II. PERFORMANCE REQUIREMENTS


    Light Vehicle Tire Standard

    The agency proposes that a new tire standard FMVSS No. 139 apply to tires used on passenger cars, multipurpose passenger vehicles, trucks, buses and trailers with a gross vehicle weight rating of 10,000 pounds or less. It would apply to all P-metric and LT tires up to load range E, and would not apply to motorcycles. The performance requirements of the current FMVSS Nos. 109 and 119; the proposed Global Tire Standard 2000 for New Pneumatic Car Tires (GTS 2000); and other proposed FMVSS No. 139 alternatives are discussed below:


    A. High Speed Test Requirements

    Current FMVSS No. 109 High Speed Test Requirement

    The current FMVSS No. 109 high speed test presses the test tire assembly against the test wheel with a load of 88% of the tires maximum load rating as marked on the tire sidewall. The test tires are inflated as specified in Table II of FMVSS No. 109, which corresponds to a pressure that is 20 kPa or 3 psi less than the maximum pressure marked on the sidewall. The tire is run for 2 hours at 50 mph and allowed to cool to 100+5o F, followed by a readjustment of the inflation to the specified pressure. After the initial break in, the tire is tested at 75 mph for 30 minutes, 80 mph for 30 minutes, and 85 mph for 30 minutes. The tire is allowed to cool for one hour before deflating and dismounting it from the test wheel and inspecting for the failure criteria.

    High Speed Test Alternatives

    The agency considered three high speed alternative upgrade test scenarios. Alternative 1 considered adoption of the Global Tire Standard 2000 (GTS-2000) proposed by the tire industry. The GTS-2000 proposal attempted to create an internationally harmonized tire standard based on a tire's speed ratings using the same approach as ECE R 30, and the Society of Automotive Engineers (SAE) Recommended Practice J15161, Laboratory Speed Test Procedure For Passenger Car Tires. The agency reviewed GTS-2000 tire industry data and determined that alternative 1 was only slightly more stringent than the current FMVSS No. 109 high speed test. While taking this data into consideration , the agency developed alternative 3, a more stringent high speed test also based on the tires' speed rating. The agency conducted research tests based on tire speed ratings to determine an appropriate level of test performance criteria. When some of the high speed research test specifications in alternative 3 appeared to be overly stringent (based on a high percentage of tires failing these criteria), the agency developed alternative 2, which would provide a single minimum performance level for all tires that is more stringent than alternative 1, but less stringent than alternative 3.

    GTS 2000 High Speed Endurance Test (Alternative 1)

    The proposed GTS 2000 High Speed Endurance test uses a procedure similar to that of FMVSS No.109, except that the test speed and tire inflation are determined by the tire's speed rating. In GTS 2000 the test tire assembly is pressed against the test wheel with a load of 80% of the tire's maximum load rating as marked on the tire sidewall. The test tires are inflated as specified in Table II-1.


    Table II-1 Inflation Pressure -kPa (psi)

    Speed Category Bias-ply Tires Radial & Bias-Belted Tires
    Ply Rating Standard Extra Load
    (Reinforced)
    4 6 8
    L, M, N 230 (33) 270 (39) 300 (44) 240 (34) 280 (40)
    P, Q, R, S 250 (36) 300 (44) 330 (48) 260 (38) 300 (44)
    T, U, H, 280 (40) 320 (46) 350 (50) 280 (40) 320 (46)
    V 300 (44) 340 (49) 370 (53) 300 (44) 340 (49)
    W, Y - - - 320 (46) 360 (52)

    The tire is tested without interruption as follows:

    Accelerate at a constant rate such that an initial test speed of 40 km/h (25 mph) less than the speed rating is reached at the end of 10 minutes.


    Table II-2
    Speed Ratings

    Speed Rating Speed (km/h) Speed (mph)
    L 120 75
    M 130 81
    N 140 87
    P 150 93
    Q 160 99
    R 170 106
    S 180 112
    T 190 118
    U 200 124
    H 210 130
    V 240 150
    W 270 169
    Y 300 188
    ZR Over 240 Over 150


    NHTSA Single Performance Level High Speed Tire Test (Alternative 2)

    After reviewing the results of the Phase I and Phase II high speed tire tests (discussed later), the agency is proposing a single performance level 90 minute upgraded high speed tire test that will be conducted in three 30 minute steps without consideration of a tire's speed rating, at the speeds of 140, 150 and 160 km/h (88, 94, and 100 mph). The agency believes that this single performance level test represents a reasonable minimum capability that all tires operating on public roads should possess. The tests are to be conducted at 85% of the maximum sidewall load at an inflation pressure of 220 kPa (32 psi) for standard load P-metric tires. Light truck (LT) tires will be tested at inflation pressures of: 320 kPa (46 psi) for load range C tires; 410 kPa (60 psi) for load range D tires; and 500 kPa (73 psi) for load range E tires. The proposed Alternative 2 high speed test requirement is more stringent than the current FMVSS No. 109, and Alternative 1 (GTS-2000) requirements, but less stringent than Alternative 3.

    NHTSA Speed Rated High Speed Tire Test (Alternative 3)

    The agency developed alternative 3, a speed rated high speed tire test similar to but more strigent than the GTS-2000 high speed tire tests. The tests were run by accelerating the test tire up to the initial test speed (ITS) for ten minutes, and then continuously without stopping, testing the tire at the four speeds (ITS, ITS + 10km/h, ITS + 20 km/h, and ITS + 30km/h) for twenty minutes at each step. Thus, the 20 minute step duration high speed tire test would require 90 minutes to complete (10 minutes up to ITS and four 20 minute speed steps = 90 minutes).

    The ITS is 30 km/h less than the speed rating of the tire. Non-speed rated tires are tested at the same speed as "Q" rated tires. Tires rated above "H" are tested at the same speed as "H" rated tires. P-metric tires are to be tested at 220 kPa inflation pressure, which represents an under-inflation pressure of about 8 percent from the maximum inflation pressure of 240 kPa. LT tires are to be held to a similar level of under-inflation. Thus, for the high speed tire test, the tire inflation pressures for load range C, D, and E are 320, 420 and 550 kPa respectively.


    TABLE II-3
    HIGH SPEED TEST COMPARISON

    TEST PARAMETERS FMVSS
    109
    GTS-2000
    Alternative 1
    NHTSA
    Single Performance
    Level
    Alternative 2
    NHTSA
    Speed Rated
    Alternative 3
    Ambient (oC) 38 25 40 40
    Load (%) 88 80 85 85
    Inflation Pressure (kPa)        
    P-metric Standard/Extra Load 220/260 - 220/260 220/260
    LT load range C/D/E - - 320/410/550 320/410/550
             
    Speed Rating (Standard/Extra)        
    L,M,N - 240/280    
    P,Q,R,S - 260/300    
    T,U,H - 280/320    
    V - 300/340    
    W,Y - 320/360    
    Test Speed* (km/h) 121/129/13 ITS, +10, +20, +30 140/150/160 ITS, +10, +20, +30
    ITS = L,M,N,P,Q 7 90,100,110,120,130   140
    R,S,T,U,   140,150,160,170   140,150,160,170
    H,V,W,Y   180,210,240,270   180
    Duration (mins) 90 50 90 90


    NHTSA High Speed Tire Test Results

    The agency conducted two series of high speed and endurance tire tests. In Phase I the agency tested one each of the 9 P-metric and 3 LT tire models listed below in Table II-4: In Phase II the agency tested five each of the 8 P-metric and 4 LT tire models which are listed in Table II-7. The "S" in the P-metric tire load range, means standard duty. The LT tires may be marked with a UTQGS grade, but this is not required of LT tires.


