual molds at temperatures of
280F to 310F for about 2 hours. Air or stream at pressures upwards of 100 psi is used
inside to provide molding pressure and in the case of steam to also reduce curing
time .The precured (or cold process) treads are cured at far lower temperatures, in
some instances below 200F, but for about 4 hours. These can be done in multiple
unit heaters using vacuum or pressure differential to adhere the tread to the casing.
Final Inspection . After removal from the curing molds, the appearance of the
finished retreads is inspected inside and out for any defects Any excessive flash
or vent rubber is trimmed off and the tire is labeled and stacked for warehousing.
Tire Retreadirig Problems
Three key factors influencing the quality of retreaded tires are: (1) tire
size, (2) casing inspection, (3) retreading practices.
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Tire Size . Tire size problems stem from two sources; the variations within
a given size from different manufacturers, and changes in original equipment size
or styling. FMVSS 109 establishes minimum size requirements for new passenger
tires. These standards specify a size factor for each size of tire; i.e., a G78-I.4
has a minimum size factor of 35. 02. The size factor is defined as the section width
plus the outside diameter of the tire and F! 1VSS 109 limits the section width for a
G78—14 to 8.93 inches. The diameter can vary as long as the sum of the two
variables is not less than 35.02 and the section width no greater than 8.93 inches.
Five new steel belted bias ply G78-14 tires were measured with the following
results:
Manufacrnrer O.D. Section Width Size Factor
A 27.05 8.32 35.37
B 27.17 8.41 35.58
C 26.81 8.49 35.30
D 27.38 8.40 35.78
E 27.31 8.26 35.57
All five tires comply with FMVSS 109 standards, but there is a variation of 0.57
inches in OD. and 0.23 inches in section width.
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Seven new G78-14, 4 ply polyester tires were then measured:
Manufacturer 0 .D. Section Width Size Factor
T 27.27 8.31 35.58
U 26.92 8.29 35.21
V 27.39 8.76 36.15
W 27.53 8.34 35.87
X 26.64 8.50 35.14
Y 27.22 8.36 35.58
Z 27.00 8.23 35.23
Again all 7 tires meet the standard, but the 0. D. varies by 0 .89 inches and
the section width by 0.53 inches. Mold size does not precisely control tire size.
Changes in cord material, ply angle, and drum sets can cause significant differences
in tire size coming from the same mold.
After the tires have been placed in operation, they will tend to grow with the
bias ply tires growing more than the steel belted bias tires. The growth of tires is
related to both tire design and materials of construction. FMVSS 117 for retreaded
tires limits the section width change to not less than minus 3 percent nor more than
plus 10 percent of the new tire specification. Thus the retreader is faced with wide
variations in 0 .D. and section width from tires that are the same “size”.
The problem is further compounded as original equipment manufacturers change
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from 14 inch wheels to 15 inch and also change the tire aspect ratios (ratio of tire
height to tire width) from 78 to 70. For example, original equipment tires for a
given model one year may be G78-14, and the following year be changed to G70—14
or perhaps G70-15.
These wide variations in tire size make it necessary that the retreader maintain
a very large inventory of matrices, if he is a hot cap processor, or a large inventory
of tread widths if he is a precured tread processor. If he does not maintain this
inventory he must be very selective in the size and type of tire he retreads, or
he forces the tire to fit his existing matrices or treads and produces an inferior
product.
Casing Inspection . Procedures for casing inspection were previously described,
however, it is often not possible to detect all defects within the casing by visual
methods of inspection. Later in this report several methods of non-destructive
testing (NDT) are described. It may be necessary to employ these advanced
techniques if retreaded passenger tires are to meet high performance standards.
Retreading Practices . Perhaps the greatest number of defective retreaded
tires result from the retread operators not following good retreading praQtices
as defined by the various equipment manufacturers, material suppliers, and
trade associations.
21
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PERFORMANCE OF RETREADED TIRES
Widespread use of retreaded passenger tires cannot be expected until it
has been proven that they can be operated with the same degree of safety and
convenience as new tires.
In 1968, Federal Motor Vehicle Safety Standard 109 (FMVSS 109) was enacted
for new passenger tires. Indoor laboratory dynamometer wheel tests are included
in this standard establishing minimum performance levels, although there are still
many questions regarding the validity or meaning of such tests. To date, there is
no data establishing a direct correlation between these tests and actual road perform-
ance. However, this standard has been accepted by the tire industry and has been
a factor in improving tire performance. The number of new tires failing the endurance
portion of this test was reduced from 5.9 percent in 1970 to 0.87 percent in 1972 and
high speed test failures were reduced from 4.5 percent to 0.11 percent during the
same period.
In 1971, Federal Motor Vehicle Safety Standard 117 (FMVSS 117) was issued and
it proposed to subject retreaded tires to a similar wheel test. However, the retreaded
tires had an unacceptably high failure rate on the test wheel. The retreaders claimed
that properly made retreaded tires perform as well as new tires under actual road
conditions, and that FT TVSS 117 was not a fair test in that it did not duplicate or cor-
relate with road conditions. The U .S. Court of Appeals heard the case and invalidated
the major performance criteria of FMVSS 117 including the indoor wheel tests.
The cost and time required to conduct actual on-vehicle road tests to qualify and
22
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evaluate the quality of tires is prohibitive. Extensive work is underway throughout
the country to develop suitable laboratory tests or other accelerated methods that will
correlate with road tests for both new and retreaded tires.
Tire Testing
The overall performance of a tire is generally measured in terms of its
performance in resçect to high speed, tread wear, traction endurance, and
strength. These characteristics are determined by means of: (1) actual road
testing on public highways using standard vehicles, (2) closed track testing
using either standard vehicles or trailers, (3) indoor wheel tests, (4) laboratory
tests. New tire manufacturers routinely use all these methods in tire development
and production control. Tire retreaders can seldom afford the luxury of such
extensive test programs. The reasons are apparent when it is considered that the
annual U. S. market for new passenger tires, approximately 185 million, is supplied
by fewer than 20 manufacturers. On the other hand, nearly 5,000 retread
manufacturers supply the 30 million passenger tires that are retreaded each year.
As a result, most retreaders rely on tread rubber suppliers, or equipment
manufacturers to do their research, testing and evaluation. This has resulted in an
absence of independent test data. Test programs are sponsored or run directly by
organizations who are associated with either the new or retread industries. The
test programs that have been sponsored by retreaders directly are generally very
limited in scope because of financial restrictions.
23
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A thorough search throughout the retread industry located only four test
programs involving a significant number of retread tires. These programs were
conducted by DOT and GSA and are described below.
DOT-ABA . The National Highway Traffic Safety Administration (NHTSA)
contracted with Automotive Research Associates, Inc. (ARA) for a series of tests
on new and retreaded tires. The final reports were issued in mid-1973.
The tire constructions tested included 4 ply nylon bias, 2 + 2 polyester fiber-
glass belted bias, and two radial types; 2 + 2 rayon steel and 2 + 3 polyester steel
and nylon. Similar constructions in the bias and belted bias allowed for a comparative
evaluation of new tires versus retreads. Differences in radial construction did not
permit a comparison between new and retreaded tires. Differences in retreading
applications were also evaluated with some tires recapped using a hot process and
others a precured tread process.
All tires were subjected to three tests. Conditions for these three endurance
tests are listed below along with current test conditions for the FMVSS 109 Endurance
Test.
(1) FMVSS 109 Erdurance Test Conditions
Environment Temp. 100F
Wheel Speed 50mph
Inflation Pressure 24psi
4 hours at 100% of rated 24 psi load
6 ft Yl 109% II ft I? It It
24
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24 hours at 117% of rated 24 psi load
34 hours total
(2) Proposed Modified 109 Endurance Test
Environment Temp. 100F
Wheel speed 5 0mph
Inflation Pressure 24psi
4 hours at 100% of rated 24 psi load
6 IT fl 109 II IT IT
24 TI 117 TI It II TI
Run to Failure at 146% of rated 24 psi load
(3) Proposed SAE Endurance Test-Indoor Wheel
Environment Temp 100F
Wheel Speed 50mph
Inflation Pressure 32psi
4 hours at 100% of rated 24 psi load every 4 hours increase load by
15 percent of original load until failure.
(4) Proposed SAE Endurance Test-Trailer
Environment Temp. Outside Ambient
Speed 70 mph
Inflation Pressure 32 psi
4 hours at 100% of rated 24 psi load.
Every 4 hours increase load by 15 percent of original load until failure.
25
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Table 1 gives the average results for the 4 ply nylon, bias construction tires.
The 146 percent over 1 oad DOT 109 test indicates that the Group F retreaded tires
performed nearly as well as the new tires, and although the Group H retreaded tires
did not run nearly as long——they did pass the existing FP iVSS 109 requirements.
The SAE modified wheel test results show the Group F retreads outperforming
the new tires, while the Group H retreads are nearly equal to the new tires.
However in the trailer test, neither group of retreads performed as well as the
new tires.
Table 2 summarizes the average test results for groups of belted bias tires.
In the 109 series both groups of retreaded tires outperformed the new tires, but
in the SAE modified wheel test both retread groups performed at a slightly lower
level than the new tires.
Again, in the SAE Trailer Endurance Test the retreaded tires performed
significantly below the level of the new tires.
Table 1 and Table 2 both indicate that the retread tires can perform as well as
new tires. The 146 percent overload DOT 109 Test indicates that the hot cap 4 ply
nylon bias retreaded tires (Group F) performed equal to the new tires (Group A),
while the precured tires in Group H only ran 36.5 percent as far. In the belted bias
constructions (Group B, G and J) the retreaded tires out-performed the new tires
with the precured tread tires running 25 percent further than the new tires.
26
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TABLE 1
DOT-ARA TESTS
BIAS PLY TIRES
New Tires Retreaded Tires
Hot Cap Precured
Code A F H
Size G78—15 G78—15 G78—15
Construction 4 P Ny 4 P Ny 4 P Ny
Hourson 109 Wheel 107.3 101.3 39.2
Ave. load at failure % 146 146 146
Hours on SAE Wheel 30.2 33.7 27.9
Ave. load at failure % 205 235 200
Hours on SAE Road 33.6 22.6 28.3
Ave. load at failure % 210 175 200
Required for PMVSS 109
Hours on 109 Wheel 34 * *
Load at completion of test(%) 117
* Indoor Wheel Test not required for retreaded tires FMVSS 117
Source: DOT Report No. 109 —ARA- 73-DOT —HS -001- 3—572-NHTSA 3-A 817
27
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TABLE 2
DOT-ARA TI STS
BELTED BIAS TIRES
New Tires Retreaded Tires
Hot Cap Precu red
Code B G J
Size G78—15 078—15 G78—15
Construction 2+2 PG 2+2 PG 2+2 PG
HoursonlO9Whee l 37.9 42.1 47.4
Ave. load at failure% 146 146 146
Hours on SAE Wheel 23.3 21.4 202
Ave. load at failure% 175 175 175
Hours on SAE Road 25.0 19.1 14.6
Ave. load at failure 190 160 145
Required for FMVSS 109
Hours on 109 Wheel 34 *
Load at completion of test (%) 117
* Indoor Wheel Test not required for retreaded tires FMVSS 117
Source: DOT Report No. 109-ARA-73-DOT-HS-0O1--3-572-NHTSA 3-A817
28
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Tires run to the SAE road test using the trailer indicated that the new tires were
superior to the retreads. The 4 ply nylon bias retreaded carcasses out-ran the
2 + 2 polyester/fiberglass retreaded carcasses by as much as 51 percent. The new
4 ply nylon tires (Group A) our-ran the new 2 + 2 polyester/fiberglass tires (Group
B) by approximately 34 percent.
The SAE wheel test comparisons indicate that, again, the retreaded tires
performed as well as the new tires. However, overall, the 4 ply nylon bias retreaded
carcasses out-ran the 2+2 polyester/fiberglass retread carcasses by as much as
48 percent.
