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 speci ed 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 signi cantly 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
speci ed 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.
Service and Appearance Care 5-53
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 speci ed 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.{WARNING
The temperature grade for this
tire is established for a tire that
is properly in ated and not
overloaded. Excessive speed,
underin ation, or excessive
loading, either separately or in
combination, can cause heat
buildup and possible tire
failure.Wheel Alignment and
Tire Balance
The tires and wheels on your
vehicle were aligned and balanced
carefully at the factory to give
you the longest tire life and best
overall performance. Adjustments to
wheel alignment and tire balancing
will not be necessary on a regular
basis. However, if you notice
unusual tire wear or your vehicle
pulling to one side or the other, the
alignment might need to be
checked. If you notice your vehicle
vibrating when driving on a
smooth road, the tires and wheels
might need to be rebalanced.
See your dealer/retailer for proper
diagnosis.
5-54 Service and Appearance Care