Pontiac 2008 Vibe Owner's Manual page 280

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
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 straight-ahead braking
traction tests, and does not include
acceleration, cornering, hydroplaning,
or peak traction characteristics.
5-66
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
⁄ ) times specified indoor laboratory test wheel. Sustained
1
2
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
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.
The temperature grade for this
: