SDSB 79-06
Technical Report
January 1979
Summary and Analysis of Comments
Received in Response to the EPA Report
Determination of Tire Energy Dissipation
Analysis and Recommended Practices
.by
Glenn Thompson
NOTICE
Technical Reports do not necessarily represent final EPA decisions or
positions. They are intended to present technical analysis of issues
using data which are currently available. The purpose in the release of
such reports is to facilitate the exchange of technical information and
to inform the public of technical developments which may form the basis
for a final EPA decision, position or regulatory action.
Standards Development and Support Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air and Waste Management
U.S. Environmental Protection Agency
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I. Introduction
This document presents, summarizes and analyzes the comments
received in response to the EPA Draft Report, "Determination of Tire
Energy Dissipation-Analysis and Recommended Practices'1. These comments
were solicited by distributing the Draft Report at the April 26 meeting
of the SAE Tire Rolling Resistance Subcommittee and by distribution of
the report to MVMA, JAMA, and AIAA.
The distributed EPA report contained two recommended practices for
determination of tire energy dissipation. The first recommended prac-
tice determined the tire energy dissipation by driving an initially cold
tire at steady speeds. As the tire approaches thermal equilibrium, the
force required to drive the tire decreases; therefore, this procedure
primarily considers the thermal transient behavior of the tire. This
procedure is consequently described as either the quasi-steady state
procedure or the thermally transient procedure. It is characterized by
steady state speeds and slow variations in the measured forces.
The second recommended practice determined the tire energy dis-
sipation as the tire was operated over the transient speed-time cycles
used for the EPA exhaust emission certification tests. In this practice,
the speed of the tire, the force required to drive the tire, and the
thermal characteristics of the tire are all transient. Consequently,
this procedure is referred to as the force transient procedure, or
simply as the transient procedure.
The subsequent comments and the analysis of these comments are
divided according to the recommended practice which was addressed. That
is, either the full transient procedure or the simpler thermally tran-
sient procedure. In the first section of this report, a synopsis of
the comments received from each commentor is presented. These comments
are subdivided according to the major topics addressed. In the second
section, the summary of comments, a summary of the comments received in
each major topic is presented. The analysis section discusses and
analyzes the summarized comments. The final section recommends courses
of action in each of the areas.
Copies of the original comments, as received, are attached, as is
a copy of the material distributed for solicitation of comments. There-
fore, this document provides a complete record of the EPA and industry
interaction in this important area.
II. Comments
Comments were received from Ford, Firestone, GM, MVMA and SAE.
These comments addressed the feasibility of the proposed thermally
transient test procedure, the feasibility of the proposed force tran-
sient test procedure, the desirability of either procedure, and rec-
ommendations suggested by the commentors.
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A. Comments on the Practicality of the Proposed Temperature
Transient Procedure
Ford;
"The data handling equipment required for the procedure defined in
Appendix A (Temperature Transient) is generally not available on tire
test machines."
Firestone;
"No test equipment capable of running either of the proposed EPA
test procedures is currently available. Design and procurement of such
equipment seems unnecessary unless an improvement in results obtained is
likely."
"The proposed quasi-steady state test would require precise speed
control, increased power to drive the test drum, rapid data sampling at
fixed time intervals and software for data processing. Such equipment
and software would have to be newly developed or acquired."
B. Comments on the Practicality of the Proposed Force Transient
Procedure
.GM;
"The energy dissipation factor would be expected to have signifi-
cant variability since it is determined from the difference between two
large numbers."
MVMA;
"It (the recommended transient practice) would also be expected to
have little resolution capability since it is derived from the dif-
ference of two large numbers, both of which are subject to test vari-
ability".
Ford;
"The tire machine required for the procedure defined in Appendix B
(Force Transient) does not exist. The highly regarded and very elab-
orate Calspan flat belt tire machine does not have the capability to run
this procedure".
Firestone:
"To obtain necessary precision in the proposed EPA transient test,
large horizontal forces must be measured and subtracted from one another
with a precision of less than one pound. This is very difficult, if not
impossible, to obtain with any available measurement instruments".
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C. Comments on the Desirability of Either EPA Test Procedure
GM:
"The preferred test, which incorporates both the driven and un-
driven wheel in combination with the EPA city and highway cycles would
require very expensive equipment and would be very time consuming to
conduct. There is no evidence that a test of this complexity is
technically justified at this time".
"This would be an additional test for industry since it does not
have the general utility needed by vehicle designers to accurately
assess effects of design related parameters (load and pressure)".
"The data resulting from such a test methodology seems to center
around the anticipated needs of the EPA and would be of little value to
industry for the tire and vehicle design process. As pointed out, the
current methods routinely used for assessing rolling resistance seem to
be satisfactory for at least obtaining major design improvements in tire
rolling resistance performance".
Ford;
"The EPA procedure looks at the tire at only one load/tire pressure
point. To adequately evaluate a tire, a range of expected load and
pressure conditions must be evaluated. If a range of pressures and
loads were evaluated, the proposed EPA test procedure would be very
time consuming."
MVMAi
"This recommended method would be of little value to industry since
it is too specific in nature (only one test load and inflation pressure)."
Firestone;
"The EPA proposed quasi-steady state procedure requires about 45
minutes for each data point and therefore would require at least 225
minutes to provide the five data points covering three loads and three
pressures to produce the data provided by the currently proposed SAE
procedure which obtains the same tire data in just 70 minutes to test
time."
"Any test of a product or machine operating in a transient condi-
tion is inherently likely to prove less repeatable than a test run with
the product or machine in equilibrium condition."
D. Industry Recommendations
SAE (letter from SAE Subcommitte Chairman, Tom Baker, of UniRoyal) -
"I am disturbed by the fact that the report implies.that existing test
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methods are unacceptable and that new ones must be developed. Yet there
is no evidence that existing methods, especially the SAE one that Glenn
helped us develop, have even been tried by the EPA. How then have they
been found unacceptable? If there is evidence to that effect, why has
Glenn not brought it to our attention so that we could improve our SAE
approach? None of us on the Subcommittee wants a method which does not
produce meaningful results."
"It seems to me that the credibility of the information provided is
of paramount importance. The credibility of the data is enhanced by the
adoption of a standardized test procedure which has the public endorse-
ment of the technical community known to be knowledgeable on the subject.
Therefore for the good of the EPA program and for the greater probability
of its public acceptance and success, I recommend that the EPA adopt the
tried and proven technology of the SAE Recommended Practice rather than
attempt to invent new tests. I believe the EPA objective will be well
served by the SAE test and we will all be satisfied with the result".
GM:
"... General Motors recommends that a carefully structured
experiment be conducted to demonstrate the effectiveness of each pro-
cedure to properly rank order a wide range of tires for their effect on
fuel economy. A carefully controlled series of fuel economy tests
having repeated measurements on different road schedules and the two EPA
laboratory cycles can then be used to confirm the fuel economy-tire
energy dissipation/rolling resistance relationship. Analysis of these
data will indicate the degree of deficiency that may result from the
more simplified current industry practices for evaluating tire perfor-
mance" .
MVMA;
"Before any recommended procedure is adopted, the EPA should
conduct a program to demonstrate that the test method has the ability to
properly rank order a wide range of tires for their effect on fuel
economy. This should then be confirmed by a carefully controlled
series of road and laboratory fuel economy tests having a suitable
number of repeat measurements. This same group of tires should also be
quantified using the current industry practices which incorporate steady-
state rolling resistance and accurately measured vehicle fuel economy
could then be assessed".
Ford:
"It is suggested that the proposed SAE procedure with monitoring of
rolling resistance during warm-up be used for EPA's needs so that tire
rolling resistance in non-thermal and thermal equilibrium conditions can
be determined".
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Firestone;
"We do have data available that show measurements which correlate
directly with flat surface measurements can be made on a drum as small
as 62.7 inches in diameter but we are not at all sure how far we can go
before drum curvature effects become significant. Further research is
required on this point, but for now we believe that a minimum test drum
diameter of 1.50 meters should be specified".
"Basically, there are known problems with the transient or quasi-
steady state test procedures and it seems logical that we should take on
these problems only if the transient tests have been proven to give tire
values which are either more repeatable or bear a more direct correlation
to actual in-use values than steady-state measurements. Neither of
these proofs exists".
"The fact that the cycle of operation proposed by EPA represents
some particular mode of consumer vehicle operation is not significant
with respect to either the question of repeatability or correlation".
III. Summary of Comments
The following summary of comments is presented in the same subject
categories as were used for the presentation of the comments.
A. Practicality of the Proposed Temperature Transient Procedure.
Few comments were received on the feasibility of the proposed
thermally transient procedure. The two comments which were received
stated that equipment commonly available at the present time would not
be adequate for this procedure. Both commentors on this aspect speci-
fically mentioned the data acquisition and processing requirements of
this proposed procedure.
B. Practicality of the Proposed Force Transient Procedure
Many commentors noted that the proposed force transient procedure
would require the measurement and subtraction of the two relatively
large forces; the force into the tire, and the force transmitted by the
tire, to determine the residual dissipated force. Since the desired
quantity is the difference of two larger quantities, most commentors
noted that it is subject to greater variability than the determination
of the rolling resistance of a free-rolling tire under steady-state
conditions.
One commentor also noted that they did not believe that any exis-
ting tire test machine was capable of running this procedure.
C. Desirability of Either EPA Test Procedure
The comments received were of the following types.
1. The procedure is more complex than a steady state procedure
and is therefore not desirable.
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2. The procedure does not address the effects of load and pres-
sure and is therefore inadequate for the tire industry. If these
effects are investigated within the current procedure, the test time
required is excessive.
D. Industry Recommendations
The majority of the recommendations received from the commentors
can be summarized as:
1. An extensive test program should be conducted to insure the
results of the proposed EPA test procedures are indicative of the inuse
effects of various tires.
2. The draft SAE Recommended Practice for determining tire roll-
ing resistance should be adopted until the results of the above recom-
mended test progrfim are available. One commentor did recommend that the
SAE procedure be modified to include data collection during the period
of tire warm-up.
In addition to the above general comments, one specific comment was
received, that the minimum roll diameter be specified as 1.5m rather
than the 1.0m currently in the EPA procedure.