Only two groups of precured retreaded tires showed superior running
performance over the hot process retreads. Group H tires on the SAE road test
were 25 percent higher than the Group F tires, however, significantly lower than
the new tire performance. Group J on the overload 109 test out—ran the hot retreaded
tires by 12 percent.
The three tests performed in this program emphasized overload as a method
by which accelerated test results could be obtained on both new and retreaded
tires. The data, therefore, should only be interpreted as a comparison between
these two basic differences under overloaded conditions. To relate these test
results to the comparable performance of a tire under actual service conditions
would be misleading in that no correlation currently exists between these simulated
tests arid actual performance in service.
29
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The value of these test results is limited since no control was exercised over
the selection of casings to be retreaded, and no control or inspection was provided
during the retreading process. Descriptions of the failure modes or the character-
istics of the condition of each tire after the tests were generalized and lacked the
necessary detail to permit an analysis to determine the cause of failure and to
determine if the failure was related to the retreading procedure or other causes.
It would be highly desirable to determine what effect, if any • the various
retreading procedures have on the integrity of the tire carcass. It would be expect-
ed that a precured process would have less effect, due to the reduced curing temp-
erature, but this series of tests indicated superior performance for hot process
retreads.
DOT-NDT TES’1 . A preliminary study of the relationship between failure of
retreads during F ] VSS 109 tests and flaws detected by non-destructive testing was
undertaken by the Transportation Systems Center of the Department of Transportation
in 1972 (Report No;DOT-TSC-NHTSA-73-1).
During this study, 137 retreaded passenger tires were purchased, subjected to
tests, run on a Standard EMYSS 109 test wheel, re-examined by non-destructive
means arid analytically sectioned.
A comparison was made of those tires having holographically identified
separations showing up on the first inspection prior to the wheel test. The 95
retreads which were considered passed had an average of 0.642 separations per
tire, while the 42 tires considered failed had an average of 1 .26 separations per
30
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tire. The remaining 10 tires encountered operating problems and did not generate
any useful data. After the wheel test, the average number of separations in the
passed category increased to 0.844, while the average number of separations in the
failed category increased to 3 .67. The inspections after the tires had failed, however,
were not completely realistic since in many cases, the separation behind a tread
chunk-out was no longer diseernable by holography and separations had a tendency
to grow and join together into one.
The relation of tire failure to construction type was considered to determine
any long term trends. The results are shown in Table 3. The results of this
project are somewhat inconclusive. Again, no attempt was made to control either
the history of the casing or the quality of the retread. Table 3 does show a very
high failure rate (53 percent) of 2 ply rayon tires and 2 ply polyester tires (44
percent). However, success of holography to predict failures is questionable in
the case of the 2 ply casings where in one instance only one separation was found,
but 8 tires failed and in the other only 2 separations were found but 7 tires failed.
The reverse situation appears to exist in the case of 4 ply bias construction
tires. Here the failure rates range from 15 to 31 percent, while the number of
separations found would indicate the probability of a much higher failure rate.
Only 10 polyester/glass belted bias tires were examined, but they showed 38
separations and a 60 percent failure rate.
In summary, the results of this project suggest that: (1) 2 ply bias
construction tires are not good candidates for retreading, (2) belted bias tires
31
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TABLE 3
TIRE FAILURE VS TYPE OF TIRE CONSTRUCTION
USE OF HOLOGRAPHY
Type
No. of Tires
Passed
No. of Tires
Passed
Separations
Located by
Holograph
Prior to
Wheel Test
Average
Separation
Percent
Failed
2Ply Rayon
7
8
1
0.1
53
2 Ply Nylon
1
0
0
0.0
0
2 ply Polyester
9
7
2
0.1
44
4 Ply Rayon
11
3
12
0.9
21
4 Ply Nylon
41
7
15
0.3
15
4 Ply Polyester
13
4
2
0.1
31
2+2 Rayon Rayon
5
0
5
1.0
0
2+2 Polyester Glass
4
6
38
3.8
60
4+2 Polyester Glass
0
1
0
0.0
100
TOTAL
91
36
28
Source: DOT Report No. DOT-TSC-NHTSA-73-1
32
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are more prone to separations than bias ply tires, (3) 4 ply bias construction
tires are the least prone to failure in the FMVSS 109 test, (4) the reliability of
holography in predicting tire failure is questionable at this time.
Table 4 provides one additional bit of information in a summary of tires failed
in relationship to th retread manufacturer. The failures range from 1 to 39 percent
and indicate the wide variation in quality between retreaders. It can also be seen
that 28 percent of all retreaded tires tested failed the FMVSS 109 wheel test.
DOT-FMVSS 109 Tests . To obtain background performance data on
retreaded passenger tires, DOT evaluated a number of retreaded tires under the
new tire standard, FMVSS 109. A 224 tire test program was initiated in 1971 to
confirm the dimensional limits and dynamic laboratory test specifications of retread-
ed tires (Test Program No. DOT-HS-042-1-053). Three retreading companies were
selected to supply a wide range of tire sizes and constructions.
Of the 224 tires tested, 26 were belted bias construction and 198 were bias
construction. Over 50 percent of the bias construction tires were 2 ply rayon or
polyester design. The remaining bias construction tires were 4 ply nylon, poly-
ester or rayon. Belted bias tires were constructed of either rayon/rayon, nylon/
berglass, or polyester/fiberglass.
Overall performance data of the tires for dimensions, endurance and high
speed wheel tests are tabulated in Table 5. Twenty—three percent of the endurance
tested tires failed to pass the 34 hours, 50 mph minimum requirement and 22 percent
failed to pass the stepped speed, high speed phase. Only 7 percent failed to meet
33
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TABLE 4
DOT-TSC
TIRE FAILURE BY RETREADER
Retreader
No. of Tires
Run
No. of Tires
Failed
Failed
A
18
5
28
B
6
2
33
C
6
1
17
D
6
0
0
E
18
6
33
F
18
7
39
G
18
4
22
F
47
15
32
TOTAL
137
40
29%
Source: DOT Report No. DOT—TSC-NHTSA-73-1
34
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TABLE 5
DOT TESTING OF RETREADED TIRES TO FMVSS 109
(TIRE FAILURES BY RETREADS)
Retreader
Dimensions
Total
Tires
Tested Failures
Endurance
Total
Tires
Tested Failures
High Speed
Total
Tires
Tested
Failures
A
81
3 (4%)
45
15 (33%)
36
10 (28%)
B
50
2 (4%)
25
4 (16%)
25
5 (20%)
C
TOTALS
93
10 (11%)
45
8 (17%)
46
9 (20%)
224
15 (7%)
117
27 (23%)
107
24 (22%)
35
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the minimum size factor or section width limits.
Failures were reported in relation to the established FMVSS 109 requirements
but were not specifically attributed to retread processing or casing defects. The
data does indicate, however, that one retreaded tire in four will not meet FMVSS 109
performance levels at a time when new passenger tires tested for DOT compliance
to the same regulation had a failure rate of only 3. 1 percent for endurance tests
and 1. 5 percent for high speed tests.
Table 6 lists test data by tire construction and shows a high percent of failures
on the high speed test for the belted bias design. These tires were originally built
prior to 1971 when the retread industry’s experience with potential casing defects
in the belted bias design was limited. As a result, many first generation belted bias
tires may have been unknowingly retreaded while having breaker edge separations.
The poor endurance performance shown by the 2 ply bias tires is evidenced
in Table 6 where 35 percent failed. Fifteen of the 18 failures were of rayon
construction, although 16 other rayon tires did pass this phase of the test.
GSA Tests . The General Service Administration in September 1972, instituted
a retread passenger tire test program. The purpose of the study was to evaluate
the tread wear and casing durability performance of retreaded bias belted (non-
steel) passenger tires under controlled testing and operational conditions.
Initially the program was established using GSA Interagency Motor Pool
vehicles for testing under operational conditions with a final test phase using new
tires being tested for qualification on the Qualified Products Lists (QPL). This
36
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TABLE 6
DOT TESTING OF RETREADER TIRES TO FMVSS 109
(TIRE FAILURES BY CONSTRUCTION)
Dimensions Endurance H gh Speed
Retreaded Total Total Total
Tire Construction Tires Tires Tires
Tested Failures Tested Failures Tested Failures
2/0 101 8 (8%) 52 18 (35%) 50 9 (18%)
(Bias)
2/2 26 2 (8%) 15 2 (13%) 11 8 (73%)
(Belted Bias)
4/0 97 5 (5%) 50 7 (14%) 46 7 (15%)
TOTALS 224 15 (7%) 117 27 (23%) 107 24 (22%)
37
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program proposed that for each vehicle equipped with retreaded passenger tires,
there would be an equal number of vehicles equipped with new QPL tires. It was
also intended that each vehicle from the Interagency Motor Pools would be operated
under substantially similar conditions to determine tread wear performance of
retreaded tires as well as develop performance comparison data for retreaded and
new QPL tires.
A total of 488 passenger vehicles were utilized from the Interagency Motor
Pool; 300 assigned to Personal Property Disposal personnel and 188 assigned
to the Gallup Motor Pool.
Nineteen retreaders supplied a total of 1,542 retreaded tires for the
Interagency Motor Pool test. These tires were utilized on 300 vehicles; 150 in the
Personnel Property Disposal and 150 in the Gallup Motor Pool. A total of 188
vehicles were actually used having new tires from the QPL.
In September 1973 the retreaded tire data was summarized and recorded.
(Table 7). From the total of 1 , 542 retreaded tires used in the test, 252 were
recorded as having failed in service. This indicates a retread tire failure rate of
16.3 percent. The tread wear data showed an average mileage of 7,179 miles having
a low of 5,683 miles and a high of 15,703 miles. A major contributor of tire failure
was directed to tread separation, although insufficient records and limited failure
descriptions did not permit a detailed analysis to determine if the failure was oriented
to the retreading process or inherent in the carcass at the time of retreading.
38
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TABLE 7
GSA-RETREAD TIRE TEST
(MOTOR POOL TEST ONLY)
VEHICLE ASSIGNED
QUANTITY RETREAD
EQUIPPED
NEW TIRE
EQUIPPED
Personnel Property Disposal
300 150
150
Gallup Motor Pool
188 150
38
TOTAL
488 300
188
Total Tires Retreaded
1,542
Total Tires Retreaded
252
Average Percent Defective
16.3%
Average Wear Mileage
7 , 179 miles
(Worn to 2/32’s)
Total Tires Worn to 2/32’s
62
DEFECT SUMMARY
Type of Defect
Number of Tires Defective
Percent of Total
Tread Separation
166
65.8%
Air Entrapment
28
11.1%
Carcass Defect
54
21.4%
Other
4
1.6%
39
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The most useful data resulting from this Motor Pool test is that shown in
Table 8. The failure rates range from 0 to 60 percent with an average failure rate
of 16.3 percent. The tread wear showed a low of 5,683 miles and a high of 15,703
miles giving an average tread wear of 7,179 miles. Considering that all the
retreaded tires were purchased from GSA approved contractors, and the tires
presumably processed according to existing 0.5 .A. specifications, it must be
concluded that much tighter specifications are required to insure a consistent,
high quality product.
Unfortunately, in October 1973, after a review of the above data, it was
decided to abort the ¶nteragency Motor Pool test phase and to move on to the QPL
test phase.
Retreaded tires tested in the QPL qualification phase of the GSA program were
obtained from 8 retreaders and compared to new tires submitted from 17 new tire
manufacturers. The test conditions were those required in Federal Specification
ZZ-T-381M where identical vehicles are driven to 16,000 miles and the tires
evaluated for tread wear.
Within the retreaded tire group, 6 of the 8 retreads used casings that had
been retreaded by the hot curing method. The other 2 groups were used as
controls and included both new and used casings as well as tires cured by the hot
process and the cold (precured) process. The BB tire group shown in Table 9
contained 12 new tires which were butted and retreaded using the hot cure method.
