10-44 Vehicle Care
Tire Designations
Tire Size
The following is 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
: 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 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) Construct ion 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
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.
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 kPa (kilopascal)
or psi (pounds per square inch).
Accessory Weight
: The
combined weight of optional
accessories. Some examples
of optional accessories are
automatic transmissio n, power
steering, power brakes, power
windows, power seats, and air
conditioning.
Aspect Ratio
: The relationship
of a tire's height to its width.
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