LDTP 78-09
Technical Report
Clayton Dynamometer-to-Road
Tire Rolling Resistance Relationship
by
Richard N. Burgeson
NOTICE
Technical reports are intended to present a technical analysis of
an issue and recommendations resulting from the assumptions and
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
-------
I. Introduction
Currently, EPA emissions and fuel economy testing is conducted on
the twin small-roll Clayton Dynamometer. It has long been assumed
that two tires at 45 PSI operated on the Clayton Dynamometer are
equivalent to four tires at 26 PSI operated on the road. This
assumption was examined in an EPA report entitled "Tire-Dynamometer
Roll Effects." That report (1) presents tire rolling resistance
data collected on both a Clayton Dynamometer and a single large-
roll (48" diameter) dynamometer. The tires tested had a cold
inflation pressure of 45 PSIG. The data generated on the single
large-roll dynamometer were then corrected for roll curvature and
to an inflation pressure of 26 PSI. The relationship between these
corrected data and the 45 PSIG Clayton data was then investigated.
A recently completed EPA study to determine the effects of tire
inflation pressure on tire rolling resistance (2) as measured on
the single large-roll dynamometer indicated that the inflation
pressure correction factor utilized in the previous study was too
large. The previous report (1) utilized a factor of 3% decrease in
tire rolling resistance for each 1 PSI inflation pressure increase.
The later study indicated that the effect was, in general, 2.21%
decrease per PSI increase. This study also indicated that the
magnitude of the effect was dependent on tire type and size.
This report compares the rolling resistance data at 45 PSI as
measured on the Clayton Dynamometer from the previous study with
the recently obtained tire rolling resistance data at 26 PSI as
measured on the single large-roll dynamometer and corrected for
roll curvature.
II. Program Design
Tire rolling resistance data generated during the two previous
studies were combined for statistical analysis. Data collected on
tires at an inflation pressure of 45 PSI on the Clayton Dynamometer
were compared with data collected on the same tires at an inflation
pressure of 26 PSI on a single large-roll dynamometer. The 26 PSI
data were corrected for roll curvature prior to data analysis so
that the assumption of "two tires at 45 PSI on the Clayton Dyna-
mometer are equivalent to four tires at 26 PSI on the road" could
be re-examined. Appendix A presents these data.
III. Analysis
The methodology used to determine the tire rolling resistance,
F and the amount of power absorbed by the tire at 50 MPH, P.TM>
was the same as that reported by the two previous EPA studies TI7,
(2). The roll curvature correction was also the same.
-------
-2-
As a method of comparison between this two data sets, the ratios of
the mean values for F and PATN were computed according to
the following equation by tire type:
R
Mean F * Clayton (45 PSl)
_ RR
CR " Mean F * Road (26 PSl)
KK
*The respective mean values for P.TN may be substituted for
FRR when computing RCR.
The parameter R is the ratio of the mean Clayton results to
the mean road results and is identical to R reported in (1).
Ideallyj if the basic assumption is correct, R should be
equal to a value of "2.0". C
The resulting computations again (1) indicate that the basic assumption is
incorrect. Tables 1 and 2 present the values of R and the
previously reported prediction values of &,,, respectively, for
each tire type tested.
Table 1
Clayton-To-Road Relationship, R , By Tire Type
CR'
Tire
Type
Radial
Bias
Belted
Bias
Clayton
(45 PSl)
PATN
(watts)
5721.960
5212.867
5829.297
FRR
(Ib/k-lb)
19.
17.
19.
282
567
644
Large Roll
Corrected
PATN
(watts) (
3099.300
3758.600
3917.700
(26 PSl)
to Road
FRR
Ib/k-lb)
10.440
12.661
13.197
(Actual
RCR
1
1
1
.85
.39
.49
Table 2
Predicted Clayton-To-Road Relationship, R , By Tire Type
Clayton
(45 PSl)
Tire ATN
Type (watts)
(Ib/k-lb)
Radial 5721.960 19.282
Bias 5212.867 17.567
Belted
Bias 5829.297 19.644
Large Roll-Corrected
To Road and 26 PSl
ATN
(watts)
3404.091
3997.113
5086.178
(Ib/k-lb)
11.470
13.469
17.138
(Predicted)
RCR
1.68
1.30
1.15
-------
-3-
It should be noted that as the tire inflation pressure on the road
increases, the rolling resistance decreases and R approaches
"2.0". Based on the effects of tire pressure on tire rolling
resistance information reported in (2), road tire pressures of 29.6,
43.5, and 57.1 PSI for radial, bias belted and bias ply tires,
respectively, would be required to produce a value of "2.0" for
R . These predictions assume that the effect of tire pressure
on rolling resistance is linear. The predicted road pressure for
radial tires is reasonable, however, the predictions for bias
belted and bias ply tires are well beyond the maximum inflation
pressure for passenger car tires. In addition, the extrapolation
of the inflation pressure effect beyond 45 PSI may not be accurate,
since data beyond 45 PSI were not included in the data base, and a
linear relationship would not be expected at high inflation pres-
sures.
