Tire design is the combination of general structural characteristics, materials, and tread pattern, but does include cosmetic, identifying or other minor variations among tires.
Uniform Tire Quality Grading
Quality grades can be found where applicable on the tire sidewall between tread shoulder and maximum section width. For example:
Treadwear 200 Traction AA Temperature A
Where:
y = average tread depth in mils
x = miles after break-in,
a = y intercept of regression line (reference tread depth) in mils, calculated using the method of least squares; and
b = the slope of the regression line in mils of tread depth per 1,000 miles, calculated using the method of least squares. This slope will be negative in value. The tire's wear rate is defined as the absolute value of the slope of the regression line.
Yo = average tread depth after break-in, mils.
Y1 = average tread depth after 16 circuits (approximately 6,400 miles), mils.
Xo = 0 miles (after break-in).
X1 = Total mileage of travel after 16 circuits (approximately 6,400 miles).
Note 1 to paragraph (e)(2)(ix)(C):
The ASTM F2493 standard reference test tire is the course monitoring tire (CMT). The base wear rate for the CMTs will be obtained by the Government by running the course monitoring tires for 16 circuits over the San Angelo, Texas, UTQGS test route 4 times per year, then using the average wear rate from the last 4 quarterly CMT tests for the base course wear rate calculation. Each new base course wear rate will be published in Docket No. NHTSA-2001-9395. The course monitoring tires used in a test convoy must be no more than one-year-old at the commencement of the test and must be used within four months after removal from storage.
Where:
a = y intercept of regression line (reference tread depth) for the candidate tire as determined in accordance with paragraph (e)(2)(ix)(A)(1) of this section.
b1 = the adjusted wear rate for the candidate tire as determined in accordance with paragraph (e)(2)(ix)(D) of this section.
Where:
Yo = average tread depth after break-in, mils
mc = the adjusted wear rate for the candidate tires as determined in accordance with paragraph (e)(2)(ix)(D) of this section.
Where base course wear raten = new base course wear rate, i.e., average treadwear of the last 4 quarterly course monitoring tire tests conducted by NHTSA.
Round off the percentage to the nearest lower 20-point increment.
([MICRO]a) = Measured candidate tire coefficient for asphalt + 0.50 - Measured standard tire coefficient for asphalt
[MICRO]c = Measured candidate tire coefficient for concrete + 0.35[MICRO] Measured standard tire coefficient for concrete
Table I - Test Inflation Pressures
[Maximum permissible inflation pressure for the following test]
Test type | Tires other than CT tires | CT tires | |||||||||||
psi | kPa | kPa | |||||||||||
32 | 36 | 40 | 60 | 240 | 280 | 300 | 340 | 350 | 290 | 330 | 350 | 390 | |
Treadwear test | 24 | 28 | 32 | 52 | 180 | 220 | 180 | 220 | 180 | 230 | 270 | 230 | 270 |
Temperature resistant test | 30 | 34 | 38 | 58 | 220 | 260 | 220 | 260 | 220 | 270 | 310 | 270 | 310 |
Table 2
Maximum inflation pressure | Multiplier to be used for treadwear testing | Multiplier to be used for traction testing |
Tires other than CT tires | ||
32 psi | .851 | .851 |
36 psi | .870 | .797 |
40 psi | .883 | .753 |
240 kPa | .866 | .866 |
280 kPa | .887 | .804 |
300 kPa | .866 | .866 |
340 kPa | .887 | .804 |
350 kPa | .866 | .866 |
CT tires | ||
290 kPa | .866 | .866 |
330 kPa | .887 | .804 |
305 kPa | .866 | .866 |
390 kPa | .887 | .804 |
Table 2A
Tire size designation | Temp resistance | Traction | Treadwear | ||||
Max pressure | Max pressure | ||||||
32 | 36 | 40 | 32 | 36 | 40 | ||
145/70 R13 | 615 | 650 | 685 | 523 | 523 | 553 | 582 |
155/70 R13 | 705 | 740 | 780 | 599 | 599 | 629 | 663 |
165/70 R13 | 795 | 835 | 880 | 676 | 676 | 710 | 748 |
175/70 R13 | 890 | 935 | 980 | 757 | 757 | 795 | 833 |
185/70 R13 | 990 | 1040 | 1090 | 842 | 842 | 884 | 926 |
195/70 R13 | 1100 | 1155 | 1210 | 935 | 935 | 982 | 1029 |
155/70 R14 | 740 | 780 | 815 | 629 | 629 | 663 | 693 |
175/70 R14 | 925 | 975 | 1025 | 786 | 786 | 829 | 871 |
185/70 R14 | 1045 | 1100 | 1155 | 888 | 888 | 935 | 982 |
195/70 R14 | 1155 | 1220 | 1280 | 982 | 982 | 1037 | 1088 |
155/70 R15 | 770 | 810 | 850 | 655 | 655 | 689 | 723 |
175/70 R15 | 990 | 1040 | 1090 | 842 | 842 | 884 | 927 |
185/70 R15 | 1100 | 1155 | 1210 | 935 | 935 | 982 | 1029 |
5.60-13 | 725 | 810 | 880 | 616 | 616 | 689 | 748 |
5.20-14 | 695 | 785 | 855 | 591 | 591 | 667 | 727 |
165-15 | 915 | 1,015 | 1,105 | 779 | 779 | 863 | 939 |
185/60 R 13 | 845 | 915 | 980 | 719 | 719 | 778 | 833 |
Figure 2 - [Part I] - DOT QUALITY GRADES
Treadwear
TRACTION AA A B C
TEMPERATURE A B C
(Part II) All Passenger Car Tires Must Conform to Federal Safety Requirements in Addition to These Grades
Treadwear
The treadwear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test course. For example, a tire graded 150 would wear one and one-half (11/2) times as well on the government course as a tire graded 100. The relative performance of tires depends upon the actual conditions of their use, however, and may depart significantly from the norm due to variations in driving habits, service practices and differences in road characteristics and climate.
