Cadillac SRX Owner's Manual page 306

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.
The following is an example of a
typical passenger vehicle
tire size.
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.
The three-digit
number indicates the tire section
width in millimeters from
sidewall to sidewall.
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 3 of the illustration, it would
mean that the tire's sidewall is
60 percent as high as it is wide.
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.
the wheel in inches.
These characters represent the
load index and speed rating of
the tire. The load index
represents the load carrying
capacity a tire is certified to
carry. The speed rating is the
maximum speed a tire is
certified to carry a load.
air inside the tire pressing
A
outward on each square inch
of the tire. Air pressure is
expressed in kPa (kilopascal)
or psi (pounds per square inch).
Diameter of
The amount of