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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
kilopascal (kPa) or pounds per
square inch (psi).
Accessory Weight: This means the
combined weight of optional acces-
sories. Some examples of optional
accessories are, automatic transmis-
sion, power seats, and air condition-
ing.
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
kilopascals (kPa) or pounds per
square inch (psi) 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: The DOT code
includes the Tire Identification
Number (TIN), an alphanumeric des-
ignator which can also identify the
tire manufacturer, production plant,
brand and date of production.
GVWR: Gross Vehicle Weight Rating
GAWR FRT: Gross Axle Weight
Rating for the front Axle.
GAWR RR: Gross Axle Weight
Rating for the rear axle.
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.
Load Index: An assigned number
ranging from 1 to 279 that corre-
sponds to the load carrying capacity
of a tire.
Maximum Inflation Pressure: The
maximum air pressure to which a
cold tire may be inflated. The maxi-
mum air pressure is molded onto the
sidewall.
Maximum Load Rating: The load
rating for a tire at the maximum per-
missible inflation pressure for that
tire.
Maximum Loaded Vehicle Weight:
The sum of curb weight; accessory
weight; vehicle capacity weight; and
production options weight.
Normal Occupant Weight: The
number of occupants a vehicle is
designed to seat multiplied by 68 kg
(150 pounds).
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