    Table II-4
    Phase I Tires

    Brand Model Size LR SR PSI UTQG
    Wear Traction Temp
    P-Metric Tires              
    Bridgestone Potenza RE92 P205/65R15 S H 44 160 A A
    Futura 2000 Radial ATD P205/75R14 S S 35 440 A B
    Dunlop D65 Touring P205/70R14 S T 35 600 A B
    Firestone Wilderness AT P255/70R16 S S 44 440 B C
    Firestone Radial ATX P235/75R15 S S 35 None None None
    Hankook Optimo Plus II P205/65R15 S H 35 320 A A
    Michelin Energy MXV4 Plus 205/65R15 S H 44 400 A A
    National XT 5000 P225/60R16 S S 35 560 A B
    Pirelli P4000 P205/60R15 S H 44 320 A A
    Light Truck Tires              
    Goodyear Wrangler AT/S LT235/75R15 C N/ 50 None None None
    Michelin XPC 4x4 235/70R16 C H 51 440 A B
    Yokohama GeoLandar H/T LT225/75R16 D S 65 None None None


    In Phase I, the agency ran 243 P-metric tire and 81 LT tire high speed tests including all combinations of 10, 20, and 30 minute test step duration; 180, 210, and 240 kPa inflation pressures for P-metric tires, 260/340, 300/390, and 350/450 kPa for the C&D Load range LT tires; and loads of 80, 90 and 100%. The tests were run by accelerating the test tire up to the initial test speed (ITS) by the end of ten minutes, and then continuously without interruption, testing the tire at the four speeds (ITS, ITS + 10km/h, ITS + 20 km/h, and ITS + 30km/h) for the time duration of each step. Thus, the 10 minute step duration tests require 50 minutes to complete (10 minutes up to ITS and four 10 minute speed steps = 50 minutes): the 20 minute step duration requires 90 minutes to complete (10 minutes up to ITS and four 20 minute speed steps = 90 minutes); and the 30 minute step duration requires 130 minutes to complete (10 minutes up to ITS and four 30 minute speed steps = 130 minutes). The ITS is 30 km/h less than the speed rating of the tire. Non-speed rated tires are tested at the same speed as "Q" rated tires. Tires rated above "H" are tested at the same speed as "H" rated tires. All the tires that were inflated to 180 kPa and 240 kPa tires were tested to failure, and the 210 kPa tires were only tested to completion, unless they failed the test. A summary of the 243 high speed P-metric tire test's time to failure is presented in the Table II-5 below, segregated by the tire's UTQGS Temperature rating:

    Table II-5
    Phase I P-Metric Tire Test Results Summary
    50 Minute High Speed Tire Test (10 min step duration)

      UTQG
    Temp
    180 kPa 210 kPa 240 kPa
    Failure Ave Time Failures Failure Ave Time Failures Failure Ave Time Failures
    80% Load A 60 minutes 0/4 50 minutes 0/4 79minutes 0/4
    80% Load B 76 minutes 0/3 50 minutes 0/3 82 minutes 0/3
    80% Load C 48 minutes 2/2 50 minutes 0/2 59 minutes 0/2
    90% Load A 54 minutes 2/4 44 minutes 2/4 60 minutes 0/4
    90% Load B 56 minutes 0/3 50 minutes 0/3 71 minutes 0/3
    90% Load C 56 minutes 1/2 50 minutes 0/2 71 minutes 0/2
    100% Load A 48 minutes 2/4 44 minutes 2/4 60 minutes 1/4
    100% Load B 52 minutes 1/3 50 minutes 1/3 71 minutes 0/3
    100% Load C 44 minutes 2/2 47 minutes 2/2 51 minutes 2/2


    90 Minute High Speed Tire Test (20 min step duration)

      UTQG
    Temp
    180 kPa 210 kPa 240 kPa
    Failure Ave Time Failures Failure Ave Time Failures Failure Ave Time Failures
    80% Load A 96 minutes 1/4 87 minutes 1/4 108 minutes 0/4
    80% Load B 107 minutes 0/3 90 minutes 0/3 122 minutes 0/3
    80% Load C 65 minutes 2/2 87 minutes 1/2 100 minutes 0/2
    90% Load A 87 minutes 2/4 77 minutes 2/4 99 minutes 1/4
    90% Load B 86 minutes 1/3 61 minutes 1/3 106 minutes 1/3
    90% Load C 77 minutes 2/2 88 minutes 2/2 60 minutes 2/2
    100% Load A 69 minutes 3/4 91 minutes 1/4 98 minutes 2/4
    100% Load B 82 minutes 3/3 84 minutes 1/3 94 minutes 1/3
    100% Load C 51 minutes 2/2 75 minutes 2/2 80 minutes 2/2


    130 Minute High Speed Tire Test (30 min step duration)

      UTQG
    Temp
    180 kPa 210 kPa 240 kPa
    Failure Ave Time Failures Failure Ave Time Failures Failure Ave Time Failures
    80% Load A 114 minutes 2/4 124 minutes 1/4 125 minutes 1/4
    80% Load B 130 minutes 0/3 130 minutes 0/3 130 minutes 0/3
    80% Load C 104 minutes 2/2 113 minutes 2/2 122 minutes 2/2
    90% Load A 117 minutes 2/4 120 minutes 2/4 124 minutes 1/4
    90% Load B 105 minutes 2/3 125 minutes 1/3 130 minutes 0/3
    90% Load C 104 minutes 2/2 102 minutes 2/2 113 minutes 2/2
    100% Load A 104 minutes 3/4 117 minutes 3/4 120 minute 2/4
    100% Load B 101 minutes 3/3 114 minutes 2/3 129 minutes 1/3
    100% Load C 93 minutes 2/2 115 minutes 1/2 105 minutes 2/2


    When the data in the three P-metric tire tables are examined, it is apparent that the number of failures increased as: the test speed increased; the length of the test increased; the load increased; and the inflation pressure decreased. As the test severity increased, the C temperature graded tires failed with greater frequency than the B or A temperature graded tires. For the two groups of tires run to their ultimate failure, the average time to failure for each of the temperature grades were: A = 60 minutes; B = 68 minutes; and C = 49 minutes.

    The agency usually expects C tires to fail earlier than B tires in the high speed test, and the B tires to fail earlier than the A tires. While both the A and B tires out lasted the C tires, the agency believes the A tires failing before the B tires is an anomaly due to the particular tires in the small sample. Two of the four A tires performed poorly. The Pirelli P4000 tires were 4 years old, thus the aging affect may have caused them to fail earlier. The Hankook Optimo Plus II tires performed poorly for an A grade tire. These two tires significantly pulled the overall average of the A graded tires down.

    A summary of the 81 high speed LT tire tests is presented in the Table II-6 below: LT tires are not required to have UTQGS grades, thus they do not have the comparative temperature ratings that were marked on the P-metric tires.


