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DOT HS 811 154 August 2009
NHTSA Tire Fuel Efficiency Consumer Information Program
Development: Phase 2 Effects of Tire Rolling Resistance Levels on
Traction, Treadwear, and Vehicle Fuel Economy
This document is available to the public from the National
Technical Information Service, Springfield, Virginia 22161
-
This publication is distributed by the U.S. Department of
Transportation, National Highway TrafficSafetyAdministration, in
the interestof informationexchange.Theopinions,findingsand
conclusions expressed in this publication are those of the
author(s) and not necessarily those of the Department of
Transportation or the National Highway Traffic Safety
Administration. The United States Government assumes no liability
for its content or use thereof. If trade or manufacturers names or
products are mentioned, it is because they are considered essential
to the object of the publication and should not be construed as an
endorsement. The United States Government does not endorse products
or manufacturers.
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TECHNICAL REPORT DOCUMENTATION PAGE
1. Report No. DOT HS 811 154
2. Government Accession No. 3. Recipient's Catalog No.
4. Title and Subtitle NHTSA Tire Fuel Efficiency Consumer
Information Program Development: Phase 2 Effects of Tire Rolling
Resistance Levels on Traction, Treadwear, and Vehicle Fuel
Economy
5. Report Date August 2009 6. Performing Organization Code
7. Author(s) Larry R. Evans,1 James D. MacIsaac Jr.,2 John R.
Harris,1 Kenneth Yates,2 Walter Dudek,1 Jason Holmes,1 Dr. James
Popio,3 Doug Rice,3 Dr. M. Kamel Salaani1
1Transportation Research Center, Inc., 2National Highway Traffic
Safety Administration, 3Smithers Scientific Services, Inc.
8. Performing Organization Report No.
9. Performing Organization Name and Address National Highway
Traffic Safety Administration Vehicle Research and Test Center P.O.
Box B-37 10820 State Route 347 East Liberty, OH 43319-0337
10. Work Unit No. (TRAIS)
11. Contract or Grant No. DTNH22-03-D-08660,
DTNH22-07-D-00060
12. Sponsoring Agency Name and Address National Highway Traffic
Safety Administration 1200 New Jersey Avenue SE. Washington, DC
20590
13. Type of Report and Period Covered Final 14. Sponsoring
Agency Code NHTSA/NVS-312
15. Supplementary Notes Project support and testing services
provided by: NHTSA San Angelo Test Facility, Akron Rubber
Development Laboratory, Inc., Smithers Scientific Services, Inc.,
Standards Testing Laboratories, Inc., and Transportation Research
Center, Inc. 16. Abstract This report summarizes the second phase
of the project to develop a tire fuel efficiency consumer
information program intended to examine possible correlations
between tire rolling resistance levels and service variables such
as vehicle fuel economy, wet and dry traction, and outdoor and
indoor treadwear. Tires of 15 different models with known rolling
resistances were installed on the same new passenger car to
evaluate their effects of on vehicle fuel economy. A 10percent
decrease in tire rolling resistance resulted in an approximately
1.1-percent increase in fuel economy for the vehicle. This result
was within the range predicted by technical literature. Reducing
the inflation pressure by 25 percent resulted in a small but
statistically significant decrease of approximately 0.3 to 0.5
miles per gallon for four of the five fuel economy cycles,
excluding the high-speed, high-acceleration US06 cycle. This value
was smaller than many values predicted by technical literature, and
possible explanations are being explored.
Tires of 16 different models with known rolling resistances were
subjected to dry and wet skid-trailer testing on asphalt and
concrete skid pads. Both the peak (maximum) and slide (fully
locked-tire) coefficients of friction were measured and indexed
against the control tire. For the tires studied, there appeared to
be no significant relationship between dry peak or slide numbers
and rolling resistance. However, these tire models exhibited a
strong and significant relationship between better rolling
resistance and poorer wet slide numbers. The peak wet slide number
displayed the same tendency, but the relationship was much weaker.
This may be significant to consumers without anti-lock braking
systems (ABS) on their vehicles since the wet slide value relates
most closely to locked-wheel emergency stops. For newer vehicles
with ABS or electronic stability control systems, which operate in
the earlier and higher wet peak friction range, the tradeoff is
less significant. For the subset of 5 tire models subjected to
on-vehicle treadwear testing (UTQGS), no clear relationship was
exhibited between tread wear rate and rolling resistance levels.
For the subset of 6 tire models subjected to significant amounts of
wear in the indoor treadwear tests, there was a trend toward faster
wear for tires with lower rolling resistance. This report concludes
with an analysis of the various options in the draft ISO 28580
rolling resistance test and their likelihood of inducing
variability in the test results, as well as a discussion of data
reporting format. 17. Key Words Tire, rolling resistance, consumer
information, tire traction, Energy Independence and Security Act of
2007 (EISA)
18. Distribution Statement This report is free of charge from
the NHTSA Web site at www.nhtsa.dot.gov
19. Security Classif. (of this report) Unclassified
20. Security Classif. (of this page) Unclassified
21. No. of Pages 153
22. Price
Form DOT F 1700.7 (8-72) Reproduction of completed page
authorized
i
http://www.nhtsa.dot.gov/
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ii
Approximate Conversions to Metric Measures
Symbol When You Know Multiply by To Find Symbol
LENGTH
in inches 2.54 centimeters cm ft feet 30 centimeters cm mi miles
1.6 kilometers km
AREA
in2 square inches 6.5 square centimeters cm2 ft2 square feet
0.09 square meters m2 mi2 square miles 2.6 square kilometers
km2
MASS (weight)
oz ounces 28 grams g
lb pounds 0.45 kilograms kg
PRESSURE
psi pounds per inch2 0.07 bar bar psi pounds per inch2 6.89
kilopascals kPa
VELOCITY
mph miles per hour 1.61 kilometers per hour km/h
ACCELERATION
ft/s2 feet per second2 0.30 meters per second2 m/s2
TEMPERATURE (exact)
F Fahrenheit 5/9 (Celsius) - 32C Celsius C
Approximate Conversions to English Measures Symbol When You Know
Multiply by To Find Symbol
LENGTH
mm millimeters 0.04 inches in cm centimeters 0.4 inches in m
meters 3.3 feet ft km kilometers 0.6 miles mi
AREA
cm2 square centimeters 0.16 square inches in2 km2 square
kilometers 0.4 square miles mi2
MASS (weight)
g grams 0.035 ounces ozkg kilograms 2.2 pounds lb
PRESSURE
bar bar 14.50 pounds per inch2 psi kPa kilopascals 0.145 pounds
per inch2 psi
VELOCITY
km/h kilometers per hour 0.62 miles per hour mph
ACCELERATION
m/s2 meters per second2 3.28 feet per second2 ft/s2
TEMPERATURE (exact) C Celsius 9/5 (Celsius) + 32F Fahrenheit
F
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TABLE OF CONTENTS
1.0 INTRODUCTION
................................................................................................................................
1
1.1 THE CONCEPT OF ROLLING RESISTANCE
....................................................................................
3 2.0
METHODOLOGY...............................................................................................................................
7
2.1 TEST TIRES
..................................................................................................................................
7 2.1.1 ASTM F2493 Radial Standard Reference Test Tire
...............................................................
7
2.2 TIRE ROLLING RESISTANCE TEST PROCEDURES
.........................................................................
8 2.2.1 ISO Draft International Standard 28580 Single-Point Rolling
Resistance ........................... 11 2.2.2 SAE J1269 & ISO
18164 Multi-Point Rolling
Resistance.................................................... 11
2.2.3 SAE J2452 Multi-Point (Speed Coast Down) Rolling
Resistance........................................ 11
2.3 FUEL ECONOMY TEST VEHICLE
................................................................................................
11 2.4 TEST WHEELS
............................................................................................................................
11 2.5 TEST MATRIX
............................................................................................................................
12 2.6 TREAD COMPOUND PROPERTIES
TESTING.................................................................................
13 2.7 ON-VEHICLE FUEL ECONOMY TESTING
....................................................................................
16
2.7.1 EPA 40 CFR Part 86 Dynamometer Fuel Economy Testing
................................................ 17 2.8
SKID-TRAILER TIRE TRACTION TESTING
..................................................................................
21 2.9 ON-VEHICLE TIRE TREADWEAR TESTING
.................................................................................
23 2.10 INDOOR TIRE TREADWEAR TESTING
.........................................................................................
25
3.0
RESULTS............................................................................................................................................
28 3.1 EFFECT OF TIRE ROLLING RESISTANCE ON AUTOMOBILE FUEL
EFFICIENCY........................... 28
3.1.1 Preliminary Analysis: Data Shifts
.........................................................................................
30 3.1.2 Highway FET Triplicate Analysis:
.......................................................................................
31 3.1.3 Air Conditioning SC03 11/20/08 to 11/25/08
....................................................................
34 3.1.4 Analysis by Date for Possible Drift in Data over Time
........................................................ 35 3.1.5
Effect of Tire Rolling Resistance on Fuel
Economy.............................................................
37 3.1.6 Effect of Reduced Inflation Pressure on Fuel Economy
....................................................... 43 3.1.7
Fuel Economy Testing
Summary..........................................................................................
50
3.2 CORRELATION OF TANGENT AT 60C TO TIRE ROLLING RESISTANCE
.................................. 51 3.3 EFFECT OF TIRE ROLLING
RESISTANCE ON
SAFETY..................................................................
53
3.3.1 Dry Traction Data
.................................................................................................................
53 3.3.2 Wet Traction Data
.................................................................................................................
56 3.3.3 UTQGS Traction Grade
........................................................................................................
