1997 GMC Sonoma Owner's Manual - Page 285

A When It's Time for New Tires C 4UTION: Rust or dirt on a wheel, or on the parts to which it is fastened, can make wheel nuts become loose after a time. The wheel could comeoff and cause an accident. When you change a wheel, remove any rust or dirt from places where thewheel attaches to thevehicle. In an emergency, can you use a cloth or a paper towel to do this; but be sure to use scraper or wire brush later,you a if need to, to get all the rust or dirt (See off. "Changing a Flat Tire" in the Index.) You need a new tire if any of the following statements are true: 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. 0 0 You can see the indicators at three or more places around the tire. You can see cord or fabric showing through the tire's rubber. The tread or sidewall is cracked, cut or snagged deep enough to show cord or fabric. The tire has a bump, bulge or split. The tire has a puncture, cut or otherdamage that can't be repaired well because of the size or location of the damage.