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SERVICE AND APPEARANCE CARE
85Z04-03E
Glossary of Tire Terminology
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 trans-
mission, power steering, power brakes,
power windows, power seats, and air con-
ditioning.
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, mea-
sured in 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:
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 Num-
ber (TIN), an alphanumeric designator
which can also identify the tire manufac-
turer, production plant, brand and date of
production.
GVWR:
Gross Vehicle Weight Rating.
This is the maximum permissible overall
weight of the fully loaded vehicle (including
all occupants, accessories and cargo).
GAWR:
Gross Axle Weight Rating.
This is the maximum permissible weight on
an individual 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. 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.
Load Index:
An assigned number ranging from 1 to 279
that corresponds to the load carrying
capacity of a tire.
Maximum Inflation Pressure:
The maximum air pressure to which a cold
tire may be inflated. The maximum air
pressure is molded onto the sidewall.
Maximum Load Rating:
The load rating for a tire at the maximum
permissible 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 150 pounds
(68 kg).
Occupant Distribution:
Distribution of occupants in a vehicle as
specified in the third column of Table 1
(shown below).
Outward Facing Sidewall:
The side of a asymmetrical tire that has a
particular side that faces outward when
Tires: