LDTP 77-5
Technical Support Report for Regulatory Action
Variations in Tire Rolling Resistance
Glenn D. Thompson
and
Myriam Torres
October 1977
Notice
Technical support reports for regulatory action do not necessarily
represent the final EPA decision on regulatory issues. They 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 recommendations 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
This paper analyzes the tire rolling resistance data obtained in a
recent EPA road load project. Variations in the observed tire rolling
resistances were analyzed versus tire type, tire manufacturer, and tire
size. The differences between tire types have been previously investi-
gated and are generally known. However, the variations by tire size and
among manufacturers have not been previously reported.
Statistically significant variations were observed for all of the
investigated parameters. The difference between the means of the rol-
ling resistance coefficients for radial versus bias ply tires was ap-
proximately 24 percent. The observed variations among manufacturers
were suprisingly large. The range of the variations among the manufac-
turers, within the class of radial or bias tires, was greater than the
difference between the overall means of these tire types. In the case
of radial tires, the range of the variations by tire size was somewhat
smaller than the difference between the tire type means, while in the
case of bias ply tires, the range of the variations by tire size was
about the same as this difference between the tire types.
The fuel economy effect of a change in tire types; that is, from
bias to radial tires, has been previously reported and is briefly dis-
cussed. From these results it is concluded that a 10 percent change in
rolling resistance will yield approximately a 2 percent change in the
vehicle fuel economy. It is estimated that the fuel economy effect of
a low rolling resistance radial tire, versus an average radial tire, is
as great as the fuel economy effect of a radial versus bias ply tire.
Consequently, there is a very good potential for reduction in national
fuel consumption if the use of low rolling resistance radial tires can
be promoted. This is particularly attractive since the technology for
these tires already exists. In addition, the implementation time for
reduction in national fuel consumption by improvements in this area is
much shorter than the time required for fuel economy improvements by
changes in automotive technology. This would occur because the life
expectancy of the tire is much less than the life expectancy of the
vehicle, hence tire replacement occurs much more frequently.
At the present time, reduction of fuel consumption through optimi-
zation of tires cannot be expected to occur since there is no uniform
method of rating and reporting tire energy dissipation. The development
of a consistent, uniform method of rating and reporting tire energy
dissipation over cyclic driving schedules, such as the EPA test sched-
ules is recommended.
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I. Purpose
This report presents the variations in tire rolling resistances
which were observed during the recent EPA road load project (1)*. The
variations are analyzed versus the type of tire construction, the tire
manufacturers and the tire size. The fuel economy effects associated
with these variations in tire rolling resistances are discussed.
II. Background
The vehicle tire has a very significant effect on the fuel con-
sumption of the vehicle. The vehicle road load, that is the total force
required to maintain the vehicle at a constant speed on a level road
surface, is the sum of the mechanical rolling frictions of the vehicle
chassis, the tire rolling resistance forces and the aerodynamic drag.
Below 40. mph, the tire rolling resistances are typically predominate and
are approximately constant with speed (2). Because of the large volume
of driving conducted below 40 mph, the tire rolling resistance has a
very significant effect on the fuel consumption of a vehicle.
The rolling resistances of 60 tires were measured during the recent
EPA road load project. Because of the fuel economy significance of the
tire rolling resistance it was decided to analyze these data and report
the conclusions.
III. Discussion
The discussion is presented in three sections. The first section
describes the EPA tire rolling resistance measurements. The results of
a statistical analysis of these measurements are presented in the second
section. Finally, the fuel economy effects of these results are discussed.
A. The Tire Measurements
In a recent project to determine vehicle road load, the rolling
resistances of approximately 60 sets of tires were measured. These
tires were tested, as received, installed on the test vehicles (1). The
test vehicles were chosen to approximately represent the sales distribu-
tion of current light-duty vehicles. These vehicles are identified in
Table 1 of Appendix A, while the tires are identified in Table 2 of Appen-
dix A.
All tire rolling resistance measurements were conducted on one of
the EPA light-duty vehicle electric dynamometers. This dynamometer is
a G.E. motor-generator type with a 48" diameter single roll. During
these experiments the normal 0-1000 Ib. load cell of the dynamometer was
replaced with a more sensitive 0-300 Ib. load cell. Prior to all
measurements, the cold tire pressures were adjusted to the inflation
pressures recommended by the manufacturer and these pressures were
recorded. These pressures are given in Table 5 of Appendix A.
* Numbers in parentheses designate references at the end of the paper.
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The vehicle was placed on the dynamometer, and then the vehicle and
dynamometer were warmed up for 30 minutes at approximately 50 mph.
After warm up, the torque necessary to motor the dynamometer and vehicle
was measured at speeds from 60 to 10 mph in 5 mph decreasing speed
intervals. For each measurement, steady state dynamometer speed and
torque signals were recorded on a strip chart for a period of approxi-
mately 100 seconds. The stabilized values were then read from the strip
chart by the dynamometer operator.
After the measurements were completed with the full vehicle weight
resting on the dynamometer rolls, the vehicle was then lifted until the
vehicle tires were just contacting the dynamometer roll. The vehicle
tires were considered to be just touching the dynamometer roll if a
person could, with difficulty, manually cause the tire to slip on the
roll when the roll was locked. With this test configuration "the torque
versus speed measurements were repeated as before. These force measure-
ments were conducted on both the front and rear axles of the vehicle.
During the rear axle measurements the transmission was shifted into
neutral.
The tire rolling resistances were computed by subtracting the
torque measurements obtained when the tire was just contacting the
dynamometer roll from the torque measurements obtained with the full
axle load on the dynamometer. A scatter plot of the data from one
vehicle, after conversion to units of force at the tire-roll interface,
is given as an example in Figure 1.
The tire rolling resistance generally appeared nearly constant over
the observed speed range, with a slight linear increase with increasing
speed. Consequently, linear least squares regressions were conducted to
yield equations for the tire rolling resistances as a function of the
simulated vehicle speed. The coefficients of the regression analyses
are given in Table 3 of Appendix A.
One purpose of this report is to estimate the fuel economy effect
of various tires. This effect will be estimated over the EPA urban and
highway driving cycles which are assumed to represent national driving
characteristics. Consequently, the tire rolling resistance forces at
the mean speeds of each of these driving cycles was considered to be the
best single estimate of the performance of the tire over the cycle.
These mean speeds are 19.6 and 48.2 mph for the urban and highway cycle
respectively. The tire rolling resistance force for approximately each
of these speeds, 20 and 50 mph, was computed from the speed dependent
coefficients. These forces, representing the measurements obtained on
the large single roll dynamometer for each vehicle axle, are presented
in Table 4 of Appendix A.
The purpose for the original tire data collection was to charac-
terize the vehicle experience. Therefore, all tire measurements were
conducted on the test vehicle for which the tires were supplied, and at
the inflation pressures recommended by the manufacturer of the vehicle.
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VEHICLE ID: 1001
TEST WEIGHT: 2680LB
LU
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OC
U-S
+ - VEHICLE FULL HEIGHT
X - TIRE DISSIPflTIVE FORCE
x • VEHICLE JUST TOUCHING
* *
* m
*
10. 20.
SPEED ((M/SEC)
30.
