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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