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.
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. See Inflation - Tire Pressure
on page 5-60.
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.
DOT Markings
: A code molded into the sidewall
of a tire signifying that the tire is in compliance
with the U.S. Department of Transportation (DOT)
motor vehicle safety standards. The DOT code
includes the Tire Identification Number (TIN), an
alphanumeric designator which can also identify the
tire manufacturer, production plant, brand, and date
of production.
GVWR
: Gross Vehicle Weight Rating.
See Loading Your Vehicle on page 4-34.
GAWR FRT
: Gross Axle Weight Rating for
the front axle. See Loading Your Vehicle
on page 4-34.
GAWR RR
: Gross Axle Weight Rating for the
rear axle. See Loading Your Vehicle on page 4-34.
Intended Outboard Sidewall
: The side of an
asymmetrical tire, that must always face outward
when mounted on a vehicle.
Kilopascal (kPa)
: The metric unit for air pressure.
Light Truck (LT-Metric) Tire
: A tire used on light
duty trucks and some multipurpose passenger
vehicles.
5-58
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