Fig. 1 - Example of Force Measurements at the Tire Roll Interface
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The purpose of this report is to discuss the observed rolling resis-
tances and to search for variations by tire type and tire manufacturer.
Therefore, in this case it is necessary to remove any vehicle induced
variations in the tire rolling resistances. Consequently tire inflation
pressure corrections were applied to the measurements to correct to a
standard average inflation pressure. Also, all data were converted to
estimates of the flat road rolling resistances to minimize any effects
of the dynamometer curvature. Finally, the tire rolling resistances
were converted to coefficients of tire rolling resistance, in terms of
pounds (or newtons) of rolling resistance force per thousand pounds (or
newtons) of vehicle weight, to minimize the effects of variations in the
weights of the test vehicles.
1. Tire Pressure Correction Effects
The rolling resistance measurements conducted in this study were
performed at the inflation pressures recommended by the vehicle manu-
facturer. To minimize the tire effects of variations in inflation
pressure, the rolling resistance forces were corrected to estimates of
the rolling resistances at the inflation pressure of 25 psi for non-
driving tires and 26 psi for the vehicle driving tires. These pressures
were the approximate mean of the observed inflation pressures. The
correction factor used, 3%/psi, was obtained from a Calspan Corporation
report for DOT (3). Approximately similar results have been reported
elsewhere in the literature (4). No recommended inflation pressures
greater than 32 psi were observed and generally the pressure correction
was for a much smaller variation. The cold tire inflation pressures
prior to the test are given in Table 5 of Appendix A.
2. Dynamometer Roll Curvature Correction
The dynamometer roll curvature results in a higher measured rolling
resistance on the dynamometer than would be observed on a flat road
surface. This is particularly important since the roll curvature effect
is dependent on the tire size. The total tire rolling resistance force
coefficients for each axle were corrected to an estimate of the flat
surface force by using the conversion factor (5):
where
F = the rolling resistance of the tire on a flat road surface
F = the rolling resistance of the tire on a cylindrical dyna-
mometer surface
r = The radius of the tire
R = the radius of the dynamometer roll
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-4-
The radii of the tires were determined by measuring the height of
the loaded tire, from the contact patch to the top of the tread and
dividing by two. Previous experiments at the EPA have shown this tech-
nique is a very good simple static measurement of the dynamic rolling
radius. Five to ten tires of each tire size were measured and the
average of the measured radii for all tires of that size was calculated.
These average rolling radii are given in Table 1. The average rolling
radius for each tire size was used in the dynamometer curvature correc-
tions for all tires of that nominal size.
Table 1
Rolling Radii versus Tire Size
Nominal Tire Size Average Rolling Radii
12 inches 0.27 m
13 inches 0.28 m
14 inches 0.31 m
15 inches 0.34 m
The rolling resistance forces for each axle, after all corrections,
are presented in Table 6 of Appendix A.
The total corrected tire rolling resistance force for each vehicle
was then computed by summing the forces of each axle. The dimensionless
rolling resistance coefficient was then computed by dividing this force
by the vehicle test weight. The concept of rolling resistance coefficient
is useful since the tire dissipative losses are very nearly proportional
to the vertical load on the tire (6). For this reason, the tire rolling
resistance coefficient is frequently used in the literature for tire
comparison. The computed tire-rolling resistance coefficients are
presented in Table 7 of Appendix A, as are the total vehicle forces and
the vehicle weight. While the rolling resistance coefficient is a
dimensionless unit, these coefficients are presented in the more common
form of the tire rolling resistance in pounds (newtons) per 1000 pounds
(newtons) of vertical load.
B. Statistical Analysis of Tire Rolling Resistance Coefficients
1. Tire Type
It has been found in past studies, and is generally accepted, that
radial tires have lower tire rolling resistance coefficients than bias
tires (7). As shown in Table 2 the mean rolling resistance at 20 mph
for the radial tires investigated in this study was 7.0 Ib/klb, while
the mean coefficient at 20 mph for the bias ply tires was 9.2 Ib/klb.
At 50 mph the means were 7.5 Ib/klb and 9.9 Ib/klb for radial and bias
tires, respectively. A "t-test" of each difference indicated the rolling
resistance coefficient for radial tires was lower than for bias tires at
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-5-
Table 2
Tire Rolling Rsistance Coefficient
Means by Tire Type
Tire Type
Radial
Radial
Bias
Bias
Conclusions
Test Speed
(mph)
20
50
20
50
Number of
Vehicles
in
Sample
Mean
Rolling
Resistance
Coefficient
Sample
Variance
48
48
16
16
6.95
7.52
9.17
9.93
2.85
3.02
2.32
2.38
The rolling resistance coefficient for radial tires is signifi-
cantly lower than the rolling resistance coefficient for bias ply tires
at both test speeds. The t-test statistics for the difference of the
means were 4.66 for the 20 mph data and 4.94 for the 50 mph data. Both
were significant at the 99% confidence level.
the 99% confidence level for both speeds. These results are graphically
displayed in Figure 2. Since tire type strongly influences the rolling
resistance coefficient, all subsequent analyses were conducted on radial
and bias ply tires separately.
2. Tire Manufacturer
The comparison of rolling resistance coefficients by tire manufac-
turer was considered an important part of this analysis since such
comparisons are not generally available. For each tire type, the mean
rolling resistance coefficient at 20 mph and at 50 mph for each tire
manufacturer was compared to the grand mean of the corresponding tire
type. The calculations are presented in Tables 3 through 6. The plots
of each manufacturer's mean and standard deviation (in the cases of more
than two observations) are shown in Figures 3 and 4.
The variations among tire manufacturers is quite noticeable. In
the case of radial tires the range of the variations among manufacturers
was greater than the difference between the grand means of radial versus
bias types of construction.
3. Tire Size
It has been suggested that tire size may have a significant effect
on the tire rolling resistance coefficient (8). Consequently, an
investigation of the rolling resistance coefficients by tire size was
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TIRE TYPE MEflNS
O- 20 MPH
D- 50 MPH
0
o
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D
RfiDIRL BIRS
TIRE TYPE
Fig. 2 - Means of the Tire Rolling Resistance Coefficients by Tire
Type. The error bars designate one standard deviation of the data.
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MRNUFflCTURER MERNS
FOR RflDIflL TIRES
O= 20 MPH
D= 50 MPH
• • >
00
• ,
(O
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1^ O'
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GOODRICH GENERflL GOODYEflR CONTINENTflL SEMPERIT
UNIROYflL FIRESTONE MICHELIN TOYO BRIDGESTONE
MflNUFflCTURERS
Fig 3. - Means of the Radial Tire Rolling Resistance Coefficients by
Manufacturer. The error bars designate one standard deviation of the
data for those manufacturers where at least three observations occurred.
If only one or two observations occurred the plotted symbols designate
the observed values.
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MRNUFflCTURER MERNS
FOR BIRS TIRES
O* 20 MPH
O 50 MPH
• T
=f
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GOODRICH GENERflL GOODTEflR CONTINENTflL SEMPERIT
UNIROYflL FIRESTONE MICHELIN TOYO BRIDGESTONE
MflNUFRCTURERS
Fig. 4 - Means of the Bias Tire Rolling Resistance Coefficients by
Manufacturer. The error bars designate one standard deviation of the
data for those manufacturers where at least three observations occurred.
