Chevrolet 1994 Astro Passenger Owner's Manual page 270

Temperature
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A, By 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.
These grades are molded on the sidewalls of passenger car tires.
While the tires available as standard or optional equipment on General
Motors vehicles may vary with respect to these grades, all such tires meet
General Motors performance standards and have been approved
for use on
General Motors vehicles. All passenger type (P Metric) tires must conform
to Federal safety requirements in addition to these grades.
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. 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.