The current trend on the part of the automobile manufacturer to
obtain fuel economy improvements is to lower tire rolling resis-
tance by recommending increased inflation pressures. In addition,
radial tires are used extensively on vehicles submitted for EPA
certification so it would appear that for most vehicles the assump-
tion of "two tires at 45 PSI on the Clayton are equivalent to four
tires on the road" is valid. Of course, the assumption only holds
for vehicles with tire inflation pressures of approximately 30 PSI.
IV. Conclusions
Based on the data present, the following conclusions may be drawn:
1) For vehicles equipped with radial tires inflated to pressures
of approximately 30 PSI, two tires at 45 PSI on the Clayton are
equivalent to four tires (at 30 PSI) on the road.
2) The Clayton Dynamometer under loads vehicles equipped with
bias belted and bias ply tires. The current light-duty vehicle
road load equation provides for vehicles with bias ply tires
(belted and non-belted). However, the magnitude of this provision
may need correction.
-------
-4-
References
1. Burgeson, R.N., "Tire-Dynamometer Roll Effects", Technical
Report LDTP-77-4, March 1978.
2. Burgeson, R.N., "Tire Rolling Resistance Measurements At
Initial Inflation Pressures of 45 PSIG and 26 PSIG", Technical
Report, Unpublished.
3. Thompson, G.D. and Myriam Torres, "Variations in Tire Rolling
Resistance", Technical Support Report for Regulatory Action,
LDTP-77-05, October 1977.
4. Schuring.D.J., "Rolling Resistance of Tires Measured Under
Transient and Equilibrium Conditions on Calspan's Tire
Research Facility," DOT-OST-76-9, March 1976.
5. Elliot, D.R.; Klamp, W.K.; and Kraemer, W.E., "Passenger Tire
Power Consumption," Society of Automotive Engineers, SAE
710575.
6. Floyd, C.W., "Power Loss Testing of Passenger Tires," Society
of Automotive Engineers, SAE 710576.
7. Crum, W.B., "Road and Dynamometer Tire Power Dissipation,"
Society of Automotive Engineers, SAE 750955.
8. Schuring, D.J., "The Energy Loss of Tires on Twin Rolls, Drum,
and Flat Roadway - A Uniform Approach," Society of Automotive
Engineers, SAE 770875.
9. Clark, S.K.; Dodge, R.N.; Banter, R.J.; and Luchini, J.R.;
"Rolling Resistance of Pneumatic Tires," University of
Michigan Report DOT-TSC-74-2; Prepared for The Department of
Transportation, Transportation Systems Center, Cambridge,
Mass., July 1974.
10. Curtis, W.W., "Low Power Loss Tires," Society of Automotive
Engineers, SAE 690108.
11. Clark, S.K., "Rolling Resistance Forces in Pneumatic Tires,"
University of Michigan Report DOT-TSC-76-1; Prepared for The
Department of Transportation, Transportation Systems Center,
Cambridge, Mass., January 1976.
12. Thompson, G.D., "Light-Duty Vehicle Road Load Determination,"
Technical Support Report for Regulatory Action, LDTP-76-03,
December 1976.