Traction
The traction grades, from highest to lowest, are AA, A, B, and C. Those grades represent the tire's ability to stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete. A tire marked C may have poor traction performance. Warning: The traction grade assigned to this tire is based on straight-ahead braking traction tests, and does not include acceleration, cornering, hydroplaning, or peak traction characteristics.
Temperature
The temperature grades are A (the highest), B, and C, representing the tire's resistance to the generation of heat and its ability to dissipate heat when tested under controlled conditions on a specified indoor laboratory test wheel. Sustained high temperature can cause the material of the tire to degenerate and reduce tire life, and excessive temperature can lead to sudden tire failure. The grade C corresponds to a level of performance which all passenger car tires must meet under the Federal Motor Safety Standard No. 109. Grades B and A represent higher levels of performance on the laboratory test wheel than the minimum required by law. Warning: The temperature grade for this tire is established for a tire that is properly inflated and not overloaded. Excessive speed, underinflation, or excessive loading, either separately or in combination, can cause heat buildup and possible tire failure.
Appendix A - Treadwear Test Course and Driving Procedures
Introduction. The test course consists of three loops of a total of 400 miles in the geographical vicinity of Goodfellow AFB, San Angelo, Tex.
The first loop runs south 143 miles through the cities of Eldorado, Sonora, and Juno, Tex. to the Camp Hudson Historical Marker, and returns by the same route.
The second loop runs east over Farm and Ranch Roads (FM) and returns to its starting point.
The third loop runs northwest to Water Valley, northeast toward Robert Lee and returns via Texas 208 to the vicinity of Goodfellow AFB.
Route. The route is shown in Figure 3. The table identifies key points by number. These numbers are encircled in Figure 3 and in parentheses in the descriptive material that follows.
Southern Loop. The course begins at the intersection (1) of Ft. McKavitt Road and Paint Rock Road (FM388) at the northwest corner of Goodfellow AFB. Drive east via FM 388 to junction with Loop Road 306 (2). Turn right onto Loop Road 306 and proceed south to junction with US277 (3). Turn onto US277 and proceed south through Eldorado and Sonora (4), continuing on US277 to junction with FM189 (5). Turn right onto FM189 and proceed to junction with Texas 163 (6). Turn left onto Texas 163, and at the option of the manufacturer:
Eastern Loop. From junction of Loop Road 306 and FM388 (2), make right turn onto FM388 and drive east to junction with FM2334 (13). Turn right onto FM2334 and proceed south across FM765 (14) to junction of FM2334 and US87 (15). For convoys that originate at Goodfellow AFB, make U-turn and return to junction of FM388 and Loop Road 306 (2) by the same route. For convoys that do not originate at Goodfellow AFB, upon reaching junction of FM2334 and US87 (15), make U-Turn and continue north on FM2334 past the intersection with FM388 to Veribest Cotton Gin, a distance of 1.8 miles beyond the intersection. Make U-turn and return to junction of FM2334 and FM388. Turn right onto FM388, proceed west to junction FM388 and Loop Road 306.
Northwestern Loop. From junction of Loop Road 306 and FM388 (2), make right turn onto Loop Road 306. Proceed onto US277, to junction with FM2105 (8). Turn left onto FM2105 and proceed west to junction with US87 (10). Turn right on US87 and proceed northwest to the junction with FM2034 near the town of Water Valley (11). Turn right onto FM2034 and proceed north to Texas 208 (12). Turn right onto Texas 208 and proceed south to junction with FM2105 (9). Turn left onto FM2105 and proceed east to junction with US277 (8). Turn right onto US277 and proceed south onto Loop Road 306 to junction with FM388 (2). For convoys that originate at Goodfellow AFB, turn right onto FM388 and proceed to starting point at junction of Ft. McKavitt Road and FM388 (1). For convoys that do not originate at Goodfellow AFB, do not turn right onto FM388 but continue south on Loop Road 306.
