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Maintenance
Tire Terminology and
Definitions
Air Pressure
The amount of air inside the tire
pressing outward on 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 exam-
ples of optional accessories are
automatic transmission, 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 pounds per square inch
(psi) or kilopascals (kPa) before a tire
has built up heat from driving.
Curb Weight
This means 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.
DOT Markings
A code molded into the sidewall of a
tire signifying that the tire is in com-
pliance with the U.S. Department of
Transportation motor vehicle safety
standards. The DOT code includes
the Tire Identification Number (TIN),
an alphanumeric designator which
can also identify the tire manufactur-
er, production plant, brand and date
of production.