-------
APPENDIX A
Tire Test Data
-------
A-l
Table A-l
Twin Small-Roll (Clayton) Dynamometer Test Data
By Tire Identification Number
Test
Tire Tire Tire Press
ID Size Type (PSI)
'v?0
:1?0
T20
iMi
r\ f f\
' r* U
070
1180
i><0
1PR
IPR
]3A
13A
138
1 ^A
1 ^M
l^R
1 PO
200
200
210
2?0
230
?30
240
->40
^C0
2SO
250
?*o
260
-70
^70
-'QO
100
300
300
'MO
T10
no
"120
320
1?0
1 .1
1 3
13
IS
1f-
r>
15
IS
15
15
IS
IS
is
is
15
IS
is
IS
is
15
is
IS
15
15
IS
IS
14
14
14
14
14
14
14
IS
14
14
14
1.4
14
14
14
14
14
,- A ''1 T A I
--AOTAL
.-' A D I A I.
.'i ASPF.
.j T A c R P
I .'i s " rr,
-"Mil AL
Ai'ij AL
-'A DIAL
Vft.lTAL
^A.MI AL
-I AC;
.0
^^.0
4S.O
45. f)
45 . 0
4S.O
45.0
45.0
45 . -1
45. n
45.0
45.0
4S.O
45.0
45.0
45.0
45.0
4S.O
Rolling
Force
(NT)
"-3.519
M.b.197
j 1 . 21 5
"v"9.757
"-.1.2.31
193.477
;' 2. 1S2
^2.089
77.830
7.QQ7
16.793
.H.l^?3
Rolling
Resistance
(Ib/k-lb)
15.r>96
18
16
14
17
19
18
,341
,20B
,40?
,210
,245
,403
19.S66
16.831
12.648
?4.030
15
18
14
17
16
18
,79Q
,169
,572
,787
,776
,225
19.570
19.744
18.233
15.54?
16.149
P0.925
19.200
16.463
16.138
18.652
16
17
IB
15
18
?0
14
16
,419
,834
,748
,789
,665
,428
,788
,2B1
Power
Absorbed
at 50 MPH
(watts)
4 /+
770
S44.-' .
510b.977
5710.80S
5^61.180
5806.17?
707 1.484
375 1.168
71 30.94=;
5391.51?
4324.211
497-1. -38
540'.} .363
540f.223
682/.277
5859.OQP
54.1 '1.688
4612.1?5
4792.309
620°.500
56s*/. 574
4*85.465
478.M.777
553'+.°10
4H72.234
14.755
5563
4685
55 3 M
6061
4388
4 M 3 1
4376
.430
.207
.844
.879
.24?
.37^
.633
-------
A-2
Table A-l (cont.)
Twin Small-Roll (Clayton) Dynamometer Test Data
By Tire Identification Number
Tire
ID
130
330
130
140
340
140
ISO
350
150
170
370
400
400
4] 0
41 0
<+?0
4?0
Tire Tire
Size Type
1^
14
14
14
14
14
1 3
13
13
13
13
IS
1.5
13
13
IS
IS
HTASR1
>" 1 A SHE
SJASHE
I ASBF
i 1 T A C CJ C*
1 **i T ^,
''- 0 (
?£ "/.
^78,
376,
371 ,
> i'.' 2 ,
106,
?'!,
P92,
175,
?66,
'? :> 3 ,
^^3,
lr^6,
?^6,
112,
,406
,348
,369
,?43
,695
,7??
,45?
,73?
,830
,339
,867
,574
,768
,859
,373
,534
,5?1
18
18
17
?0
?o
?0
15
?3
18
?2
?8
P0
19
19
?7
?0
^3
.558
.855
. 1 ?5
.956
.840
.465
.248
.102
.967
.018
.309
.077
.113
.873
.594
.074
.538
Power
Absorbed
at 50 MPH
(watts)
5-0,
559S
5081
621B
6184
607?
45?4
6853
56?8
65JJ
8400
595?
5671
5n97
8181
5Q57
6984
.
.
.
.
*
.
.
.
«
»
.
.
.
.
.
.
176
?77
695
730
133
988
801
453
40?
/81
617
930
715
?58
441
035
844
-------
A-3
Table A-2
Single Large-Roll Dynamometer Test
Date By Tire Identification Number
Roll Curvature Corrected.