    Table II-6
    Phase I LT Tire Test Results Summary
    50 Minute High Speed Tire Test (10 min step duration)

      C - 260 / D - 310 kPa C - 300 / D - 390 kPa C - 350 / D - 450 kPa
    Failure Ave Time Failures Failure Ave Time Failures Failure Ave Time Failures
    80% Load 62 minutes 0/3 50 minutes3tcnf* 0/3 72minutes 0/3
    90% Load 58 minutes 0/3 50 minutes 3tcnf 0/3 66minutes 0/3
    100% Load 57 minutes 0/3 50 minutes 3tcnf 0/3 66 minutes 0/3


    90 Minute High Speed Tire Test (20 min step duration)

      C - 260 / D - 310 kPa C - 300 / D - 390 kPa C - 350 / D - 450 kPa
    Failure Ave Time Failures Failure Ave Time Failures Failure Ave Time Failures
    80% Load 103 minutes 1/3 89 minutes 2tcnf 1/3 127minutes 0/3
    90% Load 115 minutes 0/3 87 minutes 2tcnf 1/3 124minutes 0/3
    100% Load 82 minutes 2/3 91 minutes 2/3 98 minutes 1/3


    130 Minute High Speed Tire Test (30 min step duration)

      C - 260 / D - 310 kPa C - 300 / D - 390 kPa C - 350 / D - 450 kPa
    Failure Ave Time Failures Failure Ave Time Failures Failure Ave Time Failures
    80% Load 125 minutes 2tcnf 1/3 128 minutes 2tcnf 1/3 130minutes 3tcnf 0/3
    90% Load 119 minutes 2tcnf 0/3 126 minutes 2tcnf 1/3 115minutes 1tcnf 2/3
    100% Load 97 minutes 1tcnf 2/3 121 minutes 1tcnf 1/3 128minutes 2tcnf 2/3


    When the data in the three LT tire tables are examined, it is apparent that the number of failures increased as: the test speed increased; the length of the test increased: the load increased; and the inflation pressure decreased. These were the same trends exhibited by the P-metric passenger car tires.

    An additional 280 P-metric and 140 LT high speed tire tests were conducted by the agency in Phase II testing, which consisted of a series of 4 different high speed tests with 5 tires of each model tested. The 8 P-metric and 4 LT tire models tested in Phase II are listed below:


    Table II-7
    Phase II Tires

    PHASE II Model Size LR SR PSI UTQG
    Brand Wear Traction Temp
    P-Metric Tires              
    Toyo Proxes H4 P225/60R16 S H 44 400 A A
    Uniroyal Tiger Paw Touring HR P225/60R16 S H 44 400 A A
    Dunlop D65 Touring P205/65R15 S T 35 560 A B
    Goodyear Regatta 2 P205/65R15 S T 44 560 A B
    BF Goodrich Cientra Plus P235/75R15 S S 35 560 A B
    Cooper LifeLiner Classic II P235/75R15 S S 35 560 A B
    Firestone Wilderness AT P235/75R15 S S 35 440 A C
    Michelin XH4 P235/75R15 S S 35 580 A B
    Light TruckTires              
    Pirelli Scorpion P/T LT235/75R16 C S 50 None None None
    Yokohama GeoLandar A/T LT235/75R15 C S 50 None None None
    Goodyear Wrangler HT LT245/75R16 E R 80 None None None
    Bridgestone R273 SWP 11 LT245/75R16 E Q 80 None None None


    Table II-8 Phase II High Speed Test Results Summary

    Brand Model UTQGS
    Temp Grade
    High Speed
    Test1
    High Speed
    Test 2
    High Speed
    Test 3
    High Speed
    Test 4
    P-Metric Tires
    Toyo Proxes H4 A 4P* 1F# 5P 0F 5P 0F 5P 0F
    Uniroyal Tiger Paw Touring HR A 5P 0F 5P 0F 5P 0F 5P 0F
    Dunlop D65 Touring B 5P 0F 5P 0F 5P 0F 5P 0F
    Goodyear Regatta 2 B 0P 5F 0P 5F 1P 4F 0P 5F
    BF Goodrich Cientra Plus B 0P 5F 0P 5F 0P 5F 2P 3F
    Cooper LifeLiner Classic II B 3P 2F 4P 1F 5P 0F 5P 0F
    Firestone Wilderness AT C 1P 4F 0P 5F 0P 5F 4P 1F
    Michelin XH4 B 0P 5F 0P 5F 0P 5F 5P 0F

    LT Tires Load Range High Speed
    Test1
    High Speed
    Test1
    High Speed
    Test1
    High Speed
    Test1
    Pirelli Scorpion A/T C 5P 0F 5P 0F 5P 0F 5P 0F
    Yokohama GeoLandar H/T C 5P 0F 5P 0F 5P 0F 4P 1F
    Goodyear Wrangler HT E 5P 0F 5P 0F 5P 0F 5P 0F
    Bridgestone R273 SWP 11 E 5P 0F 5P 0F 5P 0F 5P 0F


    Phase II Test Conditions

    High Speed Test 1 - 80% Load; ITS + 30 km/h (19 mph); 20 minute duration;

    P-metric tires - 210 kPa (30 psi),
    LT tires Load Range C - 310 kPa (44psi), Load Range E - 530 kPa (77 psi)
    High Speed Test 2 - 80% Load; ITS + 30 km/h (19 mph); 20 minute duration;
    P-metric tires 220 kPa (32 psi)
    LT tires Load Range C - 320 kPa (46 psi), Load Range E - 550 kPa (80 psi)
    High Speed Test 3 - 80% Load; 160/170/180 km/h (99/106/112 mph), 30 minute duration;
    P-metric tires 210 kPa(30 psi)
    LT tires Load Range C - 310 kPa (44psi), Load Range E - 530 kPa (77 psi)
    High Speed Test 4 - 85% Load; ITS + 30 km/h (19 mph); 20 minute duration;
    P-metric tires 220kPa (32 psi)
    LT tires Load Range C - 330 kPa (48psi), Load Range E - 560 kPa (81psi)

    In the Phase II tests, all of the A Temperature grade tires except one completed their tests without a failure. Two B tire models performed as well as the A tire models, while three B tire models performed as poorly as the one C tire model. All of the LT tires tested except one completed the tests without failure.

    Note that in eight cases there were discrepancies in the pass/fail outcomes of the tests for the five tires (e.g., 4 passed and 1 failed or 2 passed and 3 failed). This led the agency to examine the manufacture quality control of the tires themselves. (See discussion later in this chapter.)

    High Speed Tire Test Alternatives Analysis

    The agency reviewed the Phase I and Phase II test data, and examined the percentage of tires that would pass each of the alternatives. Table II-9 presents the percentages of tires tested that would pass each of the alternative tests.


    Table II-9
    Percent of Tires That Passed the High Speed Alternative Tests

      Phase I Tests Phase II Tests
    Alternative 1 Alternative 2 Alternative 3 Alternative 1 Alternative 2 Alternative 3
    P-metric tire % passed 100 100 67 100 100 63
    LT tires % passed NA 67 67 NA 100 75


    The percentages in Table II-9 verifies that the vast majority of tires tested can pass alternative 2 minimum performance criteria. The agency believes the selected speed levels in alternative 2 establishes a reasonable minimum performance requirement that is appropriate for safety standards of motor vehicle equipment. All the tires easily passed the alternative 1 criteria, which proved this alternative did not distinguish different tire performance levels. The agency believes alternative 3 is too stringent because it is based on a tires speed rating. Tires with higher speed ratings can fail because they are tested beyond a minimum capability necessary for safe operation. The only tires that failed alternative 3, were those tested well beyond the interstate speed limits and the capability of many vehicles sold in the U.S.


