SDSB 79-21
Technical Report
Tire Programs
Several Approaches with Significant Potential
to Decrease Fuel Consumption
by
Glenn Thompson
June 1979
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 devel-
opments 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, Noise and Radiation
U.S. Environmental Protection Agency
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Abstract
Tires have a significant effect on the fuel economy of a
vehicle because of the energy which they dissipate during use of
the vehicle. Consequently, any approaches which reduce the energy
dissipated by tires will improve vehicle fuel economy and will
reduce the national fuel consumption. Tire-related approaches to
reduce U.S. annual fuel consumption have several potential advan-
tages; primarily the rapid replacement rate of tires, at least
compared with the vehicle population, and the universal applica-
bility of improved tire technology to all light-duty vehicles and
small trucks.
Several approaches have been identified which have the po-
tential to significantly reduce annual fuel consumption. The
programs are an information program to allow consumer selection of
fuel-efficient tires and incorporation of tire inflation pressure
maintenance in existing or planned inspection programs. Both of
these potential programs are technologically feasible at the
present time.
A tire information program has the potential to reduce fuel
consumption by 3 billion gallons. It is very difficult to predict
the success of such a program, however, with 10 percent efficiency
300 million gallons would be conserved. Even if the program were
only 1 percent efficient, the resulting fuel conservation of 3
million gallons would probably offset the cost of the program.
An annual information inspection and maintenance program could
be expected to save approximately 300 million gallons. Such a
program would certainly seem to be cost effective when incorporated
into any existing or planned safety or emissions inspection pro-
gram.
A consumer information program on the fuel economy aspects of
tire inflation pressures could be effective. However, the cost
effectiveness of this approach would result more from the lower
cost of the approach than the amount of fuel saved.
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Introduction
Tires have a significant effect on the fuel economy of a
vehicle because of the energy which they dissipate during use of
the vehicle. Consequently, any approaches which reduce the energy
dissipated by tires will improve vehicle fuel economy and will
reduce the national fuel consumption. Tire related approachs to
reduce U.S. annual fuel consumption have several potential advan-
tages; primarily the rapid replacement rate of tires at least
compared with the vehicle population, and the universal applica-
bility of improved tire technology to all light-duty vehicles and
small trucks. This report discusses several approaches to reduce
tire energy dissipation which have the potential to save several
billion gallons of gasoline annually.
Discussion
EPA reports and other literature have investigated the energy
dissipation characteristics of tires.(1,2,3) From these investi-
gations the following aspects of tire or tire use have been
identified as major parameters affecting the tire energy dis-
sipation:
1. Construction.
2. Inflation Pressure.
3. Temperature.
4. Vertical Load.
Tire construction, as used in the above Table, includes
all aspects of the tire which are determined during manufacture.
For example, the choice of components such as cord type and rubber
compounding are included as well as the type of construction, such
as radial or bias ply. The tire inflation pressure is, obviously,
the cold inflation pressure of the tire. This parameter is most
noteworthy because it is determined by the vehicle operator,
presumably by following the recommendations of the tire or vehicle
manufacturer. The tire temperature is primarily dependent on
the ambient temperature which cannot be controlled and on the
length of the vehicle trip. The tire temperature is also somewhat
dependent on the tire and rim heat dissipation characteristics.
The vertical load is the weight supported by the tire and is
primarily determined by weight of the vehicle.
Considering the above definitions of the parameters affecting
tire energy dissipation, only the first two, the tire construction
and the inflation pressure, are directly tire or tire-use related.
The remaining parameters are predominantly vehicle related.
Consequently, since this report addresses tire approaches to
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reducing fuel consumption, and since vehicle-use parameters have
already been discussed by other literature, only the direct tire
parameters of construction and inflation will be discussed further
in the subsequent sections.(4)
A. Tire Construction
The best known example where tire construction affects the
fuel economy of a vehicle is the fuel efficiency of the radial tire
versus that of the bias-belted or bias-ply tire. However, data
are also available to indicate the effects of such parameters as
the tire cord material.(5)
The magnitude of the potential effects of tire construction
can be seen from the estimation that if all current non-radials
were replaced, when worn, with radial tires, the U.S. fuel consump-
tion could be decreased by approximately 2 percent.(6) This
represents about 1.4 billion gallons in the case of passenger cars
and about 2 billion gallons if light-duty trucks are included. In
addition, if optimum radial tires were selected in each case even
greater fuel savings are possible. Assuming consistent selection
of optimum tires, the U.S. annual fuel consumption could probably
be decreased by an additional billion gallons. It is also possible
that if optimal tire selection occurred consistently during vehicle
use, the vehicle manufacturer would have increased willingness to
reduce engine size, since any resulting reduction in performance
would be minimized. This synergetic action would further increase
the potential for reduction in fuel consumption.