Tire
ID
"1 0
0 1 0
020
120
050
050
1150
060
060
070
070
080
OPO
000
090
000
000
000
000
090
100
100
100
110
110
1 ?A
1 ?A
1?B
1 ?R
13A
13A
13A
13A
13A
13A
13A
13B
.13B
1 ^A
ISA
ISA
ISA
Tire
Size
1 3
13
1 3
13
14
14
14
15
IS
1 5
IS
15
IS
IS
15
IS
IS
IS
is
i i;
13
13
1 3
14
14
IS
15
15
15
15
15
IS
15
15
15
15
15
15
15
15
15
IS
Tire
Type
AOTAL
'.-> a 0 T A L
,' fl n i A L
'-< AOT AL
'ADIAL
i'ADTAL
VAOTAL
J. T ASRF1"
MASHF:
-'AHTAL
vAOIAL,
..'AHTAL
K-AOT AL.
r-.' A DIAL
vAOTAL
°A'")T AL
"AHTA!..
w A 1 1 T A L
-'AMI AL
y&njAL
4 .366
1 -9.648
1/^.336
1 ^.762
1 ^1.487
1 'b.607
1 -b.f)H5
1 *b.800
1 ^4.726
1 '-I .667
1 '4.312
> : 3 . 0 A 1
1 7 2 . 2 H 1
lhb.426
1 55.704
U.9.462
! 70.356
Rolling
Resistance
(Ib/k-lb)
12.710
9.582
12.053
1 1.169
11.713
10.517
1 1.106
10.435
1 1.970
12.530
9.639
13.819
12.097
8O O Q
*J C. *
8.802
8.560
9.005
8.763
9.292
9.1 71
12. 52^
12.583
11.9P8
12.642
12.645
1 1.626
0.764
1 1.172
11.505
12.162
13.308
12.433
14.97?
13.159
12.174
13.881
15.293
12.975
12.534
11.726
12.762
12.830
Power
Absorbed
At 50 MPH
(watts)
37 Y 3. 056
2844.448
357H.123
331^.658
3477.388
3121.08?
3297.140
3097.850
3553.406
3734.509
2861.453.
410^.344
3591.068
2b20.785
2613.1 70
2541.318
267J.164
2601 .468
?75rt.Pftfl
2 72*:'. 4 88
371*. 303
3735. **00
3558.873
375^.004
375J.H02
3451.255
?89tf .648
331^.467
34ib.398
361'). 4 77
39^0.520
369:). 030
4444.71 1
3906.478
3614.04?
4120.797
4530. Q8«
3^51 .797
3 720. "88
3481.174
378'1. 785
3-^(i^.7P5
-------
A-4
Table A-2 (cont.)
Single Large-Roll Dynamometer Test
Date By Tire Identification Number
Roll Curvature Corrected
Tire
ID
-ISA
ISA
1RO
IPO
200
200
210
210
210
220
220
230
230
TAL
^AOTAL
.'AOTAL
.^AOIAL
f.'AOTAL
r. TASPF.
H.T ASPE-
CT ASP F:
"iTASRE
«.T AS
HAS
PAOTAL
RADIAL
t-'AHIAL
-'A (HAL
v AOTAL
UHTAL
VAOJ AL
HTA5
-ST AS
HIAS
^AHJAL
K'AOIAL
MA?
HlAS
WADTAL
WAQIAL
Rolling
Force
(PSI)
26
26
26
26
26
26
26
26
26
26
26
26
26
26
26
26
?6
26
26
26
26
26
2*
26
26
26
26
?.b
?h
26
2'.
26
26
26
26
26
26
26
26
26
26
26
26
26
26
.0
. 0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.n
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.n
.0
.0
.0
.0
.n
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
26.0
1
.1
1
i
1
1
1
1
1
1
1
1
1
1
1
i
1
1
1
I
1
1
1
1
1
I
1
1
1
1
1
1
..5
1
1
1
1
1
1
1
(NT)
ys.
70.
-o.
47.
>3.
-HS.
1.
33.
14.
"->*.
^b.
'-0.
^4.
34.
2.
~-3.
.13.
'i2.
S'f.
^.
:;2.
^8.
15.
i9.
ra.
:-3.
-a.
-0.
ni.
/*.
^.
'*>.
->(>.
19.
^5.
S9.
**.
'8.
]4.
60.
r,2.
'+*.
uti.
046
233
863
284
490
205
355
269
899
934
763
951
166
460
924
^08
M50
569
91 f
433
469
251
423
334
218
405
279
957
134
077
3^4
H71
293
017
414
817
418
624
622
264
ISO
412
770
-'3.047
Power
Rolling Absorbed
Resistance At 50 MPH
(Ib/k-lb)
13.