40
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TABLE 8
GSA MOTOR POOL TEST
(RETREAD FAILURES BY CONTRACTOR)
Contractor
Total No.
Tires Retreaded
No. Defective
Tires
Percent Defective
Tires
A
18
1
5.5
B
10
1
10.0
C
762
134
17.6
D
5
3
60.0
E
101
25
24.8
F
60
12
20.0
C
20
0
0
H
5
0
0
I
55
0
0
J
65
29
44.6
K
5
0
0
L
10
4
40.0
M
45
5
11.1
N
191
22
11.5
0
100
7
7.0
P
50
5
10.0
Q
20
0
0
R
15
4
26.7
S
a
0
TOTALS
19
1542
252
16.3
41
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TABLE 9
QPL QUALIFICATION PHASE OF GSA TEST-RETREADED TIRE PERFORMANCE
F allures
Contract Type Casing Casing Improper Extrapolated Mileage to 2/32 Inch
Retreader Retread History Defects Processing ( Tire Completing 16,000 Miles )
Control AA Siped-Cold 4 New 1 0 Low 21,430 3 (Tires)
Precured 2 Used High 26,008
Control AA Regular-Cold 4 Used 3 0 20,050 (1 Tire)
Precured 2 New
Control BB Hot 416F 6 New 0 0 Low 17,429 (4 Tires)
High 20,640
Control BB Hot 416E 6 New 0 1 Low 16,259 (3 Tires)
High 17,288
N Regular 6 Used 0 4 Low 2,000 (Failed)
Hot High 6,000
T Regular 6 Used 0 4 Low 10,000 (Failed)
Hot High 12,000
J Regular 6 Used 1 3 Low 4,000 (Failed)
Hot High 12,000
M Regular 6 Used 3 0 Low 15,557 (2 Tires)
Hot High 17,598
L Regular 6 Used 3 0 15,534 (1 Tire)
Hot
F Regular 6 Used 2 2 Low 10,453 (4 Tires)
Hot High 12,000
DEFINED FAILURES
Initial Test Tires 40 12 Casing 10 Processing 4 Early Wear Out 65% Failed
pares 20 1 Casing 4 Processing 1 Early Wear Out 30% Failed
Total Test Tires 60 13 Casing 14 Processing 5 Early Wear Out 53.3%Failed
-------
Six of these 12 tires were retreaded using the tread compound required in
Interim Federal Specification ZZ-T--00416E and the other 6 were retreaded using
the tread compound required in Federal Specification ZZ—T-416F, (4 test tires and
2 spares in each case). The objective of this testing was to determine which
compound improved tread wear performance.
The AA tire group also shown in Table 9 contained 12 tires retreaded by the
precured tread method. Two different precured treads were incorporated, one being
called the “regular” and the other “siped ” (cut across tire tread to produce biting
traction edges). Six tires were retreaded using the “regular” precured treads (4 used
casings and 2 new casings) and 6 were retreaded using the “siped” precured treads
(2 used casings and 4 new casings).
Within the new QPL tire group, 46 samples, amounting to 2 tires per sample,
totaling 92 test tires, were selected at random by regional QAS personnel from a batch
of 100 or more tires. These tires represented the current production from 17 new
tire manufactures.
The test route was rated at 65 miles per mil wear and all the tires were operated
over the same route under identical operating conditions, except for the first 3,500
miles where the new tires for qualification were tested at 60 mph plus or minus 5 mph.
Thereafter, the test speeds for the new arid retreaded tires were reduced to a maximum
of 55 mph to meet State and Federal speed regulations established during the fuel crisis.
Results of the retread QPL test phase (Table 10) revealed that the 40 initial
43
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TABLE 10
FAILURE MODES OF RETREADED TIRES TESTED
(DURING QPL PROGRAM)
Number
Tires
Tested
Casing
Failure
Failures
Improper
Processing
Failures
Early
Wear-Out
Tire Removed Percent
Perf. ormed End of Test** Failure
Satisfactory *
Initial Test
Tires
40
12 Tires
(30%)
10 Tires
(25%)
4 Tires
(10%)
14 Tires
(35%)
65%
Spares
20
1 Tire
(5%)
4 Tires
(20%)
1 Tire
(5%)
14 (70%)
30%
Total Test Tires
60
13
14
5
14*
14**
533%
* Completed tread wear test of 16 ,000 miles
**Tjres remaining on vehicles upon completion of test.
Road mileage varied between 6,000 and 12 ,000 miles.
-------
retreaded tires showed an abnormal overall failure of 65 percent. These failures
were attributed to casing defects (30 percent), retread processing (25 percent),
and early wear-out (10 percent) occurring between 8,000 and 14,000 miles.
Fourteen tires (35 percent) completed the 16,000 test mileage. The 20 spare
retreaded tires which were utilized to supplement tire failures of the initial test
phase showed an overall failure of 30 percent. Causes of failures were attributed
to casing defects (5 percent), retread processing (20 percent), and early wear—out
(5 percent). Mileage of the retread spare tires ranged between 4,000 to 12,000
miles, however, most spares were not run the full duration of the test program.
A summary of the retreaded control tires (Table 9) showed that the BB tire
group, retreaded with the 416E tread compound, had 1 tire failed at 14,000 miles
due to severe radial cracking. The remaining three completed the 16,000 miles.
Extrapolated tread wear mileages to 2/32 inch wear-out, computed to a low of
16,259 miles and a high of 17,288 miles.
The BB control tire group retreaded with the 4l6F tread compound all comp-
leted the 16 , 000 miles of test. Extrapolated tread wear mileages to 2/32 inch
computed to a low of 17,429 miles and a high of 20,640 miles.
The AA control tire group retreaded with the regular cold precured process
experienced 3 failures due to casing defects. The fourth tire completed the
16,000 miles of test. Extrapolated tread wear mileage to 2/32 inch wear—out
computed to 20,500 miles.
45
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The other 3 tires evidenced extrapolated tread wear mileages computed to a
low of 19,113 miles and a high of 20,812 miles.
Control tires retreaded with the “siped” precured treads in the AA control
group experienced 1 failure due to a casing defect. The other 3 tires completed
the 16,000 test mileage. Exprapolated tread wear mileages to 2/32 inch computed
to a low of 21,430 miles and a high of 26,008 miles for the 3 tires. The casing
defect tire had extrapolated mileage of 19,345 miles.
A comparison of AA and BB retreaded control tires with the non-control
retreaded tires in Table 11 is made to consider the ability of the GSA retread
contractors to deliver a satisfactory retread tire which can compete with a new
tire. As described earlier, control tires utilized used and new casings which were
buffed and retreaded. Non-control tires were used casings which were hot
retreaded by 6 GSA retreading contractors. These tires evidenced a huge 88 per-
cent failure rate as compared to the 14 percent evidenced by the BB control tires.
The AA retreaded control tires had 50 percent failures which were all
contributed to casing defects. The precured method of retreading, with its lower
curing temperature, sh3uld not harm the tire casings. Therefore, GSA did not
consider these as retread failures. Accordingly, extrapolated mileages to 2/32
inch showed a low of 20, 050 miles to a high of 26 ,008 miles, indicating that the
precured retread process can provide tread wear mileages comparable to new tires.
Results of the new tires tested for QPL qualifications (Table 12) indicated
46
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TABLE 11
COMPARISON OF CONTROL AND NON-CONTROL RETREADED TIRES
NUMBER NUMBER PERCENT EXTRAPOLATED MILEAGE
TEST GROUPS TESTED FAILED FAILED TO 2/32 in. WEAR-OUT
Control Tires
AA (Precured 8 4 50% Low 20,050
Cold Process) High 26,008
BB (Hot Cure 8 1 14% Low 16,259
Process) High 20,640
Non-Control Tires
GSA retreader 24 21 88% Low 15,534
furnished (Hot Cure) High 17,598
Total 40 26 65%
Control tires AA utilize new and used casings.
Control tires BB utilize all new casings (new buffed and retreaded).
Non-control tires are all used casings.
47
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TABLE 12
NEW TIRES TESTED FOR QUALIFICATION
Number Tires
Tires Casing Failures Performed Removed Percent
Tested Failures Early Wear—Out Satisfactory* End of Test** Failure
Initial Test Tires 92 5 Tires 6 Tires 81 Tires N. A. 12 %
(5%) (7%) (88%)
Spare Tire 8 0 0 8 Tires 0%
(100%)
100 5 6 81* 8** 12%
* Completed tread wear test of 16,000 miles.
**Tires were removed before completion of the 16 ,000 test mileage requirement.
-------
that 11 of the 92 test tires failed between 6,000 to 15,000 miles due to early wear—out
and casing failures. This constitutes a failure rate of 12 percent. The remaining
81 tires completed the 16,000 miles of test and had extrapolated mileages to 2/32
inch computed to a low of 17,284 miles and a high of 37 p807 miles. The cut off for
listing on the QPL is estimated at 22 ,414 miles. This means that bias belted tires
exhibiting tread wear mileages over 22,414 miles will be listed on QPL.
The QPL phase of this GSA test program again reflects the extreme variations
in quality between retreaders presumably following the same set of specifications.
In summarizing the tire testing described in the preceeding pages, it must be
concluded that the available test data on the performance of retreaded passenger
tires is very limited and inconclusive. Independent performance tests on retreaded
tires have been conducted by DOT and GSA in an effort to determine the performance
of retreaded passenger tires currently marketed. These tests show extreme quality
variations between retreaders and these quality variations are such that the
“average” retreaded passenger tire has a performance level significantly below that
of a new tire. However, there are instances where retreaded passenger tires have
been shown to have performance properties approaching or equaling that of new
tires. It is unfortunate that the only significant, independent test programs
conducted to date on retreaded passenger tires have been oriented toward an
evaluation of random retreaded tires available on the open market. There have
been no independent tests, conducted on a statistically significant size sample, to
49
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determine the performance of retreaded passenger tires manufactured under optimum
and controlled conditions of casing selection, inspection and retread processing.
Retreaded Passenger Tire Failures
During the course of this project retreaders, retreader organizations, and other
people associated with retreading were interviewed. Most of those interviewed
estimated the passenger retreaded tire failure rate to be about 4 percent, that figure
being based on the percentage of tires being returned to the retreader for adjustment.
New tire adjustment rates are highly confidential, but 3 percent is the commonly
accepted rate as an industry average.
On this basis, the adjustment rate, or failure rate, for retreaded tires is only
one percent higher than that for new tires. The 4 percent figure is probably some-
what misleading since the average use of passenger retreads is considerably different
than that of new passenger tires. Although detailed figures are not available, it is
felt that most passenger retreads currently in service are used within cities and seldom
exposed to the stresses of high speed interstate highway driving. If retreaded
passenger tires were used in the same manner as new tires, it is possible that the
adjustment rate would increase. The large number of small retreaders and the reduced
value of retreaded tires makes it much less likely that adjustable retreads will be
returned to the retreader than in the case with new tires.
Very few of the retreaders interviewed were able to provide a breakdown of the
causes for retread passenger tire failures, but from the records that were available,
the data was compiled for Table 13. The major cause of retread failure is ply
50
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TABLE 13
REASONS FOR RETREAD ADJUSTMENTS
(EXCLUDING ROAD HAZARD)
PER CENT
Bead Failure 1
Out of Round 8
Casing Separation 58
Tread Separation 18
Sidewall 7
Air Leak 5
Other 3
100
51
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separations in the casing. This type of failure accounts for 58 percent of all
retread failure. Tread separation is not nearly so serious accounting for only 18
percent of the failures.
The high incidence of failures resulting from casing failures pinpoints the
largest single problem facing the retread industry—-how to determine the quality
of a used casing.