One major problem in the selection of optimum tires is the
inability of a consumer to choose such tires. At the present time,
no consistent tire grading information or labeling program for tire
energy dissipation exists. Therefore, a consumer or a fleet owner
does not have sufficient information to choose fuel efficient tires
if so desired. Also, since this information is not available in
the marketplace, there is little pressure for the tire manufacturer
to develop fuel efficient tires for aftermarket sales. However,
aftermarket sales must be considered important in any fuel conser-
vation strategy since 70 percent of all tires are sold as replace-
ment tires.(7)
EPA experience in the vehicle fuel economy labeling system
indicates that a tire labeling system could be an effective
approach to reduce U.S. fuel consumption. In the vehicle labeling
program about 50 percent of the new vehicle purchasers are aware
of the EPA-DOT vehicle fuel economy labels or the Buyer's Guide.
Of those that are aware of the labeling system, the vehicles they
purchase are approximately 20 percent more fuel efficient than
their previously owned vehicle. In comparison, for that segment of
the population unaware of the labeling program there is no sta-
tistically significant difference between the fuel economy of the
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new vehicle they purchased versus their previous vehicle.(8) This
indicates that a significant segment of the population is inter-
ested in fuel efficient vehicles and apparently the vehicle fuel
economy labeling system is assisting these people in their vehicle
selection.
It is reasonable to believe that the fuel conservationist
segment of the general population would also be interested in fuel
efficient tires. However, in this instance no information is
available to enable the consumer to purchase optimum tires. Since
the consumer action of purchasing tires is socially different from
that of purchasing a new vehicle, it is very difficult to predict
the extent of the population which would be influenced by a tire
information program. However, if this conservation program were 10
percent efficient, that is, only 10 percent of the total potential
of 3 billion gallons were conserved, this conservation of 300
million gallons is significant and approaches a savings of a
million gallons per day. Even if the program were only 1 percent
efficient, the resulting fuel conservation of 3 million gallons
would probably offset the national cost of the program.
B. Inflation Pressure
Tire inflation pressure is a very significant parameter
affecting the fuel economy of a vehicle. For example, an 8 psi
increase in tire inflation pressure would improve the fuel economy
of the current average vehicle by about one mile per gallon. If
all vehicle tire inflation pressures were increased by this amount,
the national fuel savings would be about 4 billion gallons. With
existing tires, this great an increase in inflation pressure would
cause an increase in ride harshness which would be objectionable to
some vehicle owners. However, it should be noted that the tires in
use are typically underinflated by 3 to 4 psi.(9) Correction of
this underinflation should not result in unacceptable ride char-
acteristics and could yield a fuel conservation of 2 billion
gallons.
Tire inflation pressure is an unusual parameter because it is
controlled by the vehicle operator. Consequently, if the vehicle
owner could be pursuaded to better maintain his tire inflation
pressure an immediate fuel conservation would be realized for all
vehicles in service. Conversely, it will be very difficult to
change the vehicle maintenance habits of a significant percentage
of such a large diverse group as all vehicle owners.
Several approaches to improve maintenance of tire inflation
pressures are probably worthwhile. First, a press release followed
by a small information program conducted in cooperation with any
interested automobile magazines would reach a large segment of the
automobile enthusiasts at little expense. Such a program could
logically be conducted in cooperation with DOT and/or DOE with EPA
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providing the experimental design and measurement expertise. If
industry participation is also desired, cooperation could be
solicited via TRA, API, MVMA or other manufacturers associations.
A second approach would be to incorporate a tire inflation
check in any safety or emissions inspection program. To ensure the
effectiveness of any such inflation check, the program should
include increasing the tire inflation to the recommended values if
additional air is required. Prior to implementing such a program
some experimental effort might be required to determine appropriate
pressure correction factors to enable estimation of the cold
inflation pressure from the observed inflation pressure as a
function of the tire and ambient temperatures. This would probably
be required since vehicles encountered in inspection program often
will have been operated prior to the inspection and therefore would
not have cold tires. Such correction factors would allow predic-
tion, using the tire temperature, of the necessary tire inflation
pressure in the as received condition to produce the recommended
cold inflation pressure.
If an inflation check were conducted once a year, then all
vehicles would presumably have correctly inflated tires for a
minimum of one month of the year, and probably for at least two
months. Therefore, this inflation check can be expected to save at
least one-twelth to one-sixth of the savings associated with
underinflation or about 300 million gallons. These savings should
more than offset the small incremental cost of performing the
inflation check as part of any existing inspection program.
C. Relationship of the Proposed Tire Programs to Current
EPA-DOT Fuel Conservation Programs
Reduction of vehicle fuel consumption by increasing tire
inflation pressures does not require technological innovation.