If only one or two observations occurred, the plotted symbols designate
the observed values.
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Table 3
Radials - 20 MPH
Test of the Mean Tire Rolling Resistance Coefficient
at 20 MPH for each Manufacturer vs. Grand Mean for
all Radial Tires at 20 MPH
Manufacturer
Goodrich
Uniroyal
General
Firestone
Goodyear
Michelin
Continental
Toyo
Semperit
Bridgestone
Grand
Conclusions
Number of
Vehicles
in Sample
1
8
2
15
9
6
2
3
1
1
48
Mean Rolling
Resistance
Coefficient
6.511
7.
5.
7.
7.
,583
129
,733
,067
6.469
4.123
6.213
3.844
7.214
6.954
Sample
Variance
1.391
.448
2.250
2.825
3.141
1.160
2.234
2.845
Z-Stat
.260
1.010
-1.513
1.601
.185
-.661
-2.341
-.741
825
-1
.153
Signif.
.3974
.1562
.0643
.0548*
.4267
.2546
.0096**
.2296
.0336**
.4392
* The rolling resistance coefficient at 20 mph for Firestone radial tires is
significantly larger than the grand mean rolling resistance coefficient
for all radial tires at 20 mph (confidence level is slightly less than 95%)
** The mean rolling resistance coefficients for Continental and Semperit are
significantly smaller than the grand mean rolling resistance coefficient
for all radial tires at 20 mph.
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Table 4
Bias - 20 MPH
Test of the Mean Tire Rolling Resistance Coefficient
at 20 mph for each Manufacturer vs. Grand Mean for
all Bias Tires at 20 MPH
Manufacturer
Goodrich
Uniroyal
General
Firestone
Goodyear
Bridgestone
Grand
Number of
Vehicles
in Sample
1
4
2
2
5
2
16
Mean Rolling
Resistance
Coefficient
8.555
9.249
10.716
10.809
8.587
7.618
9.173
Sample
Variance
.827
2.712
.405
260
.026
2.
3.
Z-Stat
-.410
.098
1.396
1.532
-.779
-1.401
Signif.
.3409
.4610
.0814
.0628*
.2180
.0808
2.136
Conclusions
* The rolling resistance coefficient at 20 mph for Firestone is statistically
larger than the grand mean rolling resistant coefficient for all bias tires
at 20 mph but at a confidence level of at most 93.7%.
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Table 5
Radials - 50 MPH
Test of the Mean Rolling Resistance Coefficient at 50 MPH
for each Manufacturer vs. Grand Mean for
all Radial Tires at 50 MPH
Manufacturer
Goodrich
Uniroyal
General
Firestone
Goodyear
Michelin
Continental
Toyo
Semperit
Bridgestone
Grand
Number of
Vehicles
in Sample
1
8
2
15
9
6
2
3
1
1
48
Mean Rolling
Resistance
Coefficient
6.986
8.095
5.483
8.328
7.756
6.821
4.
7.
4.
402
220
369
7.536
7.515
Sample
Variance
,397
.902
,208
,438
3.325
1.092
.541
3.021
Z-Stat
-.301
.905
-1.632
1.632
.377
-.918
-2.499
-.290
-1.792
.012
Signif.
.3821
.1827
.0516**
.0516*
.3531
.1793
.0062**
.3859
.0367**
.4952
Conclusions
* The rolling resistance coefficient at 50 mph for Firestone tires is sig-
nificantly larger than the grand mean rolling resistance coefficient for
all radial tires at 50 mph.
**
The rolling resistance coefficients for General, Continental and
Semperit tires at 50 mph are significantly smaller than the grand
mean rolling resistance coefficient for all radial tires at 50 mph.
(The confidence levels for Firestone and General are slightly less
than 95%.)
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Table 6
Bias - 50 MPH
Test of the Mean Rolling Resistance Coefficient
at 50 MPH for each Manufacturer vs.
Grand Mean for all Bias Tires at 50 MPH
Manufacturer
Goodrich
Uniroyal
General
Firestone
Goodyear
Bridgestone
Grand
Number of
Vehicles
in Sample
1
4
2
2
5
2
16
Mean Rolling
Resistance
Coefficient
9.257
9.772
11.174
11.800
9.687
8.066
9.929
Sample
Variance
.455
2.677
.427
2.386
3.814
2.381
Z-Stat
-.422
-.195
1.072
1.660
-.306
-1.580
Signif.
.3365
.4227
.1419
.0485*
.3798
.0571**
Conclusions
* The rolling resistance coefficient at 50 mph for Firestone bias tires
is statistically larger than the grand mean rolling resistance coef-
ficient for all bias tires at 50 mph.
** The rolling resistance coefficient at 50 mph for Bridgestone bias tires
is significantly smaller than the grand mean rolling resistance coef-
ficient at 50 mph for all bias tires (confidence level is slightly less
than 95%).
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conducted. The rolling resistance coefficients are plotted versus tire
size for both radial and bias ply tires in Figures 5 and 6. This
information is also presented in Table 7. For each tire type, the means
of the rolling resistance coefficients decrease with an increase in the
tire size. A paired comparison analysis of variance showed that for the
20 mph coefficients, the only significant decrease was that of the mean
for 15 inch bias tires. For the 50 mph coefficients, both the 15 inch
bias and radial tires means decreased significantly from the other tire
size means.
Table 7
Tire Size Effects
Tire Type
Nominal Sample Mean Rolling
Tire Size Size Resistance Coefficient
Sample
Variance
20 MPH
50 MPH
20 MPH 50 MPH
Radial
Bias
13 inch
13 inch
12
2
7.46
10.36
8.23
10.89
,74
,60
30
16
Radial
Bias
14 inch
14 inch
16
10
7.12
9.60
7.65
10.47
01
24
.85
,90
Radial
Bias
15 inch
15 inch
20
3
6.52
7.89
6.97
8.55
1.53
.83
1.50
1.20
Conclusions
For each speed and tire type, every pair of the above tire size
means were compared to investigate what pairs were significantly dif-
ferent from each other at the 95% confidence level.
At 20 mph, the mean rolling resistance coefficient of 15 inch bias
tires is significantly less than the rolling resistance coefficient for
13 inch bias tires.
At 50 mph, the coefficients for both 15 inch radial and 15 inch
bias tires are significantly lower than the rolling resistance coef-
ficients for other tire sizes.
Since tire size appears to have a significant effect on the rolling
resistance coefficient it may be questioned if the previous analysis by
manufacturer was influenced by tire size effects. That is, a manufacturer
might have higher than average tire rolling resistances because no 15
inch tires of that manufacturer were tested. This does not appear to be
the case, since only the Firestone rolling resistance coefficient mean
was significantly higher than the rolling resistance coefficient mean
and numerous 15 inch Firestone tires were included in the sample.
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TIRE SIZE MEflNS
FOR RRDIflL TIRES
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O
DE
O- 20 MPH
D= 50 MPH
OJ
00
(O
OJ
0
0
D
6
O
0
4-
4-
13" 14"
TIRE SIZE
15*
Fig. 5 - Means of the Radial Tire .Rolling Resistance Coefficients by
Tire Size. The error bars designate one standard deviation of the data.