Non-Destructive Testing of Tires
Recent years have seen substantial advances in the technology of nondestructive
testing (NDT) of tires. The four methods used most frequently are holography,
X-ray, infrared, and ultrasonics. These four methods are briefly described
in the following sections.
Holography . Optical holography, or holographic interferometry, is a new and
highly regarded method for accurate NDT. In this procedure coherent light is used
in recording and reconstructing three-dimensional images and light interference fringe
patterns. When the target material is stressed, subsurface anomalies appear in the
form of small surface displacements. In the case of tires, the stress is usually induced
by subjecting the tire to a slight vacuum. The interferometric pattern produced by
the surface displace nent brought about by the vacuum is readily apparent and
indicates the location, size and shape of the anomaly.
In a typical installation a holographic tire analyzer will accomodate a wide range
of tire sizes. The tire is manually spread open using four spreaders, allowed to
relax, and then placed in position on the analyzer. The cover is lowered and a
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double exposure hologram is made of the tire. The first exposure is made at
atmospheric pressure, and the other made with the tire subjected to a partial
vacuum. The resulting interference fringe patterns show the location and type of
anomalies, particularly ply separation.
A typical holographic tire analyzer will cost approximately $50,000 arid can
analyze about thirty tires in an eight hour day. At this rate, the cost for operator
time and machine depreciation would amount to at least one dollar per tire.
X—ray . X-ray has been widely used in tire analysis for many years, but it
was primarily limited to examination of the tire bead structure. The new X-ray
systems lend themselves to non-destructive testing for centering of belts, open or
overlapping cords, correct belt end locations, foreign matter in the rubber, or
trapped air voids. A modern high speed X-ray unit for tire analysis will cost
approximately $110,000 and can analyze a tire in about two minutes. In this case, the
cost for operator time and equipment depreciation would be about fifty cents per tire.
Infrared . Infrared sensing provides a qualitative thermal profile of the tire and
can detect hot spots which have proven to result in tire failure. Areas of localized
heating can be determined, but relating these to specific conditions within the tire
has been found to be difficult--except in a destructive test.
Infrared test units are currently available for a cost of $10,000, but the analysis
could require from three minutes to two hours, depending on the characteristics of
the tire being tested. This could result in a testing limit of four to six tires a day.
The cost per tire could be even higher than for holography.
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Ultrasonics . Ultrasonic non-destructive testing is based on the fact that sound
waves introduced into a material, such as a tire, can be reflected or moderated by
a discontinuity such as a void or delamination.
Most ultrasonic tire testing is by means of either the pulse echo or thru—
transmission approach. In pulse echo testing, a pulse of energy is coupled into the
speciman and the time required for the energy to be reflected to a transducer can be
measured. This measurement gives the depth of any discontinuity or other
interface of interest lending itself to the identification of ply or cord separation.
This is usually a single transducer method and allows a one sided pulsing and
receiving method without access to the inside of the tire. Thru-transmission
involves the transmission of an ultrasonic wave into the material from the sending
transducer, then out the opposite side where the energy leaving the material is
received by the receiving transducer.
Different methods for coupling are used-air to air, water to air, and water to water.
Most of the newer systems are based on air to air coupling. A typical aircoupled
ultrasonic system for testing tires will cost about $10,000 and requires about five
minutes per tire. This would result in a cost for labor and equipment of about
fifty cents per tire.
Interstate Highway Roadside Survey
Scraps of rubber litter the side of every major highway. It is generally assumed
by the passing motorist that these chunks and strips of rubber are the remains of a
retreaded tire. In order to verify the source of these tire scraps, a total of 1,067
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pieces of tire rubber were picked up along the side of Interstate highways in Ohio,
Pennsylvania, Arizona, Minnesota and Wisconsin. The results are tabulated in
Table 14.
TABLE 14
Interstate Highway Roadside Survey of Scrap Tire Rubber
Passenger
Tire
Truck
New
Tire
Retread
New
Retread
84
60
364
559
Passenger Tires——42%
retreads
Truck Tires 61%
retreads
All Samples 58%
retreads
Severe limitations must be placed on the interpretation of the data resulting from
this survey. Since there is no way to accurately determine the number of
truck, bus, and passenger car tires--retreaded or new——that have passed a
given point along the highway, accurate and precise statistical information cannot
be obtained. However, it can be established that retreaded tires are not the sole
source of scrap rubber along the roadside. In fact, along any given section of
highway, 30-50 percent of the rubber is probably from new tires.
The passenger tire figures should be viewed very critically. Although
55
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they show only 42 percent of the scrap to be from retreads, it should be recognized
that less than 20 percent of the passenger tires on a high speed interstate highway
are likely to be retreads. On the other hand, at least 40 percent of the truck and
bus tires on the interstate are likely to be retreads. However, it is also not
realistic to conclude that if 40 percent of the truck and bus tires on the road are
, and that it’ 60 percent of the scrap is from retreads, that retreads have
a higher failure rate than new tires. Since only small pieces of rubber were
available for examination, it was not possible to determine the cause of failure,
i.e., read hazard or carcass failure totally unrelated to the fact that the tire had
been retreaded.
Non-Passenger Tire Retreads
Truck, aircraft, and racing fires have long been successfully retreaded. How-
ever, in each of these cases the tire design and use differs widely, with all three
differing from the average passenger tire.
Truck fires are subjected to continuous operating speeds arid loads approach-
ing 100 percent of capacity. Aircraft tires see short durations of high speed and
heat followed by extended periods of extreme cold. Racing tires are subjected to
high heat and cornering traction for short durations, but with reduced loads. The
passenger tire is subjected to sustained Interstate highway speeds, often overloaded
and underinflated and is required to maintain its integrity over a lifetime approach-
ing 30 million flex cycles, while being subjected to variable conditions of weather,
road hazards, and perhaps the most severe of all---consumer misuse and abuse.
56
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Aircraft tires are routinely retreaded 7 to 9 times, and are able to meet and exceed
all Federal safety regulations. Truck tires frequently run 100,000 miles or more
on the original tread and then another 100,000 miles on each of 2 or 3 retreads.
Both cases present a strong argument that tires can be successfully retreaded.
However, there are critical operating and design differences between aircraft, truck,
and passenger tires which do influence the relative retreadability of these tires.
A 49 x 17, 28 ply rating airplane tire, which is used on many modern jet aircraft,
is designed to carry a 43,200 pound load at 180 pounds per square inch inflation
pressure. Under such operating conditions, the tire deflects 3.7 inches, Stated
another way, for every 1,000 pounds of carrying capacity, the tire deflects 0.086
inches. A typical 10.00-20, 12 ply rating truck tire is designed to carry a 4,760
pound load at 75 psi inflation pressure when used in dual applications. Under these
designed operating conditions, the tire deflects 1.25 inches or 0.260 inches per
1,000 pounds of load. A GR78—14, 4 ply radial passenger tire designed to carry
1,380 pounds at 24 psi inflation pressure, deflects 1.5 inches, or 1.086 for every
I , 000 pounds of load, more than 12 times the loaded deflection of the aircraft tire
and 4 times that of the truck tire.
It is obvious the passenger tire is much more flexible than the typical airplane
or truck tire. This is because a passenger tire is designed to act as a shock
absorber. The passenger tire forms an integral part of the automotive suspension
system which is designed to give optimum passenger comfort.
The aircraft tire acts in a limited capacity as a shock absorber, but it is
57
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primarily a rigid support member not intended to absorb road hazards or supply
additional riding comfort. The primary function of the truck tire is to carry high
loads for sustained periods over the highway. The shock absorbing properties
of a truck tire are minor when compared to the passenger tire. The truck tire is
designed to provide for maximum service life, not as a comfort device.
The useful strength of any tire is related to its designed carcass strength and
contained air pressure. The 49 x 17 airplane tire, discussed earlier, weighs
nearly 220 pounds and develops its strength through the use of approximately 20
ply layers and 180 psi contained air pressure. The average 10.00-20 truck tire
weighs 100 pounds, and has 6 or more ply layers and operates with 75 psi contained
air pressure. By comparison, a passenger tire with 2 or 4 ply layers operates at
24 psi contained air pressure and weighs approximately 30 pounds. It is apparent
that the stiffer, less flexing carcasses lead to increased mileage in the case of truck
tires, and more retreads in the case of airplane tires.
Passenger tires could not perform their designed function as an integral
part of the suspension system of the passenger vehicle if they were designed to
operate with stiff sidewalls and high inflation pressures. This difference in
construction and operating characteristics results in unfortunate limitations for
the retreading of passenger tires.
Due to the excessive flexing required of the passenger tire, the tread scrubs
itself away while maintaining high levels of traction, resulting in far 1e55 mileage
than that obtained with the less flexible truck tire. Also, as a result of the excessive
58
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flexing and transmittal of road shocks to the tire sidewalls, a hinge point is developed
at the edges of the tread mass or belt edges. The rigid tread shocks are transmitted
through this point to the flexible sidew ails. Belted bias and radial passenger tires
thus become susceptible to belt edge separation which may further limit
retread ability.
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IMPROVING RETREADABILITY
Tire Design
Tire technology has led to the development of three basic types of tire
construction; the bias ply, the belted bias ply, and the radial ply. Until the late
1960’s essentially all passenger tires manufactured in the United States were bias
ply. The modern radial ply tire was a European development introduced into the
United States in major quantities in the late 1960’s. The belted bias tire was an
intermediate American development which bridged the gap between the bias ply
and radial ply tire designs.
Bias Ply Construction
The early bias piy design consisted of individual layers of cotton or rayon
fabric coated with rubber having a directional or bias cord angle. In each individ-
ual layer or ply, the fabric cords were placed at an angle or bias to the direction
of tire travel. Each subsequent ply was built into the tire at an equal but opposite
angle to the ply below. In a four ply tire the first and third ply cords run in the
same direction, while the second and fourth ply cords run in the opposite direction
(see Photograph 1). This practice was necessary to give the tire stability and
strength to carry the vehicle load at optimum inflation pressures.
Cotton was originally used and the development of new, stronger, textile fibers
led to the use of rayon and nylon as improved tire cord. These were followed some
time later by the introduction of polyester tire cords for passenger tires. Today
nylon and steel are used for truck and airplane tires and rayon, polyester, glass
60
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and steel are used for passenger car tires.
The four ply bias tire is the least troublesome construction currently being
retreaded. However, the mileage potential of the bias ply tire is limited by the
squirming action of the tread as it goes through the footprint area and by its higher
operating temperature in the tread shoulders. The bias ply tire is also more
susceptable to road hazard damage than the belted tires.
The two ply bias tire was standard equipment on new ears for several years,
but never gained acceptance in the retread shops. Retreaders have indicated that
the two ply bias tire experienced a high percentage of road hazard failures.
The good experience retreaders have had with the four ply bias and the bad
experiences with two ply bias, correlates well with the DOT indoor wheel test data
reported in the previous section.
Belted Bias Construction . This construction utilized the bias design principle
discussed previously, but has the added feature of narrow pieces of ply cord placed
directly under the tread at an angle closer to the direction of travel than the bias
plies (Photograph 2). This added material is called a belt and gives rigidity to the
tread area, reducing squirm and heat build-up and resulirig in longer wearing tires.
The belted bias tires also offer increased protection from road hazard failures.
Belted bias tires were subject to many development problems which ultimately
became problems for the retreader. The early use of fiberglass as a belt material
led to extensive casing rejections by the retreader for broken belts or separated
belts. The reject level reached a point v here many refused to accept glass belted
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casings. Later generations of glass belted tires have overcome most of the early
problems and retreaders now routinely process glass belted bias tires.
Radial Tire Construction . The modern radial tire was developed in Europe
and contributed to increased tire wear while maintaining high traction capabilities.
