EPA-AA-SDSB-80-9
                           Technical Report
             An Investigation of the Fuel Economy Effects
                      of Tire Related Parameters
                                  by


                            Glenn Thompson

                                  and

                            Marty Reineman



                             May 1980
                                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 Source Air Pollution Control
                  Office of Air, Noise and Radiation
                 U.S. Environmental Protection Agency

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                                   -2-
Abstract








     A program was conducted on a test track to determine the fuel




consumption effects of radial vs. bias-ply tires, two radial tires from




different manufacturers, and increased tire pressure.  The program was




designed to eliminate ambient effects by running two identical test




vehicles simultaneously and alternating the parameter of interest between




the two vehicles.  Five different tire types were used (including the




original equipment manufacturer tires from the vehicles).









     This study demonstrated that radial tires were six percent more




fuel efficient than bias-ply tires; the radial tires from one manu-




facturer were four percent more fuel efficient than radial tires from




a different manufacturer; and radial tires inflated to 28 psig were




three percent more fuel efficient than radial tires inflated to 20




psig.  This program also determined that laboratory measurements of




rolling resistance are good predictors of track fuel consumption.








I.   Introduction









     Vehicle fuel economy is an area of significant present concern.




Therefore, it was decided that the fuel economy effects of tire con-




struction type, variations among tires of the same type, and tire in-




flation pressure, should be investigated.  This report describes the




experimental programs used in this study and presents the fuel economy




effects of these parameters for vehicles operated over the EPA city and




highway test cycles.

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                                   -3-




II.  Background









     It is well known that tires can affect the fuel economy of a




vehicle, most notably the fuel efficiency of radial tires. 1,2,37  In




addition, fuel economy effects have been attributed to variations among




tires of the same construction type and to inflation pressure.  However




in some cases, such as pressure effects, the literature contains little




data from direct observation; rather, the fuel economy effects have been




inferred from other data. J3/  In other cases the only reported data were




obtained during vehicle operation at steady speeds.  While these data




correctly indicate the presence and direction of an effect, the steady




state results may not reflect the magnitude of the fuel conservation




which would be achieved under typical vehicle operating conditions.









     An experiment was proposed to determine transient cycle fuel economy




effects of tire construction, that is, radial versus bias and the effects




of the differences between two types of radial tires.  This study also




investigated the effects of tire inflation pressure.  For this program,




the EPA urban and highway cycles were chosen as representative of typical




vehicle operation in metropolitan and rural areas, respectively.  All




testing was conducted on an oval test track at the Transportation Re-




search Center of Ohio.









III. Experimental Design









     The purpose of this experiment was to investigate the fuel economy




effects of tires and tire pressure.  In general, these effects are

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                                   -4-



relatively small, less than 5 percent.  Since typical variability of




fuel economy measurements may be of this magnitude, it was considered




important to carefully design the experiment.









     Table 1, which is based on one-tailed t-statistic tests, is the




basis of the experimental design.  This table presents the approximate




number of observations necessary to resolve differences between the




means of two sets of experimental observations with various observed




standard deviations.  For example, row 5 of this table demonstrates that




if the mean of the experimental data set one, is greater than the mean




of the data set two by 0.2, and the standard deviations of the data sets




are 0.2, then if 3 observations occurred in each set there is 90% con-




fidence that the mean of set one is larger than the mean of set two.









     Experimental data and theoretical investigations provide sufficient




basis for estimation of the magnitude of the effects anticipated.




Different tire construction types will effect vehicle fuel economy by




about 0.4 mpg or more.  Variations among a single tire type probably




induce fuel economy effects of 0.2 to 0.4 mpg, and change in tire in-




flation pressures of the order of 5 psi probably change fuel economy by




0.2 to 0.3 mpg.

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                                     -5-
                                Table 1
                                s                    Number of
          Ax              (experimental        observations required
(fuel economy effect)   standard deviation)     at confidence levels

                                               90%      95%      99%

0.1


0.2


0.3


0.4

0.3
0.2
0.1
0.3
0.2
0.1
0.3
0.2
0.1
0.3
0.2
0.1
30
13
3
7
3
1
4
2
1
2
1
1
49
22
5
12
5
2
6
3
1
3
2
1 ,
98
43
11
24
11
3
11
6
2
6
3
1

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                                   -6-




     EPA track fuel economy measurements from the test programs con-




ducted during the summer of 1978 provided test variability estimates




which indicated observed standard deviations of 0.3 to 0.2 mpg.