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TIRE SIZE MERNS
FOR BIHS TIRES
01
GO
01
OQ
LU
O
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CJ
•z.
cr
\—
CO
t—t
01
LU
QC
CD
O
QC
O = 20 MPH
D= 50 MPH
CD
OJ
6
D
13" 14"
TIRE SIZE
15'
Fig. 6 - Means of the Bias Tire Rolling Resistance Coefficients by Tire
Size. The error bars designate one standard deviation of the data.
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-11-
Likewise, those manufacturers which had lower than average rolling
resistance coefficients in one or more categories; General, Continental,
Semperit and Bridgestone might have appeared to have lower than average
rolling resistance because of a predominance of 15 inch tires by these
manufacturers. However, with the exception of Semperit, the tires by
these manufacturers included sizes smaller than 15 inches. Therefore,
only the Semperit results may be significantly influenced by tire size
effects.
The tire literature indicates that the rolling resistance of tires
decrease as the percentage of remaining tread decreases (9). Since the
vehicles were tested as received, tire wear could influence the results.
The percent of remaining tread depth could not be recorded since there
was'no method to determine the original tread depth. The influence of
this effect is believed to be minimal since many of the test vehicles
were EPA certification vehicles, volunteered by the manufacturers.
These vehicles would have nearly identical accumulated mileage, approx-
imately 5000 miles. Most of the remaining vehicles were late model
rental vehicles. These vehicles typically had low accumulated mileage,
however this parameter was uncontrolled.
C. Fuel Economy Effects
The previous section demonstrated that variations in rolling resis-
tances are observed between different tires. This section will investi-
gate the effect these variations in rolling resistances have on vehicle
fuel economy.
The fuel economy advantages of radial tires have previously been
reported in the literature (10). However, these measurements have often
been conducted at steady state conditions or over arbitrary transient
road routes. While results may have given good indications of the fuel ,
economy effects of tire variations, the cycles used have not been
standardized with respect to national driving patterns.
Recently EPA completed a project measuring the effect of radial
versus bias ply tires on vehicle fuel economy over the EPA urban and
highway driving cycles (11). In this program the fuel economies of six
vehicles were measured when these vehicles were equipped with radial and
with bias ply tires. Each vehicle was equipped with OEM tires of the
type, radial or bias-belted, which were sold as standard equipment for
that model. A matched set of tires of the alternate construction type,
bias-belted or radial, was acquired to provide a controlled comparison.
The alternate sets were furnished for the program by the vehicle manu-
facturers. These tires were also OEM tires, made by the same tire
manufacturer, with the same load rating, and with the nearest available
rolling radius as the standard equipment set. The vehicles and the
tires used are identified in Table 1 of Appendix B.
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-12-
These vehicles were operated over the EPA driving cycles on the
test track of the Transporation Research Center of Ohio. Fuel con-
sumption over these cycles was measured by integrating the fuel flow
rate determined by an in-line fuel flow meter. The results of these
measurements are given in Table 2 of Appendix B.
The estimated changes in the tire rolling resistance experienced by
the vehicles are given in Table 3 of Appendix B. In this table the tire
on the vehicle was assumed to have the mean rolling resistance coeffi-
cient of tires of that type and manufacturer, as given in Tables 3
through 6.
Theoretically, the changes in fuel economy should be related to the
changes in energy required to drive the vehicle over the cycle and the
engine efficiency of the vehicle. The energy required over the cycle is
a function of the vehicle weight and aerodynamic characteristics, in
addition to the tire rolling resistance coefficient. Also, the engine
efficiency characteristics vary. Consequently a uniform change in fuel
economy can not be expected based on a change in the tire rolling resis-
tance coefficient alone. However, the average percent change in fuel
economy, divided by the average percent change in the tire rolling
resistance coefficient, gives a sensitivity coefficient which may be
considered a "rule of thumb" number for predicting the fuel economy
effect expected from a change in the tire rolling resistance coeffi-
cient. These computed sensitivity coefficients are given in Table 4 of
Appendix B and repeated in Table 8 of the text. As anticipated, the
magnitude of the sensitivity coefficient for the low speed urban cycle
is greater than the corresponding magnitude of the coefficient for the
higher speed highway cycle, however, the difference between the coeffi-
cients is very small. Most important from a national average stand-.
point, is that both cycle coefficients and the composite coefficients
are approximately -0.2. This indicates a 10 percent decrease in the
tire rolling resistance coefficient and can be expected to yield a 2
percent increase in the national average fuel economy.
Table 8
Average
Sensitivity Coefficients
Cycle % Change in Fuel Economy
% Change in Tire Rolling Resistance Coefficient
Urban -0.20
Highway -0.19
Composite -0.19
-------
-13-
IV. Conclusion
It is concluded that there are significant effects on tire rolling
resistance coefficients from:
a) tire construction type
b) tire manufacturer
c) tire size.
The average decrease in tire rolling resistance from bias ply tires to
radial tires was about 24 percent. This was a difference of about 2.3
pounds(newtons)/kilopound(kilonewtons). The variations among tire
rolling resistance coefficients by tire manufacturer, within each tire
type were greater than this difference between the means of the tire
types. For example, within the radial tire classification the varia-
tions among manufacturers were almost 4.0 Ib (nt)/klb (knt).
In the case of .bias tires the observed decrease in the rolling
resistance coefficients from 13 inch to 15 inch tire sizes was as great
as the difference between the means of the rolling resistance coeffi-
cients for radial and bias tires. For radial tires, the decrease in
rolling resistance coefficients from 13 inch to 15 inch tire was some-
what less, about 0.9 lb(nt)/klb(knt).
The fuel economy effects of these observed variations in rolling
resistance are very significant. Based on the EPA cycles, the use of
average radial ply tires versus average bias tires improves fuel economy
about four percent. Improvements of a similar size would be expected in
transitions from average to low rolling resistance radial tires. Some-
what smaller improvements may also be expected if a general transition
were made to larger diameter tires. These improvements of about four
and two percent in the fuel economy of a typical vehicle represent
respective reductions in national average fuel consumption of about four
and two billion gallons of gasoline annually (12).
V. Recommendations
The basic recommendation is to continue investigative efforts in
this area. It must be remembered that the data reported here were
collected for the purpose of describing the vehicle road experience.
Consequently, the tires were tested in the operating condition recom-
mended by the vehicle manufacturer. While the data analysis attempts to
remove the vehicle dependent effects, it is possible that some vehicle
dependence remains. Also, the reported effects of the tire manufacturer
and tire size have not been reported elsewhere in the literature.
Therefore, these effects should be confirmed.
Should these results be confirmed, it would indicate that transi-
tions to more fuel conserving tires offers a potential for a significant
reduction in national fuel consumption in a relatively short time. The
-------
-14-
transition time could be short because the technology apparently exists
since such tires are already available in the market. The replacement
rate for tires is much more frequent than the replacement rate of the
vehicle population, thus, the effect of tire improvements on national
fuel economy would be seen more quickly than would the the effect of
changes in production vehicles.
For the most part the transition to radial tires has already
occurred, particularly in the OEM market. In 1976 approximately two-
thirds of the OEM tires were radial construction. Also, beginning in
1978 the vehicle manufacturer already has the incentive of national fuel
economy regulations to choose low rolling resistance tires for this
market. Therefore, the greatest potential area for fuel conservation is
in the region of replacement tires. This is a very significant area
since approximately 73 percent of all tires are sold in this market. Of
these tires only about 37 percent are currently radials (13).