Early designs incorporated rayon ply cords and rayon belt cords. The radial
tire gets its name from the radial ply cord direction utilized. Instead of placing
the individual plys at a bias to the direction of the tire travel, the radial ply cords
are placed nearly perpendicular to the direction of tire travel. The textile or steel
belt cords are placed at a low bias angle to the direction of tire travel giving the
tire a rigid tread area. The radial ply cords also allow the sidewall to absorb the
flextures generated in service with a minimum of friction or fatigue (see Photograph
3). The result is a superior wearing tire having high road hazard resistance,
reduced heat build-up, increased traction and superior overall performance.
Radial design tires are now beginning to reach the retreader, and as has been
true of an new tire constructions, there are problems. A high percentage of steel
belted radial casings are being rejected because of belt edge separations.
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Reasons For Casing Rejection
Twenty-four retread shops were visited to determine the manner in which
casings received for retreading were inspected and the reasons for which those not
suitable for retreading were rejected. Only limited details were obtained from the
individual retreaders, since most of them purchase casings from jobbers or
intermediaries who pick up casings from service stations, tire stores, or other
collection points. The jobbers then presort the casings before selling to a
retreader. A generalized tire collection system is outlined in Figure 1, indicating
the possible sources and avenues by which tires flow to the retreader. It was
found that there is no consistent definition of a Class I casing. Most jobbers
indicated a wide variation in the casings that would be acceptable to the retreaders
they served. Their customers generally included those retreaders who would only
accept the top 10 percent of the total casings handled, retreaders who would be
satisfied with the second 10 percent quality level, and retreaders who would accept
the third 10 percent or lower. Obviously the prices varied with the top 10 percent
commanding the highest price.
Throughout the interviews with retreaders and used tire jobbers, a definite
pattern was established as to the reasons for casing rejection, but definite numbers
were not available. In order to get actual numbers to confirm these estimates,
arrangements were made for two men to spend one week at Laidn Industries of
Chicago, Illinois
During that week, they inspected 3,780 passenger tires and recorded the
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Service
Station
Small Jobber
Collection Service
Grade
Discard
Small
Retaile 4 . s
High Quality
Retreader
Retreaders
Own
Stores
Medium Quality
R etreader
Chain and
Department
Stores
Dis card
Low Quality
R etreader
Large Independent
and Company
Retailers
Grade
Figure 1. Collection and distribution of used tire casings to the retreader.
Collection Service
a)
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cause of rejection as a function of tire construction. The Lakin facility grades nearly
2-1/2 million tires per year, and it was felt that the 3,780 tires inspected were a
thoroughly -representative sample. The results of the survey are shown in Table 15.
The major causes for rejection are illustrated in Photographs 4 through 10.
Photograph 4 is typical of damage to a bead resulting from improper mounting
or demounting of the tire from the rim. Bead damage permits air and
moisture to penetrate into the ply layer, eventually causing ply separation arid
tire failure. Two ply bias tires reflected a somewhat higher susceptability to
bead damage in the survey. This is probably due to the lighter construction
utilized in many two ply tires and the absence or minimal use of fabric chafer
strips in such tires. Photograph 5 illustrates excessive tread wear, poor balance,
and poor alignment. Not only was the tire not removed when 2/32 inch of tread
remained (as is required by law in many states and as recommended by tire
manufacturers), but only one fabric ply remains. Uneven tread wear from side
to side is evidence of misalignment, while uneven wear around the circumference
indicates poor balance. Photograph 6 is another example of excessive tread wear
resulting from poor alignment. In this instance, the edge of the top belt has
been exposed on the one side, while ample tread remains on the opposite side.
This type of tire damage is especially common in radial tires on front wheels
which require proper inflation as well as proper alignment. The 60.9 percent
rejects for textile belted bias tires is somewhat misleading due to the small
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TABLE 15
REASONS FOR PASSENGER TIRE CASING REJECTIONS
\ ype of
\Tire
Typ
\
Bead Damage
Bias Ply Bias Belted Radiai
Average
7.0%
2 Plies
10.2%
4 Plies
6.6%
Textile
Belt
Glass
Belt
6.9%
Steel
Belt
Textile
Belt
Glass
Belt
Steel
Belt
Tread Worn Out
2.9
12.2
60.9%
9.1%
12.5%
10.6%
Road Hazard Damages
1.5
.9
—
.4
12.5
.9%
Cut
9.5
10.5
17.7
25
12.5%
Fatigue
1.3
33.3%
.6%
Separation
1.5
.4
16.9
25
6.9%
SizeNot Used For
Retreads
29.2
8.7
2.2
25
10.5%
Too Many Punctures
2.2
3.1
5.2
3.4%
SevereSidewall
Cracking
13.1
15.7
8.7
8.7
33.3
12.2%
Studded
1.7
13.0
.4
.8%
Tread Cracking
.7
.9
10.0
4.5%
Previous Cap
2.9
6.1
.4
3.0%
Other -—
.9
1.7
100%
2.2%
Good
26.3
31.0
17.4
20.4
33.3
24.9%
Totai -
100%
100%
100%
100%
100%
100%
100%
100%
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sample size (only 67 as compared to 1,467 glass belted bias tires). The high
reject rate was strictly related to too many miles, and had no relation to tire
design.
Photograph 7 is an example of excessive air pressure leading to heavy wear in
the center of the tread arid the flat spot outlined by crayon indicates a belt
separation. B elt separations of this type account for a very large number of
casing rejections, especially in the early generation glass belted bias tires
(16.9 percent). In addition to the high percent of rejects at this point of
inspection, the glass belted tires also account for the highest percentage of
rejections by the retreader at post buffing inspections.
The 25 percent steel belted radial rejections due to separations are more
typically the type illustrated by the cross-section in Photograph 8. The separat-
ion between the two belt plies at the lower edge of the belts is clearly visible.
Photograph 9 is typical of the damage caused by the environment to which a
tire is exposed. This example is typical weather-checking and is common to
most tires more than 6 years old. This time period is drastically reduced in
the Los Angeles area, where high concentrations of ozone hasten the appearance
of severe sidewall cracking. The Los Angeles area casing rejection rate for
weather checking is many times the rate in the rest of the country. Among the
first line retreaders in that area, sidewall checking is the most frequent cause
for casing rejection. Lower quality retreaders frequently purchase such casings
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and paint the aid ewalls after retreading to improve the tires appearance, but
not its quality. This ozone cracking is objectionable from an appearance
standpoint but it is rarely the cause of tire failure.
Many of the rejections reported under the category of sidewall cracking,
also resulted from the physical damage incurred by bumping and scuffing curbs,
rocks and other obstacles.
Photograph 10 illustrates a cut that has penetrated the cords, resulting in a
non—retreadable casing. This picture also illustrates the tread wear indicators
that are incorporated into every tire tread design. When the solid rubber bar
appears across the width of the tread, as in this picture along side of the cut,
only 2/32 inch of tread remains. At that time, the tire should be removed
from service. A tire with minimum tread remaining is far more susceptible to
damage from cuts.
Tread cracking accounts for 10 percent of the glass belted bias tires
rejected in Table 15, but these were nearly all one design and the problem
was caused by tread rubber compounding--not the glass belt design.
Steel belted bias tires also show a 100 percent rejection, this was due to
the fact that no retreader in the area could process the tires--not to a specific
failure.
Sizes not desired for retreading is a major cause for rejection. Most of
the two ply tires were old and of a size no longer used. Steel belted radials
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were a small sample and sizes rejected were from European cars not widely
used in this country.
Tire Maintenance
Improved maintenance of tires could make an additional 10 to 15 percent of
discarded tires suitable for retreading. This increase in casings available for
retreading would permit a 50 percent increase in the number of passenger tires
presently retreaded. Nearly 24 percent of the casings rejected as unsuitable for
retreading are rejected because of (1) bead damage, (2) excess tread wear, (3)
cuts, (4) punctures (refer to Table 15). These causes for rejection can be
virtually eleminated by rigorous adherence to basic tire maintenance procedures
including: (1) exercising care in mounting and demounting tires; (2) remove
tire when 2/32 inch tread remains; (3) maintain proper alignment, balance, and
inflation and rotate tires as recommended. These are simple precautions, readily
put into effect by Federal Government agencies. Current GSA practices require
that every car be serviced at 3,000 mile intervals, arid that servicing includes
inspecting the tires and taking any remedial action indicated--such as balancing
or realignment. Getting the general public to implement these practices will be
considerably more difficult.
Improved Retreadability by Tire Design
For the first time since World War II, new tire manufacturers have an incentive
to increase the retreadability of a new tire. Raw material and evergy shortages have
become a harsh reality and it is imperative that the maximum benefits be realized
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from every tire produced. Concurrently an awareness of environmental limitations
has been growing. Solid waste disposal is a major environmental problem--and
waste tires are a major part of that problem. Many municipal waste disposal
stations will no longer accept scrap tires, and where they do, charges of 25 cents
per tire and higher are not uncommon.
To reduce the number of casings rejected for retreading, new tire manufacturers
should consider ways of protecting the bead to make it less susceptable to damage.
Returning to the use of chafers which protect the bead toe should reduce the
tendency of the bead toe rubber to tear during mounting or demounting.
If a retreaded tire is expected to have an 80,000 mile life, as could well be the
case with retreaded radials, the sidewall must be compounded to last an 8 to 10
year life without excessive weather checking.
Many problems plaguing tire retreaders result from the wide variations in tire
dimensions within a given size of tire and the many varieties of tire sizes and
desigx 4 s produced by each tire manufacturer. Leaders in the new tire industry
have acknowledged this problem, and there may now be a trend toward reducing
the number of tire types presently manufactured. This would bring American
practice more in line with European where tire sizes are limited regardless of the
manufacturcr. Although the driving force behind such a change may be to reduce
inventory and distribution costs, the retreader will benefit.
The tire retreader also benefits from changes in tire design resulting from
‘70
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constant improvements in new tire construction. New tire manufacturers constantly
have adjustment rates, or failure rates, as an incentive to improve new tire designs.
New tire designs are not placed into production until after extensive in-house
arid field testing. But, use by the consumer under a wide range of operating
conditions is the final proof of performance, and as consumer mileage accumulates,
product limitations are encountered and design changes may be required. This was
true with the bias and belted bias designs and is currently ture with the radial designs.
Retreaders were quick to point out the belt edge separation problem with the radial
tires, especially with the steel belted radials.
Design changes to increase breaker edge adhesion and reduce the belt edge
separation problem are currently being put into practice. Three such practices
are outlined in Figure 2 showing fabric overlays incorporated in different
configurations. The retreader will benefit from a reduction in this problem as
second and third generation casings become available.
71
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FABRIC
OVERLAY
PIECES
STEEL BREAKERS
- -----
FABRIC — — — — — —
OVERLAY
PIECES STEEL BREAKERS
FABRIC
OVER LAY
PIECE
STEEL BREAKERS
Figure 2. Typical design considerations to eliminate or reduce
steel breaker edge separation on radial tires.
72
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ECONOMICS OF RETREADiNG
The economics of retreading the larger and more expensive tires are widely
accepted. The average retreaded truck tire is often expected to wear as long as
a new tire and for only one-third the cost. Civilian and military aircraft also make
extensive use of retreads for economic reasons. Most aircraft tires are retreaded
7 to 9 times with each retread costing only 20 percent of the cost of a new tire, but
performing equally well.
In 1970, the U. S. Army set a goal of meeting 75 percent of their replacement
tire needs with retreaded tires. They have nearly achieved this goal, and report
savings of more than $30 million in slightly less than 5 years.
The economics of tire retreading are heavily dependent upon the initial cost of
the tire. In general, the higher the cost of a new tire, the lower the percent of
new tire cost for the retread, (i.e., a $500 airplane tire may be retreaded for 20
percent of the new tire cost, a $150 truck tire for 33 percent, and a $20 passenger
tire for 50 percent).