    B. Endurance Test Requirements


    Current FMVSS No. 109 Endurance Test Requirement

    The current endurance test in FMVSS No. 109 is conducted at 80 km/h (50 mph) for a total of 34 hours at loads of: 85% for 4 hours, 90% for 6 hours, and 100% for 24 hours of the maximum rated tire load, at an inflation pressure of 180 kPa (26 psi). The total distance for the current endurance test is 2720 km (1700 miles). The 50 mph test speed may have been an appropriate speed in 1968 when the standard was initially proposed for bias ply tires, but the agency believes that speed to be too low for evaluating the endurance of today's tires, given current vehicle performance capabilities and vehicle traffic speeds.

    Current FMVSS No. 119 Endurance Test Requirement

    The current endurance test in FMVSS No. 119 for LT tires is similar to FMVSS No. 109. The current endurance test requirements for FMVSS No. 119 is a 47-hour duration test run at the maximum inflation pressure on the tire label, at 80 km/h (50 mph) for Load Range A, B, C, and D tires at: 75% of the rated load for 7 hours, 97% of the rated load for 16 hours, and 114% of the rated load for 24 hours, and at 64 km/h (40 mph) for Load Range E tires at: 70% of the rated load for 7 hours, 88% of the rated load for 16 hours, and 106% of the rated load for 24 hours.

    GTS 2000 Endurance Test

    In GTS 2000, the tire industry proposed a global harmonized endurance test for passenger car radial tires rated Q and below. The test parameters included a load of 100/110/115% at a speed of 80 km/h (50 mph), for 34 hours duration at an inflation pressure of 180 kPa (26 psi). Agency testing indicates that all presently manufactured P-metric tires can pass the industry's proposed test with no failures.

    Endurance Test Alternatives

    The agency considered three alternative endurance upgrade test scenarios. Alternative 1 considered adoption of a protocol proposed by the Rubber Manufacturer's Association (RMA).

    This protocol (RMA 2000) is similar to the GTS-2000 endurance test for tires rated Q or less, with the main difference being the test speed was increased from 80 km/h to 120 km/h. The agency reviewed RMA 2000 endurance test data submitted by the tire industry and observed that all the tires passed the test. Taking this data into consideration, the agency conducted research tests to develop a more stringent set of performance criteria, alternative 3. When the endurance research test specifications in alternative 3 appeared to be overly stringent, the agency developed alternative 2, which is more stringent than alternative 1, but less stringent than alternative 3.

    RMA 2000 Test Protocol (Alternative 1)

    In December 2000, the RMA presented to NHTSA a test protocol, RMA 2000, that was designed and administered with the tire industry. The test protocol included the following principal parts: passenger car and light truck tire high speed tests, passenger car and light truck tire endurance tests. RMA 2000's recommended endurance test parameters are listed below:

    Passenger tires - Inflation pressure - 180 kPa; Test speed - 120 km/h; Duration - 8 hours at 85% of max rated load, 8 hours at 90% of max rated load, and 8 hours at 100% of max rated load; Ambient temperature - 38oC +/- 3oC

    LT tires - Inflation pressure - maximum load marked on tire sidewall; Test speed - 120 km/h; Duration - (Load Range A-D) 8 hours at 75% of max rated load, 8 hours at 97% of max rated load, and 8 hours at 114% of max rated load; (Load Range E) 8 hours at 70% of max rated load, 8 hours at 88% of max rated load, and 8 hours at 106% of max rated load; Ambient temperature - 38oC +/- 3oC

    NHTSA Initial Research Endurance Test Parameters (Alternative 3)

    Using data from RMA 2000 the agency developed an initial set of endurance test parameters listed below to test the endurance of current market tires:

    Ambient temperature - > 40oC

    Test speed - 120 km/h;

    Duration 8 hrs @ 100% of max load
     10 hrs @ 110% of max load
     32 hrs @ 115% of max load

    P-metric tire inflation pressure - 180 kPa
    LT tire inflation pressure - Load Range C/D/E 260/340/450 kPa

    NHTSA Proposed Endurance Test Parameters (Alternative 2)

    After the agency determined that the initial research parameters (alternative 3) may be too stringent the agency developed the alternative 2 test parameters which are less stringent than alternative 3 but more stringent than alternative 1. The main difference between alternatives 2 and 3 is that the tire loads are lighter, the duration is 10 hours shorter, and the LT tire inflations are higher. The NHTSA proposed endurance test parameters for alternative 2 are as follows:

    Ambient temperature - >40oC

    Test speed - 120 km/h;

    Duration8 hrs @ 90% of max load
     10 hrs @ 100% of max load
     22 hrs @ 110% of max load

    P-metric tire inflation pressure - 180/220 kPa Standard/Extra Load
    LT tire inflation pressure - Load Range C/D/E 320/410/550 kPa


    TABLE II-10
    ENDURANCE TEST COMPARISON

    TEST
    PARAMETERS
    FMVSS 109 FMVSS 119 RMA-2000
    Alternative 1
    NHTSA
    Proposal
    Alternative 2
    NHTSA
    Initial Research
    Alternative 3
    Ambient (oC) 38 38 38 40 40
    Load (%)          
    P-metric 85/90/100 - 85/90/100 90/100/110 100/110/115
    LT load range C/D - 75/97/114- 75/97/114 90/100/110 100/110/115
    LT load range E   66/84/101 70/88/106 90/100/110 100/110/115
    Inflation Pressure (kPa)          
    P-metric          
    Standard/Extra Load 180/220   180 180/220 180
    LT load range C/D - sidewall max sidewall max 320/410 260/340
    LT load range E   sidewall max sidewall max 550 450
    Test Speed (km/h) 80 80 120 120 120
    Duration (hours) 34 34 24 40 50


    NHTSA Endurance Test Results

    Phase I endurance testing was conducted on the same P-metric tires listed in the previous High Speed Test Requirement section, at 120 km/h (75 mph) and 140 km/h (87 mph), with loads of 100%, 115%, and 125% of the maximum rated load for a total of 50 hours, and at inflation pressures of 160 kPa (23 psi) and 200 kPa (29 psi). At speeds of 120 km/h (75 mph) and 140 km/h (87 mph), the total test distance is 6000 km (3,728 miles) and 7,000 km (4,350 miles), respectively, which is more than twice the distance of the current passenger car tire endurance test. The LT tires previously listed in the high speed tests were also endurance tested at the same speeds for 50 hours with the same percentages of the maximum rated loads. The LT tires were inflated to 75% of their respective maximum inflation pressures. The results of these Phase I endurance tests are summarized below in Table II-11.