     The magnitudes of the anticipated effects and the expected test




variability in conjunction with Table 1 indicate immediate potential




test program problems.  Only the effects of tire construction should be




readily apparent.  Consistent with this observation, these effects are




the only ones for which transient cycle results have been reported in




the literature.  Pressure effects and the effects of variations among




tires of the same generic type are probably observable with a small




number of tests, but the confidence would be low.  In addition it must




be remembered that these confidence levels are only for the test that




the mean of one set of observations is greater than mean of the other




set, and are not confidence levels on the magnitudes of the effect.




Clearly, to accurately identify the magnitude of the anticipated effects




in the presence of the anticipated variability requires an extensive




number of repeat tests.









     The only alternative to time consuming, and hence expensive re-




petitive testing is to try to reduce the measurement variability.  This




has very good potential since, for a given level of confidence, the




number of tests required are proportional to the square of the experi-




mental standard deviation.









     It is hypothesized that variations in ambient conditions are respon-




sible for much of the observed track fuel economy variability.  This is




logical since ambient conditions affect the fuel economy of a vehicle

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                                   -7-





through several mechanisms.  For example, temperature affects the tire




rolling resistance directly.  Indirectly it has an effect on the aero-




dynamic drag forces by changing the air density.  In addition, tempera-




ture affects the vehicle engine by changing the fuel-air ratio of the




combustion charge, and also has an effect on the thermodynamic efficiency




of the engine.








     Unfortunately it is impossible to control the test ambient condi-




tions for a large track.  The alternative of only testing in a narrow,




acceptable, "ambient window" is also undesirable since this tends to




make the test program very long and arduous, at least in calendar time.









     The approach of using two identical test vehicles was proposed as




a possible solution to the potential test problems of the program.  The




accepted proposal was to simultaneously operate two vehicles, identical




except for the parameter under observation, in as similar a manner as




possible.  The investigated parameter would then be changed so that




vehicle one would be in the previous test configuration of vehicle two,




and vice versa for vehicle two.  The test would then be repeated under




these vehicle configuration conditions.  Test pairs can be repeated




until acceptable confidence is obtained, either for effect of the in-




vestigated parameter or for the lack of effect.









     The major advantage of this approach is that the effects of ambient




parameters, such as temperature and wind, should be minimized.  The




assumption is that ambient changes will affect both vehicles in ap-




proximately the same manner, eliminating observation of the "first

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                                   -8-




order" ambient effects.  This allows testing over a wide ambient window,




such as a 20 C temperature range while observing little of the ambient




effects in the paired data.  This was expected to provide good experi-




mental precision and to allow completion of the project in a reasonable




calendar time.
     The disadvantages of the experimental plan is that two vehicles,




two sets of most instrumentation, and two vehicle operator teams are




required.  In addition, failure of either instrumentation set eliminates




the paired data point, hence the design is twice as vulnerable to the




probability of random equipment failure as would be a single vehicle




test program.









IV.  The Experimental Program








     The parameters investigated were tire construction type, variations




among tires of the same type, and tire inflation pressure.  For each




investigated parameter the intent was to monitor the data as collected




and to only collect sufficient data to define the effects of the para-




meter to within about + 0.5cc/km (approximately +0.1 mpg for a 20 mpg




vehicle).  The goal was to have 90% or higher confidence in these re-




sults, or conversely, to have at least 90% confidence that the effect




was less than 0.5cc/km.









     It was decided to investigate the parameters in the order of




decreasing anticipated effects, as this would maximize the probability




that a maximum number of the desired parameters could be investigated




within possible constraints of weather, available test time, or costs.

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                                   -9-




The specific parameters chosen for investigation, and the order of




investigation was:









     A. "Average" radial tires versus "average" bias-ply tires.









     B. "Good" radial tires versus "poor" radial tires.









     C.   28 psig versus 20 psig (4 psig above the recommended inflation




and 4 psig below recommended pressure).








