Pontiac 1993 Sunbird Owner's Manual page 179

Service & Appearance Care
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.
Uniform Tire Qualify Grading
The following information relates to the
system developed by the United States
National Highway Traffic Safety
Administration which grades tires by
treadwear, traction and temperature
performance. (This applies only to
vehicles sold in the United States.)
Treadwear
The treadwear grade is a comparative
rating based on the wear rate of the tire
when tested under controlled
conditions on a specified government
test course. For example, a tire graded
150 would wear one and a half (1%)
times as well on the government course
as a tire graded 100. The relative
performance of tires depends upon the
actual conditions of their use, however,
and may depart significantly from the
norm due to variations in driving habits,
service practices and differences in road
characteristics and climate.
Traction-A, B, C
The traction grades, from highest to
lowest are: A, B, and C. They represent
the tire's ability to stop on wet
pavement as measured under controlled
conditions on specified government test
surfaces of asphalt and concrete. A tire
marked C may have poor traction
performance.
Warning: The traction grade assigned to
this tire is based on braking (straight-
ahead) traction tests and does not
include cornering (turning) traction.
TemperatureA, B, C
The temperature grades are A (the
highest), B, and C, representing the
tire's resistance to the generation of