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
nom
due
to
variations
in driving habits, service practices
and
differences in
road characteristics and climate.
Traction
--
A,
B,
C
The traction grades, from highest to lowest,
are
A,
B,
and
C,
and
they 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
braking (straightahead) traction tests and does not
include cornering (turning) traction,
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
perfol’mance
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 inflated and not
overloaded. Excessive speed, underinflation, or
excessive loading,
either
separately or in combination,
can cause heat buildup and possible tire failure.
6-45
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