Geo 1995 Prizm Owner's Manual page 234

When It's Time for New Tires
One way to tell when
time for
new
tires is t(
check the treadwear
indicators, which will
it's
3
appear when your tires have
only 1/16 inch (1.6
mm)
or
less of tread remaining.
You need a new tire if
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.
a The tire has a bump, bulge or split.
The tire has a puncture, cut, or other damage that
can't be repaired well because of the size or location
of the damage.