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The grades are molded on the
sidewalls of most passenger car
tires. The Uniform Tire Quality
Grading (UTQG) system does
not apply to deep tread,
winter-type snow tires,
space-saver, or temporary use
spare tires, tires with nominal rim
diameters of 10 to 12 inches
(25 to 30 cm), or to some
limited-production tires.
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
(1.5) 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 – 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.
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. It should
be noted that the temperature
grade for this tire is established
for a tire that is properly
inflated and not overloaded.
Service and Appearance Care 5-53