IV. Analysis of Comments
A. Practicality of the Temperature Transient Procedure
No commentors questioned the feasibility of the temperature tran-
sient procedure; therefore, it is concluded that all commentors con-
sidered the proposed procedure physically feasible. Several commentors
did, however, express beliefs that the commonly available tire test
equipment is not sufficient for this procedure. Insufficient drive
motors, inaccurate speed controls, and lack of the data acquisition
equipment required by the procedure were all mentioned. The question
about drive motor size and control are somewhat surprising since the
proposed procedure does not demand any higher speeds than current industry
procedures. If the equipment is satisfactory for current industry
procedures, then it should also be satisfactory for the EPA proposed
procedure. The only possible exception is the initial acceleration
required by the EPA procedure. If this is a problem, the acceleration
rate could be decreased to at least reduce the problem.
A potential problem stated by several commentors was that the data
acquisition equipment required by the proposed EPA procedure was not
commonly available on most current tire test machines. Data acquisi-
tion equipment which would be adequate for the proposed test procedure
has recently been both purchased and rented by EPA. This equipment is
generally available as standard, "off the shelf" hardware, costing
approximately $5 to $10K. This reviewer, therefore, concludes that the
possible current lack of this equipment does not pose a major problem
with the feasibility of the procedure. One tire manufacturer and one
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automobile manufacturer have both recently offered to conduct tire
energy dissipation measurements using this proposed EPA procedure.
These offers support the conclusion that the proposed procedure is
generally feasible with much of the current equipment or with minor
modifications to this equipment.
B. Practicality of the Force Transient Procedure.
Several commentors remarked that the force transient procedure was
impractical because the desired parameter, the tire energy dissipation,
is determined by the subtraction of the force transmitted by the tire
from the energy transmitted to the tire, both quantities being larger
than the subsequent difference. Several commentors stated that they did
not believe this procedure could be performed on any existing tire test
machine.
It is an intrinsic aspect of the force transient procedure that the
tire is required to transmit force. Consequently, the problem of
monitoring a small force in the presence of larger forces cannot be
avoided. This is, of course, more difficult than a steady state or
quasi-steady state measurement conditions. This does not, however, mean
that the procedure is not feasible.
EPA recently advertised a contract to obtain tire energy dissipa-
tion measurements using this force transient procedure. All proposers
for the contract believed the approach was feasible. The results of
this contract, which was awarded to the Pennsylvania Transportation
Institute, will demonstrate the degree of practicality of this method.
All prospective contractors which responded to the EPA request for pro-
posals did anticipate modifications to existing equipment or construc-
tion of new test machines. This does support the comments that existing
equipment would require modifications or replacement to conduct this
test procedure.
C. Desirability of the Proposed EPA Procedures
The commentors presented two major points in regard to the proposed
EPA procedures. With respect to the force transient procedure the com-
ment was made that this procedure would require expensive equipment, and
that there was no evidence that such a complex test procedure was
technically justified. This comment is technically correct since few,
if any tire tests have been conducted using the force transient proce-
dure. It does however ignore some available literature data which
indicate that tires may behave differently in force transient conditions
and that a procedure which includes these conditions may be necessary to
accurately reflect the consumer use of the tire. (1)
It has consistently been the position of EPA that the expense and
complexity of the proposed force transient test should be incurred only
if this test is necessary to accurately simulate the experience of the
(1) D.J. Schuring, "Rolling Resistance of Tires Measured Under Transient
and Equilibrium Conditions on Calspan's Tire Research Facility. DOT-TSC-
OST-76-9, March 1976.
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tire in consumer use. Since these data are currently not available, but
should soon be developed as a result of a current EPA contract, it is
concluded that the decision about the necessity of a force transient
procedure be postponed until the results from the current EPA contract
are available.
Several commentors expressed the opinion that neither of the EPA
proposed test procedures were desirable since they did not address such
design parameters as load and pressure. These parameters were not
considered in the EPA practice since they are considered to be of
primary interest to the vehicle designer and only of secondary interest
to the EPA question of the tire energy dissipation. While the EPA
proposed test does not provide this sensitivity information, it is not
in any direct conflict with procedures to determine these quantities.
D. Recommendations Received from the Industry
The most prevalent comment received was that EPA should adopt the
current draft SAE procedure. This simpler procedure only considers the
energy dissipation of a tire with regulated inflation pressure when
operated in thermal equilibrium at a steady speed of 50 mph. The
following comment was typical of those received:
"Basically, there are known problems with the transient or quasi-
steady state test procedures and it seems logical that we should take on
these problems only if the transient tests have been proven to give tire
values which are either more repeatable or bear a more direct correla-
tion to actual in-use values than steady-state measurements. Neither of
these proofs exists".
Yet the same authors of this comment, D.J. Schuring et al, re-
sponded to the draft SAE procedure with a letter stating:
"The fundamental purpose of an SAE test procedure surely must be to
assess the performance of like products with respect to some aspect of
interest. The end result of running such tests must be to compare
products one with another so a choice between them can be made or so
that the uniformity of their performance can be evaluated".
"Particularly in this case, we need a test procedure which can be
used to measure the new ideas and products which are being developed and
will be developed over the next few years as part of our high-priority
search for ways to reduce fuel consumption of automobiles".
"The proposed (SAE) test procedure provides the pressure sensi-
tivity and load sensitivity of different tires but provides no possibility of
measuring accurately whether one tire will fundamentally have a higher
or lower rolling resistance than another." (emphasis added)
There are several apparent significant conflicts expressed in the
above statements which typify the comments received in this area. The
commentors prefer the simpler tests and demand proof that the more com-
plex tests are representative of in-use results before they wish to
experiment with these procedures. However, for the simpler SAE proposed
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procedure no "proof" of representativeness is demanded, even though the
above quotation demonstrates that some members of the SAE Rolling Resistance
Committee recognize fundamental inadequacies in the current SAE approach.
In the presence of the known current problems of the SAE draft procedure,
it is illogical for EPA to adopt this approach.
One commentor suggested that the proposed SAE procedure be adopted
with the additional monitoring of the tire energy dissipation during the
warm-up period. If the SAE procedure were modified to include the warm-
up phase of the tire under "capped air" conditions, this suggested
approach would be similar to the proposed EPA procedure. However, even
with this approach, some data manipulation would be required to evaluate
the tire energy dissipation during periods of the tire warm-up. The
proposed EPA procedure accomplishes this relative weighting by requiring
operation of the tire over two distinct low and high speed segments.
The average values of the tire energy dissipation may then be conveni-
ently analyzed for each test segment. It is concluded that the proposed
EPA procedure is preferred over either the current SAE procedure, or a
modified SAE procedure, which would obtain data during tire warm-up. It
is noted that the EPA approach could easily be adopted as the warm-up
phase of the current SAE procedure. This would incure a slight addi-
tional test time for each tire compared with the current SAE procedure,
but would provide both the desired thermally transient and pressure/load
sensitivity test results. This incorporation of the EPA proposed pro-
cedure as the warm-up phase for the SAE procedure is recommended.
In a different area, one commentor recommended that the minimum
roll diameter should be 1.5m instead of the current 1m. It is the
opinion of this reviewer that tire testing techniques should be tending
toward flat bed test machines. The use of a cylindrical test surface
was provided to allow use of most of the current tire dynamometers. The
choice of the minimum diameter was also chosen for this reason. Since
there is no reason to encourage the use of 1m test machines, a minimum
test machine diameter of at least 1.5m should be specified if this does
not prohibit the use of current test machines.
V. Conclusions and Recommendations
A. It is concluded that:
1. The proposed force transient procedure is physically feasible,
it may have some variability problems which are not yet resolved, and it
could not be conducted using existing test equipment. It is therefore
concluded that this procedure is not practical at the present time.
2. The proposed temperature transient procedure is feasible, and
can be conducted on many existing test machines. However, additional
data acquisition equipment may be necessary in some cases.
3. The proposed EPA temperature transient procedure for deter-
mining tire energy dissipation is superior to the proposed SAE proce-
dure for comparing tires in a manner which is more likely to reflect the
consumer experience of the tire.
4. The minimum roll diameter should be increased to at least 1.5m.
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B. It is recommended that:
1. Efforts be continued to demonstrate the practicality and
possible necessity of the force transient procedure. This work is
currently in progress by contract with the Pennsylvania Transportation
Institute.
2. The proposed EPA temperature transient cycle should remain as
the recommended EPA practice at the present time. Efforts should be
made to compare the results of this procedure to that of the draft SAE
procedure if SAE retains their current procedure. One tire and one
automobile manufacturer have offered to assist in this comparison, and
these offers of assistance should be accepted.
3. The minimum diameter of the acceptable test surface should be
increased to at least 1.5m, and preferably it should be 1.7m (67 inches)
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Attachment I
EPA TECHNICAL REPORT
"Determination of Tire Energy
Dissipation Analysis and Recommended
Practices"
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Technical Report
Determination of Tire Energy Dissipation
Analysis and
Recommended Practices
April 1978
by
Glenn D. Thompson
Richard N. Burgeson
Notice
Technical reports are intended to present a technical analysis of an
issue and recommendations resulting from the assumptions and constraints
of that analysis. Agency policy constraints or data received subsequent
.to the date of release of this report may alter the conclusions reached.
Readers are cautioned to seek the latest analysis from EPA before using
the information contained herein.
Standards Development and Support Branch .
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air and Waste Management .
U.S. Environmental Protection Agency
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Abstract
The vehicle tire has a very significant effect on the fuel consumption
of the vehicle. For example, during low speed operation the tire is the
major source of external energy dissipation by the vehicle. Because of
the large effects of the tires and because significant variations have
been observed among tires, it is important that the vehicles used for
EPA fuel economy measurements be equipped with appropriate tires.
As an initial step to insure test vehicles are equipped with appropriate
tires, EPA issued Advisory Circular AC-55A to require tire information
for those vehicles for which an alternate dynamometer power absorption
was requested. This Advisory Circular stated that requiring such tire
information, as type, size, manufacturer, sidewall cord materials, belt
material, and the number of sidewall and belt plies was an interim
approach until a standardized, acceptable test procedure for determining
tire energy dissipation was available.
This report analyzes the currently available methods and test equipment
for determining tire energy dissipation. It is concluded that a fully
transient procedure is preferred, however such a procedure could not be
conducted on equipment in current widespread use. It is however, feasible
to conduct thermally transient measurements on free rolling tires with
the prevailing equipment. Consequently, a Recommended Practice for the
Determination of Tire Energy Dissipation -Quasi Steady State Procedure
is provided as Appendix A of this report. In addition, a preferred,
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Recommended Practice for Determination of Tire Energy Dissipation -
Transient Procedure is provided as Appendix B.