     The identical test vehicles, Vehicle 1 and Vehicle 2, were 1979




Chevrolet Novas equipped with 2.3L engines, 1 bbl carburetors, and three




speed automatic transmissions.  The instruments used for measuring fuel




consumption over the EPA cycles included a Fluidyne Model 1240T fuel




flow meter, a Nucleus 5th wheel with distance readout, and a Hewlett-




Packard chart recorder.  Power was supplied to the recorder from a 125




VA inverter.  In addition, each vehicle was equipped with a Fluke




frequency counter which measured driveshaft revolutions over a reference




distance. Driveshaft revolution measurements served as a check that fuel




consumption differences were not due to changes in N/V ratio. The tires




selected for the program''are listed below:









                          Rolling Resistance




             Tire                Coefficient        Diameter (mm)




P195/75 R14 C'Good" Radial)         0.0099               648




P195/75 R14 ("Average" Radial)      0.0104               648




P205/70 R14 ("Poor" Radial).        0.0122               649




E78xl4 (Bias-ply)                   0.0144               663

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                                  -10-

     The tires were obtained from the General Motors Milford Proving

Grounds and were selected on the basis of rolling resistance measure-

ments conducted by GM using the SAE proposed rolling resistance measure-

ment procedure.  However, the rolling resistance coefficients reported

were from direct spindle force measurements divided by the compressive

load on the tire.   The radial tire descriptives, "good", "average", and

"poor" were used solely for the purpose of identifying the relative

rolling resistance ranking and thus did not imply an overall assessment

of tire quality.



     Data were collected using two technicians per vehicle; one person

controlled the accelerator and brake as necessary to follow the par-

ticular EPA test cycle while the second person steered the vehicle and

recorded fuel flow and actual distance data.  Although the design of

this experiment tended to account for vehicle and operator differences,

considerable effort was spent to minimize differences between test

vehicles.  For example, vehicle mass and tire pressure were closely

controlled and each driver/operator team continued to run tests with

their particular test vehicle throughout the test program.
                                 V


     The test squence was the same for each parameter.  The first day

was spent in any vehicle preparation necessary, installation of instru-

mentation or components and a preliminary "dry run" test to insure all

personnel were adequately instructed in the experimental needs.  After

any problems were resolved the vehicles were initially checked, then

operated over the following cycles:

First 505 sec. of LA4    (Bag 1)

Next 867 sec. of LA4     (Bag 2)

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                                  -11-




505 sec. of LA4          (Bag 3)




Next 867 sec. of LA4     (Repeat of Bag 2)




EPA Highway Fuel Economy Cycle









     At the end of this sequence a short break was taken by the vehicle




operators while the parameter under investigation was changed.  For




example, tire pressures would be adjusted so that the vehicle which




initially had the lower cold inflation pressure would now have the




higher cold inflation pressure plus the temperature related pressure




build-up which was observed from the tires which initially had the




higher cold inflation pressure.  The vehicles then returned to the track




and the previous sequence was repeated.









     After the close of each test day or at the beginning of the sub-




sequent day all vehicle and ambient conditions data related to the im-




mediately previous tests were telephoned to the EPA project officer if




an EPA representative had not been at the track site during the testing.




These data were immediately processed and plotted; therefore, never more




than one test day elapsed between data collection and review.  This




rapid data review enabled detection of any equipment or other problems




with minimal delay and also allowed the decision to continue with a




given parameter, or to proceed to a subsequent investigation, to be made




daily on the basis of the collected, analyzed data.

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                                    -12-
V.   Data Analysis
     The data obtained from this test program are presented in the

Appendix A.  Table A-l presents the fuel consumption data for the com-

parison of an "Average" Radial Tire versus an "Average" Bias-Ply Tire

for the tests conducted over the LA-4 driving cycle.  Table A-2 presents

the similar data obtained from the highway driving cycle.  Tables A-3

and A-4 contain similar data from the "good" vs "poor" radial tire

comparison, while Tables A-5 and A-6 present the pressure effects com-

parison.



     These data can be analyzed by comparing the differences between the

fuel consump.tion of the vehicles in each test configuration.  For example,

the difference, Delta 1, between vehicle 1 equipped with "average"

radial tires and vehicle 2 equipped with bias-ply tires, is compared

with the difference, Delta 2, between vehicle 1 equipped with bias-ply

tires and vehicle 2 equipped with "average" radial tires.  The values

for the deltas are presented in each of the tables of the appendix, A-l

through A-6.



     Two results may be obtained from the analysis of the paired differ-

ences.  First, the average observed fuel consumption effect of the

parameter under investigation may be obtained, and second, confidence

intervals may also be obtained for these results.



