1997 Chevrolet Astro Owner's Manual - Page 302

When It's Time for New Tires 0 0 The tire has a bump, bulge or split. 0 One way to tell when it's time for new tires is to check the treadwear indicators, which will appear when your tires have only 1/16 inch (1.6 mm) or less of tread remaining. The tire has a puncture, cut or other damage that can't be repaired well because of the size or location of the damage. Buying New Tires To find out what kind and size of tires you need, look at the Certificationrnire label. The tires installed on your vehicle when it was new had a Tire Performance Criteria Specification (TPC Spec) number on each tire's sidewall. When you get new tires, get ones with that same TPC Spec number. That way your vehicle will continue to have tires that are designed to give proper endurance, handling, speed rating, traction, ride and other things during normal service on your vehicle. If your tires have an all-season tread design, the TPC number will be followed by an "MS" (for mud and snow). If you ever replace your tires with those not having a TPC Spec number, make sure they are the same size, load range, speed rating and construction type (bias, bias-belted or radial) as your original tires. You need a new tire if any of the following statements are true: You can see the indicators at three or more places around the tire. You can see cord orfabric showing through the tire's rubber. The tread or sidewall is cracked, cut or snagged deep enough to show cord or fabric. 6-46