Buick 1993 LeSabre Owner's Manual page 260

c :
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.
Buying New Tires
To find out what kind and size of tires you need, look at
the Tire-Loading Information label.
The tires installed on your vehicle when it was new had
a Tire Performance Criteria Specification (TPC Spec)
number on each tire's sidewall. When you get new tires,
get ones with that same TPC Spec number. That way,
your vehicle will continue to have tires that are designed
to give proper endurance, handling, speed rating,
traction, ride and other things during normal service on
your vehicle. If your tires have an all-season tread
design, the TPC number will be followed by a
"MS"
(for mud and snow).
If you ever replace your tires with those not having a
TPC Spec number, make sure they are the same size,
load range, speed rating and construction type (bias,
bias-belted or radial) as your original tires.
TREAD WEAR INDICATORS
You need a new tire if:
you can see the indicators at three 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.
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