     A.  Observed Effects of the Parameter Under Investigation



     The mean observed effect of the parameter is simply one-half of the

difference of the observed deltas.   This relationship may be derived

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                                     -13-
by considering the following equations.  Let
     B  = Base fuel consumption of vehicle 1
     B  = Base fuel consumption of vehicle 2
     EI = Fuel consumption effect of the parameter under investigation
          on vehicle 1


     E_ = Fuel consumption effect of the parameter under investigation
          on vehicle 2


     For example, when vehicle 1 is equipped with radial tires and
vehicle 2 is equipped with bias-ply tires the fuel consumption of the
vehicles may be expressed as:
     FC1 = Bj- E1                                                (1)
where
     FC1 = Fuel consumption of vehicle 1
         = Fuel consumption of vehicle 2
     The difference in the fuel consumption of the vehicles is:
     Delta 1 = FC2 - FCj                                        (2)

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                                  -14-
     Likewise, when vehicle 2 is equipped with radials
                                                                 (3)
and
     Delta 2 =
                                                                   (4)
The average effect of the parameter on the two vehicles is given by:
(Delta 1 - Delta 2)/2 = [ [ (B2 - B^ + E^ -  [ (B2 - B]_) - E2]]/2
                                   -  (B2 - B1) + Ei + E2]/2
                              E2)/2                              (5)
     A graphical representation of this analysis is presented in Figure




1.  The actual fuel consumption effect due to tire construction is

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                                        -15-
                                  Figure  1
                            15  cc/km
                            10 cc/km   ,"
                             5  cc/km
                            5 cc/km  .
                            	. ,     >'

Vehicle 2 - "Average" .Radial Tires


Vehicle 1 - Bias-Ply Tires'



                         - 10 cc/km
                         - 15 cc/km  • -•
Vehicle  1 - "Average" Radial Tires

Vehicle 2 - Bias-Ply Tires
                                                                   Delta 1

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                                  -16-






equal to one-half the difference between Delta 1 and Delta 2,




0.5 [12.5-(-5.9)].   The positive intercept of the line connecting Delta




1 and Delta 2 indicates that vehicle 1 has three cc/km lower base fuel




consumption than vehicle 2.  This intercept would be zero if both vehi-




cles have identical base fuel consumption.









     The effect of each parameter, calculated in the above manner, is




presented in Tables A-l through A-6 of the Appendix.  In addition, these




results are summarized in Table 2, which is presented in the results




section of this report.









     B. Confidence Intervals









     Equation (5) of the data analysis section shows that the desired




results are expressed as the difference between two sample means.




Consequently, the standard "t" test can be used to calculate confidence




intervals about the observed differences.  Specifically, a "t" test for




the hypothesis of the difference between the observed means:
is investigated to determine the magnitude of 8 for which the null




hypothesis may be rejected with 90 percent confidence.  For example, the




comparison of the fuel consumption differences with "Average" Radial vs.




Bias-Ply Tires over the LA-4 cycle, may be investigated. In this case:

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                                    -17-
          x  = Delta 1 = 12.5 cc/km




          s1  = S.D.    =  1.8 cc/km
          jL = Delta 2 = -5.9 cc/km




          s  = S.D.    =  1.2 cc/km
     The "t" statistic value for tests with pooled variances is
          t = [(x  - x) - 6]     /n^Cn., + n, - 2)
  /nin2^nl + n2 ~




/       ^nl + n2^
                        ,-lJs,
In this case the "null" hypothesis; that x, - x2 = <5, can be rejected




with 90 percent confidence for all values of 6 less than 17.1 cc/km or




greater than 22.4 cc/km.  Alternatively, we may state with 90 percent




confidence that the true value of Delta 1 - Delta 2 lies between 17.1




cc/km and 22.4 cc/km.








     Delta 1 - Delta 2 is shown by equation (5) to be simply twice the




tire effect which is being investigated.  Consequently, we may state




that in this experiment the observed effect of radial tires was to




reduce vehicle fuel consumption by 9.2 cc/km and that there was suffi-




cient experimental precision to state that there is 90 percent con-




fidence that the true reduction in fuel consumption of the vehicles was




between 8.6 and 9.8 cc/km.









     In more common engineering terminology it may be stated that the




observed effect was 9.2 cc/km and the 90 percent confidence interval

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                                    -18-




for the observation was approximately +0.6 cc/km.









