Pontiac Sunbird Owner's Manual page 229

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Service & Appearance Care
Tiadwear
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 1 5 0 would
wear one and a half (1%) 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.
2 2 8
Traction-A, 6, C
The traction grades, from highest to
lowest are: A, B, and C. 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 (straight-
ahead) traction tests and does not
include cornering (turning) traction.
Temperature--A, 8, C
The temperature grades are A (the
highest), B, and C, representing the
tire's resistance to the generation of h
and its ability to dissipate heat when
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tested undercontrolled 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.