GMC 1997 Safari Owner's Manual page 304

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
speclfed 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.
Scheduled wheel alignment and wheel balancing are not
needed. 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.