Passenger Tire Retreading Cost Factors
Individual retreading cost components vary widely from one retreader to
another, and are heavily dependent upon volume. But, as an average, the three
73
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major cost components (excluding casing cost) fall into the following ranges:
Material Costs $3.00 to $4.00
Labor 1.50 to 2.00
Overhead 1.50 to 2.00
Total Mfg. Costs $6.00 to $8.00
Material costs, primarily tread rubber, consistently account for 50 percent or
more of manufacturing costs. Tread rubber requirements range from less than 7
pounds for a small 83 series tire to more than 11 pounds for the larger 78 series
tires. Nine pounds of tread rubber is a generally accepted average covering all
sizes of passenger tires. Hot cap tread rubber prices range from 30 cents to 45 cents
per pound depending on quality and quantity, while precured tread rubber costs
approximately 75 cents per pound.
With direct manufacturing costs averaging $7.00, most retreaders would like
to retail their product for $14.00 and would wholesale it for $10.00, again excluding
the cost of the casing. Comparing the retail price of $14.00 for retreads with a
price of $20.00 for new bias ply tires, illustrates one of the major reasons why
retreads have not beer. able to increase their share of the replacement tire market.
Most people would rather pay $20.00 for a new tire, than to pay $14.00 for a
retreaded tire.
As the price of new tires increases, the retread becomes more competive. For
example, a typical GR78-14 WSW steel belted radial retails for about $60.00. A
good retreader will process a radial for very little additional cost, but now he can
74
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retail his product for $20.00 to $25.00 and still be less than one-half the price of a
new tire. And, at the same time, he is able to increase his profit margin.
The difference between a good retreader and a poor retreader is not always
apparent in terms of direct costs. The use of the lowest quality tread rubber
instead of a premium grade will result in manufacturing savings of about $1.00 per
tire. But, manpower and equipment are equally as important in terms of quality as
direct costs. If a retreader does not have the proper equipment, or if he misuses
what he has, the result will often be a substandard product.
However, the greatest variable lies in the quality of the retreaders manpower.
Aside from the necessity of closely adhering to set operating standards, all casing
selection and inspection is performed manually. Thus, all decisions as to what is
retreaded and how it is retreaded are in the hands of the operating crew.
If reliable and economical non-destructive test methods can be perfected and
their effectiveness demonstrated, much of the human factor can be removed from
casing inspection and selection.
The retreading industry is currently seeking NDT equipment that would meet
their requirements with a capital investment of about $10 ,000. Such a cost would
permit inspections for about 50 cents per tire.
75
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THE FEASIBILITY OF REQUIRING THE FEDERAL GOVERNMENT
TO USE RETREADED TIRES
Federal Government agencies are currently engaged in an extensive program
to increase their use of retreaded tires. The main effort has been concentrated on
truck tires where both economic and performance factors have been well
established. The Army appears to have led this effort with a policy that at least
75 percent of its replacement tire needs will be met with retreaded tires. At the
present time the Army has reached the 73 percent level world—wide, and in Europe
80 percent of replacements are met with retreads. The Army program has
concentrated on truck tires with only limited passenger tire retreading. In Fiscal
1974, GSA retreaded 240 ,000 tires (including continental United States Army
retreads) with at least 80 percent being truck tires.
Available test data on the performance of retreaded passenger tires is very
limited and inconclusive. Independent performance tests on retreaded tires have
been conducted by DOT and GSA. These tests show extreme quality variations
between retreaders and a performance level generally below that of a new tire.
However, there are instances where retreaded passenger tires have been shown to
have performance properties approaching or equaling that of new tires.
There is no reliable operating or fleet data available for passenger tire
retreads such as is available for truck or aircraft retreaded tires. Retreaded
passenger tires are occasionally used for in—city fleet operation by taxi cabs or
utilities, but this experience is totally unrelated to the typical high speed and
76
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endurance levels to which the average passenger tire is subjected.
Until it can be established that a properly designed new tire, properly
maintained and then properly retreaded can meet new tire performance criteria,
the Federal Government cannot be expected to implement an unrestricted policy of
requiring the use of retreaded passenger tires.
Costs and Benefits of The Federal Government
Using Retreaded Passenger Tires
The benefits to be derived from the increased use of retreaded passenger
tires must be delayed until: (1) independent, definitive performance tests have
been completed to determine the safety of high quality retreads as compared to new
tires, (2) new standards or specifications are developed to insure that only high
quality retreaded tires are manufactured, (3) a highly reliable, but inexpensive
method for casing inspection is developed, (4) radial tire belt edge separation
problems are solved.
Once the above conditions have been successfully met, significant savings
can be realized in terms of dollars, energy, raw material, arid solid waste disposal.
In fiscal year 1973, the Federal Government owned and operated a fleet of
98,041 sedans and station wagons that traveled nearly 900 million miles. This can
be compared to a total United States passenger car mileage of 986 billion miles in
1972. Not only does the government fleet represent 0. 1 percent of the passenger
car miles traveled throughout the United States, but government purchasing and
77
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Maintenance procethres lend themselves to a well controlled and documented test
fleet. Successful use of retreaded passenger tires by this Government fleet could
be expected to have a major impact on the average consumer T s reaction to retreaded
tires. The major barriers to the increased use of retreaded passenger tires by
both the general public and the Federal Government are the uncertain quality and
the emotional connotations connected to a used product.
Tire Maintenance . Current GSA practices require that every car be serviced
at 3,000 mile intervals. This service procedure includes inspecting the tires and
taking any remedial action indicated--such as balancing or realignment. Since
these procedures are now required, there should be no additional cost involved
for providing improved maintenance services. It will be necessary to educate
both the drivers and maintenance crews in order to get strict compliance with the
proper tire maintenance procedures.
New Tire Purchasing . Existing Federal Government purchasing procedures
are adequate to meet the requirements for purchasing tires more suitable for
retreading, and at no increase in cost. The only modifications to be made in
existing procedures would be to restrict tire purchases to tires that pass a
retreadability specification in addition to meeting existing QPL requirements.
The retreadability specification would be based on actual field experience
with retreading and post retreading operation. Radial tires offer the greatest
opportunity for making major improvements in reducing solid waste and for
reducing energy and material requirements for tire manufacture, however, they
78
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are now posing serious problems for the retreader. These problems will be solved,
but some tires will be more retreadable than others and these can only be determined
by actual field experience.
Environmental tests will also be a key factor in the r treadability specifications.
A radial tire capable of a 40,000 mile first life and a secoi d 40 ,000 mile retread life
presents new requirements for sidewall aging. For the a-Jerage consumer the 80,000
miles might mean a life of 8 to 10 years, or longer.
Obviously these new retreadability specifications will require time to develop,
but the cost for introducing such improvements into a tire should be minor.
Passenger Tire Retreading . Improvements in Federal Government tire
maintenance and purchasing procedures are expected to make a major increase in
the number of passenger tire casings that would be suitable for retreading. A
concentrated educational effort could probably improve the total number of casings
that are retreadable. Current levels of casing rejections and estimated values for
maximum improvement in both the government and public sector are shown in
Table 16.
Te6ts conducted by GSA reveal a wide variation in quality throughout the
retreaded tires manufactured by GSA approved contractors, following GSA
specifications. In the QPL treadwear portion of the test, the tires supplied by
retreader “F” indicated treadwear as low as 10,453 miles, while the control tires
were as high as 26,000 miles. Tire economics hinge on the average cost per mile,
and a policy of buying from the lowest bidder without any measure of mileage can
79
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TABLE 16
REASONS FOR CASING REJECTION
Estimate’ Percent Rejected
Type of Damage Current 1 st Federal Best U. S .
Bead 7 3 4
Excessive Treadwear 11 2 6
Road Hazard 1 1 1
Cuts 12 9 10
Separations 7 7 7
Unpopular Size 11 2 8
Punctures 3 2 3
Sidewall Damage 12 6 9
Tread Cracking 4 2 3
Other 7 4 4
Total Rejected 75 38 55
Retreadable 25 62 45
80
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only be false economy.
Any change in Federal retread specifications should consider the addition
of a QPL type of tread wear qualification test, followed by random sampling of
products to insure the level of treadwear. Additional changes in Federal passenger
tire retread procurement should consider the addition of more trained inspectors
for frequent visits to the contractor, and the use of financial incentive contracts to
encourage the production of a quality product.
Maximum benefits for the Federal Government should be realized from a closed
loop system utilizing improved Government tire purchasing and maintenance proced-
ures, processing these same tires through retread shops operating in accordance
with strict Government specifications, and then placing these retreaded tires into
Federal Government service.
Potential Dollar Savings . Detailed figures were not available for the total
number of passenger tires purchased annually by the Federal Government. , it
is possible to arrive at a close approximation based on the total miles driven by
Government passenger vehicles. Assuming four belted bias tires per vehicle,
averaging 26 ,000 miles per tire, for the total 900 million miles, 138,462 tires would
be required. At an average GSA purchase price of $28.00 per tire, the Federal
Government spends about $4 million each year for passenger tires. This estimate
is in good agreement with a fiscal 1971 G A report indicating that the Federal
Supply Service (FSS) had purchased 73,219 passenger tires for $2 million and FSS
has estimated that they purchase about 50 percent of the total passenger tires used
81
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by the Federal Government.
Any economic advantage that might be realized by the use of retreads, must
be based on a true cost per mile. Consider the case of a new belted bias 078-14
having a GSA cost of $28.42, and the same size retread from a GSA retreader in the
District of Columbia for $7.65, or 27 percent of the new tire cost. There is a
tendency to ciaim a 73 percent reduction in cost, but the new belted bias tire can be
expected to average 26,000 miles or a cost of 0.11 cents per mile. While the
retread may deliver only 10,000 miles (on the basis of GSA tests), at a cost of
0.08 cents per mile, or a 27 percent savings, not 73 percent.
Figure 3 illustrates the savings possible by the use of retreaded tires. On the
basis of an annual expenditure of $4 million with zero passenger retreads, an annual
savings of $1.1 million could be realized if 40 percent of the replacement tires were
retreads purchased at 30 percent of the cost of a new tire-mile.
It is very probable that stricter GSA retreading specifications may increase the
cost of retreaded tires to the point where 50 percent of the new tire-mile cost is
more realistic. At this level the annual savings for 40 percent retreads is $800,000.
Present GSA retreading specifications require that the GSA furnish all casings
to the retreader. This is a good policy because it insures that all casings being
retreaded at least met Government standards as new tires. The policy does limit
the number of tires that can be retreaded. Table 16 indicates that as many as 62
percent of the discarded casings could be retreaciable, provided the recommended
maintenance and purchasing policies were followed. But, it seems very unlikely
82
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3. 5
0 20 40 60 80
100
PERCENT FEDERAL GOVERNMENT RETREADS
Figure 3. Dollar savings as a percent of Federa’ Government
passenger retreads and as a percent of new t re-mi1e costs.
0
-I
I
3.0
2.5
2.0
1.3
1.0
0.5
83
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that anything exceeding 40 percent retreadable could be attained in the near future.
An increase to even 40 percent will require nearly doubling the number of
casings now suitable for retreading.
The possibility does exist for the Federal Government to use retreaded fires
for all replacements. In such a case retreaded tires for 50 percent of a new
fire-nile cost, would save $2 million per year. However, this would entail the use
of non—government purchased casings, resulting in less control of the quality of
final product. A situation that would be difficult to justify at this time.
Potential Solid Waste Reduction . In 1973 the American public discarded nearly
143 miUion passenger tires (more than 3 billion pounds) into the nations solid waste
stream, The Federal Government contributed about 150 , 000 of these tires.
Retreading fires can make a significant reduction in the number of tires discarded
annually, as can improvements in fire design to give a longer wearing tire. The
benefits to be derived by both the improved mileage tire and retreading are
illustrated in Figures 4 arid 5 and tabulated in Tables 17 and 18.