Alternate Route When FM 189 and Texas 163 are Closed. This alternate test course route consists of a Modified Southern Loop, the Eastern Loop and Northwestern Loop described above, and a Modified Northwestern Loop.
Modified Southern Loop. The course begins at the intersection (1) of Ft. McKavitt Road and Paint Rock Road (FM 388) at the northwest corner of Goodfellow AFB. Drive east via FM 388 to junction with Loop Road 306 (2). Turn right onto Loop Road 306 and proceed south to junction with US 277 (3). Turn onto US 277 and proceed south through Eldorado and Sonora (4), continuing on US 277 approximately 5.5 miles (from traffic light at separation of US 277 and Loop 467) to picnic area on right. Reverse route at this location and proceed north to junction of Loop 306 and FM 388 (2).
Eastern Loop and Northwestern Loop. From junction of Loop Road 306 and FM 388 (2), complete the Eastern Loop, the Northwestern Loop, and then, from junction of Loop Road 306 and FM 388 (2), repeat the Eastern Loop.
Modified Northwestern Loop. Proceed north on Northwestern Loop as normal until reaching the intersection of FM 2105 and Texas 208 and turn right onto Texas 208. Proceed on Texas 208 until the intersection with FM 2034. Turn left onto FM 2034 and continue on FM 2034 to the intersection with US 87. Turn left onto US 87. At the intersection of US 87 and FM 2105 turn left onto FM 2105 and proceed to the intersection with US 277. Turn right onto US 277 and proceed to the intersection of Loop Road 306 and FM 388 (2).
Repeat Eastern Loop. Turn left onto FM 388 and repeat the Eastern Loop. For convoys that originate at Goodfellow AFB, continue on FM 388 and proceed to starting point at junction of Ft. McKavitt Road and FM 388 (1). For convoys that do not originate at Goodfellow AFB, turn left onto Loop Road 306.
Driving instructions. The drivers shall run at posted speed limits throughout the course unless an unsafe condition arises. If such condition arises, the speed should be reduced to the maximum safe operating speed.
Braking Procedures at STOP signs. There are a number of intersections at which stops are required. At each of these intersections a series of signs is placed in a fixed order at follows:
Sign Legend
Highway Intersection 1000 (or 2000) Feet
STOP AHEAD
Junction XXX
Direction Sign (Mereta')
STOP or YIELD
Procedures.
Appendix B - Traction Skid Pads
Two skid pads have been laid on an unused runway and taxi strip on Goodfellow AFB. Their location is shown in Figure 4.
The asphalt skid pad is 600 ft. * 60 ft. and is shown in black on the runway in Figure 4. The pad is approached from either end by a 75 ft. ramp followed by 100 ft. of level pavement. This arrangement permits the skid trailers to stabilize before reaching the test area. The approaches are shown on the figure by the hash-marked area.
The concrete pad is 600 ft. * 48 ft. and is on the taxi strip. The approaches to the concrete pad are of the same design as those for the asphalt pads.
A two lane asphalt road has been built to connect the runway and taxi strip. The road is parallel to the northeast-southwest runway at a distance of 100 ft. The curves have super-elevation to permit safe exit from the runway at operating speeds.
Appendix C - Method of Least Squares
The method of least squares is a method of calculation by which it is possible to obtain a reliable estimate of a true physical relationship from a set of data which involve random error. The method may be used to establish a regression line that minimizes the sum of the squares of the deviations of the measured data points from the line. The regression line is consequently described as the line of "best fit" to the data points. It is described in terms of its slope and its "y" intercept.
The graph in Figure 5 depicts a regression line calculated using the least squares method from data collected from a hypothetical treadwear test of 6,400 miles, with tread depth measurements made at every 500 miles.
In this graph, xj,yj (j = 0, 1, . . ;. 8) are the individual data points representing the tread depth measurements (the overall average for the tire with 6 measurements in each tire groove) at the beginning of the test (after break-in) and at the end of each 800-mile segment of the test.
The absolute value of the slope of the regression line is an expression of the mils of tread worn per 1,000 miles, and is calculated by the following formula:
The "y" intercept of the regression line (a) in mils is calculated by the following formula:
Appendix D - User Fees
49 C.F.R. §575.104
For Federal Register citations affecting §575.104, see the List of CFR Sections Affected, which appears in the Finding Aids section of the printed volume and at www.fdsys.gov.