12.
I.
1.
0.
0.
0.
0.
0.
9.
9.
10.
9.
10.
12.
1 1.
7.
9.
9.
10.
9.
12.
8.
fl.
12.
12.
14.
14.
1 0.
13.
10.
9.
11.
8.
9.
12.
9.
14.
16.
12.
11 .
10.
11.
183
821
362
092
806
182
646
037
160
560
547
615
351
127
270
591
821
984
634
425
977
672
693
988
971
306
933
382
629
487
273
555
771
964
446
036
747
959
164
070
459
726
204
12.279
<7.440 10.351
44.
335
10.870
(watts)
391 l
3mio
3372
3292
3208
3022
316;i
2979
3016
2837
2834
3151
2776
.625
.014
.940
.928
115
.880
.366
.601
.035
.947
.137
.348
.068
3006.220
3h42
3441
2321
2963
2*5^
309-)
2961
37M
2580
2668
3-ibO
3hS3
44 3 J
4269
3155
40UJ
304^
2836
34^'f
2660
2803
3573
2-^ i
44nu
4798
35H3
3401
3184
3326
.60S
.033
.851
.^25
,9?n
.043
.703. '
.709
.584
.035;
.401
.363
.066
.367
.434
.750
.462
.540
.351
.948
.082
.133
.494
.781
.461
.138
.722
.010
.156
364S.350
3072
.844
3227.007
-------
APPENDIX B
Test Tire Description By
Identification Number
-------
B-l
B-l
Tire Description
ID Number
010
020
050
060
070
080
090
100
110
12A
12B
13A
13B
15A
16A
16B
180
200
210
220
230
240
250
260
270
290
300
310
320
330
340
350
360
370
380
390
400
410
420
(both
Manufacturer
Goodyear
Goodyear
Goodyear
Goodyear
Goodyear
Goodyear
Goodyear
Goodyear
Goodyear
B.F. Goodrich
B.F. Goodrich
B.F. Goodrich
B.F. Goodrich
B.F. Goodrich
B.F. Goodrich
B.F. Goodrich
Firestone
Goodyear
Uniroyal
Goodyear
General
Uniroyal
Goodyear
Uniroyal
Firestone
Firestone
Uniroyal
Firestone
Goodyear
Uniroyal
Firestone
Uniroyal
Goodyear
Firestone
Uniroyal
Firestone
Uniroyal
B.F. Goodrich
B.F. Goodrich
studies combi
Size
BR 70X13
BR 70X13
HR 78X14
H 78X15
HR 78X15
HR 70X15
HR 78X15
B 78X13
H 78X14
HR 78X15
HR 78X15
H 78X15
H 78X15
HR 78X15
HR 70X15
HR 70X15
GR 78X15
HR 78X15
GR 78X15
GR 78X15
GR 78X15
LR 78X15
ER 78X14
FR 78X14
FR 78X14
HR 78X15
ER 78X14
ER 78X14
E 78X14
E 78X14
E 78X14
B 78X13
BR 78X13
BR 78X13
BR 78X13
B 78X13
HR 78X15
B 78X13
GR 78X15
Model
Polyglass Radial WT
Polyglass Radial
Polyglass Radial WT
Custom Power Cushion Polyglass
Polyglass Radial
Polyglass Radial WT
Custom Polysteel Radial
Cushion Belt Polyglass
Cushion Belt Polyglass
Silvertown Steel Radial
Silvertown Steel Radial
Custom Long Miler
Custom Long Miler
Silvertown Belted
Silvertown Lifesaver XL-100
Silvertown Lifesaver XL-100
Steel Belted Radial
Steel Belted Radial Custom Tread
Steel Belted Radial PR6
Steel Belted Radial Custom Tread
Dual Steel II Radial
Steel Belted Radial PR6
Steel Belted Radial Custom Tread
Steel Belted Radial
Steel Belted Radial
Steel Belted Radial
Steel Belted Radial
Steel Belted Radial
Custom Power Belted Cushioned Polyglass
Fastrak Belted
Sup-R-Belted Deluxe Champion
Fastrak Belted
Steel Belted Radial
Steel Belted Radial
Steel Belted Radial
Deluxe Champion
Steel Belted Radial
Silvertown Bias
Lifesaver 78 Steel Belted Radial
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