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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 Performa nce Criteria (TPC)
standards.
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 a half (1½) 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 significantl y from the norm due to
variations in driving habits, service practices and
differences in road characteri stics and climate.
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-ahea d
braking traction tests, and does not include
acceleration, cornering, hydroplaning, or peak
traction characteristics.
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 controlle d 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
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