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Determination of Tire Energy Dissipation
I. Purpose
This report presents test procedures for the determination of tire
energy dissipation information. The determination of tire energy dissipation
information will enable more appropriate, realistic testing of vehicles
for both exhaust emissions and fuel economy measurements. The decisions
made in developing these test procedures for determination of tire
energy dissipation are documented in this report.
II. Background
During low speed operation, the tire is the major source of energy
dissipation by the vehicle. Consequently, the vehicle tire has a very
significant effect on the fuel consumption and emissions (especially
oxides of nitrogen) of the vehicle.
A recent experimental effort reported variations in tire rolling resistance
with respect to tire type, tire size, and tire manufacturer. (1)*
Consequently, to improve exhaust emissions and fuel economy tests, EPA
issued Advisory Circular AC 55A to require tire information for those
vehicles for which an alternate dynamometer poxjer absorption was requested.
This Advisory Circular stated that requesting such tire information as
* Numbers within parenthesis designate references given at the end
of the paper.
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type, size, manufacturer, sidewall cord materials, belt material, and
the number of sidewall and belt plies, was an interim approach until a
standardized, acceptable test procedure for determining tire energy
dissipation was available.
III. Discussion
The development of a laboratory test procedure to simulate the "real
world" experience of some device always represents compromises between
the simulation accuracy and the test expediency. The decisions in these
areas must, of course, depend on the purpose the user intends for the
resulting information. This section presents the questions which arose
during the development of the EPA recommended practices for tire energy
dissipation determination and the decisions which were made. The subsequent
sections present the actual recommended procedures for tire energy
dissipation determination.
A. Applications for Tire Energy Dissipation Information
Tire energy dissipation information is desired for the following reasons:
- Support of the EPA exhaust emission certification and fuel economy
measurement programs;
- To provide direction, incentive, and reward for the production of
low energy dissipation tires; and
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To provide public information and guidance on the fuel economy
effects of tire selection.
The information necessary to support the EPA exhaust emission and fuel
economy measurements is the most important and immediate need for EPA.
During the EPA tests the vehicle tires dissipate approximately 30
percent of the energy delivered to the vehicle wheels. The choice .of
tires installed on the EPA test vehicles and on the production vehicles
is presently virtually uncontrolled.* By comparison, test vehicle
inertia simulation and the dynamometer power absorption each have approx-
imately the same effect on the vehicle energy dissipation over the
composite of the two cycles as do the vehicle tires. Each of these two
parameters, however, is controlled to approximately + 3 percent.
EPA awareness or control of tire selection for the test vehicles is only
important if variations exist among tires. This has been investigated
and average differences of approximately 25 percent were observed between
tire types. Within tire types, significant variations by manufacturers
were observed as were variations by tire size. (2)
The second reason for EPA interest, to provide incentive and reward for
the use of low energy dissipation tires is of major importance, but not
quite the same immediate concern as the previous reason. This incentive,
at least for OEM tires, already exists in the fuel economy standards.
* Some control does exist over tire selection in the case of vehicles
using requested alternate dynamometer power absorptions. However,
even this control is based on such parameters as tire type, size,
manufacturer, etc., and does not directly consider the tire energy
dissipation.
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The important aspect is to focus the tire development efforts toward
improved tire performance for the consumer.
The third reason, to provide public information and guidance on the fuel
economy effects of various tires, is probably the most important long
range goal. This area is extremely important for fuel conservation
because of the important role of the tire on fuel consumption, and since
approximately 80 percent of all tires sold are aftermarket replacement
tires. Even with the potential national importance, this goal must be
considered as secondary for EPA compared to supporting current programs.
The important aspect is to avoid EPA actions or decisions which might
compromise this long range objective.
B. Tire Test Approaches
Practices for tire testing range from energy dissipation measurements
under steady state free rolling conditions to measurements under conditions
which simulate the tire experience on the vehicle. The major difference
is that simulation of the tire experience on a vehicle must involve
transient conditions and transmitted forces which are not present in the
simpler steady state practices. The following chart outlines the transient
versus steady state differences.
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Steady State Vehicle Simulation
Warmed up tire Initially cold tire, tire temperature increases
during the test
Constant inflation pressure Inflation pressure increases as the tire
temperature increases
Free rolling tire Forces transmitted by the tire (driving
and braking)
Steady speed Transient speeds
In addition to the transient versus steady state question, th« question
of a dynamometer roll or wheel versus a flat surface belt type test
machine must be considered. All of these areas will be discussed in the
following sections.
1. Initially Cold Tire vs. Warmed Up Tire
Tire energy dissipation significantly decreases as the tire warms up, as
shown in Figure 1. (3) This effect occurs for two reasons. As the tire
warms up, the temperature of the contained air increases, which results
in an increase in inflation pressure and a subsequent decrease in the
tire deflection. In addition, the rubber hysteresis decreases with
increasing temperature, therefore the energy dissipation for a given
deflection also decreases with increasing tire temperature.
Any tire test which attempts to simulate vehicle use must start with a
cold tire. Depending on the length of the test period, a temperature
transient test procedure may have the advantage of requiring less total
test time than measurements on a tire at thermal equilibrium since
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35-
30
Tire 25
Dissipative
Force
20
15 4
10
200
+
1
400
600
800 1000 1200
Time (seconds)
Figure 1 - Typical Tire Energy Dissipation
Force vs. Time
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light-duty vehicle tires require approximately 30 minutes to reach
thermal equilibrium.
The disadvantage of the thermally transient test is that multiple or
continuous data sampling is required during the test. Also, the thermal
experience of the tire prior to the test becomes a significant factor in
the test results.
The thermally transient cycle is considered preferred for the EPA
recommended practice because of the improved simulation of the normal
tire experience. For example, considering the data of Figure 1, the
tire energy dissipation at thermal equilibrium is about 20 percent lower
than the average tire energy dissipation over the first 20 minutes of
the tire operation.
2. Inflation Pressure Build vs. Constant Inflation Pressure
This question is strongly related to the transient temperature question
since the temperature effect is primarily a temperature-pressure effect.
If simulation of the tire experience on the vehicle is Important, then
the effects of the inflation pressure increase with increasing tem-
perature must be considered. As in the previous case, no major dis-
advantages are incurred with a test practice of this nature, therefore
this is considered to be the preferred method.' Separation of this
effect into individual temperature and pressure effects is difficult and
is artificial since the separation does not occur during consumer vehicle
use.
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3. Forces Transmitted by the Tire vs. the Free Rolling Tire
When the tire is used on a vehicle, all tires often transmit negative
(braking) forces. In addition, the drive tires must transmit the
positive drive forces.
Unfortunately, measuring the tire energy dissipation for a tire under
tractive effort is considerably more difficult than measurements on a
free rolling tire. This difficulty occurs because the transmitted
tractive forces are much greater than the tire energy dissipation forces.
In effect two large quantities, the input force and the output force,
must both be measured and then subtracted to obtain the small difference
which is the tire energy dissipation. For example, the force necessary
to maintain a vehicle at a steady 50 mph are typically 100 to 150 pounds
at the road-drive tire interface. During accelerations the forces may
approach 1000 pounds. By comparison the drive tire dissipation forces
would typically be 30 pounds.
Because of the greater difficulty in performing tire energy dissipation
measurements on tires transmitting forces, few facilities exist which
can conduct such tests. Consequently, there is very little information
in the literature on tire energy dissipation during force transmission.
However, limited data reported by Calspan for a single tire .indicates
that tire energy dissipation increases as the tractive effort of the
tire increases. (4) A plot of these data is presented in Figure 2. In
general, this is to be expected since the tire undergoes greater deformation
-------
,60
Tire
^Q Dissipative
Force
420
-1000
~500 500 1000
Transmitted Longitudinal Force (lb)
Figure 2 - Tire Energy Dissipative
Force is Transmitted Force
-------
when transmitting high forces and this deformation must result in greater
tire energy dissipation. Consequently, energy dissipation measurements
on free rolling tires probably underestimate the on-road tire energy
dissipation. In addition, there is reason to believe that tires with
different construction parameters, such as ply angle, or different cord
materials, may behave differently when transmitting force. (5)
In general, measurements of tire energy dissipation when the tire is
transmitting force would be the preferred test method. However, at the
present time this is not considered practical for most test facilities.
4. Transient Speed vs. Steady Speed
In typical consumer use, vehicle tires are operated in speed transient
modes. Therefore, from the vehicle simulation standpoint, a speed
transient test is desired. The forces responsible for tire energy
dissipation are, however, relatively speed independent, at least for
moderate speeds. (6) Therefore, there is reduced need for a speed
transient cycle to consider direct speed induced effects on the tire
rolling resistance. The tire power dissipation however does increase
with speed since the power is the product of the force and velocity.
Therefore the rate of energy dissipation and the rate at which heat is
generated in the tire does increase with vehicle speed. Consequently,
the thermal experience of the tire may be speed dependent even if the
forces are not.
-------
The speed transient experience of tires in consumer use is primarily
important because the drivu tires are the vehicle mechanism for generating
the transient vehicle speeds and this requires the tires to transmit
large forces. Consequently, for a tire test procedure, a speed transient
cycle is primarily important if this is used as a method of requiring
the tire to transmit large forces. Therefore, the question of a speed
transient cycle for a tire test is really the same as the previous
question of tire force transmission.
A speed transient test, with mechanical inertia simulation, does have
some advantages as an approach for generating transmitted forces. The
primary advantage is that the inertia system is basically energy "conservative".
That is, energy supplied by the tire to accelerate the flywheels will be
returned to the tire during deceleration. Consequently only the net
energy supplied to the tire must be measured and the load forces supplied
to the test machine by the inertia simulation need not be monitored. In
effect the flywheel approach eliminates the need to measure two large
quantities and compute a difference. Consequently only one transducer
need be calibrated with great precision. Even here some reduction in
transducer precision may be tolerable as long as the response is symmetric
in traction and braking. The only disadvantage is that the flywheel
bearing losses must be knov/n to compensate for the measured energy
dissipation.
The mechanical flywheel, speed transient approach is the preferred
approach since this method requires the tire to transmit tractive
-------
force, correctly simulates the rate of energy dissipation during consumer
use and appears to have potential test machine advantages.