     The observed values, and the approximate 90 percent confidence




interval associated with each effect are shown in Table 2.  These re-




sults are only slightly less precise than the experimental goal of




obtaining results with a precision of +0.5 cc/km at the 90 percent




confidence level.








     It is also informative to examine the null hypothesis x, - x~ = 0.









When this hypothesis is examined it can be stated that there is a 99.9




percent certainty that the fuel consumption of radial and bias-ply tires




are different, with the radial tires showing about 9.2 cc/km lower fuel




consumption.  Similarly, the radial vs. radial comparison, and the tire




pressure comparison results are statistically significant at the 99.9




percent confidence level.








     It is often convenient to discuss investigated effects in terms of




percent changes in fuel consumption.  Therefore, the percentage effects,




computed by dividing the observed effect of the investigated parameter




by the mean fuel consumed in all tests during the parameter investi-




gation are presented.  The 90 percent confidence limits, also expressed




as a percentage of the mean fuel consumption, are also presented in




Table 2.

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                                    -19-
VI.  Results
     The results of the data analysis are presented in Table 2.  As

expected, the effect of a transition from bias-ply to radial tires had

the greatest effect, almost 6 percent.  This result is very similar to

the results of previous investigations.^/


     The comparison of "good" versus "poor" radial tires resulted in a

fuel consumption effect of about 3.5 percent while changing the tire

inflation pressure by 8 psi resulted in fuel consumption change of

approximately 3 percent.  The observed pressure effect, 0.4 percent/psig,

is similar to the effect which had been theoretically predicted.5j


     A notable aspect of the results is that the effect of tire related

parameters is very similar for either the LA-4 or the HFET driving

cycles.  Modeling of the energy demand of the vehicle over the test

cycle indicates that tire contribution is approximately the same percentage

of the total energy demand for each cycle.  Consequently, the experi-

mental results would be theoretically expected unless anomolous tire

behavior occurred under transient conditions.


     The effect on vehicle fuel consumption of the radial versus bias-

ply tire comparison and the "good" versus "poor" radial tire comparison

can be investigated as a function of the tire rolling resistances.

These data are graphically presented in Figures 2 and 3. The slopes of

the fuel consumption versus rolling resistance lines are presented in

Table 3.  Also presented in Table 3 are the slopes of the lines pre-

sented in terms of the percentage fuel consumption effect divided by the

percentage change in the rolling resistance coefficient.

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                                               Table 2


                            Summary of Data Comparing Tire Constructions,
                         Variations Between Radial Tires,  and Tire Pressures


                         "Average" Radial         "Good" Radial
                           vs. Bias-Ply         vs. "Poor" Radial          28 psig vs.  20 psig

                         LA-4      HFET           LA-4      HFET              LA-4    HFET

Observed Effect (cc/km)   9.2       6.0            5.5       4.0               3.6     3.7

Limits of the 90 Percent +0.6      +1.0           +0.7      +1.2              +1.1    +1.3
Confidence Interval
on the Observed
Effect (cc/km)                                                                                               i
                                                                                                             M
                                                                                                             O
Average Fuel Consump-   158.4     112.0          155.6     110.3             153.7   109.8                   '
tion During Comparative
Tests (cc/km)

Percentage Effect (%)     5.8       5.4            3.5      " 3.6               2.3     3.4

Limits of the 90        +0.4     +0.9          +0.5     +1.2             +0.7   +1.2
Percent Confidence
Interval on the
Percentage Effect (%)

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                                      -21-
                               Table 3
             Summary of Rolling Resistance Data Comparing
        Tire Constructions, and Variations Between Radial Tires
                         Slope of Observed Relationship

                                  Ace/km / ARRC
                                  LA-4



                              1.675 x 10;
                              1.275 x 10'

"Good" Radial vs. "Poor" Radial
"Average" Radial vs. Bias-ply

     Vehicle 1
     Vehicle 2
     Vehicle 1
     Vehicle 2

Mean Values for each cycle

Grand Mean Values
(both cycles)
                              1.696 x 10:
                              2.130 x 1CT
                                           HFET
2.525 x 10;
2.100 x 10"
1.826 x 10:
2.913 x 10"
                              1.694 x 10

                                     2.018 x 10
2.341 x 10"
   3
                                                           Sensitivity Coefficient

                                                               % change in FC
                                                               % change in RRC
                   LA-4
0.184
0.142
 0.171
 0.214
         HFET
0.200
0.163
0.132
0.205
 0.178    0.175

