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261Car 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.
WARNING
Mixing tires could cause you to lose
control while driving. If you mix tires of
different sizes or types (radial and bias-
belted tires), the vehicle may not handle
properly, and you could have a crash.
Using tires of different sizes may also
cause damage to your vehicle. Be sure to
use the same size and type tires on all
wheels. It’s all right to drive with your
compact spare temporarily, it was devel-
oped for use on your vehicle. See
“Compact spare” on page 270.
WARNING
If you use bias-ply tires on your vehicle,
the wheel rim flanges could develop
cracks after many miles of driving. A tire
and/or wheel could fail suddenly, causing
a crash. Use only radial-ply tires with the
wheels on your vehicle.
93U SM 06.book Page 261 Friday, February 18, 2005 1:15 PM