59 3.3.4 Correlation of Tangent at 0C to Wet Traction
Properties................................................. 61
3.4 EFFECTS OF TIRE ROLLING RESISTANCE ON TREADWEAR
RATE.............................................. 62 3.4.1
Analysis of Wear Data From Indoor Treadwear Testing
...................................................... 65
4.0
CONCLUSIONS.................................................................................................................................
78 5.0 REQUIREMENTS
.............................................................................................................................
79 6.0 ROLLING RESISTANCE (Fr) VERSUS ROLLING RESISTANCE COEFICIENT
Cr)......... 85
6.1 THEORY OF FR AND
CR..............................................................................................................
85 6.1.1 Using Cr from a Single-Load Test to Predict Rolling
Resistance at Any Load.................... 90
6.2 DISCUSSION
...............................................................................................................................
94
iii
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Appendix 1. Tire and Rim Association, Inc. - Maximum Load
Formula for P Type Tires..... 100 Appendix 2. Detailed Test Matrix
.....................................................................................................
101 Appendix 3. Examples of Data Acquired From Indoor Treadwear
Test ...................................... 103 Appendix 4. Raw Dry
Traction Testing Results -
Asphalt..............................................................
124 Appendix 5. Raw Dry Traction Testing Results - Concrete
........................................................... 126
Appendix 6. Raw Wet Traction Testing Results - Asphalt
............................................................. 128
Appendix 7. Raw Wet Traction Testing Results -
Concrete...........................................................
130 Appendix 8. UTQG Adjusted Wet Traction Testing Results
......................................................... 132
Appendix 9. ASTM E501 Reference Tire Wet Traction Testing Results
...................................... 134 Appendix 10. ASTM E501
Reference Tire Dry Traction Testing Results
.................................. 135
iv
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LIST OF FIGURES
Figure 1. Where Does the Energy Go?
...........................................................................................
4
Figure 2. Contribution of Tire Rolling Resistance to Vehicle
Fuel Economy Versus Speed......... 5
Figure 3. Magic Triangle: Traction, Treadwear, and Rolling
Resistance....................................... 6
Figure 4. Force Method Rolling Resistance Test
Machine...........................................................
10
Figure 5. Torque Method Rolling Resistance Test Machine
........................................................ 10
Figure 6. Sample TGA Weight Loss
Curve..................................................................................
14
Figure 7. Tan as a Function of Temperature From the Tension Test
........................................ 15
Figure 8. Tan as a Function of Temperature From the Shear Test
............................................ 16
Figure 9. Vehicle Fuel Economy Dynamometer Testing
.............................................................
18
Figure 10. NHTSA San Angelo Skid-Trailer
...............................................................................
22
Figure 11. UTQGS Treadwear Course
.........................................................................................
25
Figure 12. Indoor Treadwear
Equipment......................................................................................
27
Figure 13. Vehicle Fuel Economy Dynamometer Exhaust Collection
Bags and Control System32
Figure 14. Highway FET Schedule Fuel Economy Versus Bag
Collection Number................... 32
Figure 15. Air Conditioning SC03 Fuel Economy Versus Tire
Rolling Resistance by Analysis
Group
....................................................................................................................................
35
Figure 16. Rolling Resistance of Tires Tested Versus Day of
Testing......................................... 36
Figure 17. Highway FET (Bag #1) Mileage Versus Tire Rolling
Resistance .............................. 39
Figure 18. Highway FET (Bag #2) Mileage Versus Tire Rolling
Resistance .............................. 39
Figure 19. Highway FET (Bag #3) Mileage Versus Tire Rolling
Resistance .............................. 40
Figure 20. City FTP Mileage Versus Tire Rolling Resistance
..................................................... 40
Figure 21. High Speed US06 Mileage Versus Tire Rolling
Resistance ....................................... 41
Figure 22. Air Conditioning SC03 Mileage Versus Tire Rolling
Resistance............................... 41
Figure 23. Cold City FTP Mileage Versus Tire Rolling
Resistance............................................. 42
Figure 24. Percentage Change in Fuel Economy Versus Percentage
Change in.......................... 43
Figure 25. Tire to Dynamometer Roller Contact / 2008 Chevrolet
Impala LS Engine ................ 46
Figure 26. Highway FET (Bag #1) Fuel Economy by Tire Type and
Inflation Pressure............. 47
Figure 27. Highway FET (Bag #2) Fuel Economy by Tire Type and
Inflation Pressure............. 47
Figure 28. Highway FET (Bag #3) Fuel Economy by Tire Type and
Inflation Pressure............. 48
Figure 29. City FTP Fuel Economy by Tire Type and Inflation
Pressure.................................... 48
Figure 30. High Speed US06 Fuel Economy by Tire Type and
Inflation Pressure...................... 49
Figure 31. Air Conditioning SC03 Fuel Economy by Tire Type and
Inflation Pressure ............. 49
Figure 32. Cold City FTP Fuel Economy by Tire Type and Inflation
Pressure ........................... 50
Figure 33. Highway FET (Bag #2) Fuel Economy Versus Tire Rolling
Resistance by Tire Type
and Inflation Pressure
...........................................................................................................
51
Figure 34. ISO 28580 Rolling Resistance (lbs)Versus Tangent at
60C by Tire Type ............. 52
Figure 35. Dry Traction Numbers Versus ISO 28580 Rolling
Resistance ................................... 55
Figure 36. Dry Traction Ratios to E501 Course Monitoring Tire
Versus Rolling Resistance ..... 56
Figure 37. Wet Traction Numbers Versus ISO 28580 Rolling
Resistance................................... 58
Figure 38. Wet Traction Ratios to E501 Course Monitoring Tire
Versus Rolling Resistance..... 59
Figure 39. UTQG Adjusted Traction Coefficient for Asphalt Versus
ISO 28580 Rolling
Resistance
.............................................................................................................................
60
Figure 40. UTQG Adjusted Traction Coefficient for Concrete
Versus ISO 28580 Rolling
Resistance
.............................................................................................................................
61
v
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Figure 41. Slide Traction Number on Wet Concrete Versus Tangent
at 0C Measured in
Tension..................................................................................................................................
62
Figure 42. Projected Tire Mileage to Wearout (Average and
Minimum) Versus ISO 28580
Rolling Resistance
................................................................................................................
64
Figure 43. Average and Fastest Treadwear Rate Versus ISO 28580
Rolling Resistance............. 65
Figure 44. Projected Tire Lifetime for Indoor Treadwear Test
.................................................... 67
Figure 45. Treadwear Rate for Indoor Treadwear Test
................................................................
68
Figure 46. Projected Tire Lifetime for Indoor Treadwear Test
.................................................... 73
Figure 47. ISO 28580 Rolling Resistance Versus Tire Weight Loss
........................................... 74
Figure 48. Rolling Resistance as Percent of the Original Rolling
Resistance .............................. 75
Figure 49. Percentage of Original Rolling
Resistance..................................................................
77
Figure 50. Temperature Correction Factor - ISO
28580...............................................................
83
Figure 51. Drum Diameter Correction Factor - ISO
28580..........................................................
84
Figure 52. SAE J1269 Recommended Test - Evaluates Response of
Rolling Resistance Force
Over a Range of Three Pressures and Two
Loads................................................................
87
Figure 53. ISO 18164 Annex B - Response of Rolling Resistance
Force (Fr) Over a Range of
Three Speeds, Two Pressures, and Two
Loads.....................................................................
88
Figure 54. ISO 28580 Test Conditions for Standard Load Passenger
Tires................................. 89
Figure 55. Theoretical Single-Load Rolling Resistance
(Fr)........................................................ 90
Figure 56. Theoretical Single-Load Rolling Resistance
Coefficient (Cr) .................................... 91
Figure 57. Rolling Resistance of 16 Passenger Tires
...................................................................
92
Figure 58. Rolling Resistance Coefficient of 16 Passenger Tires
................................................ 93
Figure 59: Rolling Resistance Force (SAE J1269 Single-Point,
Pounds) .................................... 97
Figure 60: Rolling Resistance Coefficient (SAE J1269)
..............................................................
97
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LIST OF TABLES Table 1. 2005 Motor Vehicle Crash Data From FARS
and GES, Crashes by Weather Condition 6
Table 2. Phase 2 Tire Models
.........................................................................................................
8
Table 3. Test
Matrix......................................................................................................................
13
Table 4. Analysis of Tread Composition by
TGA........................................................................
14
Table 5. DMA Results for Tangent at 0C and 60C
................................................................
16
Table 6. 2008 EPA Fuel Economy 5-Driving Schedule Test (Source:
EPA, 2009)..................... 19
Table 7. Fuel Economy Test
Schedules........................................................................................
21
Table 8. Phase 2 Wet and Dry Skid-Trailer Test
Tires.................................................................
23
Table 9. On-Vehicle Treadwear
Testing.......................................................................................
24
Table 10. Indoor Treadwear
Testing.............................................................................................
26
Table 11. Test
Parameters.............................................................................................................
26
Table 12. Test Matrix by Date
......................................................................................................
29
Table 13. Events Identified as Possible Data Shift
Correlates......................................................
31
Table 14. Analysis of Variance for Highway FET Fuel Economy by
Tire Type and Collection
Bag Number
..........................................................................................................................
33
Table 15. Air Conditioning SC03 Schedule, mpg for SRTT Tire by
Date................................... 34
Table 16. Change in Fuel Economy Over Total Time of Testing
................................................ 36
Table 17. Data Excluded from Fuel Economy
Analyses..............................................................
37
Table 18. ANOVA Results for Effect of Tire Rolling Resistance on
Fuel Economy .................. 38
Table 19. Percentage Change in Fuel Economy Versus Percentage
Change in Tire Rolling
Resistance
.............................................................................................................................
