Chevrolet 1998 Tracker Owner's Manual page 280

When It's Time for New Tires
Kust 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 come off and cause
an accident. When you change a wheel, remove
any rust or dirt from places where the wheel
attaches to the vehicle. In an emergency, you can
use a cloth or a paper towel to do this; but be
sure to use a scraper or wire brush later, if you
need to, to get all the rust or dirt off. (See
"Changing a Flat Tire" in the Index.)
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.
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
The tread or sidewall is cracked, cut or snagged
The tire has a bump, bulge or split.
0
The tire has a puncture, cut or other damage that
deep enough to show cord or fabric.
can't be repaired well because of the size or location
of the damage.