Hummer 2007 H3 Owner's Manual page 371

Tire Size
The following examples show the different parts of
a tire size.
Passenger (P-Metric) Tire
Light Truck (LT-Metric) Tire
(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.
(A) Light Truck (LT-Metric) Tire: The United
States version of a metric tire sizing system.
The letters LT as the first two characters in the
tire size means a light truck 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 75, as
shown in item C of the light truck (LT-Metric) tire
illustration, it would mean that the tire's sidewall is
75 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.
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