    Table II-11
    50 Hour P-Metric Tire Endurance Test

    Speed UTQG
    Temp
    160 kPa (23psi) 200 kPa (29 psi)
    Ave Time to Failure Pass/Fail Ave Time to Failure Pass/Fail
    120km/h (75 mph) A 50 hours 4P 0F 50 hours 4P 0F
    120km/h (75 mph) B 38 hours 1P 2F 43 hours 2P 1F
    120km/h (75 mph) C 19 hours 0P 2F 35 hours 1P F
    140km/h (87 mph) A 42 hours 3P 1F 50 hours 4P 0F
    140km/h (87 mph) B 12 hours 0P 3F 25 hours 0P 3F
    140km/h (87 mph) C 17 hours 0P 2F 8 hours 0P 2F


    50 Hour LT Tire Endurance Test

    Speed Load
    Range
    C - 240 kPa (35 psi)
    D - 300 kPa (44 psi)
    C - 290 kPa (42 psi)
    D - 380 kPa (55 psi)
    Ave Time to Failure Pass/Fail Ave Time to Failure Pass/Fail
    120km/h (75 mph) C 36 hours 1P 1F 48 hours 1P 1F
    120km/h (75 mph) D 32 hours 0P 1F 35 hours 0P 1F
    140km/h (87 mph) C 15 hours 0P 2F 13 hours 0P 2F
    140km/h (87 mph) D 20 hours 0P 1F 37 hours 0P 1F


    Many of the P-metric tire failures occurred at the combination of low inflation pressure 160 kPa (23 psi) and speed of 140 km/h (87 mph). At a test speed of 120 km/h (75 mph) with an inflation pressure of 200 kPa (29 psi), 2 of the 9 P-metric tires (one B and one C Temperature rated) failed to complete the 50-hour test. Examination of the data in the P-metric Tire and LT Tire tables shows that the number of failures increased and time to failure decreased as: the test speed increased; and the inflation pressure decreased. Also in the P-metric table, the A temperatue rated tires performed better than the B rated tires, which performed better than the C rated tires.

    In Phase II Endurance Test 2, the agency tested tires with loading conditions of 100/110/115%, which are identical to the loads recommended by the tire industry for the endurance test in GTS-2000, at 180 kPa (26 psi) inflation pressure and 120 km/h (75 mph) for 50 hours. This combination of parameters for P-metric tires represents a 50 percent increase in the speed, a 50 percent increase in the duration, and up to a 15 percent increase in the load, which constitutes a more stringent test than the current endurance test in FMVSS No. 109. In Endurance Tests 1 and 3, the test loads were 100/115/125% and the test speed was 100 km/h (62 mph).

    The LT tires were tested to the same parameters as the P-metric tires, except that the inflation pressures were 25 percent under-inflated from the maximum inflation pressure for load range C and D tires. Therefore, the test inflation pressures proposed for LT load range C and D tires subjected to the endurance test are 260 kPa (38 psi) and 340 kPa (50 psi), respectively. The load range E tires were tested at 450 kPa (65psi).

    In the Phase II Endurance tests of P-metric tires, 2 (A temperature rated) tire models of the 8 tires models completed the tests without any failures in their 5 samples. The remaining tire B and C rated models experienced at least one failure in the five samples used during the test. Most of the LT tire models had one of the five tires fail a test. The most notable exception was the Bridgestone R 273 which had all five tires fail Endurance Test 3.

    NHTSA Proposed Endurance Phase II Testing

    The proposed alternative 2 endurance test requirement is more stringent than the current FMVSS Nos. 109 and 119 requirements. But these proposed conditions are not the same as those tested in the Phase I (Table II-11) or Phase II (Table II-12). The agency believes that this lower than tested stringency represents a reasonable minimum capability that all tires operating on public


    Table II-12
    Phase II Endurance Test Summary

    Brand Model UTQGS
    Temp Grade
    Endurance Test 1 Endurance Test 2 Endurance Test 3
    P-Metric Tires
    Toyo Proxes H4 A 5P* 0F# 5P 0F 5P 0F
    Uniroyal Tiger Paw Touring HR A 5P 0F 5P 0F 5P 0F
    Dunlop D65 Touring B 5P 0F 3P 2F 5P 0F
    Goodyear Regatta 2 B 5P 0F 1P 4F 0P 5F
    BF Goodrich Cientra Plus B 5P 0F 3P 2F 4P 1F
    Cooper LifeLiner Classic II B 1P 4F 2P 3F 1P 4F
    Firestone Wilderness AT C 5P 0F 3P 2F 1P 4F
    Michelin XH4 B 5P 0F 1P 4F 1P 4F
    LT Tires  
    Brand Model UTQGS
    Temp Grade
    Endurance Test 1 Endurance Test 2 Endurance Test 3
    Pirelli Scorpion A/T C 5P 0F 4P 1F 4P 1F
    Yokohama GeoLandar H/T C 4P 1F 4P 1F 5P 0F
    Goodyear Wrangler HT E 4P 1F 4P 1F 4P 1F
    Bridgestone R273 SWP 11 E 4P 1F 4P 1F 0P 5F

    Phase II Test Conditions
    Endurance Test 1 - 100/115/125% Load, 100 km/h, P-metric 180 kPa (26 psi), LT 75% of Max Inflation
    Endurance Test 2 - 100/110/115% Load, 120 km/h, P-metric 180 kPa (26 psi), LT 75% of Max Inflation
    Endurance Test 3 - 100/115/125% Load, 120 km/h, P-metric 180 kPa (26 psi), LT 75% of Max Inflation

    roads should possess. The selected inflation pressure is also set at a level well above the warning criteria of the Tire Pressure Monitoring System (TPMS). In actual use, the agency would expect properly inflated and not overloaded tires that "pass" the endurance test to be capable of withstanding sustained use at 75 mph for more than 40 hours, since this a legal interstate speed limit in nearly all states.

    Endurance Tire Test Alternatives Analysis

    The agency reviewed the Phase I and Phase II test data, and estimated the percentage of tires that would pass each of the alternatives. Table II-13 presents the percentages of tires tested that would pass each of the alternative tests.


    Table II-13
    Percent of Tires That Passed the Endurance Alternative Tests

      Phase I Tests Phase II Tests
    Alternative 1 Alternative 2 Alternative 3 Alternative 1 Alternative 2 Alternative 3
    P-metric tire % passed 100 89 56 100 75 25
    LT tires % passed 100 100 33 100 75 -0-

    All the tires easily passed the alternative 1, the RMA 2000 endurance test, which proved this alternative did not distinguish different tire performance levels. Conversely, very few tires passed alternative 3. The initial NHTSA research test parameters were deemed to be too stringent. The agency believes alternative 2 establishes a reasonable minimum performance requirement that is appropriate for safety standards of motor vehicle equipment.


    C. Low Pressure - Endurance Test / Low Pressure - High Speed Test

    Currently, there are no high speed, low pressure test requirements or low pressure, endurance test requirements in the existing FMVSS Nos. 109 &119. NHTSA conducted two tests to evaluate tire performance at the low inflation threshold level being proposed for Tire Pressure Monitoring Systems (TPMS) for light vehicles.

    The TREAD Act requires that light vehicles be equipped with a TPMS, effective November 1, 2003, to indicate to the driver when any of the tires are significantly under-inflated. When vehicles are equipped with a TPMS, the agency believes that some drivers may be less likely to check their tire pressures until the warning lamp is illuminated. As a result, the agency proposed, in the TPMS rulemaking, to establish a low pressure threshold at which the low pressure warning light must be activated. The agency believes that the new upgraded tire standard should include a linkage with the proposed requirements of the TPMS standard. The TPMS standard would allow each vehicle manufacturer to establish the level of under-inflation [The agency proposed two alternatives of 80%-75% of the recommended cold inflation pressure with a minimum of 140 kPa (20 psi)] at which the low inflation pressure warning lamp would be illuminated.