38
Table 20. Predicted Change in Fuel Economy for 1 psi Change in
Tire Inflation Pressure......... 44
Table 21. ANOVA Results for Effect of Tire Inflation Pressure
Reduction on Fuel Economy... 50
Table 22. Correlation of Rolling Resistance to Tangent at 60C
.............................................. 52
Table 23. Correlation of Properties to Rolling Resistance
........................................................... 53
Table 24. Dry Traction Results, Traction Number and Ratio to
E501 Reference Tire ................ 54
Table 25. Pearson Product Moment Correlation of Dry Traction to
Rolling Resistance ............. 54
Table 26. Wet Traction Results, Traction Number and Ratio to
E501 Reference Tire................ 57
Table 27. Pearson Product Moment Correlation of Wet Traction to
Rolling Resistance............. 57
Table 28. Pearson R Product Moment Correlation of Wet Traction
to ........................................ 62
Table 29. Analysis of Tire Wear Data
..........................................................................................
63
Table 30. Wear Rates and Projected Mileage to 2/32nds Tread
Depth .......................................... 64
Table 31. Indoor Treadwear Tire Wear
Data................................................................................
66
Table 32. Projected Mileage to 2/32nds Inch of Tread Depth
........................................................ 66
Table 33. Projected Lifetime Versus Rolling Resistance Mild Wear
at Tread Center .............. 69
Table 34. Projected Lifetime Versus Rolling Resistance Severe
Wear at Tread Center ........... 70
Table 35. Projected Lifetime Versus Rolling Resistance Mild Wear
at Shoulder..................... 71
Table 36. Projected Lifetime Versus Rolling Resistance Severe
Wear at Shoulder ................. 72
Table 37. Analysis of Rolling Resistance
Change........................................................................
76
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LIST OF EQUATIONS Equation 1. Rolling Resistance Calculation,
Force Method (ISO 28580)......................................
9
Equation 2. Rolling Resistance Calculation, Torque Method (ISO
28580) ................................. 10
Equation 3. Input Cycle
................................................................................................................
27
Equation 4. SAE J1269 Linear Regression Equation for Passenger
Car Tires............................. 87
Equation 5. ISO 28580 Rolling Resistance
Coefficient................................................................
89
Equation 6. T&RA Load Formula for P Type Tires (S.I. Units)
............................................ 100
viii
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DEFINITIONS
SAE The Society of Automotive Engineers International is an
international standards organization providing voluntary standards
to advance the state of technical and engineering sciences. SAE
International, 400 Commonwealth Drive, Warrendale, PA 15096-0001,
Tel 877-606-7323, www.sae.org
ISO The International Organization for Standardization is a
worldwide federation of national standards bodies that prepares
standards through technical committees comprised of international
organizations, governmental and non-governmental, in liaison with
ISO. ISO Central Secretariat, 1, ch. de la Voie-Creuse, Case
postale 56, CH-1211 Geneva 20, Switzerland, Telephone +41 22 749 01
11, Fax +41 22 733 34 30, www.iso.org
SAE J1269 (Rev. September 2006) SAE multi-point standard:
Rolling Resistance Measurement Procedure for Passenger Car, Light
Truck and Highway Truck and Bus Tires: This procedure is intended
to provide a standard method for gathering data on a uniform basis,
to be used for various purposes (for example, tire comparisons,
determination of load or pressure effects, correlation with test
results from fuel consumption tests, etc.). A single-point test
condition (SRC or standard reference condition) is included. The
rolling resistance at this condition may be calculated from
regression of the multi-point measurements or measured directly at
the SRC.
SAE J2452 (Issued June 1999) Stepwise Coastdown Methodology for
Measuring Tire Rolling Resistance: This SAE Recommended Practice
establishes a laboratory method for determination of tire rolling
resistance of Passenger Car and Light Truck tires. The method
provides a standard for collection and analysis of rolling
resistance data with respect to vertical load, inflation pressure,
and velocity. The primary intent is for estimation of the tire
rolling resistance contribution to vehicle force applicable to SAE
Vehicle Coastdown recommended practices J2263 and J2264.
ISO 18164:2005(E) Passenger car, truck, bus and motorcycle tires
-- Methods of measuring rolling resistance: This International
Standard specifies methods for measuring rolling resistance, under
controlled laboratory conditions, for new pneumatic tyres designed
primarily for use on passenger cars, trucks, buses and
motorcycles.
ISO 28580 Draft International Standard (DIS) Tyre Rolling
Resistance measurement method single-point test and measurement
result correlation designed to facilitate international cooperation
and, possibly, regulation building. Passenger Car, Truck and Bus
Tyres: This recommendation specifies methods for measuring rolling
resistance, under controlled laboratory conditions, for new
pneumatic tyres designed primarily for use on passenger cars,
trucks and buses. Tyres intended for temporary use only are not
included in this specification. This includes a method for
correlating measurement results to allow inter-laboratory
comparisons. Measurement of tyres using this method enables
comparisons to be made between the rolling resistance of new test
tyres when they are free-rolling straight ahead, in a position
perpendicular to the drum outer surface, and in steady-state
conditions.
ix
http://www.sae.org/http://www.iso.org/
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Rolling Resistance (Fr) (ISO/DIS 28580) Loss of energy (or
energy consumed) per unit of distance travelled. NOTE 1: The SI
unit conventionally used for the rolling resistance is the newton
metre per metre (N m/m). This is equivalent to a drag force in
newtons (N). (Also referred to as RRF).
Rolling Resistance Coefficient (Cr) (ISO/DIS 28580) Ratio of the
rolling resistance, in newtons, to the load on the tyre, in
knewtons. This quantity is dimensionless. (Often multiplied by 1000
kg/metric tonne (MT) for reporting. Also referred to as RRC).
Mean Equivalent Rolling Force (MERF) (SAE 2452) The average
rolling resistance of a tire, at a given load/inflation condition,
over a driving cycle with a specified speed-time profile. This
implicitly weights the rolling resistance for each speed using the
length of time spent at that speed during the cycle. For the
purpose of this document, MERF is a combined weighting of MERFs
calculated using the standard EPA urban and highway driving cycles.
Specifically, this weighting is 55 percent for the EPA Urban (FTP)
Cycle and 45 percent for the EPA Highway Fuel Economy Cycle.
Standard Mean Equivalent Rolling Force (SMERF) (SAE 2452) For
any tire is the MERF for that tire under standard load/inflation
conditions defined in 3.10. For this document, the final SMERF is
also calculated by weighting the SMERF obtained for the EPA urban
and highway cycles, as discussed previously for MERF
calculation.
Tire Spindle Force, Ft (ISO/DIS 28580) Force measured at the
tire spindle in newtons.
Tire Input Torque, Tp (ISO/DIS 28580) Torque measured in the
input shaft at the drum axis, measured in newton-meters.
Capped Inflation (ISO/DIS 28580) Inflating the tire and fixing
the amount of inflation gas in the tire. This allows the inflation
pressure to build up, as the tire is warmed up while running.
Parasitic Loss (ISO/DIS 28580) Loss of energy (or energy
consumed) per unit of distance excluding internal tire losses, and
attributable to aerodynamic loss of the different rotating elements
of the test equipment, bearing friction, and other sources of
systematic loss which may be inherent in the measurement.
Skim Test Reading (ISO/DIS 28580) Type of parasitic loss
measurement, in which the tire is kept rolling, without slippage,
while reducing the tire load to a level at which energy loss within
the tire itself is virtually zero.
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EXECUTIVE SUMMARY
The first phase of development of the tire fuel efficiency
rating system consisted of the evaluation of five laboratory
rolling resistance test methods, using 25 light-vehicle tire
models, in duplicate at two independent laboratories. Results of
this evaluation are documented in the Phase 1 report on the
project. The agencys evaluation showed that all of the rolling
resistance test methods had very low variability and all methods
could be cross-correlated to provide the same information about
individual tire types. The rank order grouping of tire types was
statistically the same for each of the rolling resistance test
methods evaluated. However, the relative rankings of the tires
within the population of the 25 models tested shifted considerably
when tires were ranked by either rolling resistance force or
rolling resistance coefficient.
It was concluded from Phase 1 that while multi-point rolling
resistance test methods are necessary to characterize the response
of a tires rolling resistance over a range of loads, pressures,
and/or speeds, either of the two shorter and less expensive
single-point test methods were sufficient for the purpose of simply
assessing and rating individual tires in a common system. Of the
two single-point methods, the ISO 28580 Draft International
Standard (DIS) has the advantage of using defined lab alignment
tires to allow comparison of data between labs on a standardized
basis. The use of any of the other single or multi-point test
standard would require extensive development of a method to allow
direct comparison of results generated in different laboratories,
or even on different machines in the same laboratory. In addition,
the Commission of the European Communities (EU) has selected ISO
28580 international standard as the basis of its rolling resistance
rating system. Use of ISO 28580 would allow international
harmonization of U.S. and European test practices.
This report summarizes the results of testing done to examine
possible correlations between tire rolling resistance levels and
operating parameters such as vehicle fuel economy, wet and dry
traction, and outdoor and indoor treadwear. With the exception of
the OE tires on the fuel economy vehicle, all tires used in Phase 2
were previously tested in one to two indoor rolling resistance
tests in Phase 1. Fifteen different tire models were installed on
the same new passenger car to evaluate the effects of tire rolling
resistance levels on vehicle fuel economy using a test that
approximately followed the EPAs new 5-cyle dynamometer test. A
10-percent decrease in tire rolling resistance resulted in
approximately 1.1-percent increase in fuel economy for the vehicle.
This result was within the range predicted by technical literature.
Reducing the inflation pressure by 25 percent resulted in a small
but statistically significant decrease of approximately 0.3 to 0.5
miles per gallon for four of the five fuel economy cycles,
excluding the high-speed, high-acceleration US06 cycle. This value
was smaller than many values predicted by technical literature, and
possible explanations are being explored.
