EPA-AA-SDSB-84-5a
Technical Report
Investigation of the Rolling
Resistance of Fuel-Efficient and
High Performance Tires
By
Nancy Egeler
August 1984
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 Sources
Office of Air and Radiation . -
U. S. Environmental Protection Agency
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Foreward
A second phase of the Rolling Resistance Test Program was
determine the rolling resistance of two groups of tires:
Group 1 - those tires thought, on the basis of advertising
and promotional claims, to be low rolling resistance (and
thus fuel efficient), and
Group 2 - those tires thought (on the same grounds) to be
"high performance" tires.
Tests were performed to learn if tires advertised as
fuel-efficient had lower rolling resistance than the high sales
tires previously sampled, and to determine if the high
performance tires had higher rolling resistance than regular
performance automobile tires. This report presents the test
results of the above two groups of tires.
I. Tire Selection Criteria
Some of the desired models were located by searching
through periodicals for tires advertised as: 1) low rolling
resistance or fuel efficient, and 2) high performance. If only
a manufacturer name was given in the advertisement, the
manufacturer was called for recommendations. One model was
chosen because it had performed well in a previous test
program. In addition, fifteen high performance models - were
volunteered for testing by the California State Office of
Procurement. (They wished to consider rolling resistance data
from this program in the procurement of tires for the
California Highway Patrol.) All models except those
volunteered by the California State Office of Procurement, were
purchased at retail stores in the Ann Arbor area.
Selection of tires for this portion of the program was
restricted by test capacity. Approximately 45 tests remained
from the total allocated testing capacity. Because of this
restriction, and because two previous test programs [1,2]
showed good homogeneity among tires of one model, only two
tires from each model selected were purchased. The California
State Office of Procurement sent three tires from each model
for testing. Such small sample sizes sacrifice some
statistical accuracy; however, this was deemed acceptable on
the basis of previous findings. [1,2]
All tires tested in this portion of the program were of
radial-ply construction and '14-inch nominal diameter (except
three models donated from the California State Office of
Procurement). However, it was not possible to obtain all "tires
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with the same aspect ratio and section width. All tires were
purchased as close to the size P195/75R14 as possible.
II. Test Contractor.
As with the previous portion of this program, the actual
testing was conducted by Standards Testing Laboratories, Inc.
(STL) of Massillon, Ohio. STL has had extensive experience in
tire testing, and provided consistent test results for the
previous portion of the program.
III. Test Procedure
The test procedure used was the spindle-force' method
described in "EPA Recommended Practice for the Determination of
the Rolling Resistance Coefficients."[3] This procedure is
outlined in the accompanying report EPA-AA-SDSB-84-5,
"Characterization of the Rolling Resistance of Aftermarket
Passenger Car Tires."
IV. Results
Mean RRC was computed for each model within the two
groups. The results for each group were then compared to those
obtained for the radials tested in the previous part of the
program. Group 1 tires were expected to have lower rolling
resistance than the radials from the previous test matrix,
since the previously tested radials were purchased about one
year earlier and tire technology can be assumed to have
improved since then, and since these tires were specifically
chosen because of their advertised low rolling resistance.
Conversely, it was expected that the tires of Group 2 would
likely sacrifice rolling resistance, and hence some fuel
economy benefits, in exchange for performance.
Finally, to investigate the consistency of the results,
the coefficient of variation (standard deviation divided by
mean RRC) was examined for each model line.
A, Group 1 - Low Rolling .Resistance/Fuel Efficient Tires
The overall mean rolling resistance coefficient (RRC) for
Group 1 tires was only slightly lower than the mean RRC for the
previously tested group of tires. The overall mean RRC for
Group 1 tires, 0.011307, was only 1.0 x 10"s lower than the
overall mean RRC of 0.011308 for the 170 radial tires tested in
the previous program. The percentage difference between Group
1 and the 170 radials from the other matrix was only 0.0088
percent. The wide range of mean RRC values in Group 1 accounts
for the proximity of mean RRC for Group 1 to the mean of the
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tires of the previously tested. Mean RRC for models in Group 1
ranged from 0.0087 to 0.0127. Three models had excellent
rolling resistance and thus lowered the overall mean
considerably: Bridgestone RD-116, Bridgestone RD-108, and Toyo
714. The remaining five models had only mediocre rolling
resistance and raised significantly the overall mean RRC of
Group 1. Table 1 lists mean rolling resistance force, mean RRC
(in increasing order), and the standard deviations of each
model.
B. Group 2 - High Performance Tires
The high performance tires generally had considerably
higher rolling resistance than the previously tested tires.
The mean RRC for the 27 high performance tires tested was
0.0136, 17 percent higher than the mean RRC of 0.0113 for the
previous matrix. Table 2 lists the results for Group 2 in
order of increasing mean RRC.