5. Flat Bed vs. Dynamometer Wheel
The final question is the advantages of a flat bed test machine versus a
cylindrical test wheel.
The flat bed has the obvious advantage of being the logical equivalent
of the road surface. There are also significant engineering advantages
to a flat belt test machine. The major advantage is that the tire
energy dissipation is different on a flat surface versus a cylindrical
surface. Consequently, correction factors must be used to compare data
from curved surface test machines to flat surface results. (7) Also,
conversion factors must be used to compare data from curved surface
machines of different diameters or even to compare curved surface data
collected by different types of transducers, i.e.^ torque versus force
sensors. These correction factors are, on the average, reasonably
accurate for a large collection of tires. However, they may not be
precisely accurate for any given tire. Consequently, tires may rank
differently for different cylindrical surface test machines. Conversely,
however, all flat bed machines should, at least, rank tires in the same
order.
The disadvantages of a flat bed machine are their cost and availability.
Only one such device, the Calspan facility, is currently commercially
-------
active. A smaller flat bed test facility, the prototype for the Calspan
machine, exists at the University of Pennsylvania. In addition, General
Motors has a flat bed tire test facility currently under construction.
Even though the flat bed approach is the preferred method, the limited
availability of these test machines precludes extensive use of this type
of tire test apparatus in the near future.
IV. Conclusions
The preferred tire test procedure should be thermally transient, require
the tire to transmit torque, and should be conducted on a flat test
surface. However, wide usage of such a procedure is not practical at
the current time because of test facility limitations.
Since EPA has a definite, immediate need for tire energy dissipation
information, a recommended practice for obtaining this information on
available facilities is necessary. The capability limitations of those
facilities which are widely available at this time preclude measurements
on tires which are transmitting force. Therefore a simpler procedure
which can be performed in the majority of the existing facilities should
be considered. This procedure should be a thermally transient, steady
state speed measurement of free rolling tire energy dissipation on a
cylindrical test machine. It is concluded that such an approach can
yield useful information, at least, when comparing tires tested at one
facility. A recommended practice of this nature is presented as Appendix
A of this report.
-------
It is also concluded that there are potential problems in any procedure
which only considers free rolling tires on a cylindrical surface. For
this reason data collection by more preferred procedures should be
encouraged. Consequently, a recommended practice for determination of
tire energy dissipation when the tires are transmitting forces to a flat
surface should be provided for eventual use. This fully transient test
procedure is presented as Appendix B of this report.
-------
References
1. G.D. Thompson and M. Torres, "Variations in Tire Rolling Resistance"
EPA Technical Support Report for Regulatory Action, October 1977.
2. IBID
3. D.J. Schuring, "Rolling Resistance of Tire Measured Under Transient
and Equilibrium Conditions on Calspans Tire Research Facility",
Final Report to U.S. Department of Transportation, Office of Systems
Development and Technology under Contract DOT-TSC-OST-76-9, March 1976.
4. IBID
5. I. Gusakov, telephone conversation.
6. G.D. Thompson, "Light-Duty Vehicle Road Load Determination", EPA
Technical Support Report for Regulatory Action, April 1977.
7. S.K. Clark, "Rolling Resistance Forces in Pneumatic Tires", Interim
Report prepared for the U.S. Department of Transportation, Transporation
Systems Center under Contract DOT-TSC-1031, January 1976.
-------
Appendix A
Recommended Practice for Determination of Tire Energy
Dissipation - Quasi Steady State Procedure
-------
This recommended practice provides a procedure to determine tire energy
dissipation for a free rolling tire at primarily steady state speed but
considering the thermally transient nature of the energy dissipation
during the tire warm up.
A. Test Dynamometer Requirements
The test dynamometer shall be a large diameter (greater than 1 m)
cylindrical surface machine. The test machine shall be capable of
supplying a force on the tire perpendicular to the test surface and be
able to measure the torques required to rotate the tire. During this
process the machine must be capable of maintaining a constant speed,.and
capable of measuring this speed and the peripheral distance traveled by
the test surface.
1. Vertical force - The test machine shall be capable of imposing
constant forces between 2000 nt and 8000 nt on the tire perpendicular to
the test surface. The machine shall be capable of maintaining the load
on tire constant to within + 40 nt and shall be capable of measuring
this load to within +10 nt.
2. Tire Dissipation Forces - The test machine shall be capable of
measuring the torques required to rotate the test tire to within +
2 nt-m (1 ft-lb).
3. Test Speed - The machine shall be capable of maintaining the desired
test speed to within + 1 m/sec (2 mi/hr) and shall be capable of measuring
-------
this speed to within +0.1 m/sec. (0.2 mi/hr)
4. Loaded Radius - The test machine shall have a method of measuring
the loaded radius of the tire; that is, the perpendicular distance from
the axis of rotation of the tire to the test surface. This distance
measurement shall be accurate to within + 1 mm (+_ 0.05 in.)
5. The Test Surface - The test surface of the machine shall be a
bonded abrasive aggregate of approximately number 80 grit.
B. The Test Cell Requirements
The requirements for the test cell, is that the ambient temperature be
well controlled. In addition, the support services of compressed air
should be available for tire inflation as should the necessary gauges to
measure tire inflation.
1. Temperature - The temperature in the test cell and in any area used
to store the tire within four hours prior to testing shall be maintained
at 20°C + 2°C (68°F+4°F).
2. Tire Inflation Pressure Gauges - The gauges .used to measure the
tire inflation pressures shall be accurate to within +_ 0.5 kPaG (+ 0.07
psi).
-------
C. Test Procedure
The test procedure consists of the following steps;
Tire break-in
Equilibration of the tire to the test ambient temperature
Installation of the tire on the test machine
Operation of the tire over the test cycle
1. Tire Break-In - The test tires shall be mounted on appropriate rims
and shall be operated for a minimum of 100 km and a maximum of 500 km
prior.to testing. An appropriate rim is one of an approved contour and
width as specified for the test tire in the current yearbook of the Tire
and Rim Association Inc. The tire break-in may be conducted with a
vehicle on a road or track surface, or may be accumulated on the tire
test machine. During the break-in period, the compressive load on the
tire shall be at least 80% of the maximum design load of the tire.
2. Equilibration to the Test Temperature - After tire break-in the
tire shall be stored in an environment of 20°C + 2°C for a minimum of
four hours preceeding the test. During this period the tire inflation
pressure should be checked and adjusted if necessary to the cold inflation
pressure for the test. The test inflation pressures shall be the
appropriate design cold inflation pressures specified in the current
-------
Yearbook of the Tire and Rim Association Inc. for the tire size and
load. Any adjustment of the inflation pressure should occur approx-
imately one hour before the test period to provide adequate time for any
air introduced into the tire to reach the equilibrium temperature.
3. Installation on the Test Machine - The tire shall be installed on
the test machine and the load on the tire perpendicular to the test
surface shall be adjusted to 80% of the maximum design load of the tire,
for the test pressure. The alignment of the loaded tire shall be:
- Perpendicular to the test surface + 1°
Slip angle 0+0.25°
Camber angle 0° +0.50°
At this time the inflation pressure of the tire shall be checked and
recorded. The tire inflation pressure may be adjusted, up to a maximum
adjustment of 10 kPa (1.5 psi) at this time. Tire inflation shall be
correct to within + 1 kPa (0.15 psi)
4. Operation Over the Test Cycles - The test machine shall be accelerated
from rest to the test speed of 10 m/sec at the approximate rate of 1
2
m/sec . The test speed of 10 m/sec shall be maintained for 1,200 seconds
(20 min.), after which the tire shall be brought to a stop with a deceleration
2
rate of approximately 1 m/sec . A graphical representation of this test
cycle is given in the attachment of this appendix.
-------
The tire shall then be allowed to remain at rest on the test machine for
600 seconds (10 minutes).
After completion of the 10 minute stationary phase the tire shall be
2
accelerated from rest to a speed of 20 m/sec at the rate of 1 m/sec .
The test speed of 20 m/sec shall be maintained for 800 seconds (13.33
minutes) after which the tire shall be brought to a stop with a deceleration
rate of 1 m/sec. A graphical representation of this test cycle is
included in the attachment of this Appendix.
During all steady speed test phases the torques necessary to rotate the
tire and the velocities of the test surface shall be measured. These
data shall be recorded, preferably each second, but a minimum frequency
of once every five seconds is acceptable.
D. Data Analysis
The data analysis consists of three steps, computation of the total
energy required for each cycle, subtraction of the energy dissipation
from the residual friction of the test machine to determine the net tire
energy dissipation and finally the computation of an energy dissipation
coefficient.
1. Computation of the Total Energy Dissipation - The torque necessary
to drive the tire shall be multiplied by the angular velocity of this
shaft transmitting the drive torque to determine the instantaneous
poxver. That is:
-------
pi -
where: P. = the power dissipated during the i time interval
T. = the torque measured during the i time interval
A.-L
ti> = the angular velocity during the i time interval
The instantaneous powers shall then be multiplied by the sample time
period and summed to give the total energy dissipation over each test
cycle:
E = Z p.t.
s .xi
where:
E = the total system energy dissipation
S
t. = the length of the i time interval
2. The Tire Energy Dissipation - The tire energy dissipation shall be
calculated from the total system energy by subtraction of the energy
dissipation caused by the mechanical friction of the system. That is:
E = E - E,
t s f
where:
E = the tire energy dissipation
E, = the energy dissipation caused by friction in the test machine
-------
The methods used to determine E will depend on the specific design of
the test machine. The quantity E,. should, of course, only include those
friction losses which were included in the measurement of E . If the
s
quanity Ef varies with time during the test cycle this variation must be
considered.
A specific energy dissipation coefficient can now be computed from the
tire energy dissipation of each cycle by dividing this quantity by the
total distance the test surface traveled and by the load on the tire
perpendicular to this surface.
e = E /LD
where:
e = specific energy dissipation coefficient
L = the load on the tire normal to the test surface
D = the distance traveled by the test surface
It should be noted that e is a dimensionless coefficient and is equivalent
to the average rolling resistance coefficient over the test cycle.
-------
Attachment
to
Appendix A
Graphical Representation
of the Quasi Steady State Cycles
-------
20,
Speed
(m/sec)
1200 second
low speed
segment
0 .,
800 second
high speed
segment
600 second
"rest"
time
Graphical Representation of
the Quasi - Steady State Cycles
-------
Appendix B
Recommended Practice for Determination nf
Energy Dissipation - Transient Procedure
-------
This recommended practice provides a procedure to determine tire energy
dissipation under transient conditions. This recommended practice
closely simulates the tire experience on consumer vehicles. Conse-
quently it considers both driving tires exerting tractive forces and
non-driving or free rolling tires. The EPA driving cycles are chosen as
test.cycles representative of consumer vehicle use.