      0.176

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 160
 150 !-
 ,140
 130
 120
                                   -22-
             .   .                  Figure  2
             Fuel C9nsumption as a Function of Rolling Resistance
                        "Average" Radial  vs.  Bias-Ply
                                             Veh. 2
                                                   7eh. 1
                                                                     .-a
                                                                        LA-4
 100
'   90  r
                                          Veh. 1
                                                                    —a
                                                         HFET
 110
                          Veh. 2
                    0.0104
                                                                    0.0144
   0.009
0.010
0.011
0.012
0.013
                                                                0.014
                                                            0.015
                       Rolling Resistance Coefficient
                               (Lbf/ 1000 Lbf)

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                                         -23-
                                        Figure  3
                 Fuel Consumption as  a  Function  of  Rolling  Resistance
                            "Good" Radial vs.  "Poor"  Radial
   1160 [
    150
    140
    130  j)
a
o
en -<
a o;
o o
u
    120
a)
    110
    100
     90  i)
          0.009
                                       Veh.  2
                                                        LA-4
                                                    HFET
                    0.0099
                              0.0122
0.010
0.011
0.012
0.013
                                                                      0.014
                                                            0.015
                             Rolling Resistance Coefficient
                                      Lbf/ 1000 Ibf

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                                    -24-





Presented in this manner, the slope of the line may be considered as a




fuel consumption/tire rolling resistance sensitivity coefficient.  The




data indicate that fuel consumption effects related by Acc/km divided by




ARRC (the slope) is more pronounced for the highway cycle test results




than the LA-4 results.  The sensitivity coefficients are calculated




using the average values for vehicle 1 and vehicle 2 fuel consumption




and the average RRC coefficients for the particular paired comparison.




The calculated sensitivity coefficients are approximately equal for all




comparison results.  Consequently, the mean value, 0.176, can be inter-




preted as a 1.8 percent change in fuel consumption for each 10 percent




change in the tire rolling resistance coefficient.  This may be used as




a good "rule of thumb" for predicting the vehicle fuel consumption




effects of changes in tire rolling resistance.








VII. Conclusions








     The results of this test program yielded the following conclusions.








     (1)  A typical radial tire is 5 to 6 percent more fuel efficient




than a typical bias-ply tire.  This result was achieved with high




experimental precision over transient driving cycles and diverse ambient




conditions.  In practice, data were collected over a temperature range




of 40-80°F with winds of 0-15 mph.  Consequently, this result should be




very representative of the effects of these tires in typical consumer




service.









     (2)  Significant variations can exist between the fuel efficiency




of radial tires from two different manufacturers.  In this program an

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                                     -25-






effect of 3.5 percent was observed under conditions typical of consumer




vehicle use.









     (3)  A substantial reduction in fuel consumption will occur with




increased tire inflation pressure.  In. this study, representative of




typical vehicle use and typical inflation pressures, a vehicle fuel




consumption reduction of 0.4 percent was observed for each 1 psig in-




crease in tire inflation pressure.









     (4)  The rolling resistance coefficient of a tire is a good pre-




dictor of the vehicle fuel consumption effects of the tires.  Conse-




quently, the tire rolling resistance coefficient is a good measure of




the relative fuel efficiency of tires.  As a general estimate, a 10




percent change in tire rolling resistance will result in a 1.8 percent




change in the fuel consumption of the vehicle.

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                               -26-   '
                            References
\J   W. K. Klamp, "Power Consumption of Tires Related to How They are

     Used," Proceedings of the 1977 SAE-DOT Conference, Tire Rolling

     Losses and Fuel Economy - An R & D Planning Workshop.


2j   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.


3/   G. D. Thompson, "Fuel Economy Effects of Tires" U.S. Environmental

     Protection Agency Technical Report SDSB 79-13.


tjj   G. D. Thompson and M. Torres, "Variations in Tire Rolling Resis-

 . M.  -tance - A Real World Information Need," Proceedings of the 1977

     SAE-DOT Conference, Tire Rolling Losses and Fuel Economy - An R & D

     Planning Workshop.


