Chevrolet 1994 Lumina Owner's Manual page 191

Uniform Tire Quality
Grading
The following information relates to the
system developed by the United States
National Highway Traffic Safety
Administration which grades tires by
treadwear, traction and temperature
performance. (This applies only to
vehicles sold in the United States.)
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 norm 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 . 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, 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.
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.
These grades are molded on the sidewalls
of passenger car tires.
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