Pontiac 2009 G8 Owner's Manual page 249

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
:
number indicates the tire
section width in millimeters
from sidewall to sidewall.
(C) Aspect Ratio
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.
Vehicle Service and Care
The three-digit (E) Rim Diameter
the wheel in inches.
(F) Service Description
These characters represent the
A two-digit 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.
9-45
Diameter of
:
: