10-50 Vehicle Care
(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.
Belt
: A rubber coated layer of
cords that is located between
the plies and the tread.
Cords may be made from steel
or other reinforcing materials.
Bead
: The tire bead contains
steel wires wrapped by steel
cords that hold the tire onto
the rim.
Bias Ply Tire
: A pneumatic tire
in which the plies are laid at
alternate angles less than
90 degrees to the centerline of
the tread.
Cold Tire Pressure
: The
amount of air pressure in a tire,
measured in kPa (kilopascal)
or psi (pounds per square inch)
before a tire has built up heat
from driving. See Tire Pressure
on page 10‑53.
Curb Weight
: The weight of a
motor vehicle with standard and
optional equipment including
the maximum capacity of fuel,
oil, and coolant, but without
passengers and cargo.
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