_5/   G. D. Thompson, Op Cit  (3)

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                              -27-




                           Appendix A

                            Table A-l

  Fuel Consumption and Paired Fuel Consumption Differences for
Comparison 1 ("Average" Radial vs Bias-Ply Tires) Using LA-4 Cycles.
  Vehicle 1:
  "Average"
  Radial Tires
    (cc/km)
                  Vehicle 2:
                  Bias-Ply
                  Tires
                     (cc/km)
Difference
Delta 1
 (cc/km)








Mean
S.D.
149.3
148.8
154.7
147.6
151.2
158.1
151.9
151.6
151.7
3.4
160.4
163.2
166.7
157.9
162.9
171.3
163.4
167.3
164.3
4.2
+ 11.1
+ 14.4
+ 12.0
+ 10.3
+ 11.7
+ 13.2
+ 11.5
+ 15.7
+ 12.5
1.8
Vehicle 1:
Bias-Ply
Tires
Vehicle 2:
"Average"
Radial Tires
Difference
Delta 2
     (cc/km)
                     (cc/km)
  Observed Effect  =
                    12.5 - (-5.9)

                         2
 (cc/km)








Mean
S.D.
159.1
159.9
157.2
161.1
163.9
167.3
161.7
164.2
161.8
3.2
154.5
154.8
150.0
155.3
156.6
160.3
155.6
160.2
155.9
3.3
- 4.6
- 5.1
- 7.2
- 5.8
- 7.3
- 7.0
- 6.1
- 4.0
- 5.9
1.2
                                     =  9.2 cc/km
Average Fuel Consumption For
A-II T 7 / m                   =
All LA-4 Tests
                                           /,
                                        cc/km

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                               -28-
                            Table A-2

"Average" Radial vs. Bias-Ply Comparison using Highway Cycles

  Vehicle 1:          Vehicle 2:          Difference
  "Average"
  Radial Tires
 Bias-Ply
 Tires
Bias-Ply
    (cc/km)
   (cc/km)
   (cc/km).
  (cc/km)
  Observed Effect
4.7 - (-7.2)
    2
   (cc/km)




Mean
S.D.



109.2
111.7
107.7
108.4
109.3
1.7
Vehicle 1:
Bias-Ply
Tires
114.8
115.4
111.8
113.6
113.9
1.6
Vehicle 2:
"Average"
Radial Tires
+ 5.6
+ 3.7
+ 4.1
+ 5.2
+ 4.7
0.9
Difference


  (cc/km)




Mean
S.D.
116.0
118.0
115.6
114.4
116.0
1.5
107.9
109.3
110.1
107.9
108.8
1.1
- 8.1
- 8.7
- 5.5
- 6.5
- 7.2
1.5
                                   =  6.0 cc/km
  Average Fuel Consumption For   ,, „ ..    „
  All HFET Tests               = 1I2'° CC/km

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                               -29-
                             Table A-3

   Fuel Consumption and Paired Fuel Consumption Differences for
Comparison 2 C'Good" Radial vs. "Poor" Radial), using LA-4 Cycles.
   Vehicle 1;
   "Good"
   Radial Tires.
Vehicle 2:
"Poor"
Radial Tires.
Difference
(cc/km)
150.1
146.3
158.0
156.3
153.2
154.0
152.8
147.5
147.4
151.7
153.1
151.1
148.2
150.9
Mean 151.5
S.D. 3.4
Vehicle 1 :
"Poor"
Radial Tires.
(cc/km)
160.5
163.2
154.5
155.6
160.4
153.6
155.4
153.9
154.9
154.5
(cc/km)
159.8
157.2
168.4
168.8
163.5
164.0
161.2
156.7
154.3
160.9
161.2
159.2
158.0
162.3
161.1
4.2
Vehicle 2:
"Good"
Radial Tires.
(cc/km)
158.2
155.9
154.0
155.3
157.1
154.6
157.2
154.3
152.2
150.3
(cc/km)
+ 9.7
+ 10.9
+ 10.4
+ 12.5
+ 10.3
+ 10.0
+ 8.4
+ 9.3
+ 6.9
+ 9.2
+ 8.1
+ 8.1
+ 9.8
+ 11.4
+ 9.6
1.5
Difference


(cc/km)
- 2.3
- 7.3
- 0.5
- 0.3
- 3.3
+ 1.0
+ 1.8
+ 0.4
- 2.7
- 4.2

-------
                                -30-
                             A-3 (cont'd)
         153.6                 153.6                 0.0
         152.1                 154.6               + 2.5
         150.8                 152.1               + 1.3
         155.7                 151.9               - 3.8
         157.1                 155.7               - 1.4
         155.7                 152.9               - 2.8
Mean     155.7                 154.4               - 1.4
S.D.       3.2                   2.2                 2.6