Transitions to fuel efficient tires in the replacement market,
particularly within the category of radial tires, is limited by the
amount of information available to the consumer. The average tire
purchaser simply does not have the essential rolling resistance infor-
mation or the associated fuel economy information available to select a
tire on this basis. If fuel economy improvements are to be obtained by
consumer selection of low rolling resistance tires, then this essential
information must be made available.
The evaluation of the rolling resistances of tires should be based
on measurements of the energy dissipation of the tire over typical
operating conditions. The current EPA driving cycles are the logical
beginning for a cyclic tire energy dissipation procedure, therefore, the
feasibility of a program based on these cycles should be investigated.
-------
-15-
Referencea
1. G.D. Thompson, "Light-Duty Vehicle Road Load Determination", EPA
Technical Support Report fpr Regulatory Action, December 1976.
2. D.A. Clemming and P.A. Bowers, "Tire Testing for Rolling Resistance
and Fuel Economy", Tire Science and Technology, TSTCA Vol. 2, No.
4, November 1974.
3. D.J. Schuring, "Rolling Resistance of Tire Measured under Transient
and Equilibrium Conditions on Calspan's 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. J.D. Walter and F.S. Conant, "Energy Losses in Tires", Tire Science
and Technology, TSTCA, Vol. 2, No. 4, November 1974.
5. S.K. Clark, "Rolling Resistance Forces in Pneumatic Tires", Interim
Report prepared for the U.S. Department of Transportation, Trans-
portation Systems Center under contract DOT-TSC-1031, January 1976.
6. C.W. Floyd, "Power Loss Testing of Passenger Tires", Paper 710576
presented at SAE Mid-Year Meeting, Montreal, Canada, June 1971.
7. D.R. Elliott, W.K. Klamp, and W.E. Kraemer, "Passenger Tire Power
Consumption", Paper 710575 presented at SAE Mid-Year Meeting,
Montreal, Canada, June 1971.
8. S.K. Clark, R.N. Dodge, "The Influence of Tire Geometry on the
Rolling Resistance Efficiency of Commercial Vehicle Tires," Interim
Report prepared for the U.S. Department of Transportation, Office
of University Research, under contract DOT-OS-50113, September
1976.
9. S.K. Clark, R.N. Dodge, R.J. Ganter, J.R. Tuchini, "Rolling Resis-
tance of Pneumatic Tires", Interim Report prepared for the U.S.
Department of Transportation, Transportation Systems Center under
contract DOT-TSC-316, July 1974.
10. W.B. Crum, R.G. McNall, "Effects of Tire Rolling Resistance on
Vehicle Fuel Consumption", Tire Science and Technology, TSTCA Vol.
3, No. 1, February 1975.
11. J.D. Murrel, "Dynamometer and Track Measurements of Passenger Car
Fuel Economy Influences", EPA-TAEB report, September 1977.
12. D.B. Shonka, P.O. Patterson, A.S. Loebl, "Transportation Energy
Conservation Data Book: Suppliement IV", prepared for Transpor-
tation Energy Conservation Division, ERDA, August 1977.
13. C.S. Slaybaugh Ed., "Modern Tire Dealer", January 1977, Rubber/
Automotive Publications Inc., Akron, Ohio.
-------
APPENDIX A
-------
A-l
VEHICLE
IDENTIFICATION
NUMBER
101
201
301
401
502
601
804
901
1001
1102
1201
1301
1401
1501
1601
1702
1802
1901
2102
2203
2301
2401
2502
2602
2706
2802
2906
3011
3102
3212
3304
3402
3505
3613
3908
4014
4102
4202
4302
4402
4507
4607
4701
4801
4903
5103
5203
5303
5403
5503
5601
5603
5701
5802
6002
6102
6202
6402
6502
6702
6802
6909
8101
8401
MODEL
YEAR
1974
1975
1975
1975
1975
1975
1974
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1973
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1976
1975
1975
TABLE 1
TEST FLEET
MANUFACTURER
Chevrolet
Chevrolet
Pontiac
Pontiac
Ford
Oldsmoblle
American Motors
Chevrolet
Chevrolet
Ford
Bulck
Buick
Buick
Buick
Chevrolet
Ford
Ford
Buick
Mercury
Plymouth
Buick
Buick
Lincoln
Mercury
Toyota
Mercury
Toyota
Saab
Ford
Tr iumph
American Motors
Ford
Volkswagen
Honda
Mazda
Fiat
Mercury
Ford
Mercury
Ford
Datsun
Datsun
Pontiac
Oldsmobile
Dodge
Plymouth
Plymouth
Plymouth
Plymouth
Chrysler
Pontiac
Chrysler
Oldsmobile
Ford
Mercury
Ford
Ford
Ford
Ford
Ford
Ford
Volvo
Chevrolet
Oldsmobile
TEST
MODEL BODY WEIGHT
NAME STYLE (LBS)
Impala Sedan 4560
Chevelle Sedan 4100
Firebird Sedan 3640
Ventura Sedan 3520
Pinto Sedan 2800
Cutlass Sedan 4250
Gremlin Sedan 2970
Impala Stationwagon 5250
Vega Sedan 2680
Granada Sedan 3510
Century Sedan 4140
Special Sedan 4020
Skylark Sedan 3720
Apollo Sedan 3910
Monza Sedan 3490
Mustang Mach 1 Sedan 3000
Mustang Sedan 3020
Skyhawk Sedan 3200
Capri II Sedan 2570
Valiant Sedan 3600
LeSabre Sedan 4870
Estate Stationwagon 5590
Continental Sedan 5450
Capri Sedan 2350
Corolla Sedan 2470
Comet Sedan 3320
Celica Sedan 2760
99 Sedan 2710
Mustang Mach 1 Sedan 3320
TR6 Convertible 2650
Pacer Sedan 3330
Maverick Sedan 3320
Rabbit Sedan 2170
CVCC Sedan 1900
RX-3 Stationwagon 2680