A. Test Dynamometer Requirements
The tire test machine (dynamometer) should be a flat belt machine which
can accommodate two tires, one tire representing the vehicle driving
tire and one representing the non-driving tire. Each tire shall receive
a force normal to the test surface which is equivalent to 80% of its
load rating. The system should be driven by driving one tire, the
"driving tire" such that the peripheral velocity of the test surface
corresponds to the EPA driving schedules. Graphical plots and speed
versus time listings for each of the driving schedules are provided as
an attachment to this recommended practice. The torque or force requirement
of the driving tire shall be measured during each second of the driving
schedules. The tire forces and the instantaneous velocity of the test
surface shall be recorded throughout the cycle.
1. Vertical force - The test machine shall be capable of imposing
constant forces between 2000 nt and 8000 nt on the tire perpendicular to
the test surface. The machine shall be capable of maintaining the load
on tire constant to. within + 40 nt and shall be capable of measuring
this load to + 10 nt.
-------
2. Tire Dissipation Forces - The test machine shall be capable of
measuring the forces required to drive the test tire to within + 1 nt.
3. Test Speed - The machine shall be capable of maintaining the
desired test schedule speed to within + 1 m/sec (2 mi/hr) and shall be
capable of measuring this speed to within +0.1 m/sec. (0.2 mi/hr)
4. Inertia Simulation - The tire test dynamometer shall be adjusted to
apply an inertia simulation appropriate for a vehicle with a mass equivalent
to the total normal load upon the test tires. That is, of the available
increments of simulated inertial mass, that simulated inertia which is
nearest to the total normal load force on the tires divided by the
2
gravitational constant (9.80m/sec ) shall be selected.
The inertia increments shall be 50 kg or less and the accuracy of the
inertial simulation shall be within + 1 kg of the selected inertia;
5. Loaded Radius - The test machine shall have a method of measuring
the loaded radius of the tire; that is, the perpendicular distance from
the axis of rotation of the tire to the test surface. This distance
measurement shall be accurate to within +_ 1 mm (+ 0.05 in.)
6. The Test Surface - The test surface of the machine shall be a
bonded abrasive aggregate of approximately number 80 grit.
-------
B. The Test Cell Requirements
The requirements for the test cell, is that the ambient temperature be
well controlled. In addition, the support services of compressed air
should be available for tire inflation as should and the necessary
gauges to measure tire inflation.
1. Temperature - The temperature in the test cell and in any area used
to store the tire within four hours prior to testing shall be maintained
at 20°C + 2°C (68°F + 4°F).
2. Tire Inflation Pressure Gauges - The gauges used to measure the
tire inflation pressures shall be accurate to with + 0.5 kPa (0.07 psi) .
C. Test Procedure
The test procedure consists of the following steps:
Tire.break-in
- Equilibration of the tire to the test ambient temperature
Installation of the tire on the test machine
- Operation of the tire over the test cycle
-------
1. Tire Break-In - The test tires shall be mounted on appropriate rims
and shall be operated for a minimum of 100 km and a maximum of 500 km
prior to testing. An appropriate rim is one of an approved contour and
width as specified for the test tire in the current yearbook of the Tire
and Rim Association, Inc. The tire break-in many be conducted with a
vehicle on a road or track surface, or may be accumulated on the tire
test machine. During the break-in period, the vertical load on the tire
shall be at least 80% of the maximum design load of the tire.
2. Equilibration to the Test Temperature - After tire break-in the
tire shall be stored in an environment of 2Q°C +_ 2°C for a minimum of
four hours preceeding the test. During this period the tire inflation
pressure should be checked and adjusted if necessary to the cold inflation
pressure for the test. The test inflation pressures shall be the appropriate
design cold inflation pressure specified in the current Yearbook of the
Tire and Rim Association, Inc. for the test tire size and load. Any
adjustment of the inflation pressure should occur prior to the last hour
of the temperature equilibration period to provide adequate time for any
air introduced into the tire to reach the equilibrium temperature.
3. Installation on the Test Machine - The tire shall be installed on
the test machine and the load on the tire perpendicular to the test
surface shall be adjusted to 80% of the maximum design load of the tire.
The alignment of the loaded tire shall be:
Perpendicular to the test surface + 0.30°
Slip angle 0+0.25°
-------
Camber angle 0° + 0.50°
At this time the inflation pressure of the tire shall be finally checked
and recorded. The tire inflation pressure may be adjusted up to a
maximum of 10 kPa (1.5 psi) at this time. Tire inflation pressure shall
be correct to within + 1 kPa (0.15 psi)
4. Operation Over the Test Cycles -
a. The tires shall be operated over the cold transient portion of
the EPA urban driving schedule (the first 505 seconds).
b. The tire shall be operated over the hot stabilized portion of
the EPA urban.driving schedule (from the 505 to the 1371 second
points).
c. The tires shall be allowed to "rest" on the test machine for
10 minutes and then the first 505 seconds of the EPA urban cycle
shall be repeated. This is the hot transient segment of the test.
d. After completion of the second 505 seconds of the EPA urban
cycle the tires shall be immediately operated over the EPA Highway
Fuel Economy Cycle.
During all dynamic test phases the force necessary to drive the tire
shall be monitored as shall the velocities of the test surface. These
data shall be recorded, each second.
-------
D. Data Analysis
The data analysis consists of three steps, computation of the total
energy required for each cyle, substraction of the energy dissipation
from the residual friction of the test machine to determine the net tire
energy dissipation and finally the computation of an energy dissipation
coefficient.
1. Computation of the Total Energy Dissipation - The force necessary
to drive the tire shall be multiplied by the test surface velocity to
determine the instantaneous power. This is:
Pi = fiVi
where:
p. = the power required during the i interval
f. = the force measured during the i interval
v. = the velocity of the i interval
The instantaneous powers shall then be multiplied by the sample time
period and summed to give the total energy dissipation over each test
cycle:
-------
E = I p.t.
.8 . Pl X
where:
E = the total system energy dissipation
s
t. = the length of the ± time interval
2. The Tire Energy Dissipation - The tire energy dissipation shall be
calculated from the total system energy by subtraction of the energy
dissipation caused by the mechanical friction of the system. That is:
E = E - E-
t s f
where:
E = the tire energy dissipation
Ef = the energy dissipation caused by friction in the test machine
during the test cycle.
The methods used to determine E will depend on the specific design of
the test machine. The quantity E, should, of course, only include those
friction losses which were included in the measurement of E . If the
s
quantity E, varies with time during the test cycle, this variation must
be considered.
-------
A weighted average energy dissipation coefficient can now be computed
for the urban cycle by dividing the total tire energy dissipation by
the total distance the test surface traveled and by the total load on
the tires perpendicular to this surface.
eu=0.43
0.57
where:
e = specific energy dissipation coefficent for the .urban cycle
E = the tire energy dissipated over the initial segment of the
urban test cycle (4a)
E = the tire energy dissipated over the second test segment of the
S L
urban cycle (4b)
D = the distance traveled during the initial segment of the urban
test cycle (4d)
D = the distance traveled during the second segment of the urban
S I-
cycle. (4b)
the total load on both tires normal to the test surface
-------
E, = the tire energy dissipated over the repeat of the first urban
test segment (4c)
D, = the distance traveled over the repeat of the first urban test
segment (4c)
0.43 and 0.57 are the weighting factors representing 43 percent of all
urban trips as starting with initially cold tires and 57 percent of
urban trips starting with warm tires.
It should be noted that e is a dimensionless coefficient and is equivalent
to the average rolling resistance coefficient over the urban test
cycle.
An average energy dissipation coefficient can be computed for the
highway cycle in a similar, but simpler manner. This energy dissipation
coefficient is:
e, = E. /D, L
h nw hw
where:
e, = the energy dissipation coefficient for the highway cycle
n
E, = the energy dissipation over the EPA highway cycle
nw
D = the distance traveled over the highway cycle
-------
L = the total load on both tires normal to the test surface
The energy dissipation coefficients for the two cycles can be harmonically
averaged to yield a composite energy dissipation coefficient. The
composite energy dissipation coefficient is given by:
e =
"c 0.55 0.45
*h
where:
e =. the composite energy dissipation coefficient
0.55 and 0.45 are the weighting factors based on 55 percent of all
mileage represented by the urban cycle and 45 percent of all mileage
represented by the highway cycle.
