Cadillac 1998 Seville Owner's Manual page 322

Treadwear Temperature
--
A, B, C
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
--
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.
Warning: The traction grade assigned to this tire is based
on braking (straight ahead) traction tests and does not
include acceleration, cornering, hydroplaning, or peak
traction characteristics.
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, an
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.