128 Sedan 2180
Montego Sedan 4560
Gran Torino Sedan 4570
Marquis Sedan 4990
LTD Sedan 4860
280Z Sedan 3110
B210 Sedan 2310
Lemans Sedan 4230
Cutlass SupremeSedan 4330
Dart Sedan 3610
Valient Custon Sedan 4260
Gran Fury Sedan 4840
Scamp Sedan 3680
Valiant Sedan 3620
New Yorker Sedan 5120
Lemans Sedan 4320
Newport Sedan 4840
Delta 88 Sedan 4770
Granada Sedan 3760
Montego Sedan 4500
LTD Sedan 5020
Torino Sedan 4420
LTD Sedan 5060
Torino Stationwagon 5210
Gran Torino Stationwagon 5000
Gran Torino Sedan 4600
264DL Sedan 3290
Corvette Sedan 3850
Toronado Sedan 5170
-------
A-2
TABLE 2
TIRE DESCRIPTION
ID
0101
0201
0301
0401
0502
0601
0804
0901
1001
1102
1201
1301
1401
1501
1601
1702
1802
1901
2102
2203
2301
2401
2502
2602
2706
2802
2906
3011
3102
3212
3304
3402
3505
3613
3908
4014
4102
4202
4302
4402
4507
4607
4701
4801
4903
5103
5203
5303
5403
5503
5601
5603
5701
5802
6002
6102
6202
6402
6502
6702
6802
6909
8101
8401
MANUFACTURER
GOODRICH
UNIROYAL
UNIROYAL
GENERAL
FIRESTONE
FIRESTONE
FIRESTONE
GOODYEAR
GENERAL
FIRESTONE
UNIROYAL
FIRESTONE
UNIROYAL
UNIROYAL
GOODYEAR
FIRESTONE
FIRESTONE
UNIROYAL
GOODYEAR
GOODYEAR
UNIROYAL
FIRESTONE
MICHELIN
CONTINENTAL
TOYO
FIRESTONE
TOYO
SEMPERIT
MICHELIN
MICHELIN
FIRESTONE
FIRESTONE
CONTINENTAL
BRIDGESTONE
BRIDGESTONE
MICHELIN
UNIROYAL
UNIROYAL
MICHELIN
FIRESTONE
TOYO
BRIDGESTONE
UNIROYAL
GOODRICH
GOODYEAR
GOODYEAR
GOODYEAR
GOODYEAR
GOODYEAR
GOODYEAR
UNIROYAL
GOODYEAR
UNIROYAL
FIRESTONE
GOODYEAR
FIRESTONE
FIRESTONE
FIRESTONE
GOODYEAR
GENERAL
GENERAL
MICHELIN
GOODYEAR
FIRESTONE
TYPE
BIAS
BIAS
BIAS
BIAS
RADIAL
RADIAL
BIAS
BIAS
BIAS
RADIAL
RADIAL
RADIAL
RADIAL
BIAS
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
BIAS
RADIAL
RADIAL
BIAS
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
BIAS
RADIAL
RADIAL
BIAS
BIAS
RADIAL
BIAS
BIAS
RADIAL
RADIAL
RADIAL
BIAS
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
RADIAL
DESCRIPTION
G 78-15
G 78-14
F 78-14
F 78-14
BR78-13
GR78-15
6.45-14
L 78-15
A 78-13
DR78-14
GR78-15
FR78-15
FR78-14
E 78-14
BR78-13
195/70R13
190/70R13
BR78-13
165SR13
DR78-14
HR78-15
LR78-15
230SR15
165SR13
185/70HR13
DR78-14
185/70HR14
165SR15
DR70-13
185SR15
6.95-14
DR78-14
155SR13
6.00S12
155SR13
145SR13
HR78-14
HR78-14
JR78-15
HR78-15
195/70HR14
155/6.1513
GR78-15
GR78-15
D 78-14
D 78-14
LR78-15
E 78-14
E 78-14
JR78-15
GR78-15
HR78-15
H 78-15
FR78-14
HR78-14
HR78-15
HR78-14
LR78-15
HR78-14
HR78-14
JR78-14
185SR14
GR78-15 F
JR78-15
-------
A-3
TABLE 3
REGRESSION COEFFICIENTS
ID
0101
0201
0301
0401
0502
0601
0804
0901
1001
1102
1201
1301
1401
1501
1601
1702
1802
1901
2102
2203
2301
2401
2502
2602
2706
2802
2906
3011
3102
3212
3304
3402
3505
3613
3908
4014
4102
4202
4302
4402
4507
4607
4701
4801
4903
5103
5203
5303
5403
5503
5601
5603
5701
5802
6002
6102
6202
6402
6502
6702
6802
6909
8101
8401
DRIVING
A
(NT)
76.182
69.682
76.373
71.451
55.387
68.166
79.993
74.341
76.744
30.407
98.372
46.631
50.241
86.593
39.212
56.213
73.240
53.471
46.485
44.149
89.550
88.606
41.021
37.919
-6.761
27.733
47.383
31.906
69.702
49.000
79.946
64.990
18.437
47.619
46.001
26.975
132.244
85.202
61.592
68.730
62.980
47.277
67.365
69.927
66.040
58.705
47.075
40.020
79.322
56.476
60.255
66.405
76.031
64.147
70.702
87.241
75.627
97.069
69.242
33.696
53.527
47.097
59.739
70.915
B
(KG/SEC)
0.635
0.810
0.305
0.289
0.145
0.617
0.730
1.049
0.276
0.708
-0.789
0.676
1.000
-0.608
0.637
0.564
0.297
0.856
0.580
-0.633
0.364
0.995
0.639
0.138
1.540
0.418
0.436
0.328
0.139
0.119
0.798
0.687
0.167
0.175
0.064
0.324
0.505
0.868
0.694
0.506
0.269
0.437
0.672
0.541
0.570
0.575
0.160
1.540
0.533
0.768
0.815
0.658
0.858
0.342
0.482
0.589
0.692
0.420
0.583
0.119
0.768
-0.018
0.907
-0.035
NON-DRIVING
A
(NT)
114.778
123.098
123.098
115.314
81.985
72.462
100.238
104 . 881
92.313
50.929
91.932
93.828
86.315
123.098
86.202
69.056
74.448
82.243
67.495
21.178
108.010
86.186
76.672
16.797
57.807
100.708
35.769
18.202
92.667
46.007
100.238
108.100
16.797
20.527
53.398
39.645
95.874
135.400
124.442
145.133
59.390
62.766
62.457
86.218
109.712
59.503
122.697
92.273
92.582
119.843
80.086
103.466
129.581
101.203
109.818
117.844
153.439
124.460
124.729
77.671
84.692
62.098
79.239
81.411
B
(KG /SEC)
0.597
0.525
0.525
0.412
0.452
0.188
0.538
-0.011
0.216
0.923
0.326
0.235
0.307
0.525
0.715
0.560
0.416
0.583
0.601
1.949
0.097
1.013
-0.123
0.083
0.550
0.367
0.520
0.234
0.377
0.273
0.538
0.305
0.083
0.069
0.280
0.062
-0.696
0.815
0.230
0.059
-0.063
0.139
0.692
0.348
0.603
2.035
-0.073
0.402
0.666
0.985
0.415
0.883
0.808
0.597
-0.190
0.305
0.196
0.548
0.275
0.-170
0.308
0.386
0.363
0.560
-------
A-4
TABLE 4
UNCORRECTED FORCES
ID
0101
0201
0301
0401
0502
0601
0804
0901
1001
1102
1201
1301
1401
1501
1601
1702
1802
1901
2102
2203
2301
2401
2502
2602
2706
2802
2906
3011
3102
3212
3304
3402
3505
3613
3908
4014
4102
4202
4302
4402
4507
4607
4701
4801
4903
5103