Sixteen tire models were subjected to dry and wet skid-trailer
testing on asphalt and concrete skid pads. Both the peak (maximum)
and slide (fully locked-tire) coefficients of friction were
measured and indexed against the control tire. For the tires
studied, there appeared to be no significant relationship between
dry peak or slide numbers and rolling resistance. However, these
tire models exhibited a strong and significant relationship between
better rolling resistance and poorer wet slide numbers. The peak
wet slide number displayed the same tendency, but the relationship
was much weaker. This may be significant to consumers without
anti-lock braking sys
xi
-
tems (ABS) on their vehicles since the wet slide value relates
most closely to locked-wheel emergency stops. For newer vehicles
with ABS or electronic stability control systems, which operate in
the earlier and higher peak friction range, the tradeoff is less
significant. The agencys current Uniform Tire Quality Grading
Standards (UTQGS) (575.104) rate wet slide traction but not wet
peak traction. For the subset of five tire models subjected to
on-vehicle treadwear testing (UTQGS), no clear relationship was
exhibited between tread wear rate and rolling resistance levels.
For the subset of six tire models subjected to significant amounts
of wear in the indoor treadwear tests, there was a trend toward
faster wear for tires with lower rolling resistance.
The Requirements section of the report contains an analysis of
the various options in the draft ISO 28580 rolling resistance test
and their likelihood of inducing variability in the test results.
The lab alignment procedure in ISO 28580, which for passenger tires
uses two dissimilar tires to calibrate a test lab to a master lab,
states that it will compensate for differences induced from tests
conducted using different options under the test standard. These
options include the use of one of four measurement methods (force,
torque, power, or deceleration), textured or smooth drum surface,
correction of data to a 25C reference temperature, and correction
of data from tests conducted on a test drum of less than 2.0-m in
diameter to a 2.0-m test drum. The variability in test results
induced by allowing the various test options, as well as the
effectiveness of the temperature and test drum correction equations
is not currently known to the agency. Some recommendations are
included.
Concluding the report is a special discussion regarding the use
of rolling resistance (Fr) or rolling resistance coefficient (Cr)
as the basis for data reporting and ratings. The ISO 28580 standard
calculates a rolling resistance (Fr, energy loss per unit distance)
from one of four different measurement methods. Since, rolling
resistance varies with the load on the tire, and tires of different
load indexes are tested at different loads, the rolling resistance
coefficient is used to allow a relative comparison of the energy
consumption of tires of all sizes and load ranges. However, the
normalization of Fr to generate Cr is not consistent across the
range of tire sizes and load ranges in what is expected to be about
20,000 different tires in a common system. If the Cr coefficient is
used as a basis, the data will be skewed towards better ratings for
larger tires. While this would have negligible effects for
consumers picking out tires of a given size, there are concerns
about the confusion of consumers if the overall tire fuel economy
system was to rate tires that consume more fuel at a given set of
conditions better than tires that consume less fuel at those same
conditions.
xii
-
1.0 INTRODUCTION
Reducing energy consumption is a national goal for many reasons,
from economic and national security to improving air quality and
reducing greenhouse gas emissions. Also, rising energy prices are
having their effect on consumers and businesses, and have
contributed to increases in the Consumer Price Index in recent
years. Hall and Moreland define tire rolling resistance as the
energy consumed per unit distance of travel as a tire rolls under
load.[1] A vehicles fuel economy is affected by tire rolling
resistance, therefore, fuel saving could be achieved by reducing
tire rolling resistance. Low-rolling-resistance original equipment
(OE) tires are used by auto manufactures to help meet the Federal
fuel economy standards for new passenger cars and light trucks.
However, consumers often purchase less fuel-efficient tires when
replacing their vehicles OE tires, as well as when purchasing
subsequent sets of replacement tires. For example, during 2007
there were an estimated 51 million OE passenger and light truck
tires sold in the United States, as opposed to an estimated 237
million replacement passenger and light truck tires.[2] Therefore,
the rolling resistance of replacement tires could have a
significant impact on the fuel economy of the U.S. light-vehicle
fleet.
In the Consolidated Appropriations Act of 2004, Congress
provided funding through the NHTSA to the National Academy of
Sciences (NAS)1 to develop and perform a national tire fuel
efficiency study and literature review.[3] The NAS was to consider
the relationship that low rolling resistance tires designed for use
on passenger cars and light trucks have with vehicle fuel
consumption and tire wear life. The study was to address the
potential of securing technically feasible and cost-effective fuel
savings from low rolling resistance replacement tires that do not
adversely affect tire safety, including the impacts on performance
and durability, or adversely impact tire tread life and scrap tire
disposal, and that does fully consider the average American drive
cycle. The study was to further address the cost to the consumer
including the additional cost of replacement tires and any
potential fuel savings. The resulting NAS Transportation Research
Board report of April 2006 concluded that reduction of average
rolling resistance of replacement tires by 10 percent was
technically and economically feasible, and that such a reduction
would increase the fuel economy of passenger vehicles by 1 to 2
percent, saving about 1 to 2 billion gallons of fuel per year
nationwide. However, as is common in such studies, the NAS
committee did not have a mechanism to generate its own test data2
and conclusions were based upon available literature and data.[4]
The tire industry eventually supplied rolling resistance data for
214 passenger and light truck tire models to the NAS committee (177
Michelin
1 Ultimately the Committee for the National Tire Efficiency
Study of the Transportation Research Board, a division of the
National Research Council that is jointly administered by the
National Academy of Sciences, the National Academy of Engineering,
and the Institute of Medicine. 2 NAS cautioned that much of the
available technical literature on tire rolling resistance dates
back to the mid-1970s to mid-1980s. Data on todays passenger tires
was difficult to obtain.
1
-
manufactured, 24 Bridgestone-manufactured, and 13
Goodyear-manufactured passenger and light truck tires).3
The Transportation Research Board report suggests that safety
consequences of a 10-percent improvement in tire rolling resistance
were probably undetectable. However, the committees analysis of
grades under UTQGS (FMVSS No. 575.104) for tires in its study
indicated that there was difficulty in achieving the highest wet
traction and/or treadwear grades while achieving the lowest rolling
resistance coefficients. This was more noticeable when the sample
of tires was constrained to similar designs (similar speed ratings
and diameters). A lack of access to the raw rating numbers instead
of the final grades provided by the manufacturers prohibited a more
detailed analysis.
Subsequent to the publication of the NAS committee report, NHTSA
initiated a research program to evaluate five laboratory rolling
resistance test methods, using 25 currently available light vehicle
tire models, in duplicate at two independent laboratories. Results
of this evaluation are documented in the Phase 1 report of the
project. The agencys evaluation showed that all of the rolling
resistance test methods had very low variability and all methods
could be cross-correlated to provide the same information about
individual tire types. Differences of as much as 30 percent in
measured rolling resistance force were observed between different
models of tires of the same size. It was concluded that while
multi-point rolling resistance test methods are necessary to
characterize the response of a tires rolling resistance over a
range of loads, pressures, and/or speeds, either of the two shorter
and less expensive single-point test methods were sufficient for
the purpose of simply assessing and rating individual tires in a
common system. Of the two single-point methods evaluated, the ISO
28580 Draft International Standard (DIS) has the advantage of using
defined lab alignment tires to allow comparison of data between
labs on a standardized basis. The use of any of the other single or
multi-point test standard would require extensive development of a
method to allow direct comparison of results generated in different
laboratories, or even on different machines in the same laboratory.
Also, the Commission of the European Communities (EU) has selected
ISO 28580 international standard as the basis of its rolling
resistance rating system. Use of ISO 28580 would allow
international harmonization of U.S. and European test
practices.
In December 2007, Congress enacted the Energy Independence and
Security Act of 2007 that mandated that NHTSA establish a national
tire fuel efficiency rating system for motor vehicle replacement
tires within 24 months. While the existing research program was
sufficient to meet the requirements for the testing and rating
requirements, NHTSA initiated a second phase of research to address
the safety and consumer information requirements. Portions of Phase
2 of the project retested up to 15 models of Phase 1 tires, as well
the original equipment tires on the fuel economy test vehicle, to
examine possible correlations between tire rolling resistance
levels and operating parameters such as vehicle fuel economy, wet
and dry traction, and outdoor and indoor
3 NAS: Before the committees final meeting, several tire
manufacturers, acting through the Rubber Manufacturers Association,
made available measurements of the rolling resistance of a sample
of more than 150 new replacement passenger tires as well as some
original equipment (OE) tires. Although the sample was not
scientifically derived, the data proved helpful to the committee as
it sought to answer the various questions in the study charge. The
timing of the datas availability late in the study process limited
the statistical analyses that could be undertaken by the committee.
Reference [4], Page ix.
2
-
treadwear. This was accomplished through on-vehicle EPA
dynamometer fuel economy tests, wet and dry skid-trailer traction
tests, on-vehicle treadwear tests and experimental indoor
tread-wear tests.
1.1 The Concept of Rolling Resistance
In the latest version of the book The Pneumatic Tire, which was
commissioned and published by NHTSA, LaClair describes the concept
of rolling resistance in simple terms[5]:
When a tire rolls on the road, mechanical energy is converted to
heat as a result of the phenomenon referred to as rolling
resistance. Effectively, the tire consumes a portion of the power
transmitted to the wheels, thus leaving less energy available for
moving the vehicle forward. Rolling resistance therefore plays an
important part in increasing vehicle fuel consumption. Rolling
resistance includes mechanical energy losses due to aerodynamic
drag associated with rolling, friction between the tire and road
and between the tire and rim, and energy losses taking place within
the structure of the tire.