One should note the low rolling resistance of the
Firestone Super 125. The difference between the mean RRC of
the Firestone Super 125 and the mean RRC of the other tires in
Group 2 is certainly significant, and this model definitely
lowered the overall mean RRC of this group.
C. Consistency of Results
To determine the consistency of our results, we examined
the coefficient of variation of the models in Group 1 and
Group 2. The coefficient of variation ranged from 0.0104
percent to 16.6 percent, with a mean coefficient of variation
of 2.04 percent. Since 16.6 percent coefficient of variation
is nearly five times the next highest coefficient of variation
(3.52 percent), the "outlier" having the coefficient of
variation of 16.6 percent (Bridgestone RD-108) was deleted.
Without the RD-108, the mean coefficient of variation for all
models tested is 1.2 percent, which agrees well with the mean
coefficient of variation from the previous matrix of 1.5
percent. These figures signify that despite the small sample
size used in the analysis, the results (with the exception of
the RD-108s) were both very consistent and comparable to
previous results.
V. Conclusions
Based upon this examination of eight supposedly
fuel-efficient, low rolling resistance models, it was
determined that the majority'tested did not have substantially
lower rolling resistance than did the tires of the same
construction type previously tested. Three models, however,
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Table 1
Group 1 Rolling Resistance Cata - Means
by Brand and Model
Rolling Resistance
Force (Ibf)
Brand and Model
Bridgestone RI>-116
Bridges tone RD-108
Toyo 714
Pirelli P8
Montgomery Ward
Gas Miser
Continental TS 771
BF Goodrich
Arizonian
Dunlop Elite 70
Combined
N
2
2
2
2
2
2
2
2
16
Size
185/70SR14
175/70SR14
195/70HR14
165/65R14
P195/75R14
195/70SR14
P195/75R14
P205/70R14
X [1]
8.06
10.25
10.88
9.06
13.36
13.01
13.73
14.59
11.62
s [2]
0.0919
.1.7112
0.0990
0.2334
0.1414
0.0990
0.3748
0.0424
2.3506
RRC
X
0.00872
0.01040
0.01063
. 0.01167
0.01193
0.01213
0.01227
0.01273
0.01131
s
0.00011
0.00174
0.00011
0.00032
0.00011
0.00008
0.00033
0.00004
0.00135
[I]x = mean
[2] s = standard deviation
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Table 2
Group 2 Polling Resistance. Data - Means
by Brand and Model
Rolling Resistance
Force (Ibf)
Brand and Model
Firestone Super 125 [3]
BF Goodrich Pursuit
[3]
BF Goodrich Comp T/A
Avon Turbospeed
Kel ly-Spr ingf i eld
Charger 65
Goodyear NCT60
BF Goodrich Pursuit[3]
Goodyear Eaglet 3]
Armstrong Turbo ETX[3]
Yokohama 352
Pirelli P7
Combined
N
3
3
2
2
2
2
3
3
3
2
2
27
Size
P225/70R15
P225/70R15
205/70VR14
205/70HR14 .
P215/65HR14
185/60HR14
P205/70R14
P205/70HR14
P225/70HR15
195/60HR14
205/55R14
* Cl]
15.18
17.60
15.72
15.86
15.41
12.49
15.99
16.04
19.94
14.07-
14.99
15.97
s [23
0.2214
0.5640
0.0495
0.0707
0.0191
0.1344
0.0058
0.2685
0.3403
0.0990
0.0919
1.8879
KMJ
X
0.01093
0.01254
0.01318
0.01331
0.01335
0.01394
0.01395
0.01401
0.01422
0.01550
0.01658
0.01364
s ' •
0.00019
0.00044
0.00003
0.00001
0.00017
0.00014
O.OOO01
0.00024
0.00025
0.00013
0.00010
0.00145
[1] x = mean
[23 s = standard deviation
[33 This model line volunteered for testing by the California State Office of Procurement.
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did have excellent rolling resistance. The investigation of 11
high performance tire models revealed that, on the average,
these tires have approximately 17 percent higher rolling
resistance than regular performance tires. Thus, it appears
possible that one sacrifices some fuel economy with the use of
high performance tires. The variations observed in the
analysis of "low rolling resistance" tires and of high
performance tires were consistent with those results obtained
in the previous part of the program.
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References
1. "Characterization of the Rolling Resistance of Aftermarket
Passenger Car Tires-," Nancy Egeler, U.S. EPA Technical Report
No. EPA-AA-SDSB-84, July 1984.
2. "Rolling Resistance Measurements - 106 Passenger Car
Tires," Gayle Klemer, U.S. EPA Technical Report No.
EPA-AA-SDSB-81-03, August 1981.
3. "EPA Recommended Practice for the Determination of the
Rolling Resistance Coefficients," Glenn D. Thompson, U.S.
EPA-SDSB, March 1980 amended August 1980.
4. "The Measurement of Passenger Car Tire Rolling
Resistance," SAE Information Report J1270, October 1979.
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