Government passenger cars are presently operating with a mixture of bias,
belted bias, and a few radial tires. If the Federal Government was limited to only
bias ply tires (average tread life of 20,000 miles), they would discard 180,000
tires per year. Retreading 100 percent of these tires would reduce the discards to
90,000, but this same reduction can be achieved by using radial tires (average of
40,000 miles). Additional reductions in the number of Government tires scrapped
annually can be achieved by retreading the radials. Radial retreads were
84
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0
20 40 60
80
PERCENT FEDERAL GOVERNMENT RETREADS
Figure 4. Tires discarded to solid waste as a percent of
Federal Government passenger tires retreaded.
100
0
C l ,
200
150
100
50
85
-------
PERCENT TOTAL U. S. RETREADS
Figure 5. Tires discarded to solid waste as a percent of
total U. S. passenger tires retreaded.
(I )
0
•s-.
-1
200
150
100
50
0 20 40 60 80 100
86
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TABLE 17
EFFECT OF RETREADING AND TIRE
DESIGN ON THE NUMBER OF PASSENGER TIRES
DISCARDED ANNUALLY BY THE FEDERAL GOVERNMENT
(IN THOUSANDS OF TIRES)
Tire Design
Percent
Retreaded
0
20
30
40
100
Bias
180
162
153
144
90
Belted Bias
138
124
117
110
69
Radial 1
90
81
77
72
45
Radial 2
90
83
80
77
56
Basis: Bias tire ; 20,000 miles on original tread, retread 20,000 miles
Belted bias tire ; 26,000 miles on original tread, retread 20,000 miles.
Radial tire 1 ; 40,000 miles on original tread, retread 40,000 miles.
Radial tire 2 40,000 miles on original tread, retread 25,000 miles.
87
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TABLE 18
EFFECT OF RETREADING AND TIRE
DESIGN ON THE TOTAL NUMBER O1
PASSENGER TIRES DISCARDED ANNUALLY iN THE U.S.
(IN MILLIONS OF TIRES)
Tire Design
Percent Retreaded
0
20
30
40
100
Bias
197
177
168
158
99
Belted Bias
151
137
129
121
76
Radial 1
99
89
84
79
49
Radial 2
99
91
88
84
61
Basis: Bias tire ; 20 ,000 miles on original tread, retread 20 ,000 miles.
Belted bias tire ; 26,000 miles on original tread, retread 26,000 miles.
Radial tire 1 ; 40,000 miles on original tread, retread 40,000 miles.
Radial tire 2 ; 40 , 000 miles on original tread, retread 25 , 000 miles.
88
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evaluated at two levels of tire mileage. There is considerable disagreement within
the retread industry as to the desirability of a 40,000 mile retread. The 40,000
mile tread life can be obtained with existing technology, but the major concern
centers on the integrity of the tire casing and its ability to withstand the effects of
aging, weathering, abuse, and flexing over an 80,000 mile lifetime. As a result
of this concern, many retreaders are proposing a 25,000 mile retread until more
actual operating experience is available.
It is apparent that the Government could achieve a reduction in tire disposal
from their present 150,000 tires per year to 99,000 by converting to radial tires
and a further reduction to 75,000 to 80,000 by retreading the radial tires. However,
major reductions resulting from the retreading of radial tires will not be realized
until problems, such as belt edge separations, have been resolved.
Similar reductions can be experienced by the total U . S. population. In 1973,
the 143 million discarded tires were comprised primarily of bias and belted bias
tires with a few radials included. A complete switch to radial tires with an average
40,000 mile tread life would reduce the 143 million tires to 99 million, (a 31 percent
reduction). Retreading at the present rate of 20 percent would further reduce this
to 91 million tires for a total reduction of 37 percent. A 50 percent increase in the
number of discarded tires to 84 million, giving an overall reduction of 40 percent
from the present 143 million.
Similar values in terms of total pounds of solid waste discarded are given in
Figure 6 for Federal Government tires and in Figure 7 for total U .S. tires.
89
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6.0
5.0
4.0
3.0
2.0
0
PERCENT FEDERAL GOVERNMENT RETREADS
Figure 6. Solid waste generated annually as a percent of
Federal Government passenger tires retreaded.
0)
0
-4
U ,
z
2
1.0
20 40 60 80
100
90
-------
0
PERCENT TOTAL U. S. RETREADS
Figure 7. Solid waste generated annually as a percent of
total U. S. passenger tires retreaded.
10 20 30 40 50
6000
5000
4000
3000
2000
1000
91
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The change over to radlals is proceeding at a rapid pace with 1974 figures
indicating original equipment (0 .E.) tires to be 40 percent radials, up from 2 percent
in 1972, and replacement tires reached 20 percent radial as compared to 4 percent
in 1972. It is now estimated that by 1980, nearly 90 percent of O.E. tires will be
radials, as will 40 percent of all replacement tires.
Potential Reduction in Raw Material Requirements
A second benefit to be derived from the increased recycling of tires by retread-
ing, will be a reduction in petroleum consumption. Industry sources have
estimated that it requires seven gallons of crude oil to make the average passenger
tire. Five gallons as raw material feedstock, and two gallons to supply the
required energy. Retreading a tire requires only about 1/3 as much crude oil.
This energy savings represents the energy that would be conserved from the
retreading of a tire rather than the production of a new replacement tire. Replace—
ment of the tread requires an average of 9 pounds of material as compared to 27
pounds for the average total tire.
The material requirements for manufacturing tires for the Federal Government
as a function of the percentage of tires retreaded is shown in Figure 8 and Table 19.
By changing from its present mix of passenger tire constructions to radial
tires the Government could save about 7,000 barrels of crude oil per year. Reaching
a 40 percent retread level with radials would save about 9,000 barrels of crude oil
per year (a 39 percent reduction from present material and energy requirements
92
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Federal passenger tire manufacture).
Material requirements for the manufacture of passenger tires for the U .S. are
shown in Figure 9 and Table 20.
Changing the U .S. passenger tire utilization from belted bias tires with 20
percent being retreaded to radial tires would save about 6 million barrels of crude
per year, retreading 20 percent of the radials, an additional 1 .3 million barrels,
while 30 percent retreaded radials would save an additional 0.6 million barrels,
for a total reductions of 8 million barrels per year. (A 33 percent reduction from
the present crude oil requirements for passenger tire manufacture.)
93
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TABLE 19
EFFECT OF RETREADING AND TIRE DESIGN ON BARRELS
OF CRUDE OIL REQUIRED TO MANUFACTURE PASSENGER TIRES
FOR THE FEDERAL GOVERNT ENT
(IN THOUSANDS OF BARRELS)
Tire Design
Percent Retreaded
0
20
30
40
100
Bias
25.7
24.1
23.4
22.6
17.9
BeltedBias
22.4
21.0
20.3
19.6
15.3
Radiall
16.2
15.1
14.5
13.9
10.5
Radial2
16.2
15.6
15.2
14.9
13.0
Basis: 1 pound of tire material requires approximately0 .007 barrels of crude oil
Bias tire ; average weight 25 pounds, retread weight 9 pounds
Belted bias ; average weight 2? pounds, retread weight 9 pounds.
Radial tire 1 ; average weight 30 pounds, retread weight 9 pounds.
Radial tire 2 ; average weight 30 pounds, retread weight 9 pounds.
94
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TABLE 20
EFFECT 01? RETREAD AND TIRE DESIGN ON BARRELS OF
CRUDE OIL REQUIRED TO MANUFACTURE TOTAL U .S. PASSENGER TIRES
(EN MILLIONS OF BARRELS)
Tire Design
Percent
Retreaded
0
20
30
40
100
Bias
28.2
26.4
25.6
24.8
19.6
Be ltedBias
24.6
23.0
22.2
21.5
16.8
Radiall
17.8
16.5
15.9
15.2
11.5
Radial2
17.8
17.1
16.7
16.3
14.2
Basis: 1 pound of tire material requires approximately 0.006 barrels of crude oil.
Bias tire ; average weight 25 pounds, retread weight 9 pounds.
Belted bias ; average weight 27 pounds, retread weight 9 pounds.
Radial tire 1 ; average weight 30 pounds, retread weight 9 pounds.
Radial tire 2 ; average weight 30 pounds, retread weight 9 pounds.
95
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20 40 60 80
PERCENT FEDERAL GOVERNMENT RETREADS
Figure 8. Annual material requirements as a percent of
Federal Government passenger retreads.
100
6.0
3.0
4. 0
3. 0
2. 0
U )
0
- 4
E
s - a
2
36
30
t 1
r
C l )
24
rj
C )
0
In I — .
°
0 .
0
C
C o
p
0 .
C l )
12
1.0
6
0
96
-------
o 20 40 60 80
PERCENT TOTAL U. S. RETREADS
Figure 9. Annual material requirements as a percentage
of total U. S. passenger tire retreads.
0
-4
-4
6000
5000
4000
3000
2000
1000
36
30
24
18
12
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til
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0
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97
-------
APPENDIX
98
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GLOSSARY OF TERMS AND ABBREVIATIONS
Aspect Ratio
A numerical term which expresses the relationship between the standing
height of the tire and the cross section width. (H/W=Aspect Ratio).
Bead
That part of the tire that is shaped to fit the rim. Made of high tensile steel
wires that are wrapped in woven fabric and then held by the plies.
Bead Heel
Outer bead edge that contacts the rim flange.
Bead Toe
The inner bead edge of the tire
Br a1cer
Special cord fabric cushion between tire tread and cord body which reduces
road shock effect on carcass while permitting less tread squirm and resultant
increased tread wear.
Buttress
Portion of tread running around shoulder and blending into sidewall.
Chafer
Reinforcing fabric and rubber around the bead in the rim flange area to
prevent chafing of the tire by the rim parts.
Cushion
The thickness of rubber over, under and between the breaker plies.
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Cushion Gum
A tacky rubber compound, usually approximately 1/32nd inch gauge, used
to form cushion and adhesion between fabrics and between tread and ply.
Dip
A rubber and chemical solution into which the cords are dipped to get adhesion
with the rubber in calendering and in service.
Durometer
A device to measure the hardness of rubber. For example, a tire tread may
be de ned as 60 Durometer which means that it shows this degree of hard-
ness when tested with the durometer.
Elasticity
The property of matter by virtue of which it tends to return to its original
size and shape after removal of the stress causing deformation such as
stretching, compression, or torsion. It is the opposite of plasticity.
Flash
Fin produced by excess rubber squeezed out between edges of mold during
curing process.
Flipper
Reinforcing fabric around the bead wire for strength and to tie the bead wire
into the tire body.
Green Tire
The completed rubber/fabric tire construction just prior to being cured into
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its final shape.
Modulus
A term used to denote resistance to being stretched.
Mold
The heated cavity in which tires are vulcanized.
Nonskid
Tread pattern providing skid protection.
Non-Skid Depth
The groove depth of the tread (used to indicate remaining wear left in tire).
Ozone
A form of oxygen produced by electricity. Accelerates ageing in tires.
Ozone Checking
Formation of fine cracks in surface of rubber due to ozone in air.
Ply
Layer of rubber—coated parallel cords forming unit of tire carcass.
Ply Adhesion
Strength of attraction or adhesion between adjacent plies.
Polymer
A material consisting of large units (molecules) made by joining many
smaller building blocks (simple molecules). Usually used to describe
synthetic rubber.
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Post Inflation
The process of inflating a tire immediately after it is removed from the factory
mold and keeping it under inflation until it has cooled. Also known as
“Pressure Tempering”.
Radial Cracking
Surface openings, generally in shoulder or sidewall of tire, running parallel
to tire radius.
Radial Ply
A tire with cords running radially from bead to bead (90 degrees to center—
line of the tire).
Ribs
Tread sections running circumferentially around tire.
Section Height
Distance between tread crown and bead seat.
Section Width
Measurement of distance through cross sectional width of a tire at widest
part, exclusive of scuffing rib when inflated to normal pressure and not
under load.
Seventy-eight Series
A tire which when mounted will have an aspect ratio of seventy-eight.
