Uniform Tire Quality Grading - Chevrolet 1999 S10 Pickup Owner's Manual

Uniform Tire Quality Grading

The following information relates to the system developed
by the United States National Highway Traffic Safety
Administration, which grades tires by treadwear, traction
and temperature performance. (This applies only to
vehicles sold in the United States.) The grades are molded
on the sidewalls of most passenger car tires. The Uniform
Tire Quality Grading system does not apply to deep tread,
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winter type snow tires, space
tires, tires with nominal rim diameters of 10 to 12 inches
(25 to 30 cm), or to some limited
While the tires available on General Motors passenger
cars and light trucks may vary with respect to these
grades, they must also conform to Federal safety
requirements and additional General Motors Tire
Performance Criteria (TPC) standards.
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 a half (1 1/2) 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
6-48
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saver or temporary use spare
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production tires.
norm due to variations in driving habits, service practices and
differences in road characteristics and climate.
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Traction AA, A, B, C
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
traction tests, and does not include acceleration,
cornering, hydroplaning, or peak traction characteristics.
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Temperature A, B, C
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 Vehicle Safety
Standard No. 109. Grades B and A represent higher levels
of performance on the laboratory test wheel than the
minimum required by law.
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