LaClair also points out that the term rolling resistance is
often mistaken as a measure of the force opposing tire rotation,
when instead is actually a measure of rolling energy loss[6]:
Although several authors recognized the importance of energy
consumption, the concept of rolling resistance as a retarding force
has persisted for many years. Schuring provided the following
definition of rolling resistance as a loss in mechanical energy:
Rolling [resistance] is the mechanical energy converted into heat
by a tire moving for a unit distance on the roadway. He proposed
the term rolling loss instead of rolling resistance so that the
long-standing idea of a force would be avoided. Schuring pointed
out that although rolling resistance -- defined as energy per unit
distance -- has the same units as force (J/m = N), it is a scalar
quantity with no direction associated with it.
Defining rolling resistance as an energy loss is advantageous
when considering its effects on the fuel efficiency of a vehicle.
The U.S. Department of Energy estimates that approximately 4.2
percent of the total energy available in the fuel you put in your
tank is lost to rolling resistance during the operation of the
vehicle (Figure 1).[7] However, Duleep and NAS point out that the
peak first law (thermodynamic) efficiency of a modern spark-ignited
gasoline engine is in the 3436 percent range (40-42% for diesels),
and therefore tire rolling resistance consumes about a third of the
usable energy actually transmitted to the wheels (i.e., 1/3 of the
available tractive energy). Therefore, considering rolling
resistance in terms of the energy in the fuel tank is not a useful
measure.[8],[9] For instance, in Figure 1 only 12.6 percent of the
energy in the fuel is finally transmitted to the wheels. The 4.2
percent of original fuel energy used by rolling resistance is
actually 33 percent (4.2%/12.6%) of the total usable energy
available to the wheels.
3
-
Only about 15 percent of the energy from the fuel you put in
your tank gets used to move your car down the road or run useful
accessories, such as air conditioning. The rest of the energy is
lost to engine and driveline inefficiencies and idling. Therefore,
the potential to improve fuel efficiency with advanced technologies
is enormous.
Rolling Resistance 4.2 percent For passenger cars, a 5 to 7
percent reduction in rolling resistance increases fuel efficiency
by 1 percent. However, these improvements must be balanced against
traction, durability, and noise.
Figure from Department of Energy, 2009 Figure 1. Where Does the
Energy Go?
Additionally, the contribution of tire rolling resistance to
fuel economy varies with the speed of the vehicle. At lower speeds,
tire rolling resistance represents a larger percentage of the fuel
consumption (Figure 2) than at higher speeds.[10]
4
-
Figure 2. Contribution of Tire Rolling Resistance to Vehicle
Fuel Economy Versus Speed (Reprinted with permission from the
Automotive Chassis: Engineering Principles,
2nd Edition, Reed Educational and Professional Publishing Ltd.,
2001)
In any discussion of rolling resistance, it is important to
consider that the rolling resistance level of a tire evolves during
use. It is reported in literature that a tires rolling resistance
level, and therefore its effects on vehicle fuel economy, can
decrease by more than 20 percent from a new tread to completely
worn.[11],[12] Therefore, calculations of the benefits of lower
tire rolling resistance derived from measurements of new tires will
likely understate the benefits to a vehicle in terms of absolute
fuel economy over the lifetime of the set of tires. However, since
both new-vehicle fuel economy and new-tire rolling resistance
change with time, and are dependent on usage conditions, age, and
maintenance levels, attempts to calculate lifetime benefit can vary
widely.
While the hysteretic losses of the tire (primarily the tread)
consume a large amount of the available tractive energy, the tires
also provide the traction necessary to start, stop, and steer the
vehicles. Substances soft enough to provide traction on wet, dry,
snow, dirt, gravel, etc., surfaces will also wear. Therefore, the
topics of rolling resistance, traction, and treadwear are linked in
what the tire industry refers to as the magic triangle (Figure 3).
The triangle is a useful graphic since it conveys the point that a
shift to improve properties in one corner of the triangle can
diminish properties in both of the other corners if more advanced
and often more expensive tire compounding and construction
technologies are not employed.
5
-
Rolling Resistance
Traction
Treadwear Figure 3. Magic Triangle: Traction, Treadwear, and
Rolling Resistance
From a safety standpoint, the obvious concern from the magic
triangle is a loss of tire traction to achieve lower rolling
resistance (better vehicle fuel economy). Since 85 percent of all
crashes in 2005 occurred during normal dry weather conditions, and
10 percent in the rain (Table 1.), the effects of lower rolling
resistance on wet and dry traction are of primary importance.[13]
Longitudinal wet and dry tire traction are easily measured with
skid-trailer testing. Conversely, while crashes occur on snow,
sleet, and ice about 4 percent of the time, measuring tire traction
on the varying permutations of these surfaces is not easily
done.
Table 1. 2005 Motor Vehicle Crash Data From FARS and GES,
Crashes by Weather
Condition
Weather Condition All Crashes Percent Normal (dry) 5,239,000
85.1% Rain 584,000 9.5% Snow/Sleet 264,000 4.3% Other 72,000 1.2%
Total 6,159,000 100%
6
-
2.0 METHODOLOGY
2.1 Test Tires
The majority of the tire models selected for Phase 1 were size
P225/60R16 or 225/60R16, which in 2007 was the most popular size of
replacement tire in the United States. Phase 1 of the project
evaluated the rolling resistance of 25 passenger and light-truck
tire models. However, time and budget constraints, as well as
equipment limitations, limited Phase 2 to retests of 5 to 16 of the
Phase 1 models in different portions of the project (Table 2). The
original equipment tires on the fuel economy test vehicle added a
17th tire model to the Phase 2 test matrix. The Phase 2 tire models
ranged from 14- to 17-inch rim codes, Q to W speed ratings, 9 to 15
lbf (7 to 11 Cr) in rolling resistance per ISO 28580, 19 to 36 lbs
in weight, 300 to 700 in treadwear rating, and A to AA in UTQGS
traction (wet) rating.
The Phase 1 passenger tires, all purchased as new, were not
subjected to optional break-ins listed in the various rolling
resistance tests prior to the warm-up and measurement phases of the
tests. Therefore, Phase 1 tires experienced approximately 50 to 75
miles of straight-line mileage on the laboratory rolling resistance
machine prior to Phase 2 testing. This produced no detectable
treadwear, but did serve to break-in the tires. It has been
reported by LaClair that tire rolling resistance will decrease
about 2-5 percent during a break-in period of 60 minutes at 80 km/h
(50 total miles).[14] Therefore, it is anticipated that the rolling
resistance of the tires retested in Phase 2 for on-vehicle fuel
economy, traction, and treadwear is approximately 2-5 percent lower
than a brand new tire subjected to these tests. However, it should
also be noted that most of these tests are normally completed with
tires that are broken-in prior to testing (vehicle fuel economy -
2,000 miles, outdoor traction - 200 miles, outdoor treadwear - 800
miles).
2.1.1 ASTM F2493 Radial Standard Reference Test Tire
Tire model M14 is an ASTM F2493 SRTT tire. The ASTM F2493 -
Standard Specification for P225/60R16 97S Radial Standard Reference
Test Tire (SRTT) provides specifications for a tire for use as a
reference tire for braking traction, snow traction, and wear
performance evaluations, but may also be used for other
evaluations, such as pavement roughness, noise, or other tests that
require a reference tire. The standard contains detailed
specifications for the design, allowable dimensions, and storage of
the tires. The F2493 SRTT is a variant of a modern 16-inch Uniroyal
TigerPaw radial passenger vehicle tire and comes marked with a full
USDOT Tire Identification Number and UTQGS grades. The SRTTs were
used extensively throughout the laboratory, test surface, and fuel
economy phases of the test program to monitor the stability of the
testing. The SRTTs had the added advantage of being near the center
of the range of passenger tire rolling resistances in the program
(Table 2).
7
-
Table 2. Phase 2 Tire Models Ti
re M
odel
Cod
e
MFG
Size
Load
Inde
x
Spee
d R
atin
g
Mod
el
UTQ
GS
Trea
d-w
ear
UTQ
GS
Trac
.
UTQ
GS
Tem
p.
Perf
orm
ance
Le
vel
ISO
285
80 R
ollin
g R
esis
tanc
e, F
r (lb
f)
ISO
285
80 R
ollin
gR
esis
tanc
e C
oef
ficie
nt ,
Cr
Wei
ght (
lbs.
)
G12 Goodyear P225/60R16 97 S Integrity 460 A B Passenger All
Season, TPC 1298MS
9.47 7.36 22.0
G8 Goodyear 225/60R16 98 S Integrity 460 A B Passenger All
Season
9.83 7.44 22.9
G11 Goodyear P225/60R17 98 S Integrity 460 A B Passenger All
Season
10.02 7.58 24.5
B11 Bridgestone P225/60R16 97 H Potenza RE92 OWL
340 A A High Performance All Season
10.13 7.87 25.1
G9 Goodyear P205/75R14 95 S Integrity 460 A B Passenger All
Season
11.27 9.19 19.2
M14 Uniroyal P225/60R16 97 S ASTM 16" SRTT
540 A B ASTM F 2493-06 Reference
11.96 9.30 25.5
M13 Michelin 225/60R16 98 H Pilot MXM4 300 A A Grand Touring All
Season
12.07 9.13 24.7
G10 Goodyear P205/75R15 97 S Integrity 460 A B Passenger All
Season
12.09 9.46 20.4
B10 Bridgestone 225/60R16 98 Q Blizzak REVO1*
- Performance Winter 12.11 9.16 26.9
D10 Cooper 225/60R16 98 H Lifeliner Touring SLE
420 A A Standard Touring All Season
13.56 10.26 25.2
B14 Bridgestone P225/60R16 97 V Turanza LS-V 400 AA A Grand
Touring All Season
13.90 10.80 28.6
U3 Dunlop (Sumitomo)
P225/60R17 98 T SP Sport 4000 DSST
360 A B Run Flat 13.91 10.52 36.4
B15 Dayton 225/60R16 98 S Winterforce* - Performance Winter
13.99 10.58 26.7
P5 Pep Boys (Cooper)
P225/60R16 97 H Touring HR 420 A A Passenger All Season
14.02 10.89 25.7
R4 Pirelli 225/60R16 98 H P6 Four Seasons
400 A A Passenger All Season
14.98 11.33 24.3
B13 Bridgestone P225/60R16 97 T Turanza LS-T 700 A B Standard
Touring All Season
15.01 11.66 29.4
B12 Bridgestone P225/60R16 98 W Potenza RE750 340 AA A Ultra
High Performance Summer
15.22 11.51 27.4
Original equipment tires on the fuel economy test vehicle.