Shoulder
Outer edges of tread.
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Sidewall
Zone of tire between buttress and bead.
Sipe
To cut across a tire tread to produce biting traction edges.
Sixty Series Tire
A tire which when mounted will have an aspect ratio of approximately sixty.
Size Factor
The sum of the section width and the overall diameter
Specific Gravity
Ratio of the weight of a given volume of any substance to that of the same
volume of water. The higher the specific gravity, the denser or heavier
the substance.
Squeegee
A thick rubber added between plies.
Static Loaded Radius
Distance from center of wheel to ground on vehicle which has rated load,
normal inflation, and is not in motion.
Tapered Bead
Tires with a taper on the base of the bead for compression on the rim to
seal tubeless tires and to prevent slip.
Tread
Portion of tire which coms in contact with the road.
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Tread Depth
The distance in thirty-seconds of an inch measured from the tread surface
to the bottom of the grooves in a tire.
Tread Elements
The parts of the tread design which are separated from each other and made
distinct by the sipes and rib or lug design molded into the tire.
Tread Radius
The radius of the circle that coincides with the arc of the tread cross section.
The longer the tread radius, the flatter the tread will be.
Tread Wear Indicators
Narrow bars of rubber molded at a height of 2/32 inch across the bottom of
the tread grooves. When the tread wears down to these bars, the tire
should be replaced.
Vents
Raised embellishments on tire to aid molding.
Vulcanization
Process of combining rubber with sulphur or certain other additives under
influence of heat and pressure to eliminate tackiness when warm, and brittle-
ness when cool, and to otherwise improve the useful properties of rubber.
Also known as curing.
Weather Checking
Fine hairline cracks in surface of rubber, caused by oxidation and other
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atmospheric effects.
wsw
White sidewall tire.
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REFERENCES
1. AMF, Tire Equipment Division. Santa Anna, California, 1974.
2. Automobile Facts and Figures. Motor Vehicle Manufacturers Association of the
United States, Inc. 72p., 1973—74.
3. Automotive Research Associates, Inc. Modified FMVSS 109 Endurance Test and
SAE proposed Endurance Test Procedure. For Department of Transportation,
March 1973. (Report No. 109-ARA-73-DOT-HS-001-3—572—1)
4. Bandag, Retreading Process Company. Muscatine, Iowa, 1974.
5. Baumgardner, H. R. The Technology Boom in Retread Equipment. In
Proceedings; Akron Rubber Group Technical Symposium, Division of
Rubber Chemistry, ACS, Winter 1967.
6. Bobo, S. N. Preliminary Study of The Relationship Between Failure of Retreads
During FMVSS 109 Tests and Flaws Detected By Non-destructive Testing.
For Department of Transportation Publication No. DOT-TSC-NHTSA-731.
Aug 1973.
7 Bock, R. L. Speed and Load Programming of Endurance Type Tire Test Machines.
In Proceedings; Society of Automotive Engineers, Automotive Engineering
Congress, Detroit, Michigan, Jan 12—16, 1970. 6 p.
8. Braner, Dr. H. M. An Analysis of The Domestic Retreading Industry. Ranno
Printing Co., Inc. December 12, 1965. 109 p.
9. Clark, S. K. ., H. N. Dodge, D. W. Lee, and J. Luchine. Pressure Effects On
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Worn Passenger Car Tire Carcasses. Department of Transportation
Publication No. UM-010654-2-I. Washington, U. S. Government Printing
Office, May 1974. 31 p.
10. Del Gatto, J.V. Bandag Retreads; A Gripping Story. Rubber World ; 49-50,
Nov. 1973.
11. Department of Transportation, Dockets for FMVSS 109 and FMVSS 117.
12. Dobie, W. J. Problems of Obtaining Multiple Optima In Passenger Car Tire
Performance. In Proceedings; Society of Automotive Engineers, Mid-year
meeting, Chicago, Illinois, May 19—23, 1969. 12 p.
13. Dubrown, R. Big Wheels In Natural Rubber. Rubber Developments; 23 (3):
90—95, 1970.
14. Eldredge, R. W. A Systems and Methods Analysis of The Reuse of Consumer
Goods; for the Rubber Manufacturers Association. Oct.13, 1971.
15. Fox, C. Reconditioning of Aircraft Tyres. Rubber Developments No. 4:
149—152, 1965.
16. General Services Administration. Federal Motor Vehicle Fleet Report, for
fiscal year ending June 30, 1973. Washington, Apr. 1974. 22p.
17. General Services Administration, Federal Supply Schedule. Pneumatic Tires
and Inner Tubes. Nov.1, 1974 toApr. 30, 1975. IssuedOct.11, 1974. 25p.
18. General Services Administration, Federal Supply Service. Tire Retreading
Price Schedule. Sept. 1, l974throughAug. 31, 1975. 25p.
19. General Services Administration. Federal Specifications For Pneumatic
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Tire Retreads, And Repair Materials. ZZ-T-416F, ZZ-T-00 441C, ZZ-T-381M.
20. General Services Administration, Retread Tire Tests, Unpublished Report,1974.
21. Jones, P. B., and R. Garfield. Technology and The Retread. Journal of The
IRI, Oct. 1969.
22. Kennametal, Retreading Equipment. Slippery Rock, Pa., 1974.
23. Lavery, A. L. Nondestructive Tire Testing Studies. Department of Transportation
National Highway Traffic Safety Administration Publication No. 72-7, U.S.
Government Printing Office, Oct. 1972, 30p.
24. Leigh, Dr. W. W. Retread Marketing. N.T.D.R.A. 1974 guidelines National
Tire Dea.lers and Retreaders Association, May 1974. 34p.
25. Litant, I. Some Preliminary Observations On Retread Manufacturing Practices.
Department of Transportation Publication No. DOT-TSC-NHTSA- 72-5.
Washington, U .S .Government Printing Office, Dec. 1972, lip.
26. Long Mile Rubber Company, Certimile System. Dallas, Texas, 1974.
27. Marangoni, U .5 .A. Retreading Equipment. Winona, Minn., 1974.
28. Marshall, S. New Retreading Process Extrudes Rubber Directly On To Casing.
Rubber World ; 44-45, Jan. 1973.
29. Oliver, Tirecap Supply Company. Oakland, California, 1974.
30. Pettigrew, R. J. and F. H. Roninger. Rubber Reuse And Solid Waste
Management: Enviromental Protection Publication SW-22c. Washington,
U.S .Government Printing Office, 1971. 120 p.
31. Prinsep, L. Tyre Retreading. Tyres and Accessories : 32-33, Nov./Dec.1970.
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32. Proceedings; Second Symposium on Nondestructive Testing of Tires, Atlanta,
Georgia, Oct. 1—3, 1974. 30 p.
33. Ring Tread System, International (RTS). Milano, Italy, 1974.
34. Rosenthal, Dr. 0. nd I. E. Enste. The Manufacture of Camelbacks. Indian
Rubber Bulletin ; 25—30, November 1968.
35. Rubber Manufacturers Association. Care and Service of Automobile Tires, 1974.
36. Rubber Manufacturers Association. Shop bulletins. Tire Repairing and
Retreading.
37. Spelman, R. H. Determination of Passenger Tire Performance Levels-High Speed.
In Proceedings; Society of Automotive Engineers, Mid-year meeting,
Chicago, Ill., May 19—23, 1969. 6p.
38. Taylor, I. When Glass Belt Casings Exceed Matrix Dimension. rIodern Tire
Dealer : Retreadmonth 1-5, Feb. 1970.
39. Taylor, I. Retread Standard 117 Is Tough, But Not Impossible. Modern Tire
Dealer : Retreadmonth 1—3, June 1971.
40. Uni-tread, Retreading Process Company. St. Louis, Mo., 1974.
41. Vogel, P. E. Nondestructive Testing. Rubber A , 33-39, Nov. 1974.
42. Vukan, F. S. and T. P. Kuebler. Determination of Passenger Tire Performance
Levels Tire Strength and Endurance. In Proceedings; Society of Automotive
Engineers, Mici—year meeting, Chicago, Ill., May 19-23, 1969. ‘7p.
43. Watson, M. and A. Fans. Processing 78-Series Belted Tires. Modern Tire
Dealer : Retreadmonth 5-12, June 1970.
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Safety Adminstration, Tire Division, Washington, D. C.
56. Personal Interview. Department of Transportation, National Highway Traffic
Safety Administration, Office of Standard Enforcement (Tires), Washington,
D.C.
57. Personal Interview. Department of Transportation, Transportation Systems
Center, Cambridge, Mass.
58. Personal Interview. Firestone Tire and Rubber Company, Akron, Ohio.
59. Personal Interview. Four Day Tire Enterprises, Gardena, California.
44. White, A. J. Evaluation of Tire Repair System. U. S. Army Tank Automotive
Command, TechnicalReportNo. 10181. October, 1968. 27p.
45. Personal Interview. Atlas Supply, Springfield, New Jersey.
46.
47.
48.
49.
50.
51.
52.
53.
54.
Personal Interview.
Personal Interview.
Personal Interview.
Personal Interview.
Personal Interview.
Personal Interview.
Personal Interview.
Personal Interview.
Personal Interview.
American Retreader Association, Louisville, Ky.
American Trucking Association, Washington, D. C.
A.M.F.-Voit, Santa Anna, California.
Bandag, Muscatine, Iowa.
Barnes and Delaney Tire Company, Long Beach, Calif.
Bernard Tire, Manchester, New Hampshire.
B.F. Goodrich Tire and Rubber Company, Akron, Ohio.
Copper State Tire Company, Phoenix, Arizona.
Daley Tire Service, Monsey, New York.
Department of Transportation, National Highway Traffic
55. Personal Interview.
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60. Personal Interview. General Services Administration, Federal Supply
Service, Automotive Division Standards and Quality Control, Wash., D.C.
61. Personal Interview. General Services Administration, Federal Supply
Service, Tire Procurement, Washington, D. C.
62. Personal Interview. General Services Administration, Property Rehabilitation
Division, Washington, D. C.
63. Personal Interview. General Services Administration, Motor Pool Services,
Washington, D. C.
64. Personal Interview, General Services Administration, Office of Audits and
Investigation, Washington, D. C.
65. Personal Interview. General Tire and Rubber Co.,Akron, Ohio.
66. Personal Interview. Lakin and Sons, Chicago, Illinois.
67. Personal Interview. Malerba Silver City Tire Co., Meriden, Conn.
68. Personal Interview. Marangoni Retreading Equipment, Winona, Minn.
69. Personal Interview. Merchants Tire Co., Boston, Mass.
70. Personal Interview. Montgomery Wards, Chicago, Ill.
71. Personal Interview. National Tire Dealer and Retreader Association,
Washington, D. C.
72. Personal Interview. Noyes Tire Company, Westbrook, Maine.
73. Personal Interview. P. I. E. Inc.,Oakland, Calif.
74. Personal Interview. R. E. Darling Co., Tucson, Ariz.
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75. Personal interview.
76. Personal interview.
77. Personal Interview.
78. Personal Interview.
79. Personal Interview.
80. Personal interview.
81. Personal interview.
S. Attleboro, Mass
82. Personal interview.
83. Personal interview.
Washington, D. C.
84. Personal Interview.
85. Personal Interview.
86. Personal Interview.
Royal Tire Company, Atlanta, Ga.
Rubber flanufacturers Association, Washington, D. C.
S & S Tire Retreaders, Akron, Ohio.
Sears, Roebuck, Chicago, Illinois.
Texas Tire Company, Houston, Texas.
Tire Retreading rnstitute, Washington, D. C.
Tire Retreading Institute, Research and Development,
Trac-Treads, Atlanta, Ga.
U. S. Army Materiel Systems Analysis Agency,
U. S. Army Tank Automotive Command, Warren, Mich.
University of Michigan, Ann Arbor, Michigan
Worster Trucking, North East, Pennsylvania.
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