-------
Attachment to
APPENDIX B
EPA Urban and Highway Fuel
Economy Driving Schedules
-------
1
2
3
u
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
4l
42
43
44
45
46
47
48
49
50
51
52
53
b4
55
56
57
5R
59
bO
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0.0
0.0
0.0
0.0
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0.0
o.o
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
3.00
5.90
8.60
11.50
14.30
10.90
17.30
18.10
20.70
21.70
22.40
22.50
22.10
21.50
20.^0
20.40
1 9 . 8 0
17.00
14.90
14.91)
15.2U:
15.50
16.00
17.10
19.10
21.10
22.70
22.^0-
22.70
22.60
21.30
1 V . 0 0
17.10
lD..",0
15.^0
17.70
1 V . 8 0
21 .60
?3..?0
2^.20
hi
62
63
64
65
66
b7
68
69
70
71
72
73
74
75
76
77
78
79
HO
81
82
83
84
85
86
87
88
«9
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
11*
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24 .'-O
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24. HU
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?<«.M)
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25. Hi
25.^0
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?D.^O
24.90
?D.OO
25.40
2^.00
26.00
2a.70
26.10
26.70
27.50
28.60
29.30
29.80
30.10
30.40
30.70
30.70
30.50
30.40
30.30
30.40
30.80
30.40
29.90
29.50
29. RO
30.30
30.70
30.90
31.00
30.90
30.40
29.80
29.90
30.20
30.70
31.20
31.«0
.12.20
.12.40
32.20
31.70
2*. 60
25.30
22.00
1 rt . 7 0
15.40
121
122
123
124
125
126
127
128
129
130
I'M
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
160
12.10
H . >-0
5 . "-" 0
2.?0
0.0
.o.n
u.o
0.0
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c.o
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o.n
0.0
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0.0
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0.0
0.0
0.0
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0.0
o.n
0.0
0.0
0.0
0.0
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3.30
6.60
9.90
13.20
16.50
19.80
22.20
24.30
25.80
2o. 40
25.70
25.10
P4.70
25.00
?5.?0
25.40
25.rtO
181
1*2
183
184
185
186
187
188
169
190
191
192
193
194
195
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197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
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?38
?39
240
27.20
26. SO
24.00
22.70
19.40
17.70
17.20
1W.10
18.60
20.00
22.20
24.50
27.30
30.50
33.50
36.20
37.30
39.30
40.50
42.10
43.50
45.10
46.00
46.80
47.50
47.50
47.30
47.20
47.00
47.00
47.00
47.00
47.00
47.20
47.40
47.90
48.50
49.10
49.50
50.00
50.60
51.00
51.50
52.20
53.20
54.10
54.60
54.90
55.00
54.90
54.60
54.60
54.80
55.10
55.50
55.70
55.10
56.30
56.60
56.70
241
?42
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
?96
297
?96
299
300
56.70
56.50
56.50
56.50
56.50
56.50
56.50
56.40
56.10
55.80
55.10
54.60
54.20
54.00
53.70
53.60
53.90
54.00
54.10
54.10
53.80
53.40
53.00
52.60
52.10
52.40
52.00
51.90
51.70
51.50
51.60
51.80
52.10
52.50
53.00
53.50
54.00
54.90
55.40
55.60
56.00
56.00
55.80
55.20
54.50
53.60
52.50
51.50
51.50
51.50
51.10
50.10
50.00
50.10
50.00
49.60
49.50
49.50
49.50
49.10
-------
301
302
303
304
30b
306
3U7
308
309
310
311
312
313
314
315
316
317
316
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
3bl
352
353
3S4
355
356
3b?
3b8
359
360
4 H . * 0
4 H . ! 0
* 7 . ? 0
i> n . ] 0
471.00
«4j.HO
42.60
41.SO
^0.30
3d. 50
37.00
3b.20
33.*0
32.50
31.50
30.60
30.50
30.00
29.00
27. SO
24. HO
21.50
20.10
19.10
18.50
17.00
15.50
12.50
10. HO
8.00
4.70
1.40
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.00
4.30
7.60
10.90
14.20
17.30
20.00
2-r.::0
2.J.70
2b.20
2&.60
2M>. 10
3u.OO
30.80
361
362
363
364
365
366
367
368
3b9
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
4JB
419
420
31.60
32.10
32. RO
33.60
34.50
34.60
34.90
34. BO
34.50
34.70
35.50
36.00
36.00
36.00
36.00
36.00
36.00
36.10
36.40
36.50
36.40
36.00
35.10
34.10
33.50
31.40
29.00
25.70
23.00
20.30
17.50
14.50
12.00
8.70
5.40
2.10
0.0
0.0
0.0
0.0
0.0
0.0
2.60
5.90
9.20
12.50
15.80
19.10
22.40
25.00
25.60
27.50
29.00
30.00
30.10
3u.OO
29.70
29.30
2.i. SO
2a.OO
421
422
423
4^4
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
460
PS.no
21. 'Q
16.40
1-5. SO
11 . * 0
M.bO
5.20
l."0
0.0
0 . 0
U.O
0.0
0.0
o.o
0.0
0-0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
3.30
6.60
9.90
13.20
16.50
19.80
23.10
26.40
27.80
29.10
31.50
33.00
33.60
34.80
35.10
35.60
36.10
36.00
36.10
36.20
36.00
35.70
36.00
36.00
35.60
35.50
3b.4.0
3b.20
JD. 20
3b..^0
3b.?0
3H.20
33.20
481
482
483
464
485
a,86
.87
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
b34
535
536
537
538
539
b40
35.00
35.10
3b.20
3b.50
35.20
35.00
3S.OO
35.00
34. HO
34.60
34.50
33.50
32.00
30.10
26.00
25.50
22.50
19.80
16.50
13.20
10.30
7.20
4.00
1.00
0.0
0.0
0.0
0.0
0.0
0.0
1.20
3.50
5.50
6.50
8.50
9.60
10.50
11.90
14.00
16.00
17.70
19.00
20.10
21.00
22.00
23.00
23.80
24.50
24.90
2S.OO
25.00
25.00
2s. 00
2b .00
2b.oO
2b.oO
2rj.PO
/i o . 0 0
2-3. A0
2^.20
541
542
543
544
545
546
547
548
549
5bO
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
b93
S94
595
59b
597
598
599
bOO
2S.OO
25.00
25.no
24.40
23.10
19.80
16.50
13.20
9.90
6.60
3.30
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
3.30
6.60
9.90
13.00
14.60
16.00
17.00
17.00
17.00
17.50
17.70
17.70
17.50
17.00
16.90
16.60
17.00
17.10
17.00
16.60
16.50
16.50
16.60
17.00
17.60
18.5 0
19.20
20.20
21.00
21.10
21.20
21.60
-------
^01
602
603
60u
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
6.20
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
f52
653
654
655
656
657
658
6S9
660
22.00
22.AO
22. SO
2t'.. SO
22. SO
22.70
23.70
25.10
26.00
?r>.50
27.00
26.10
22.80
19. SO
16.20
12.90
9.60
6.30
3. CO
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
o.o
2.00
4.50
7.RO
10.20
12.^0
14.00
is.:
-------
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
7
956
9bv
''bO
26.^0
2b.SO
26. SO
2t>.50
26.30
26.20
2b.20
25.^0
25.60
25.^0
25.90
25.80
25.50
24.fcO
23.50
22.20
21.60
21.60
21.70
22.60
23.40
24.00
24.20
24.40
24.90
25.10
2b.20
?b.30
2b.SO
25.20
25.00
25.00
25.00
?4.70
24.50
24.30
24.30
24.^0
25.00
25.00
24.60
24.^0
24.10
24.50
2b.lO
25.60
25.10
24.00
22.00
2U.10
16.90
1 J . 6 0
ID. 30
'.00
.3.70
0 . '* Q
u.o
0.0
11 . '"'
2 . 0 0
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
lOOb
1009
1010
1011
1012
1013
1014
1015
1016
1 0 1 7
1018
1019
1020
5.30
8.60
11.90
15.20
17.50
16.60
20.00
21.10
22.00
23.00
24.50
26.30
27.50
28.10
2b.40
28.50
28. SO
28.50
27.70
27.50
27.20
26.80
26.50
26.00
25.70
25.20
24.00
22.00
21.50
21.50
21. HO
22.50
23.00
22. BO
22.80
23.00
22.70
22.70
22.70
23.50
24.00
24.60
24. HO
25.10
25.50
25.60
25.50
25.00
24.10
23.70
23.20
2^.90
22.50
22.00
21 .60
20. SO
1 / . 5 0
]4.?U
10.90
7.60
irvi
1(V2
1023
lfV<.
1025
1026
1027
102B
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
If.' 77
1078
1079
JObO
~. 30
1 .('0
(i . n
0.0
o.O
0.0
U . 0
0.0
0.0
u.o
0.0
0.0
o.r.
0.0
0.0
0.0
0.0
0.0
n.n
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.20
4.00
7.30
10.60
13.90
17.00
H.50
20.00
21. HO
23.00
24.00
24.80
25.60
26.50
26.80
27.40
27.90
2H.30
2H.OO
27.50
27.00
2'/.no
2b.30
24.50
22. SO
21. SO
20.60
i y . o o
1 081
1UH2
)0b3
1 084
10h5
lOrtb
10o7
1088
1"89
10^0
1091
1092
10*3
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
11-12
1133
1134
1135
1136
1137
1 1 3B
1 1 39
1140
15.00
12.3 fi
11.10
1 0 . n 0
10. dO
*.50
9.10
H.70
« . 6 0
8. MO
9.00
8.70
ri.^0
y . o o
7.00
5.00
4.20
2.60
1.00
0.0
0.10
0.60
1.60
3.60
6.^0
10.00
12.80
14.00
14.50
16.00
14.10
20.00
21.00
21.20
21.30
21.40
21.70
22.50
23.00
23.80
24.50
25.00
24.90
24.80
25.00
25.40
25.80
26.00
25.40
26.f>0
26.90
2 7 . n o
27.00
'e. f . o o
2*.°0
26. HO
^'i.MU
Po.SO
26.40
26.00
1141
1142
1143
11 <*4
1145
1146
1147
114fl
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1 196
1 197
1198
1 19V
1200
25.50
2H.60
23.50
21.50
20.00
17.50
16.00
14.00
10.70
7.40
4.10
0.80
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
2.10
5.40
8.70
12.00
15.30
18.60
21.10
23.00
23.50
23.00
22.50
20.00
16.70
13.40
10.10
6.80
3.50
0.20
0.0
0.0
0.0
0.0
0.0
o.o
0.0
0.0
0 .0
0.0
0.20
1.50
3.50
b.50
-------
1?01
1202
1203
1204
1205
1206
1207
1208
1209
1210
1?11
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1?38
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
12<+9
1250
1251
1252
1253
1254
1255
!25b
12b7
1258
1259
1260
9.? 0
12.00
12.vO
13.00
12.M)
12. MO
13.10
1J.10
l<+.oo
15.50
17.00
18.60
19.70
21.00
21.50
21.80
21.80
21.50
21.20
21.50
21.80
22.00
21.90
21.70
21.50
21.50
21.40
20.10
19.50
19.20
19.60
19. 80
20.00
19.50
17.50
15.50
13.00
10.00
8.00
6.00
4.00
2.50
0.70
0.0
0.0
0.0
0.0
0 . 0
o.o
0.0
0.0
1.00
1.00
I . 0 0
1.00
1.00
1.60
3. no
4.00
5.00
12M
l?'tV
12*3
1 ? f i «
Ir'hb
12nt>
12*7
1 2bH
12iv
1270
1271
1272
1273
127«.