   Observed Effect  =  9-6 ~  ("1'4)    =   5.5 cc/km


   Average Fuel Consumption For   -,<-,-,-    /,
    .,, T, ,  _                   = 155.6 cc/km
   All LA-4 Tests

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                            -31-
                          Table A-4

   Fuel Consumption and Paired Differences for Comparison 2
     ("Good" Radial vs. "Poor" Radial) using Highway Cycles
Vehicle 1;
"Good" Radial
Tires
Vehicle 2:
"Poor" Radial
Tires
Difference
 (cc/km)
 (.cc/km)
  (cc/km)






Mean
S.D.



107.8
108.5
109.8
107.5
105.7
109.6
108.2
1.5
Vehicle 1 :
"Poor" Radial
Tires
114.2
116.1
114.7
108.9
110.0
114.1
113.0
2.9
Vehicle 2:
"Good" Radial
Tires
+ 6.4
+ 7.6
+ 4.9
+ 1.4
+ 4.3
+ 4.5
+ 4.2
2.7
Difference


 (cc/km)
 Ccc/km)
 (cc/km)








Mean
S.D.
112.7
109.9
110.7
110.9
109.7
113.7
114.1
114.8
112.1
2.0
106.2
105.7
108.6
107.7
109.8
108.1
108.5
110.4
108.1
1.6
- 6.5
- 4.2
- 2.1
- 3.2
+ 0.1
- 5.6
- 5.6
- 4.4
- 3.9
2.2
Observed Effect  =
 4.2 - (-3.9)
     2
                                    =  4.0 cc/km
Average Fuel Consumption For     inr>  _    ,,
All HFET Tests                =110.3 cc/km

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                            -32-
                          Table A-5

   Fuel Consumption and Paired Differences for Comparison 3
            (28 PSIG vs. 20 PSIG) using LA-4 Cycles









Mean
S.D.










Mean
S.D.
Vehicle 1 :
28 PSIG
OEM Tires
(cc/km)
149.9
155.8
152.2
152.8
150.1
152.2
2.4
Vehicle 1:
20 PSIG
OEM Tires
(cc/km)
155.2
150.4
157.0
151.1
162.3
154.6
155.1
4.3
Observed Effect
Vehicle 2:
20 PSIG
OEM Tires
(.cc/kml
152.9
160.4
155.6
156.4
153.8
155.8
2.9
Vehicle 2:
28 PSIG
OEM Tires
(cc/km)
154.2
145.3
153.5
148.6
155.1
153.0
151.6
3.8
= 3.7 - (-3.5) _ , _
Difference


(cc/km)
+ 3.0
+ 4.6
+ 3.4
+ 3.6
+ 3.7
+ 3.7
0.6
Difference


(cc/km)
- 1.0
- 5.1
- 3.5
- 2.5
- 7.5
- 1.6
- 3.5
2.3

Average Fuel Consumption For
All LA-4 Tests
=  153.7 cc/km

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                             -33-
                          Table A-6

    Fuel Consumption and Paired Differences for Comparison  3
          (28 PSIG vs. 20 PSIG) using Highway Cycles
Vehicle 1:
28 PSIG
OEM Tires
Vehicle 2;
20 PSIG
OEM Tires
Difference
 (cc/km)
 (cc/km)
 (cc/kra)
 (cc/km)
 (cc/km)




Mean
S.D.



110.0
110.7
105.2
110.6
109.1
2.6
Vehicle 1 :
20 PSIG
OEM Tires
115.5
112.6
109.6
110.9
112.2
2.6
Vehicle 2:
28 PSIG
OEM Tires
+ 5.5
+ 1.9
+ 4.4
+ 0.3
+ 3.0
2.3
Difference


   (cc/km)




Mean
S.D.
107.9
112.9
110.3
113.7
111.2
2.6
104.1
108.5
106.0
108.5
106.8
2.1
- 3.8
- 4.4
- 3.7
- 5.2
- 4.3
0.7
Observed Effect  =
3.0 - (-4.3)
    2
                                  =3.7 cc/km
Average Fuel Consumption    nrir. „    ,,
 For 111 HFET Tests      =  109'8 Cc/kffi

-------