Tire Terminology And Definitions - Chevrolet 2006 SSR Pickup Owner's Manual

Tire Size
The following illustration shows, an example of, a typical
passenger car 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: 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
illustration, it would mean that the tire's sidewall is
75 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: The service description
indicates the load range and speed rating of a tire. The
load index can range from 1 to 279. 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.