    Low Pressure Endurance Test (Alternative 1)

    This test is predicated upon the notion that a low pressure test would be most appropriate on tires that have completed the endurance test because a significantly underinflated condition for a tire is more likely to occur in a tire after several weeks of natural air pressure loss or due to a slow leak. The agency conducted 90 minute low pressure endurance test at 140 kPa (20 psi) inflation pressure, at a speed of 120 km/h (75 mph) and 100% load on the tires (2 samples of each of the 12 brands) that passed the endurance test. Similar tests were performed using the LT tires at 58 percent of their maximum sidewall inflation pressure. These low threshold values were selected based on the lowest inflation pressure at which a tire load is provided by the tire industry standardizing bodies. The results indicate that all 24 tires tested completed the test without failure.

    This test provides an extra safeguard to ensure that tires which were able to successfully complete the endurance testing can also complete an additional 90 minute test at low inflation pressure. The agency believes that this test would establish some minimum safeguard for low inflation pressure operation for a short duration. Thus, when a driver receives the TPMS warning, there is still time for him/her to take corrective action before the tire fails, assuming that the tire is not experiencing a very rapid loss of pressure.

    Low Pressure High Speed Test (Alternative 2)

    This proposed test provides a linkage between the proposed TPMS requirements and the proposed high speed test. While it would evaluate tires at a lower load than that specified in the Low Pressure Endurance test, the Low Pressure High Speed test would ensure that a manufacturer designs a tire so that its high speed performance would comply with the test requirements not only at recommended inflation pressure, but also at a low inflation pressure.

    The 90 minute Low Pressure High Speed Test is conducted in three 30 minute speed steps of 140, 150, and 160 km/h (87, 93, and 99 mph) at 67% load and 140 kPa (20 psi) inflation pressure. A tire is considered to have passed the test if it completes the 30-minute step at 160 km/h (100 mph). NHTSA recently conducted testing of the above parameters on 8 tire brands. The results indicate that 30 percent of tires with an "S" speed rating, 63 percent of tires with an "R" speed rating, and 75 percent of tires with a "Q" speed rating would not pass this test. However, 70 percent of tires with an "S" speed rating, and all "T" and "H" rated tires would have completed the test. The agency estimates that about 30 percent of all light vehicle tires currently on the market would fail this test.

    The agency believes that this test would ensure that the tire manufacturer designs a tire so that its high speed performance would comply with high speed requirements at both the recommended inflation pressure and also at a low inflation pressure.


    D. Road Hazard Impact Test Requirements

    Both FMVSS No 109 & 119 have a tire strength requirement, which states, "each tire will have a minimum breaking energy." The test is conducted by forcing a 19mm (3/4 inch) diameter cylindrical steel plunger with a hemispherical end perpendicularly into the tread. The breaking energy is determined by means of the following formula: W = [(FxP)/2] where W=Energy, F=Force, and P=Penetration. This test was relevant thirty years ago when the standard was issued, and all tires were bias ply. With practically all tires being radials now, it is essentially a non-test because the plunger bottoms out on the rim before penetration occurs.

    The agency is proposing to update the strength test by adopting the SAE J1981, Road Hazard Impact Test, as a substitute for the strength (plunger) test. The SAE J1981 test is a dynamic procedure that uses a pendulum to strike the tire. The proposed minimum performance requirements are based on the current strength test values in FMVSS Nos. 109 and 119. For standard load P-metric tires, the proposed breaking energy, W is 294 joules (2600 inch-pounds) for tires with a width of 160 mm or greater, and 220 joules (1950 inch-pounds) for tires with a width less than 160 mm.

    The proposed breaking energy values for LT tires are derived from the current requirements in FMVSS No. 119 and are as follows: 362 joules (3200 inch-pounds) for load range C tires; 515 joules (4550 inch-pounds) for load range D tires; and 577 joules (5100 inch-pounds) for load range E tires.

    The agency is conducting tests on a sample of tires to determine the suitability of the test and current compliance with this test. These tests have not been completed yet.


    E. Bead Unseating Test Requirements

    The current resistance-to-bead unseating test is designed to evaluate how well the tire bead remains on the rim during turning maneuvers. The bead unseating test forces currently used in FMVSS No. 109 are based on bias ply tires and are typically not stringent enough for radial tires. For this reason, the industry, in GTS-2000, recommended that the test be deleted from the standard because radial tires are able to satisfy the test easily. Results from the agency's 1997-1998 dynamic rollover testing, however, provide a strong rationale for seeking to replace, rather than delete, the bead unseating requirement in FMVSS No. 109. In this testing, vehicles experienced bead unseating on three of twelve test vehicles. This bead unseating occurred during severe maneuvers. Such bead unseating in the real world poses serious safety concerns. Therefore, NHTSA proposes to replace the current bead unseating test in FMVSS No. 109 with a more stringent and appropriate test developed by Toyota, called the Toyota Air Loss Test.

    The Toyota Air Loss Test was developed by Toyota to evaluate tubeless tire performance. While the current FMVSS No. 109 bead unseating test applies force in the middle of the sidewall, the Toyota Air Loss Test applies force at the tire tread surface edge. The tire tread surface edge is the actual location at which force occurs due to tire/road interface during severe vehicle maneuvers. There are two general methods for conducting the Toyota test:

    NHTSA proposes to adopt the Air Loss Bench Test Method because the test is independent of vehicle type, although the agency seeks comments on both methods. This test method uses a force of 2.1 times the maximum tire load labeled on the sidewall, which is applied at the tread surface. The wedge-shaped device applies a force on the tire, laterally, at the tread surface. This force simulates the lateral force at the tread surface, which a tire experiences during severe maneuvers that could produce bead unseating of the tire.

    Toyota has provided a description of the test apparatus and the test method used for the bench test. The apparatus includes a tire mounting hub that positions the tire vertically at an angle 5 degrees to the vertical axis, a hydraulic-powered sliding wedge-shaped block that applies force to the tire tread surface, and a control panel that includes controls for monitoring and regulating the tire's inflation pressure and a load indicator. The test procedure recommends inflating the tire to an initial inflation pressure of maximum (design) inflation pressure plus 50 kPa. Therefore, the initial inflation pressure for a P205/65R15 standard load tire (rated at a load limit of 635 kg ( 1400 lbs.) at an inflation pressure of 240 kPa) is 290 kPa. Force, using the wedge-shaped block, is applied at a rate of 200 millimeters per second (mm/s) to a properly mounted tire and is maintained for a duration of 20 seconds. A tire successfully completes the test if there is no [measured] air loss.

    Recently the agency has conducted research using the Toyota test apparatus and test to verify that the recommended force levels are appropriate for a minimum safety requirement. Based on the agency's evaluation of this bead unseating method, it proposes 180 kPa for an inflation pressure in P-metric tires and 2.0 times the maximum tire load labeled on the tire sidewall for an application load appropriate for a minimum safety standard. The test inflation pressure for other tires are identical to the inflation pressures used in the proposed endurance test, which specifies 260 kPa, 340 kPa, and 410 kPa for LT tires load range C, D, and E, respectively

    The agency has not completed testing a sample of tires to determine the suitability of the test and current compliance with this test.


