(F) Tire Size : A combination of
letters and numbers define a
tire’s width, height, aspect ratio,
construction type, and service
description. The letter T as
the first character in the tire size
means the tire is for temporary
use only.
(G) TPC Spec (Tire
Performance Criteria
Specification)
: Original
equipment tires designed to
GM’s specific tire performance
criteria have a TPC specification
code molded onto the sidewall.
GM’s TPC specifications meet or
exceed all federal safety
guidelines.
Tire Size
The following illustration shows
an example of a typical
passenger vehicle tire size.
(A) Passenger (P-Metric) Tire
:
The United States version of a
metric tire sizing system. The
letter P as the first character in
the tire size means a passenger
vehicle tire engineered to
standards set by the U.S. Tire
and Rim Association.
(B) Tire Width
: The three-digit
number indicates the tire
section width in millimeters from
sidewall to sidewall.
(C) Aspect Ratio
: A two-digit
number that indicates the tire
height-to-width measurements.
For example, if the tire size
aspect ratio is 60, as shown in
item C of the illustration, it would
mean that the tire’s sidewall is
60 percent as high as it is wide.
(D) Construction Code
: A letter
code is used to indicate the type
of ply construction in the tire.
The letter R means radial ply
construction; the letter D means
diagonal or bias ply construction;
and the letter B means
belted-bias ply construction.
(E) Rim Diameter
: Diameter of
the wheel in inches.
(F) Service Description
: These
characters represent the load
range and speed rating of the
tire. The load index represents
the load carry capacity a tire is
certified to carry. The load index
can range from 1 to 279. The
speed rating is the maximum
speed a tire is certified to carry
a load. Speed ratings range
fromAtoZ.
Service and Appearance Care 5-39
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