Standard reference test tires used as control tires throughout
all phases of the study.
*Snow tires will not be rated in the national tire fuel
efficiency consumer information program.
2.2 Tire Rolling Resistance Test Procedures
Tire rolling resistance is measured in a laboratory under
controlled conditions. The test conditions vary between the various
SAE and ISO test standards, but the basic premise is the same in
that a tire is mounted on a free-rolling spindle with no camber or
slip angle, loaded against a large-diameter powered test drum,
turned by the drum to simulate on-road rolling operation, and some
measure of rolling loss evaluated. Referring back to the book The
Pneumatic Tire[5]:
Rolling resistance is the effort required to keep a given tire
rolling. Its magnitude depends on the tire used, the nature of the
surface on which it rolls, and the operating conditions - inflation
pressure, load and speed.
8
-
This description is important because it emphasizes that rolling
resistance is not an intrinsic property of the tire, rather a
function of many operating variables. This is why multi-point
laboratory tests measure a tires rolling resistance over a range of
inflation pressures, loads, and for some tests, a range of speeds.
Conversely, single-point point rolling resistance test methods use
a single set of these variables to estimate the rolling resistance
of the tire under nominal, straight-line, steady state operating
conditions (the vast majority of a tires rolling operation). In the
case of a laboratory test, rolling resistance (energy loss) is
calculated by measuring the amount of additional force, torque, or
power necessary to keep the tire rolling at the test conditions. A
fourth method, which is not widely used, is a deceleration method
in which the energy source is de-coupled from the system and the
rate of loss of angular momentum (energy loss) imparted by the tire
is measured.
The two domestic test labs used by the agency had machines that
used either the force or the torque measurement method. A picture
of a laboratory rolling resistance test using a force method can be
seen in Figure 4. The machine measures a reaction force at the axle
of the test tire & wheel assembly. The drum is brought up to
speed and the tire is warmed up to an equilibrium temperature. The
tire is then lightly loaded to measure parasitic losses caused by
the tire spindle friction, aerodynamic losses, and the test
drum/drive system bearings. The tire is then loaded to the test
load and successive readings are taken until consistent force
values are obtained. During the test, the loaded radius (rL) of the
tire is measured during the steady-state conditions. In ISO 28580
the Rolling Resistance (Fr) at the tire/drum interface is
calculated from the measured force at the spindle (Ft), multiplied
by a ratio of the loaded tire radius (rL) to the test wheel radius
(R), minus the skim load (Fpl).
Fr = Ft[1+(rL/R)]-Fpl
Equation 1. Rolling Resistance Calculation, Force Method (ISO
28580)
9
-
Ft = Spindle Force
rL
R
Fr = Calculated Rolling Resistance at Tire/Drum Interface
1.7 meter Drum
Motor
Torque Cell 1.7 meter roadwheel
80 grit Surface
T = torque
Figure 4. Force Method Rolling Resistance Test Machine
Another test lab used by the agency used a torque method
machine. The torque method measures the torque required to maintain
the rotation of the drum. The drum is connected to the motor
through a torque cell (Figure 5). The drum is brought up to speed
and the tire is warmed up to an equilibrium temperature. The tire
is then lightly loaded to measure the losses caused by the axle
holding the tire and aerodynamic losses from the tire spinning. The
tire is then loaded to the test load and successive readings are
taken until consistent torque (Tt) values are obtained.
Fr = Tt/R-Fpl
Equation 2. Rolling Resistance Calculation, Torque Method (ISO
28580)
Figure 5. Torque Method Rolling Resistance Test Machine
10
-
In one additional calculation, the rolling resistance force (Fr)
calculated by any of the methods is divided by the nominal test
load on the tire to produce the rolling resistance coefficient
(Cr). Since the rolling resistance coefficient (Cr) is not linear
between tires of different load ranges, the rolling resistance (Fr)
for each tire was compared to the traction, treadwear, and fuel
economy measures in the Phase 2 analysis.
Tires in Phases 1 and 2 were subjected to up to three tests. The
first and possibly second test may have been the same indoor
rolling resistance test or two different tests, followed by
traction, treadwear or fuel economy testing. A detailed test matrix
is provided in Appendix 2. A description of the laboratory rolling
resistance tests used in Phase 1 follows:
2.2.1 ISO Draft International Standard 28580 Single-Point
Rolling Resistance
Tires from all 17 tire models used in Phase 2, though not
necessarily the exact tires, were previously tested using the draft
ISO 28580 test method.
2.2.2 SAE J1269 & ISO 18164 Multi-Point Rolling
Resistance
Tires from all 17 tire models in Phase 2, though not necessarily
the exact tires, were previously tested with SAE J1269, and 11
models were previously tested with ISO 18164 (both tests are very
similar). Data from this multi-point test allows estimation of tire
rolling resistance at the test vehicle load and the two inflation
pressures used in the vehicle fuel economy testing.
2.2.3 SAE J2452 Multi-Point (Speed Coast Down) Rolling
Resistance
With the exception of the original equipment (OE) tires, tires
from 16 tire models in Phase 2, though not necessarily the exact
tires, were previously tested with SAE J2452. Data from this
multi-point test allows estimation of tire rolling resistance at
the test vehicle load, two inflation pressures, and speeds used in
the vehicle fuel economy testing.
2.3 Fuel Economy Test Vehicle
A 2008 Chevrolet Impala LS was selected as the test vehicle for
fuel economy testing since it came equipped with P225/60R16 tires,
and GM original equipment tires have a Tire Performance Code (TPC)
that allows purchase of replacement tires with the same
specifications as the OE tires. These OE tires (tire type G12)
became the 17th group of tires in Phase 2 and had the lowest
rolling resistance of any tire tested in the program (Table 2).
2.4 Test Wheels
Tires were tested on wheels of the corresponding measuring rim
width for their size. Wheels of each size used in the test program
were purchased new, in identical lots to minimize wheel-towheel
variation. A tire participating in multiple tests throughout the
test program was mounted
11
-
once on a single new wheel and continued to be tested on that
same wheel until completion of all tests.
2.5 Test Matrix
The EISA legislation requires a national tire fuel efficiency
consumer information program to educate consumers about the effect
of tires on automobile fuel efficiency, safety, and
durabil-ity.[15] Phase 2 of the project was therefore designed to
examine the effects of tire rolling resistance levels on vehicle
fuel economy, traction, and treadwear. Phase 1 tires were retested
in one of five Phase 2 test protocols: On-vehicle EPA dynamometer
fuel economy (Dyno. FE), wet and dry skid-trailer traction,
on-vehicle treadwear, an experimental indoor treadwear test, or
tread rubber analysis by thermogravimetric analysis (TGA) and
dynamic mechanical analysis (DMA) (Table 3). Due to time and cost
considerations, as well as the physical constraints the fuel
economy test vehicle and skid-trailer, the four tests used a subset
of the 17 available Phase 2 tire models selected to cover the range
of rolling resistance values in the experiment.
12
-
Table 3. Test Matrix Code MFG Size Load
Index Speed Rating
Model RR (lbf)
Dyno. FE
Wet & Dry
Traction
On-vehicle
Treadwear
Indoor Treadwear
TGA /
DMA G12 Goodyear P225/60R16 97 S Integrity 9.47 x x G8 Goodyear
225/60R16 98 S Integrity 9.83 x x x x x G11 Goodyear P225/60R17 98
S Integrity 10.02 x x x B11 Bridgestone P225/60R16 97 H Potenza
RE92 OWL 10.13 x x x x x
G9 Goodyear P205/75R14 95 S Integrity 11.27 x x M14 Uniroyal
P225/60R16 97 S ASTM 16"
SRTT 11.96 x x x x x
M13 Michelin 225/60R16 98 H Pilot MXM4 12.07 x x x x x G10
Goodyear P205/75R15 97 S Integrity 12.09 x x B10 Bridgestone
225/60R16 98 Q Blizzak
REVO1 12.11 x x x
D10 Cooper 225/60R16 98 H Lifeliner Touring SLE
13.56 x x x
B14 Bridgestone P225/60R16 97 V Turanza LS-V
13.90 x x x
U3 Dunlop (Sumitomo)
P225/60R17 98 T SP Sport 4000 DSST
13.91 x x x
B15 Dayton 225/60R16 98 S Winterforce 13.99 x x x P5 Pep
Boys
(Cooper) P225/60R16 97 H Touring HR 14.02 x x x
R4 Pirelli 225/60R16 98 H P6 Four Seasons
14.98 x x x
B13 Bridgestone P225/60R16 97 T Turanza LS-T
15.01 x x x x x
B12 Bridgestone P225/60R16 98 W Potenza RE750
15.22 x x x
Original equipment tires on the fuel economy test vehicle.
Standard reference test tires used as control tires throughout all
phases of the study.