    F. Accelerated Aging Test Requirements

    During the Firestone hearings and the passage of the TREAD Act, some members of Congress expressed the view that there is a need for an aging test to be conducted on light vehicle tires. The agency tentatively concludes that we agree there is a need for an aging test in the proposed light vehicle tire standard because most tire failures occur at mileages well beyond 2,720 kilometers (1,700 miles) to which tires are exposed in the current FMVSS No. 109 Endurance Test. The proposed endurance test, while accumulating 4,800 kilometers (3,000 miles) on a tire, still will not expose the tire to the type of environmental factors experienced on vehicles at 40,000 kilometers or beyond.

    There are no current requirements for accelerated tire aging in FMVSS Nos. 109 and 119, and no industry-wide recommended practice for accelerating the aging of tires exists. The agency, therefore, proposes the following three alternative tests for consideration and comment: 1) Adhesion Test, 2) Michelin's Long-term Durability Endurance Test, and 3) Oven Aging. NHTSA envisions adopting one of these alternative tests. These tests are discussed in detail below:

    Adhesion (Peel) Test (Alternative 1)

    The Adhesion (peel) test is based on the American Society for Testing and Materials (ASTM) 413-98, Standard Test Methods for Rubber Property - Adhesion to Flexible Substrate. The Adhesion (peel) test evaluates a tire's resistance to belt separation by determining the adhesion strength, measured by force per unit width, required to separate a rubber layer from a flexible

    substrate such as fabric, fiber, wire, or sheet metal. The adhesion levels of a tire will vary based on rubber formulations, the different materials used to construct a tire, and the curing process.

    The test methods in ASTM D 413-98 cover the determination of adhesion strength between plies of fabric bonded with rubber or adhesion of the rubber layer in articles made from rubber attached to other material. They are applicable only when the adhered surfaces (adjacent tire belts) are approximately plane or uniformly circular in belting, hose, tire carcasses, or rubber-covered sheet metal.

    The test methods described in this ASTM standard determine the force per unit (pounds per inch) width required to separate a rubber layer from a flexible substrate such as fabric. There are two general methods for this test:

    Due to the greater accuracy of the tension testing machine, the agency proposes to utilize the Machine Method to apply a peel strength requirement for new tires after they complete a 24-hour test with parameters similar to the proposed 40-hour endurance test. The parameters for this 24-hour test are as follows:

    For a tire to satisfy the proposed test, it must exhibit a minimum peel strength of 30 pounds per inch at the end of the 24-hour test period. NHTSA tentatively selected this value based on Ford and Firestone data.

    Michelin's Long-term Durability Endurance test (Alternative 2)

    The alternative 2 accelerated aging method being considered by the agency is based on a method utilized by Michelin. This method uses a road wheel endurance test with the following controlled parameters to simulate testing the tire to tread wear-out: load, inflation pressure, speed, and duration. The test tire is inflated with a 50/50 blend of O 2/N 2 and run for between 250 - 350 hours. Michelin has estimated that this test correlates with approximately one year of real-world tire durability for every 100 hours of testing. For example, a 250-hour test correlates with approximately 2 years of real world field operation.

    The Michelin long-term durability endurance test research findings were initially published at a 1985 International Rubber Conference. The research pointed toward four factors as comprising the best balance to achieve good/accurate correlation with field data - 1) filling gas; 2) test speed; 3) test temperature; and 4) tire load. Michelin discovered that if any one or several of these factors was disproportionately altered in an attempt to make the test more stringent or to complete the test faster, the result was a test failure condition that displayed an abnormal failure mode and did not reflect actual field conditions. Therefore, temperature and mechanical stress must be controlled to avoid failures that are not representative of real-world conditions.

    The following test parameter values have been developed, through a multi-year research program at Michelin, to minimize variance from field test end conditions and minimize test hours:

    These values were chosen to make each test parameter proportionally severe without exceeding a critical temperature which, in turn, would lead to failure conditions unrepresentative of real-world conditions/ actual field conditions.

    The agency has not completed testing to determine current compliance with these tests.


    G. Tire Variability Analysis

    The agency examined tire variability using the PHASE II data from the Standards Testing Laboratories, Inc. Five tires of the same brand/model were tested in each of the endurance and high-speed tests.

    A. Variability in the same production run (production lot), same brand/model Endurance Tests P-Metric Tire Results

    By design, endurance tests #1, #2 and #3 represent a progressively increasing scale of stringency. (see the footnote to Table II-12. It would be expected that the same brand/model tires would accumulate more failures moving from Test #1 to Test #2 to Test #3.

    - Results:     4 of 8 tire brand/model failures were inconsistent with this theory.

    4 of 8 tire brand/model failures were consistent with this theory.

    For the endurance tests, for the same brand/model, the samples of tires selected had the same serial number (i.e., same production run) from test to test with the exception of 3 tire brands having two different serial numbers in the same test or different tests. Three of the tire brand/models (Dunlop D65, Cooper Lifeliner and Michelin XH4) with failure inconsistencies had results confounded by a second serial number representing a different production run. The 4th tire with failure inconsistencies (B.F. Goodrich) had the same serial number tire throughout all endurance tests. [For the purposes of this analysis, serial number (SN) designates a different production run from the same or different assembly plant for a particular tire brand/model.]

    These results appear to indicate tire-to-tire variability within the same production run and, as expected, variability across different production runs. Factors that might account for variability include the manual assembly operations used at various points in the construction of a tire (e.g., installation of belts). There could also be rubber compound variations.

    B. Variability in the same production run (production lot), same brand/model

    High Speed Test P-Metric Tire Results

    Based on the performance parameters, the high speed tests were re-ordered from "least" stringent to "most" stringent with the result; #2, #4, #1 and #3. (Designated test numbers - see the footnote to Table II-8 for a description of the tests). Test #1 is more stringent than Test #2 because lower tire pressure is a more stringent condition. The design of Test #3 is equal to or more stringent than Test #1 based on the Initial Test Speed (i.e., 6 out of the 8 tires were tested above their speed rating and 2 tires were tested at their speed rating). Finally, the design of Test #4 is slightly more stringent than Test #2 because of a 5 percent higher loading.

    It would be expected that the same brand/model tires would accumulate more failures moving from Test # 2 to Test # 4 to Test # 1 to Test# 3. Similar to the endurance test series above, there were tire failures inconsistent with the above theory:

    C. Tire Failures by Test Procedure for the P-Metric Tires

    The following Tables (II-14 and II-15) show that; (1) the endurance tests are linearly increasing in stringency based on the number of tire failures, (2) the high speed tests results are not linearly increasing in stringency and (3) a higher percentage of tires failed the high speed tests than the endurance tests for the P-metric tires tested.


    Table II-14
    Number of Tire Failures for the Endurance Test Procedure

    Endurance Tests #1 #2 #3 Totals
    Design Stringency #1 ALeast@ #2 #3 AMost@  
    No. of Tire Failures/Total No. of Tires Tested 4/40 17/40 18/40 39/120
    Percent Tire Failures       32.5 %


    Table II-15
    Number of Tire Failures for the High Speed Test Procedure

    High Speed Tests #1 #2 #3 #4 Totals
    Design Stringency #2 ALeast@ #4 #1 #3 AMost@  
    No. of Tire Failures/Total No. of Tires Tested 21/40 8/40 23/40 19/40 71/160
    Percent Tire Failures         44.4 %

    The "most" stringent high speed test produced fewer failures than the "least" stringent high speed test. This inconsistent result appears to be related to tire-to-tire variability.