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
- 12«6
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
131^
1315
1316
1317
1 3 .1 ft
1?19
1320
- . > o
** * > » vj
S'i.CO
1 !.. = «
>.M)
-.-0
7.»G
1 . ' 0
1 1 . 0 U
l-.no
1 7.00
r-^.'-o
? 1 . 0 0
? 1 . .-> 0
22.20
^.).00
2 .J.hO
2^.10
2^. 50
24. SO
2". 00
23.^0
23.50
23.50
23.50
23.50
23.50
2t.OO
2^.10
2^.50
24.70
25.00
25.40
25.^0
25.70
26.00
26.20
27.00
27. hO
28.30
29.00
29.10
29.00
28.00
2<+.70
21.40
18.10
14.80
11. HO
a. 20
i*.^0
1 .eo
0 . 0
0.0
0.0
0.0
0 . 0
(> . 0
O.n
0 . 0
1321
i:s£2
1323
1.12^
1325
132fc
1327
13c'b
13^9
1330
1331
1332
1333
133^
1335
1336
1337
1338
1339
13<»0
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
13bO
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
0.0
0.0
0.0
o.n
0.0
0 . 0
0.0
0.0
0.0
0.0
0.0
0.0
o.n
0.0
0.0
0.0
o.n
1.50
<*.HO
,-t.lO
11.40
13.20
15.10
11.80
18.30
19.50
20.30
21.30
21.90
22.10
22.40
22.00
21.60
21.10
20.50
20.00
19.60
18.50
17.50
16.50
15.50
I'+.OO
11.00
B.OO
5.20
2.50
0.0
0.0
o.n
0.0
0.0
0.0
-------
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
2i
33
C C
23
24
25
?6
?_1
?P
?9
30
31
j2
33
34
35
3 h
37
33
39
4 0
41
42
43
44
45
<-6
47
48
49
50
51
52
53
S4
55
56
57
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-------
Attachment II
Comments Received in Response
to the EPA TECHNICAL REPORT
"Determination of Tire Energy
Dissipation Analysis and
Recommended Practice"
-------
IANO SAE COMMITTEE CORRESPONDENCE
SEA
AIR
SPACE
Society of Automotive Engineers, Inc.
Committee: Rolling Resistance Subcommittee Reply To = T.P. Baker
Uniroyal Inc.
6600 E. Jefferson
Detroit, Michigan
June 7, 1978
Mr. Charles L. Gray
Acting Director,
Emission Control Technology Division
United States Environmental Protection Agency
Ann Arbor, Michigan If8l05
Dear Mr» Gray,
I have reviewed the technical report entitled "Determination of Tire
Energy Dissipation-Analysis and Recommended Practices" by Messrs Burgeson
and Thompson, which was distributed to the members of the SAE Rolling Re-
sistance Subcommittee at its last meeting, April 26 by Mr. Thompson and
yourself. My observations are as follows:
As you know, the SAE has developed a rolling resistance test procedure
which is now at the balloting stage in the Highway Tire Committee. It will
become an official SAE Recommended Practice within a few months. Glenn
Thompson is a member of the Rolling Resistance Subcommittee and as such has
helped us develop our procedure.
I am sure that Glenn is aware that the objectives of the technical people
who have participated in this endeavor are identical with those stated in the
report as EPA objectives, i.e. to obtain test results which are meaningful and
valid in what Glenn calls the "real world". Unfortunately, Glenn assumes that
the ideal way to achieve these objectives must be "the development of a
laboratory test procedure to simulate the 'real world* experience" of the tire.
In this respect I think that be is at odds with the rest of the technical
community. Simulation is often a good approach, but not necessarily the best
one.
I am disturbed by the fact that the report implies that existing test
methods are unacceptable and that new ones must be developed. Yet there is
no evidence that existing methods, especially the SAE one that Glenn helped
us develop, have even been tried by the EPA. How then have they been found
-------
unacceptable? If there is evidence to that effect, why has Glenn not brought
it to oar attention so that we could improve our SAE approach? None of us on
the subcommittee wants a method vhich does not produce meaningful results.
The EPA's primary objective as stated in the report is "to provide public
information and guidance on the fuel economy effects of various tires". It
seems to me that the credibility of the information provided is of paramount
importance. The credibility of the data is enhanced by the adoption of a
standardized test procedure which has the public endorsement of the technical
community known to be knowledgable on the subject. Therefore for the good of
the EPA program and for the greater probability of its public acceptance and
success, I recommend that the EPA adopt the tried and proven technology of the
SAE Recommended Practice rather than attempt to invent new tests. I believe
the EPA objective will be well served by the SAE test and we will all be
satisfied with the result*
If on the other hand the EPA uses the SAE method and discovers that the
test results do not adequately rank tires for their fuel economy effects, then
the EPA will have performed a valuable public service by showing us all that
we are on the wrong track and that a better method is needed.
As for the two test procedures described in the appendices of the report,
they are innovative and intriguing. I would like to see them used, experimentally
so that they could be evaluated against existing methods. Further discussion
in the absence of data can be little more than speculative comment.
Sincerely,
T.P. Baker
Chairman
/mjb
cc: Rolling Resistance Subcommittee
-------
Engineering Staff
Current Product Engineering
General Motors Corporation
June 6, 1978
Mr. Charles L. Gray
Acting Director
Emission Control Technology Division
U.S. Environmental Protection Agency
Ann Arbor, MI 48105
Dear Mr. Gray:
Attached are my comments you requested on the proposed draft on the
"Determination of Tire Energy Dissipation- - Analysis and Recommended
Practices." We would be pleased to meet with your staff to discuss
this in more detail if you should find this desirable.
Sincerely,
Richard C. Moore
Tire-Wheel Systems
/kv
attachment
cc: K. G. Peterson
F. D. Smithson
G. J. Barnes - Environmental Activities Staff
T. Baker - Uniroyal
-------
GENERAL MOTORS RESPONSE TO EPA DRAFT ON "DETERMINATION OF TIRE
ENERGY DISSIPATION - ANALYSIS AND RECOMMENDED PRACTICE"
General Motors agrees with the EPA that tire development should be focused
toward improved fuel economy for the consumer. We also recognize that in the
real world, tires are continually operating in a complex domain of transient
conditions. Some of these are temperature, pressure, speed, load, driving,
braking, steering, road surface irregularities, and tire wear. The technical
challenge upon industry is to improve vehicle fuel economy in general and to
meet federal fuel economy standards in particular. Recognizing that tires
play a significant role in vehicle fuel economy, then it becomes imperative
that test methodologies be established that can effectively assess the principal
performance characteristics of tires that relate to vehicle fuel consumption.
We don't think that there is a practical way at this time to address all of
Jzhe real world transient conditions that tires experience. However, steady
state tests utilizing free rolling tires have been developed and the .resulting
data provides good correlation with vehicle fuel economy tests. The success
"of these correlations lead us to believe that a relatively simple steady state
test would provide more meaningful results in the near future than a more
complex test procedure.
There are several concerns regarding the proposed EPA tire energy dissipation
test procedure. The data resulting from such a test methodology seems to center
around the anticipated needs of the EPA and would be of little value to industry
for the tire and vehicle design process. As pointed out, the current methods .
routinely used for assessing rolling resistance seem to be satisfactory for
at least obtaining major design improvements in tire rolling resistance perfor-
mance. The improvements in drive torque and transient effects which are not
already suitable reflected from improvements in steady state performance will
be addressed when suitable laboratory facilities become available. We are
unaware of any instance today where tire improvements based on steady state
measuring techniques would be misleading as it relates to road fuel economy.
Some of the additional concerns regarding the proposed procedure are summarized
as follows:
The energy dissipation factor would be expected to have significant varia-
bility since it is determined from the difference between two large numbers.
This would be an additional test for industry since it does not have the
general utility needed by vehicle designers to accurately assess effects
of design related parameters (load and pressure).
The preferred test which incorporates both the driven and undriven wheel
in combination with the EPA city and highway cycles would require very
expensive equipment and would be very time consuming to conduct. There
is no evidence that a test of this complexity is technically justified
at this time.
Transient type testing as proposed has many unresolved concerns that need
careful investigation. For example, what are test variabilities, data
resolution, effect of finned aluminum wheels (high heat transfer), drum
and wheel inertias, and speed tolerances.
-------
-2-
The last and principal concern is the implication that steady state measure-
ment methodology will result in misleading information that is directionally
wrong for improved fuel economy for the consumer. Since the ability of the
proposed procedure to accurately and repeatably rank order tires for their
relationship to vehicle fuel economy is unknown, then General Motors rec-
ommends that a carefully structured experiment be conducted to demonstrate
the effectiveness of each procedure to properly rank order a wide range of
tires for their effect on fuel economy. A carefully controlled series of
fuel economy tests having repeated measurements on different road schedules
and the two EPA laboratory cycles can then be used to confirm the fuel
economy - tire energy dissipation/rolling resistance relationship. Analysis
of these data will indicate the degree of deficiency that may result from
the more simplified current industry practices for evaluating tire performance.
-------
WASHINGTON NEW YORK
1909 K STREET. N.W.. SUITE 300 366 MADISON AVENUE
MOTOR VEHICLE MANUFACTURERS ASSOCIATION
of the United States, Inc.
3(10 NEW CENTER BUILDING DETROIT, MICHIGAN 48202 AREA 313-872-4311
S. E. KNUDSEN, Chairman
V. J. ADDUCI. President and Chief Executive Officer
THOMAS H. HANNA, Vice President
May 31, 1978
Mr. Charles L. Gray
Acting Director
Emission Control Technology
Division
U.S. Environmental Protection
Agency
Ann Arbor, Michigan 48105
Dear Mr. Gray:
The MVMA Ad Hoc Subcommittee on Tire Energy Dissipation
has reviewed the draft EPA report entitled "Determination of
Tire Energy Dissipation Analysis and Recommended Practices".
Pursuant to that review, we submit the following comments for
your consideration.
MVMA is in general agreement with EPA that tires play a
significant role on a vehicle's fuel economy. Also recognized
is the importance of focusing future tire development toward
improved fuel economy for the consumer. EPA must establish
procedures and methodology for determining vehicle fuel economy,
and, if these determinations are to be of value, a method of
assuring that test components are representative of actual
production is important. The industry's role is to furnish
test vehicles having components that represent design intent
since many components are not yet in full production.
The new concept pursued by EPA, as evidenced by the
subject draft, is to quantify certain tires utilized during
th» vehicle certification process. These data are intended
to support the emission certification and fuel economy programs.
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Mr. Charles L. Gray - 2 - May 31, 1978
It could be used by EPA in two ways: 1) by selecting tires
to be used in laboratory fuel economy measurements, or 2) to
be used for future reference when vehicle audits are conducted
and energy dissipation data are obtained for compliance on
production tires.