5203
5303
5403
5503
5601
5603
5701
5802
6002
6102
6202
6402
6502
6702
6802-
6909
8101
8401
20
DRIVING
(LBS)
18.403
17.293
17.782
16.644
12.743
16.564
19.450
18.821
17.807
8.259
20.529
11.842
13.305
18.245
10.096
13.771
17.062
13.741
11.616
8.653
20.863
21.919
10.506
8.802
1.575
7.075
11.528
7.832
15.949
11.255
19.577
15.991
4.480
11.057
10.470
6.715
30.745
20.899
15.241
16.468
14.699
11.507
16.495
16.808
15.992
14.353
10.904
12.092
18.904
14.240
15.184
16.251
18.817
15.108
16.863
20.796
18.393
22.666
16.738
7.814
13.577
10.552
15.253
15.872
MPH
NON-DRIVING
(LBS)
27.003
28.729
28.729
26.752
19.339
16.668
23.616
23.556
21.187
13.305
21.322
21.566
20.021
28.729
20.816
16.650
17.573
19.661
16.381
8.678
24.477
21.411
16.989
3.943
14.101
23.378
9.086
4.562
21.590
10.892
23.616
24.915
3.943
4.753
12.567
9.037
20.154
32.077
28.438
32.746
13.225
14.390
15.432
20.082
25.876
17.467
27.437
21.552
22.152
28.922
18.838
25.035
30.755
23.951
24 . 306
27.105
34.888
29.081
28.593
17.803
19.659
14.736
18.543
19.428
50
DRIVING
(LBS)
20.317
19.735
18.702
17.515
13.180
18.425
21.651
21.984
18.640
10.393
18.150
13.880
16.320
16.412
12.016
15.471
17.957
16.322
13.365
6.744
21.961
24.919
12.433
9.218
6.218
8.335
12.843
8.821
16.368
11.614
21.982
18.062
4.984
11.585
10.663
7.692
32.267
23.516
17.334
17.994
15.510
12.824
18.521
18.439
17.711
16.087
11.387
16.735
20.511
16.555
17.641
18.235
21.404
16.139
18.316
22.572
20.479
23.932
18.496
8.173
15.892
10.497
17.987
15.766
MPH
NON-DRIVING
(LBS)
28.803
30.312
30.312
27.994
20.702
17.235
25.238
23.523
21.838
16.087
22.305
22.274
20.947
30.312
22.972
18.338
18.827
21.419
18.193
14.555
24.769
24.466
16.618
4.193
15.759
24.484
10.654
5.268
22.727
11.715
25.238
25.834
4.193
4.961
13.411
9.224
18.056
34.534
29.131
32.924
13.035
14.809
17.518
21.131
27.694
23.603
27.217
22.764
24.160
31.891
20.089
27.697
33.191
25.751
23.733
28.025
35.479
30.733
29.422
18.315
20.587
15.900
19.638
21.116
-------
A-5
ID
0101
0201
0301
0401
0502
0601
0804
0901
1001
1102
1201
1301
1401
1501
1601
1702
1802
1901
2102
2203
2301
2401
2502
2602
2706
2802
2906
3011
3102
3212
3304
3402
3505
3613
3908
4014
4102
4202
4302
4402
4507
4607
4701
4801
4903
5103
5203
5303
5403
5503
5601
5603
5701
5802
6002
6102
6202
6402
6502
6702
6802
6909
8101
8401
TABLE 5
PRESSURES
NON-DRIVING
(PSI)
28.0
24.0
26.0
24.0
22.0
26.0
24.0
22.0
24.0
24.0
26.0
32.0
24.0
26.0
30.0
26.0
26.0
24.0
27.0
28.0
24.0
24.0
26.0
27.0
24.0
24.0
24.0
27.0
26.0
20.0
26.0
24.0
27.0
22.7
26.0
24.0
24.0
24.0
26.0
26.0
28.0
24.0
26.0
24.0
28.0
28.0
26.0
28.0
28.0
24.0
26.0
26.0
26.0
24.0
24.0
24.0
24.0
26.0
24.0
24.0
24.0
25.0
20.0
20.0
DRIVING
(PSI)
28.0
24.0
24.0
24.0
22.0
26.0
24.0
32.0
26.0
26.0
26.0
32.0
24.0
26.0
32.0
26.0
26.0
26.0
31.0
28.0
24.0
28.0
26.0
31.0
24.0
26.0
24.0
27.0
26.0
24.0
24.0
26.0
27.0
22.7
26.0
26.0
24.0
24.0
26.0
26.0
28.0
24.0
24.0
24.0
28.0
28.0
26.0
28.0
30.0
24.0
24.0
26.0
25.0
24.0
24.0
26.0
24.0
26.0
34.0
32.0
24.0
26.0
20.0
26.0
-------
A-6
TABLE 6
CORRECTED FORCES
ID
0101
0201
0301
0401
0502
0601
080A
0901
1001
1102
1201
1301
1401
1501
1601
1702
1802
1901
2102
2203
2301
2401
2502
2602
2706
2802
2906
3011
3102
3212
3304
3402
3505
3613
3908
4014
4102
4202
4302
4402
4507
4607
4701
4801
4903
5103
5203
5303
5403
5503
5601
5603
5701
5802
6002
6102
6202
6402
6502
6702
6802
6909
8101
8401
20
DRIVING
(LBS)
16.074
13.659
14.914
13.146
9.600
13.672
15.363
13.724
14.300
6.523
16.944
11.482
10.509
15.302
9.612
11.743
14.549
11.035
10.194
7.680
16.216
17.037
8.671
7.724
1.265
5.588
9.106
6.652
13.600
7.666
16.419
12.631
3.932
8.571
8.928
5.393
24.284
16.507
12.580
13.592
13.046
9.240
13.614
13.064
14.194
12.739
9.000
10.733
16.778
11.068
12.532
13.413
15.531
11.933
13.319
16.165
14.527
18.708
13.220
6.172
10.724
8.592
10.389
10.811
MPH
NON-DRIVING
(LBS)
22.936
21.990
21.990
20.476
14.090
13.356
18.076
22.273
17.540
10.834
17.086
20.391
15.325
23.393
20.335
13.784
14.548
16.277
15.596
7.491
18.437
18.187
13.614
3.754
10.974
19.036
6.955
3.766
17.874
8.204
18.076
20.288
3.362
3.566
10.404
7.482
15.427
24.553
22.788
26.240
11.415
11.198
11.624
15.127
22.335
15.076
21.985
18.602
20.202
21.785
14.190
20.061
23.905
18.333
18.604
21.720
26.704
23.303
28.870
17.106
15.047
11.999
12.184
15.568
50
DRIVING
(LBS)
17.746
15.588
15.685
13.834
9.930
15.207
17.101
16.030
14.969
8.209
14.980
13.458
12.890
13.765
11.440
13.193
15.313
13.107
11.728
5.986
17.070
19.369
10.261
8.089
4.994
6.583
10.144
7.492
13.957
7.910
18.437
14.267
4.374
8.980
9.093
6.177
25.486
18.574
14.306
14.851
13.766
10.298
15.286
14.332
15.719
14.278
9.398
14.854
18.204
12.868
14.560
15.050
17.666
12.748
14.467
17.545
16.175
19.753
14.609
6.456
12.553
8.548
12.252
10.739
MPH
NON-DRIVING
(LBS)
24.465
23.201
23.201
21.427
15.082
13.810
19.317
22.242
18.079
13.099
17.874
21.061
16.033
24.682
22.441
15.182
15.587
17.732
