1998 Chevrolet Astro Owner's Manual - Page 310

Temperature -- A, B, C 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 wearor 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. 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 a specified indoor laboratory on test wheel. Sustained high temperature can cause the material of the tire todegenerate 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 underthe 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 that is properly inflated and not tire overloaded. Excessive speed, underinflation, or excessive loading, either separately or in combination, can cause heat buildup and possible tire failure. Wheel Replacement Replace any wheel that is bent, cracked, orbadly rusted or corroded. If wheel nuts keep coming loose, the wheel, wheel bolts and wheel nutsshould be replaced. If the wheel leaks air, replace it (except some aluminum wheels, which can sometimes be repaired). See your dealer if any of these conditions exist. 6-48