1994 GMC Suburban Owner's Manual - Page 311

When It's Time for New Tires TREAD WEAR INDICATORS 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 2/32 inch (1.6 mm) or less of tread remaining. You need a new tire if 0 You can see the indicators at three or more places around the tire. You can see cord or fibric showing through the tire's rubber. 0 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. 0 6-65