Chevrolet 2008 Colorado Owner's Manual page 328

(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) 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.
5-62
(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 70,
as shown in item C of the illustration, it would
mean that the tire's sidewall is 70 percent as high
as it is wide.
(D) Construction Code
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
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 from A to Z.
A letter code is used to
:
These characters
: