Tire Terminology And Definitions - Chevrolet 2006 Colorado Owner's Manual

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.
(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.
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(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 from A to Z.
Tire Terminology and Definitions
Air Pressure: The amount of air inside the tire pressing
outward on each square inch of the tire. Air pressure
is expressed in pounds per square inch (psi) or
kilopascal (kPa).
Accessory Weight: This means the combined weight
of optional accessories. Some examples of optional
accessories are, automatic transmission, power steering,
power brakes, power windows, power seats, and air
conditioning.
Aspect Ratio: The relationship of a tire's height to
its width.