2.6 Tread Compound Properties Testing
The tread rubber of 16 Phase 1 passenger tires was analyzed for
compound composition by thermogravimetric analysis (TGA). The
mechanical properties of the treads were evaluated by dynamic
mechanical analysis (DMA). TGA is a useful tool for characterizing
polymer compositions. The weight loss as a function of temperature
has been used to determine polymer loading, rubber chemical
loading, carbon black loading, and ash levels. For polymers with
very different thermal stabilities, the TGA curves can be used to
determine the amount of each polymer present. Thermogravimetric
analysis was performed using about 10 mg of sample of each tire
tread. The purge (He) gas flow rate to the TGA was set at 10ml/min
during weight loss measurements. The heating rate was 10C/min to
improve the resolution of small variations in the decomposition
curves. At 600C, the purge gas was switched over to air for carbon
black combustion. These average values represent the average of
three measurements. Figure 6 shows a representa
13
-
Wei
ght R
etai
ned
(%)
120
100 Volatile Components
80
60 Polymer
40
20 Carbon Black
Ash (Zinc Oxide, Silica, 0
0 200 400 600 800 1000 Temperataure (degC)
tive weight loss curve with the regions that represent each
component identified. The results of the TGA analysis are shown in
Table 4.
Figure 6. Sample TGA Weight Loss Curve
Table 4. Analysis of Tread Composition by TGA Tire Black,
Type
Tire #
Polymer,% (325-550C)
Volatiles, phr (25325C)
phr (550
850C) Ash, phr (Residue)
Total Filler, phr
Silica, phr
Total Formulation,
phr B10 3104 57 18 32 25 51 19 169 B11 3129 56.8 18 31 27 52 21
170 B12 3154 49 25 54 25 73 19 198 B13 3179 51.3 22 44 29 67 23 189
B14 3204 52 25 13 54 62 48 186 D10 3313 46.9 33 77 3 77 0 207 B15
3337 54.3 19 63 3 63 0 178 U3 3362 52.4 18 33 40 67 34 185 G8 3412
60.4 15 38 12 45 6 159 G9 3441 52.9 23 60 6 60 0 183 G10 3466 58.3
22 45 4 45 0 165 G11 3491 63.3 15 33 11 37 5 152 M13 3620 54.3 19
10 55 59 49 178
14
-
Tire Type
Tire #
Polymer,% (325-550C)
Black, phr Volatiles, Total Total
(550-phr (25- Ash, phr 325C) 850C) (Residue)
Filler, Silica, Formulation, phr phr phr
P5 3670 47.1 29 79 4 79 0 206 R4 3695 48.3 30 42 35 71 29 201
M14 3720 55 19 30 32 57 26 176
Typical examples of temperature sweep data by the tension method
and the shear method are shown below in Figure 7 and Figure 8. The
viscoelastic (dynamic mechanical) properties of a tire tread have
been correlated to the performance of tires.[16],[17],[18],[19]
Decreased tangent at 60C is used as a predictor of the tread
compounds contribution to tire rolling resistance. In-creased
tangent at 0C has been shown to correlate to the wet traction
performance of the tire. Since these properties tend to move in
parallel, lowering the tangent at 60C while maintaining a high
tangent at 0C normally requires utilization of advanced and often
more expensive com-pounding technologies. The DMA results for high
tangent at 0C and 60C are shown in Table 5.
0.00.10.20.30.40.50.60.70.8
-150 -100 -50 0 50 100Temperatue (C)
Tang
ent D
elta
Figure 7. Tan as a Function of Temperature From the Tension
Test
15
-
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
-100 -50 0 50 100
Temperature (deg C)
Tang
ent D
elta
Figure 8. Tan as a Function of Temperature From the Shear
Test
Table 5. DMA Results for Tangent at 0C and 60C
Tire Type
Tire #
Rolling Resistance*
(lbf)
Tension Shear Tan at
0C Tan at
60C Ratio 0/60 Tan at
0C Tan at
60C Ratio 0/60
G8 3412 9.83 0.169 0.0762 2.22 0.164 0.0689 2.38 G11 3491 10.02
0.174 0.086 2.02 0.177 0.0754 2.35 B11 3129 10.13 0.194 0.0771 2.52
0.174 0.067 2.60 G9 3441 11.26 0.245 0.188 1.30 0.18 0.152 1.18 M14
3720 11.96 0.287 0.193 1.49 0.202 0.146 1.38 M13 3620 12.06 0.254
0.147 1.73 0.168 0.117 1.44 G10 3466 12.09 0.242 0.181 1.34 0.184
0.151 1.22 B10 3104 12.11 0.2 0.155 1.29 0.16 0.133 1.20 D10 3313
13.56 0.26 0.192 1.35 0.183 0.16 1.14 B14 3204 13.90 0.313 0.145
2.16 0.233 0.132 1.77 U3 3362 13.91 0.256 0.173 1.48 0.202 0.147
1.37 B15 3337 13.98 0.208 0.15 1.39 0.158 0.123 1.28 P5 3670 14.02
0.271 0.207 1.31 0.161 0.156 1.03 R4 3695 14.98 0.296 0.201 1.47
0.211 0.159 1.33 B13 3179 15.01 0.265 0.168 1.58 0.19 0.138 1.38
B12 3154 15.22 0.387 0.193 2.01 0.28 0.146 1.92 *ISO 28580
single-point rolling resistance
2.7 On-Vehicle Fuel Economy Testing
The effects of tire rolling resistance on automobile fuel
efficiency was evaluated by installing 15
different tire models on a new 2008 Chevrolet Impala LS and
evaluating its fuel economy in the
2008 five-cycle EPA fuel economy test.[20] Testing was completed
under contract by the Transportation Research Center, Inc. (TRC,
Inc.) emissions laboratory. Since tire inflation pressure
affects the operational rolling resistance of a tire, the
vehicle fuel economy measurements were
conducted at two different tire inflation pressures. Testing was
completed at the vehicle placard
16
-
pressure of 210 kPa (30 psi). Six models were tested at both the
placard inflation pressure of 210 kPa and at 158 kPa (23 psi),
which represents the tire pressure monitoring system (TPMS)
activation threshold of 25 percent inflation pressure reduction. It
is important to note, for reasons that will be explained, that
these tests were research and not official EPA fuel economy ratings
of the test vehicle. The many tire sets and repeats of test for
statistical analysis/dual inflation pressure resulted in the test
vehicle acquiring nearly 6,000 miles by the end of testing. The EPA
estimates that new vehicles will not obtain their optimal fuel
economy until the engine has broken in at around 3,000 to 5,000
miles.[21] Therefore the fuel economy of the test vehicle was
expected to improve slightly during the course of testing, a factor
that was tracked and accounted for by the repeated testing of the
control and OE tires at regular intervals throughout the
testing.
2.7.1 EPA 40 CFR Part 86 Dynamometer Fuel Economy Testing
Per EPA 40 CFR Part 86, the new 2008 Chevrolet Impala LS test
vehicle was broken in for 2,000 miles on a test track. To keep the
original equipment tires in the same low mileage state as the Phase
1 tires, the vehicle was broken-in on a spare set of replacement
tires of the original equipment size. For this reason, even the
fuel economy tests of the Impala with the original equipment tires
were not official EPA test numbers. The original equipment tires
were reinstalled on the vehicle at placard inflation pressure and
the road load coastdown procedure was completed. The coastdown
procedure generates vehicle-specific coefficients for dynamometer
settings and fuel economy calculations.
The fuel economy dynamometer is housed in an environmental
chamber to control the temperature for ambient (68 to 86 degrees
F), heated (95 degrees F) or cold (20 degrees F) temperatures. The
vehicle dynamometer is a 1.22-meter (48-inch) diameter, smooth
surface drum located in the floor of the chamber. The vehicle is
placed atop the dynamometer rolls and restrained to prevent
movement (Figure 9a). A fan meeting standard specifications is
located in front of the vehicle to provide cooling (Figure 9b). A
computer is mounted inside the vehicle to provide the driver with a
prescribed speed pattern that must be followed for each test cycle
(Figure 9c). The exhaust gas is routed from the vehicle exhaust
tailpipe via hoses to a collection system connected to gas
analyzers (Figure 9d).
17
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Figure 9a. Tire on 1.22 Meter Dynamometer Figure 9b. Chamber and
Fan
Figure 9c. Drive Cycle Computer Figure 9d. Exhaust Coupling
Figure 9. Vehicle Fuel Economy Dynamometer Testing
Details of the 2008 EPA fuel economy test can be found in Table
6, which is from the EPAs www.fueleconomy.gov Website.[22]
18
http://www.fueleconomy.gov/
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Table 6. 2008 EPA Fuel Economy 5-Driving Schedule Test (Source:
EPA, 2009) Driving Schedule Attributes
Test Schedule
City (FTP) Highway (HwFET)
High Speed (US06)
AC (SC03) Cold Temp (Cold CO)
Trip Type Low speeds in stop-and-go urban traffic
Free-flow traffic at highway speeds
Higher speeds; harder acceleration & braking
AC use under hot ambient conditions
City test w/ colder outside temperature
Top Speed 56 mph 60 mph 80 mph 54.8 mph 56 mph Average Speed
21.2 mph 48.3 mph 48.4 mph 21.2 mph 21.2 mph
Max. Acceleration
3.3 mph/sec 3.2 mph/sec 8.46 mph/sec 5.1 mph/sec 3.3 mph/sec
Simulated Distance
11 mi. 10.3 mi. 8 mi. 3.6 mi. 11 mi.
Time 31.2 min. 12.75 min. 9.9 min. 9.9 min. 31.2 min. Stops 23
None 4 5 23 Idling time 18% of time None 7% of time 19% of time 18%
of time Engine Startup*
Cold Warm Warm Warm Cold
Lab temperature
68-86F 95F 20F
Vehicle air conditioning
Off Off Off On Off
*A vehicle's engine doesn't reach maximum fuel efficiency until
it is warm.
