I
ng 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,
though. It was developed
for use on your vehicle.
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.) The
grades are molded on the sidewalls of most passenger
car tires. The Uniform 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-production 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
Performance 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 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 Jn
road characteristics and climate.
6-46
d
Traction -- A, B, C
The traction grades, from highest to lowest, are A, B,
and C, and 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 (straightahead) 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.
Wheel Alignment and Tire Balance
The wheels on your vehicle were aligned and balanced
carefully at the factory
to give you the longest tire life
and best overall performance.
In most cases, you will
not need to have your wheels
aligned again. However, if
you notice unusual tire
wear or your vehicle pulling one way or the other, the
alignment may need to be reset.
If you notice your
vehicle vibrating when driving
on a smooth road, your
wheels may need to be rebalanced.
Wheel Replacement
Replace any wheel that is bent, cracked, or badly rusted
or corroded. If wheel nuts keep coming loose,
the wheel,
wheel bolts and wheel
nuts should be replaced. If the
wheel leaks air, replace
it (except some aluminum
wheels, which can sometimes be repaired). See your
GM dealer if any of these conditions exist.
Your dealer will know
the kind of wheel you need.
Each new wheel should have the same load-carrying
capacity, diameter, width, offset and be mounted the
same way as
the one it replaces.
6-47