    The Dunlop D65 tire had zero failures in the more stringent high speed test series, but had one failure in the lesser stringent endurance Test #2. This clear inconsistency may be related to serial number or production run variability as Dunlop D65 endurance Test #2 used the same serial number throughout (C363200) but the Dunlop D65 high speed tests involved 8 different serial numbers excluding C363200. For the Dunlop D65, there was production run to production run variation. [Keep in mind the previous result, for 15 out of 16 of the high speed tests the PASS or FAIL outcome was consistent despite various serial numbers being involved.]

    The Uniroyal Tiger Paw Touring tire had zero failures in either the endurance tests or the high speed tests. This implies low tire-to-tire variability. All Uniroyal tires for both test series came from the same production run [i.e., same TIN (tire identification number) BEXOEM9U0501]. Table II-12 was constructed to test the hypothesis that the number of tire failures is proportional to the number of differing serial numbers in the tire test sample.

    There appears to be a poor correlation (qualitatively speaking) between the number of brand/model failures and the number of different serial numbered tires used to represent that brand/model in the test procedures. "Production lot" to "production lot" differences don't appear to be a big factor in this data set (i.e., the high speed tests had the greatest number of different serial numbers, but previous analysis showed that 15 out of 16 were consistent in PASS/FAIL outcome.) Therefore, given the consistency among production runs in this case, the variation appears to be due to tire-to-tire variation and test condition differences (endurance vs. high speed). The agency believes that the variation in the test equipment would be minimal.


    Table II-16
    Tire Failures by Number of Unique Serial Numbers by Brand/Model

    Brand/Model No. of Endurance
    Test Failures
    No. of High Speed
    Test Failures
    Total Failures Endurance Test,
    No. of Unique SN s
    High Speed Test,
    No. of Unique SNs
    Uniroyal Tiger Paw 0 0 0 1 1
    Toyo Proxes H4 0 1 1 1 6
    Dunlop D65 Touring 2 0 2 2 8
    Cooper Lifeliner Classic II 11* 3 14 2 5
    B.F. Goodrich Cientra 3 18 21 1 3
    Firestone Wilderness AT 6 15 21 1 4
    Michelin XH4 8 15 23 2 5
    Goodyear Regatta 2 9 19 28 1 6
    Total 39 71 110 11 38

    NOTE: Column 5 serial numbers are included in Column 6 serial numbers, generally. So, Column 6 represents the total number of different serial numbers or production runs involved. It is unknown if the different production runs occurred at the same plant (same personnel) or at different plants (different assembly personnel).

    Table II-16 shows that the Cooper Lifeliner Classic II tire had 11 failures at the less stringent endurance test series, but only 3 failures in the more stringent high speed test series. This is a clear inconsistency related to tire-to-tire variability. The less stringent test series involved only 2 unique serial numbered Cooper tires, yet the higher stringency tests involved 5 unique serial numbered Cooper tires.

    D. LT Tire Test Data

    Tables II-17 and II-18 summarize the endurance and high-speed test results for LT tires.


    Table II-17
    Endurance Test Results -LT Tires

    Endurance Tests        
    Test Number #1 #2 #3  
    Design Stringency #1 ALeast@ #2 #3 AMost@  
    No. of Tire Failures/No. of Tires Tested 3/20 4/20 7/20 14/60
    Percent Failures       23.22 %


    Table II-18
    High Speed Test Results - LT Tires

    High Speed Tests          
    Test Number #1 #2 #3 #4 Totals
    Design Stringency #2 ALeast@ #4 #1 #3 AMost@  
    No. of Tire Failures/No. of Tires Tested 0/20 1/20 0/20 3/20 4/80
    Percent Failures         5 %

    Conclusions for LT Tires from Tables II-17 and II-18

    1. For the LT tires, the number of tire failures increased as expected in a similar manner to the P-metric tire data for the endurance tests.

    2. For LT tires, the number of tire failures increased inconsistently as the tests increased in stringency. Results were mixed. This result is similar to that for the P-metric tires.

    3. The high speed tests for the truck tires were less stringent than the endurance tests which is the opposite of the P-metric tire results.

    4. Thirteen unique serial numbered truck tires were used for the endurance tests and 32 unique serial numbers were used for the high speed tests.

    5. Overall, the Phase II tire test procedures were relatively benign for the truck tires.


    E. Repeatability

    Repeatability measures the percent variation across one tire brand/model for each unique test procedure. Table II-19 shows the repeatability range across the 8 tire brands tested for both test procedures. As shown in Table II-19, the endurance tests had a much wider range of variability than the high speed tests.

    With the finely instrumented test dummies used in NHTSA crash testing, the agency typically expects coefficients of variation of less than +/- 10 percent. When the vehicle is added to the test, some of the specific variations increase into the +/- 20 percent range. The agency is not accustomed to seeing variability as high as those seen in the endurance test for some of the tire brand/models.


    Table II-19
    Endurance and High Speed Test Procedure Variability
    based on "Test Stand Time*"
    P-metric Tires
    (n=5 tires)

    Tire Brand/Model Endur. #1 Endur. #2 Endur. #3 High Speed #1 High Speed #2 High Speed #3 High Speed #4
    Toyo Proxes H4 0** 0 0 5.6 0 0 0
    Uniroyal Tiger Paw 0 0 0 0 0 0 0
    Dunlop D65 0 8.7 0 0 0 0 0
    Goodyear Regatta 2 0 30.7 36 3.4 27.3 10.9 4.2
    B.F. Goodrich Cientra Plus 0 11.6 16.2 10.0 9.5 16.2 28.2
    Cooper Lifeliner Classic II 0 27.7 33.1 5.1 2.0 0 0
    Firestone Wilderness AT 0 41.8 20.9 7.5 7.1 12.5 0
    Michelin XH4 0 49.2 44.2 7.6 2.0 6.5 0


    Table II-20
    Endurance and High Speed Test Procedure Variability
    based on "Test Stand Time*"
    LT-Tires
    (n=5 tires)

    Tire Brand/Model Endur. #1 Endur. #2 Endur. #3 High Speed #1 High Speed #2 High Speed #3 High Speed #4
    Pirelli Scorpion 0** 16.2 24.1 0 0 0 0
    Yokohama Geo-Landar 35.2 10.9 0 0 0 0 2.2
    Goodyear Wrangler GT 0 0 13.7 0 0 0 0
    Bridgestone SWP II 4.2 0.9 16.4 0 0 2.2 0

    Conclusion: In Table II-20, the LT tires exhibited less variability. Also, the LT tires had a narrower repeatability range compared to the P-metric tires for both test procedures.

    Table II-21 compares the P-metric and LT tire failure rates for both test procedures. The P-metric tires had higher failure rates for both the given test procedures compared to the LT tires tested. The high speed tests are more stringent for the P-metric tries whereas the high speed tests, are less stringent for LT tires.


    Table II-21
    Summary of The Percent of Tire Failures by Tire Type
    Based on the Endurance Test Series and the High Speed Test Series

    Tire Type/Test Type No. of Failures/Total
    Number
    Percent Failures
    P-Metric Car Tire Endurance Tests 39/120 32.5 %
    P-Metric Tire High Speed Tests 71/160 44.4 %
    LT Tire Endurance Tests 14/60 23.33%
    LT Tire High Speed Tests 4 /80 5.00%