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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 Inflation Pressure: The amount of air pressure
in a tire, measured in pounds per square inch (psi)
before a tire has built up heat from driving. See
Inflation - Tire Pressure on page 5-61.
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 compliance 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 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.
There are 6.9 kPa’s to one psi.
Light Truck (LT-Metric) Tire: A tire used on light duty
trucks and some multipurpose passenger vehicles.
5-59