1997 Buick Regal Owner's Manual - Page 318

When &)sT h e for New Tires One way to tell'when it's time fornew tires is to check the treadwear indicators, which will appear whenyour tires have only 1/16 inch (1.6 mm) or less of tread remaining. Rust or dirton a wheel, or on the parts to which it is fastened, canmake wheel nuts become loose after a time. The wheel could come and cause off an accident. When you change a wheel, remove any rust or dirt from places where the wheel attaches to thevehicle. In anemergency, you can but use a cloth or a paper towel to do this; be sure touse a scraper orwire brush later,if you need to, to get all therust ordirt off. (See "Changing a Flat Tire" in theIndex.) You need a new tire if any of the following statements are true: 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. 0 6-42