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238 Car care
Uniform Tire Quality Grading
Quality grades can be found where applica-
ble on the tire sidewall between tread shoul-
der and maximum section width. For exam-
ple:
Treadwear 200 Traction AA Temperature
A
The following information relates to the
system developed by the United States
National Highway Traffic Safety Administra-
tion, which grades tires by treadwear, trac-
tion and temperature performance. (This
applies only to vehicles sold in the United
States.) The grades are molded on the side-
walls of most passenger car tires. The Uni-
form Tire Quality Grading system does not
apply to deep tread, winter-type snow tires,
space-saver or temporary use spare tires,
tires with nominal rim diameters of 10 to 12
inches (25 to 30 cm), or to some limited-pro-
duction tires.
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 Perfor-
mance 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 (1.5) times as well on the govern-
ment course as a tire graded 100. The rela-
tive 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 prac-
tices 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 repre-
sent the tire’s ability to stop on wet pave-
ment as measured under controlled condi-
tions on specified government test surfaces
of asphalt and concrete. A tire marked C
may have poor traction performance. Warn-
ing: 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.
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 dis-
sipate 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 temper-
ature can lead to sudden tire failure. The
grade C corresponds to a level of perfor-
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.