Automobile manufacturers are currently receiving a benefit for
increased tire inflation pressures in the EPA-DOT fuel economy
programs. Consequently, recommended tire inflation pressures are
now increasing and an average recommended inflation pressure of 35
psi is anticipated in the early 1980 "s. The proposed tire pressure
inspection and maintenance program would help ensure that these
increased recommended inflation pressures would also provide fuel
conservation for vehicles in consumer use.
Fuel conservation from selection of low energy dissipation
tires is also currently practiced by vehicle manufacturers in the
EPA-DOT fuel conservation programs. Consequently, EPA has already
proposed test techniques for determining tire energy dissipation in
a manner representative of typical tire use.(10) A tire energy
dissipation information program is also technologically feasible
using the same test methods. Such a program could simply classify
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tires in several energy dissipation categories; for example, class
a, b, c, and d tires. An alternate approach would be to present
estimated comparative tire operating costs in dollars per thousand
miles. The necessary information to convert from tire energy
dissipation to estimates of average tire operating costs is already
available from the EPA-DOT fuel economy programs. This approach
of presenting estimated operating costs, perhaps in pamphlet or
other form, is considered superior to an energy dissipation ranking
system because it would be conceptually obvious for the average
consumer. In addition, by comparing the operating costs, the
anticipated tire mileages and the purchase price of tires, a
consumer could, if desired, select tires which would provide the
lowest total cost per mile of vehicle operation.
There is no question of the technological feasibility of
either of the proposed programs which simply try to provide the
vehicle consumer with sufficient information and encouragement to
maintain the vehicle in as efficient condition as when it was
manufactured. In the absence of some programs of this nature, the
discrepancies between the measured fuel economies and the average
in-use vehicle fuel economy must be expected to increase.
Conclusions
Consumer choices of optimum tires and maintenance of recom-
mended tire inflation pressures each have the total potential to
reduce annual U.S. fuel consumption by approximately 3 billion
gallons.
It is difficult to predict, however, the percentage of this
total potential which might be obtained by government programs.
Even if only 10 percent of the total potential could be obtained
from a tire labeling and information program, this would be 300
million gallons annually. With this savings such a program could
be cost effective and should be investigated further.
If all tires were maintained to the inflation pressure recom-
mended by the vehicle manufacturer, U.S. annual fuel consumption
could presently be reduced by about 2 billion gallons. This
potential savings is anticipated to increase as recommended tire
inflation increases in future years, since actual in-use pressures
are not anticipated to increase as rapidly as are the recommended
pressures.
An annual inflation inspection and maintenance program could
be expected to save approximately 300 million gallons. Such a
program would certainly seem to be cost effective when incorporated
into any existing safety or emissions inspection program.
A consumer information program on the fuel economy aspects of
tire inflation pressures could be cost effective. However, the
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cost effectiveness of this approach would result more from the low
cost than from the amount of fuel saved. A significant advan-
tage of such a program is that it could be developed in an ex-
tremely short time period.
All of the above approaches are technically feasible and do
not require any technological innovations. These programs would
help to ensure that some of the fuel economy improvements for which
manufacturers have received benefit in the EPA-DOT vehicle programs
would retain their efficiency throughout the useful life of the
vehicle. Consequently, these programs would help to reduce the
observed discrepancies between EPA fuel economy measurements and
the fuel economies achieved by consumer vehicles.
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Abstract
Tires have a significant effect on the fuel economy of a
vehicle because of the energy which they dissipate during use of
the vehicle. Consequently, any approaches which reduce the energy
dissipated by tires will improve vehicle fuel economy and will
reduce the national fuel consumption. Tire-related approaches to
reduce U.S. annual fuel consumption have several potential advan-
tages; primarily the rapid replacement rate of tires, at least
compared with the vehicle population, and the universal applica-
bility of improved tire technology to all light-duty vehicles and
small trucks.
Several approaches have been identified which have the po-
tential to significantly reduce annual fuel consumption. The
approaches are: an information program to allow consumer selection
of fuel-efficient tires, and incorporation of tire inflation
pressure maintenance in existing or planned inspection programs.
Both of these potential programs are technologically feasible at
the present time.
A tire information program has the potential to reduce fuel
consumption by 3 billion gallons annually. It is very difficult to
predict the success of such a program, however, with 10 percent
efficiency 300 million gallons would be conserved. Even if the
program were only 1 percent efficient, the resulting fuel conserva-
tion of 3 million gallons would probably offset the cost of the
program.
An annual inflation inspection and maintenance program could
be expected to save approximately 300 million gallons. Such a
program would certainly seem to be cost effective when incorporated
into any existing or planned safety or emissions inspection pro-
gram.
A consumer information program on the fuel economy aspects of
tire inflation pressures could also be cost effective. However,
the cost effectiveness of this approach would result more from the
low cost of the approach than from the amount of fuel saved.
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