Whole vehicle preconditioning must be done between the ambient
and cold test cycles. Therefore, instead of running all five fuel
economy cycles sequentially in their traditional order, testing
with the 15 sets of tires was split into blocks that facilitated a
much more rapid test throughput. In addition, to gather more data
for statistical purposes, two extra HwFET cycles were run
sequentially after the first HwFET cycle. The testing was conducted
at the placard tire inflation pressure of 210 kPa (30 psi) and
repeated at the TPMS warning activation pressure of 158 kPa (22.3
psi) for selected tires.
Vehicle Preconditioning Vehicle preconditioning begins with
draining the existing fuel from the vehicles fuel tank and
replacing it with a 40 percent fuel tank capacity fill of the
specified fuel. The vehicle is then driven through one Urban
Dynamometer Driving Schedule (UDDS). This procedure is followed by
a soak period of at least 12 hours, but not exceeding 36 hours. All
preconditioning procedures are performed at the conditions of the
test schedule.
FTP Schedule Testing Following the vehicles soak period, the
vehicle is pushed, not driven, onto a chassis dynamometer for a
cold start exhaust emissions test (75 FTP). The Federal test
procedure (FTP) simulates normal city driving and collects dilute
exhaust emissions into bags for analysis in three phases: the cold
transient (CT), the cold stable (CS), and the hot transient (HT).
The UDDS is followed during the CT and CS, and, following a
ten-minute soak on the dynamometer, the first phase, or
19
-
bag, of the UDDS is repeated for the HT. The results of these
phases are combined to provide grams per mile (g/mi) for total
hydrocarbons (THC), non-methane hydrocarbons (NMHC), carbon
monoxide (CO), carbon dioxide (CO2) and oxides of nitrogen (NOx).
Fuel economy, in miles per gallon, is determined via the carbon
balance method.
HwFET Schedule Testing Following each FTP test, the vehicle is
kept on the chassis dynamometer and the Highway FET (HwFET) driving
cycle was run twice. The first running of the HwFET served only to
stabilize vehicle temperatures and emissions, therefore fuel
economy was not measured during this cycle. The cycle is repeated
and all emissions measurements are taken as described for FTP
testing with the exception that a single bag is used to collect the
dilute exhaust sample (single phase). Fuel economy, in miles per
gallon, is again determined via the carbon balance method. The
Phase 2 testing protocol added two additional repeats for the HwFET
cycle that were run and measured sequentially.
US06 Schedule Testing This test type is the aggressive-driving
portion of the supplemental FTP (SFTP), consisting of higher speeds
and acceleration rates.
SC03 (AC2 Alternate) Schedule Testing This test type has been
introduced to represent the engine load and emissions associated
with the use of air conditioning units in vehicles. Since the TRC,
Inc. emissions lab lacks the solar-loading equipment necessary to
run a full SC03 test, the AC2 alternative was used. This
alternative was only valid for 2000-2001 model year vehicles unless
approved by the EPA, therefore the result for each individual cycle
is reported in this report but not composite 5-cycle numbers for
the vehicle.[23] The AC2 alternative mimics the SC03 except that
the thermal load is simulated by placing the vehicles air
conditioning temperature control to full hot, air conditioning on,
and the drivers side window left down. In addition, the test cell
is kept at 76 F and 50 grains of water per pound of dry air versus
the SC03 requirement of 95 F and 100 grains of water per pound of
dry air. All other procedures follow the SC03.
Cold CO Schedule Testing This test follows the same driving
cycle as the FTP, but the test is performed at 20 F and the vehicle
is filled with Cold CO specific fuel. The vehicle is operated
through one UDDS preparation cycle at 20 F. Then, the vehicle is
parked in a soak chamber maintained at 20 F for a minimum of 12 and
a maximum of 36 hours prior to beginning each test. Following the
20 F. soak, the vehicle is pushed into the dynamometer chamber
(which is at 20 F) and then operated through the normal FTP
test.
The program was completed in blocks of tests, with the M14
control tires and G12 OE tire run multiple times to track possible
vehicle, tire and test equipment drift. The completed test cycles
are summarized in Table 7.
20
-
Table 7. Fuel Economy Test Schedules Pressure City (FTP) Highway
(HwFET)* High Speed (US06) AC (SC03) Cold
Temp (Cold CO) 210 kPa 19 57 19 19 19 158 kPa 6 16 6 6 6
*Two extra cycles completed after first run to gauge statistical
variability.
2.8 Skid-Trailer Tire Traction Testing
FMVSS No. 575.104, Uniform tire quality grading standards
requires manufacturers to provide a (wet slide) traction grade for
all tires subject to standard and manufactured after April 1, 1980.
A formal description follows[24]:
To assist consumers purchasing new vehicles or replacement
tires, NHTSA has rated more than 2,400 lines of tires, including
most used on passenger cars, minivans, SUVs and light pickup
trucks. Traction grades are an indication of a tire's ability to
stop on wet pavement. A higher graded tire should allow a car to
stop on wet roads in a shorter distance than a tire with a lower
grade. Traction is graded from highest to lowest as "AA", "A", "B",
and "C". Of current tires: 3 percent are rated AA, 75 percent are
rated A, 22 percent are rated B, only 1 line of tires rated C.
The UTQGS skid-trailer traction testing was performed at the
NHTSA test facility on Goodfellow Air Force Base in San Angelo,
Texas. The traction grading tests are now performed on a
purpose-built oval at the base rather than the original test
surface diagram shown in 575.104. The test pavements are asphalt
and concrete skid pads constructed in accordance with industry
specifications for skid surfaces. ASTM E 5014 reference (control)
tires are used to monitor the traction coefficient of the two
surfaces (which varies based on environmental conditions, surface
wear, etc.). During a normal wet traction test, a vehicle tows a
skid-trailer (Figure 10) at 40 mph across the test surfaces. Water
is dispersed ahead of the tire from a water nozzle just before the
brake is applied. Instrumentation measures the horizontal force as
the brake is applied to one wheel of the trailer until lock-up, and
then held for a few seconds and released. The tests are repeated
for a total of 10 measurements on each surface. The candidate
(test) tires are conditioned by running for 200 miles on a pavement
surface. The candidate tires are then fitted to the trailer, loaded
to a specified load and pressure, then subjected to the same
testing completed on the control tires. The average sliding
coefficient of friction for the candidate tire on each surface is
corrected using the coefficients of the control tire to yield an
adjusted traction coefficient for the candidate tire on each test
surface.
4 ASTM E 501-94 Standard Specification for Standard Rib tire for
Pavement Skid Resistance Tests. Available from American Society for
Testing and Materials, http://astm.org.
21
http:http://astm.org
-
Figure 10. NHTSA San Angelo Skid-Trailer
Phase 2 traction tests were conducted with tires of 16 models
previous tested in Phase 1. Two tires had the highest traction
grade AA, 14 tires were graded A (Table 8). Since these tires
experienced some break-in during the 50- to 70-mile rolling
resistance tests, these tires were only conditioned for 70 miles on
a pavement surface rather than the normal 200 miles.5 Since the
tires were not new, and had a reduced break-in, the results
generated are for research purposes and are unofficial. The test
matrix was also repeated on dry asphalt and concrete test surfaces.
The number of measurements on the dry surfaces was reduced to
preserve the limited test surface area from rubber buildup.
Since modern antilock brakes (ABS) and electronic stability
control (ESC) operate in the lower slip and higher friction region,
the peak coefficient recorded during the traction testing was also
used for comparisons in Phase 2 in addition to the slide values
used for UTQGS wet traction.
5 Two additional tires of a Phase 1 tire model were broken -in
for the full 200 miles and compared to a set of two that had the
50- to 70-mile roadwheel break-in. There was no significant
difference in their traction numbers.
22
-
Table 8. Phase 2 Wet and Dry Skid-Trailer Test Tires Ti
re M
odel
Cod
e
MFG
Size
Load
Inde
x
Spee
d R
atin
g
Mod
el
UTQ
GS
Trea
d-w
ear
UTQ
GS
Trac
.
UTQ
GS
Tem
p.
Perf
orm
ance
Le
vel
ISO
285
80 R
ollin
g R
esis
tanc
e, F
r (lb
f)
Wei
ght (
lbs.
)
B14 Bridgestone P225/60R16 97 V Turanza LS-V 400 AA A Grand
Touring All Season 13.90 28.6
B12 Bridgestone P225/60R16 98 W Potenza RE750 340 AA A Ultra
High Performance Summer
15.22 27.4
D10 Cooper 225/60R16 98 H Lifeliner Touring SLE 420 A A Standard
Touring All Season 13.56 25.2
P5 Pep Boys (Cooper)
P225/60R16 97 H Touring HR 420 A A Passenger All Season 14.02
25.7
R4 Pirelli 225/60R16 98 H P6 Four Seasons 400 A A Passenger All
Season 14.98 24.3
B11 Bridgestone P225/60R16 97 H Potenza RE92 OWL 340 A A High
Performance All Season 10.13 25.1
M13 Michelin 225/60R16 98 H Pilot MXM4 300 A A Grand Touring All
Season 12.07 24.7
B13 Bridgestone P225/60R16 97 T Turanza LS-T 700 A B Standard
Touring All Season 15.01 29.4
M14 Uniroyal P225/60R16 97 S ASTM 16" SRTT 540 A B ASTM F
2493-06 Reference 11.96 25.5
G8 Goodyear 225/60R16 98 S Integrity 460 A B Passenger All
Season 9.83 22.9
G11 Goodyear P225/60R17 98 S Integrity 460 A B Passenger All
Season 10.02 24.5
G9 Goodyear P205/75R14 95 S Integrity 460 A B Passenger All
Season 11.27 19.2
G10 Goodyear P205/75R15 97 S Integrity 460 A B Passenger All
Season 12.09 20.4
U3 Dunlop (Sumitomo)
P225/60R17 98 T SP Sport 4000 DSST 360 A B Run Flat 13.91
36.4