As stated in the discussion of the subject draft, the
reasoning by EPA to have a method "to provide direction,
incentive and reward for the production of low energy dissipation
tires" has been previously recognized by industry, and a
relatively uniform cost effective procedure has been developed
by SAE and is out on ballot for approval at the present time.
The approach proposed by EPA to determine a tire's energy
dissipation characteristics includes the transient behavior
of tires for an arbitrariTy^selected test cycle. This
recommended method would be of little value to industry since
it is too specific in nature (only one test load and inflation
pressure). It would also be expected to have little resolution
capability since it is derived from the difference of two large
numbers, both of which are subject to test variability. The
approach being pursued by SAE is to initially establish an
objective method of quantifying a tire's steady-state
performance. The analyzed data thus obtained can readily be
interpreted to meet the needs of both vehicle chassis engineers
and tire designers. It is believed that the principal tire
design changes and vehicle modifications which reduce the
steady-state rolling resistance will also result in reductions
of energy dissipation during transient conditions. The influence
of transient behavior and power transmission can only be properly
assessed when suitable laboratory facilities are developed.
The EPA has implied, merely by the generation of the subject
draft, that current industry practices utilizing steady-state
measurement techniques could be misleading. The MVMA is unaware
of any instance where the currently obtained steady-state rolling
resistance would be misleading as it relates to vehicle fuel
economy measurements made on flat roads. One of our principal
concerns, however, is the reversal in tire rank order performance
that can occur between the flat roadway and the laboratory twin
roll facilities where EPA fuel economy is evaluated.
The ability of the proposed procedures to accurately and
repeatably rank order tires for their relationship to vehicle
fuel economy is unknown. Before any recommended procedure is
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Mr. Charles L. Gray - 3 - May 31, 1978
adopted, the EPA should conduct a program to demonstrate that
the test method has the ability to properly rank order
a wide range of tires for their effect on fuel economy. This
should then be confirmed by a carefully controlled series of
road and laboratory fuel economy tests having a suitable number
of repeat measurements. This same group of tires should also
be quantified using the current industry practices which
incorporate steady-state rolling resistance and accurately
measured vehicle fuel economy could then be assessed.
Finally, as a general comment, MVMA suggests that, before
embarking on an additional complex recommended practice, the
need and feasibility for s'uch practice should be clearly
demonstrated.
MVMA is grateful for the opportunity to respond to these
proposed recommended practices. If you desire to discuss
these comments in further detail, please contact me.
Sincerely,
J
.
Harry B. Weaver, Manager
Environmental Activities Department
HBW/srd
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June 20, 1978
Mr. T. P. Baker
Uniroyal Tire Co.
66OO 3. Jefferson
Detroit, MI 43232
Bear 3?pm:
₯0 are writing to you on behalf of Pirsatona tedbnical personnel in
response to tiis request from SPA for comments on their proposed
rs commendation a for tire energy dissipation teats.
Dr. Sciiuring has studied the technical content of this EPA report
carefully and has no particular Quarrels with the eicplanation" of the
basic nature of tira losses*
However, we are all in strong disagreement with the proposed test
procedures '.fhich neasure tire properties at other than equilibrium
conditions.
Basically, there are known problems with the transient or quasi-steady
state test procedures and it seems logical that we should take OA thes
problems only if the transient teats have 'been proven to give tire vaT
which are either aore repeatable or bear a more direct correlation to
actual in-use values than staady-state measurements. Keither of thesa
proofs exists,
fact that the cycle of operation proposed by SPA represents some
particular mode of consumer vehicle operation is not significant with
rsspec.t to either the question of repeatability or correlation.
Lacking any proven relation 'KdLth flat road ia-use value st neither of
the two nroposed tests should be accepted in face of their obvious
difficulties:
1. Any test of a product or machine operating in a transient conditio
is inherently likely to prove less repeatable than a test run with the
product or machine in equilibrium condition.
2. Limited data obtained by our coxopany on both a flat-bed tester and
on a 62.?" diameter drum indicate a very good correlation between
equilibrium and transient tire performance on a .relative basis. We
know of no data that show that other than equilibrium condition tests
show better correlation with the real world. Lacking such proof,
there is no satisfactory reason for choosing conditions which are
inherently likely to produce less repeatable results,
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2
3. To obtain necessary precision ia -the proposed EPA transient test,
large horizontal forces must be measured and subtracted from one anot}
with a precision of less than one pound. This is very difficult, if
not impossible, to obtain with any available measurement instruments.
4. The proposed quasi-steady state test would require precise speed
control, increased power to drive the test drum, rapid data sampling
at fixed time intervals and software for data processing. Such
equipment and software would have to be newly developed or acquired.
5. Tha EPA proposed quasi-steady .state procedure requires about 45
minutes for each data point and therefore would require at least 225
minutes to provide the five data points covering three loads and three
pressures to produce the data provided by the currently proposed SAS
procedure which obtains the same tire data in just 70 minutes of test
tiiae.
6. No test equipment capable of running either of the proposed EPA
test procedures is currently available. Design and procurement of
such equipment seems unnecessary unless an improvement in results
obtained is likely.
V/s are concerned about the proposed minimum test drum diameter of one
meter. It is well known that test drums of very small diameter cause
unnatural distortions in the tire tread/bait region which significant?
affect tire rolling loss measurements.
We do have data available that show measurements Xfhich correlate
directly with flat surface measurements can be mada on a drum as small
as 62.? inches in diameter but we are not at all sure hoif far we can
go before drum curvature effects become significant. Further researcl
is required on this point, but for now we believe that a mini mum test
drum diameter of 1.50 meters should be specified.
We have a minor objection to the statement in the EPA discussion that
"during low speed operation the tire is the major source of energy
dissipation by the vehicle." The literature supports a conclusion the
tires'represent only 5% - 10/£ of vehicle energy dissipation. The vehj
engine dissipktea something like 80^ of the total energy available in
the fuel.
We believe the generally sound theoretical reasoning in the EPA pre-
sentation does not lead to their conclusions about the proper tire
tost procedures. We feel we should offer to work with EPA to obtain
a data base to prove or disprove the claimed advantages of their two
test cycle proposals over the more practical equilibrium test conditior
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3
Since Mr. iChompson quotes Dr. Schuring as an authority in his pre-
sentation, we would be glad to have Dr. Schuring1 s name used in
rebuttal. Please work with Dr. Schuring directly ±t you choose to
quote him. We would suggest that he might best be used to provide
short technical discussions on specific points which could be sub-
mitted as appendices to your committee response.
Very truly yours,
D. J. Schuring Iu 0?. Dorsch K. L. Canrobell
a&S 0?ire Boll. Sesist. SAS Eire Roll. SAE Highway
Subcoraiaittee Resist. Subcom. Tire Coiamittee
ZXC:np
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LAND
SEA
AIR
SPACE
SAE COMMITTEE CORRESPONDENCE
May 30, 1978
Society of Automotive Engineers, Inc.
Committee: Rolling Resistance Subcommittee
Reply To:
Ford Motor Company
Room 208, Dynamometer
P. 0. Box 2053
Dearborn, Mich. I»8l2
Mr. Charles L. GrayActive>Erector
Emission Control Technology Division
U. S. Environmental Protection Agency
Ann Arbor, Michigan ^105
Dear Sir:
I have reviewed the draft of an EPA report "Determination of Tire Energy
Dissipation Analysis and Recommended Practices" submitted to the sub-
committee at the April 26, 19?8 meeting and my comments are attached.
Yours truly,
A. S. Myint
re
cc: T. P. Baker
T. Northrop
Attach.
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COMMENTS ON EPA TIRK ROLLING RESISTANCE
The EPA procedures are intended to give some sort of tiro rolling index that
ir. rclatable to use in the FTP transient situations. A major question of how
this may relate to actual customer use cannot be answered. Ac tho tiro vrniia
up, tho tire pressure increases (with captive air pre.inure) and the rolling
resistance decreases. This pressure increase is a function of the tiro's
ability to dissipate heat generated due to rolling losses. Some of the hcn.t
ir; transferred to the road surface and in turn is transferred from the road to
tho surrounding atmosphere. It is expected that the heat transfer charac-
teristics of a concrete or asphalt highway is different from a small drum in
the laboratory. And, again, a flat belt tire machine with a water bearing will
have different heat transfer than a steel drum.
This all results in different prepsure build-ups (and, therefore, different
rolling resistances) for a given tire on different surfaces. This creates the
possibility that a tire ranking in the laboratory may not bo the same as what
it could be if it could be measured on the road under non-equilibrium thermal
condition.
Tho proposed SAE tire rolling resistance procedure is conducted at three
different constant pressure levels. These can be related to stabilized rood
operation since the tire pressures can be measured on the road. The road
tire pressure then can be related to rolling resistance that was measured in the
laboratory through the pressure/rolling resistance relationship.
Tho EPA procedure looks at the tire at only one load/tire pressure point. To
adequately evaluate a tire, a range of expected load and pressure conditions
must be evaluated. If a range of pressures and loads were evaluated, the pro-
posed EPA test procedure would bo very time consuming. This is because the tire
would have to be "cold soaked" between each load/tire pressure test point. If a
tost were conducted at 5 load/tire pressure points, the test including soak time
would require nearly 2h hours. The time on the tire machine alone would be over
3-1/2 hours.
Tho data handling equipment required for the procedure defined in Appendix A
is generally not available on tire tost machines. Some r.ort of data logger and/
or computer system would be required to record data at tho specified interval .
rate between one to five seconds. Also, the system would have to calculate the
tiro rolling resistance energy requirements.,
Tho tire machine required for the procedure defined in Appendix D does nob exist
Tho highly regarded and very elaborate Calspan flat bolt tiro machine does not
have tho capability to run this procedure.
Tho SAE proposed tire rolling resistance procedure evaluates at five load/tiro
proouure hob stabilized conditions. This procedure con bo started with n cold
_tirop Tho rolling resistance of tho tire could bo observed during warm-up an
tlio SAE procc'lure with no additional test time and this would provide oomo iu-
into "cold" tire rolling resistance.
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In summary, the proposed EPA test procedures are overly complex and in the ^
long run may not adequately meet the goals of the EPA. It is suggested that
the proposed SAE procedure with monitoring of rolling resistance during warm-
up be used for EPA's needs so that tire rolling resistance in non-thormal and
thermal equilibrium conditions can be determined.- From this learning process
future direction for tire rolling resistance testing can be determined in- ^
telligently.
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