17.321
12.563
18.657
20.781
13.317
3.992
12.264
19.937
8.155
4.348
18.815
8.824
19.317
21.036
3.576
3.722
11.103
7.636
13.820
26.433
23.343
26.382
11.251
11.524
13.195
15.917
23.904
20.372
21.809
19.648
22.033
24.022
15.132
22.194
25.799
19.710
18.166
22.457
27.157
24.627
29.707
17.598
15.758
12.947
12.903
16.920
-------
A-7
TABLE 7
ROLLING RESISTANCE COEFFICIENTS
AND
TOTAL ROLLING RESISTANCE FORCES
ROLLING
ID
0101
0201
0301
0401
0502
0601
0804
0901
1001
1102
1201
1301
1401
1501
1601
1702
1802
1901
2102
2203
2301
2401
2502
2602
2706
2802
2906
3011
3102
3212
3304
3402
3505
3613
3908
4014
4102
4202
4302
4402
4507
4607
4701
4801
4903
5103
5203
5303
5403
5503
5601
5603
5701
5802
6002
6102
6202
6402
6502
6702
6802
6909
8101
8401
TEST
WEIGHT
(LBS)
4560
4100
3640
3520
2800
4250
2970
5250
2680
3510
4140
4020
3720
3910
3490
3000
3020
3200
2570
3600
4870
5590
5450
2350
2470
3320
2760
2710
3320
2650
3330
3320
2170
1900
2680
2180
4560
4570
4990
4860
3110
2310
4230
4330
3610
3580
4840
3680
3620
5120
4320
4840
4770
3760
4500
5020
4420
5060
5210
5000
4600
3290
3850
5170
TOTAL
20MPH
(LBS)
39.010
35.649
36.904
33.622
23.690
27.028
33.439
35.997
31.840
17.357
34.030
31.873
25.834
38.695
29.947
25.527
29.097
27.312
25.790
15.171
34.653
35.224
22.285
11.478
12.239
24.624
16.061
10.418
31.474
15.870
34.495
32.919
7.294
12.137
19.332
12.875
39.711
41.060
35.368
39.832
24.461
20.438
25.238
28.191
36.529
27.815
30.985
29.335
36.980
32.853
26.722
33.474
39.436
30.266
31.923
37.885
41.231
42.011
42.090
23.278
25.771
20.591
22.573
26.379
FORCES
50MPH
(LBS)
42.211
38.789
38.886
35.261
25.012
29.017
36.418
38.272
33.048
21.308
32.854
34.519
28.923
38.447
33.881
28.375
30.900
30.839
29.049
18.549
35.727
40.150
23.578
12.081
17.258
26.520
18.299
11.840
32.772
16.734
37.754
35.303
7.950
12.702
20.196
13.813
39.306
45.007
37.649
41.233
25.017
21.822
28.481
30.249
39.623
34.650
31.207
34.502
40.237
36.890
29.692
37.244
43.465
32.458
32.633
40.002
43.332
44.380
44.316
24.054
28.311
21.495
25.155
27.659
RESISTANCE
20MPH
(LBS)
8.555
8.695
10.138
9.552
8.461
6.359
11.259
6.857
11.881
4.945
8.220
7.929
6.944
9.896
8.581
8.509
9.635
8.535
10.035
4.214
7.116
6.301
4.089
4.884
4.955
7.417
5.819
3.844
9.480
5.989
10.359
9.915
3.361
6.388
7.214
5.906
8.708
8.985
7.088
8.196
7.865
8.848
5.966
6.511
10.119
7.770
6.402
7.971
10.216
6.417
6.186
6.916
8.267
8.049
7.094
7.547
9.328
8.303
8.079
4.656
5.602
6.259
5.863
5.102
COEFF
50MPH
(LBS)
9.257
9.461
10.683
10.017
8.933
6.828
12.262
7.290
12.331
6.071
7.936
8.587
7.775
9.833
9.708
9.458
10.232
9.637
11.303
5.152
7.336
7.182
4.326
5.141
6.987
7.988
6.630
4.369
9.871
6.315
11.338
10.633
3.663
6.685
7.536
6.337
8.620
9.848
7.545
8.484
8.044
9.447
6.733
6.986
10.976
9.679
6.448
9.375
11.115
7.205
6.873
7.695
9.112
8.632
7.252
7.968
9.804
8.771
8.506
4.811
6.154
6.533
6.534
5.350
-------
APPENDIX B
-------
B-l
Table 1
Fuel Economy Test Vehicles
Vehicle and Tire Identification
Vehicle
Bias
Tire
Radial Ply Tire
1.
2.
3.
4.
5.
6.
AMC Pacer
Chevrolet Impala
Datsun B-210
Dodge Aspen
Station Wagon
Ford Granada
Ford Pinto
Goodyear
6.95 - 14
Goodrich
H78 - 15
Bridges tone
155 - 13
Goodyear
E78 - 14
Goodyear
C78 - 14
Goodyear
A78 - 13
Goodyear
DR70 - 14
Goodrich
HR78 - 15
Toyo
155SR - 13
Goodyear
FR78 - 14
Goodyear
DR78 - 14
Goodyear
BR78 - 13
-------
Table 2
Measured Fuel Economies
Urban Fuel Economy
Bias Radial Percent
Highway Fuel Economy
Bias Radial Percent
Composite Fuel Economy
Bias Radial Percent
Vehicle
AMC Pacer
Chevrolet Impala
Datsun B-210
Dodge Aspen SW
Ford Granada
Ford Pinto
Tire
14.4
10.9
24.3
14.2
14.0
18.2
Tire
14.5
12.0
25.1
15.3
13.5
19.0
Improvement
0.7
10.1
3.3
7.8
-3.6
4.4
Tire
18.3
17.2
35.6
19.9
17.8
24.9
Tire Improvement
18.3
18.3
36.8
20.8
18.3
26.0
0.0
6.4
3.4
4.5
2.8
4.4
Tire
15.9
13.0
28.4
16.3
15.5
20.7
Tire
16.0
14.2
29.3
17.3
15.3
21-6
Improvement
0.6
9.2
3.2
6.1
-1.3
-4.4
I
N>
AVERAGE
3.8
3.6
3.7
-------
Table 3
Estimated Changes in Tire Rolling Resistance
During Fuel Economy Measurements
Estimated Tire Rolling Resistance
Coefficient at 20 mph
Bias Radial Percent
Estimated Tire Rolling Resistance
Coefficient at 50 mph
Bias Radial Percent
Weighted Average
55/45 Weighting
Bias Radial Percent
Vehicle
AMC Pacer
Chevrolet
Impala
Datsun B-210
Dodge Aspen SW
Ford Granada
Ford Pinto
Tire
8.59
8.56
7.62
8.59
8.59
8.59
Tire
7.07
6.51
6.21
7.07
7.07
7.07
Change
-17.7
-24.0
-18.5
-17.7^
-17.7
-17.7
Tire
9.69
9.26
8.07
9.69
9.69
9.69
Tire
7.76
6.99
7.22
7.76
7.76
7.76
Change
-19.9
-24.5
-10.5
-19.9
-19.9
-19.9
Tire
9.05
8.86
7.82
9.05
9.05
9.05
Tire
7.36
6.72
6.63
7.36
7.36
7.36
Change
-18.7
-24.2
-15.2
-18.7
-18.7 '
1
-18.7
CJ
AVERAGE
-18.9
-19.1
-19.0
-------
B-4
Table 4
Average
Sensitivity Coefficients
Cycle % Change in Fuel Economy
% Change in Tire Rolling Resistance Coefficient
Urban -0.20
Highway -0.19
Composite -0.19
------- |