(C) Aspect Ratio:A two-digit
number that indicates the tire
height-to-width measurements.
For example, if the tire size
aspect ratio is 75, as shown
in item C of the light truck
(LT-Metric) tire illustration,
it would mean that the tire’s
sidewall is 75 percent as high
as it is wide.
(D) Construction Code
:A letter code is used to indicate
the type of ply construction in
the tire. The letter R means
radial ply construction; the
letter D means diagonal or
bias ply construction; and the
letter B means belted-bias
ply construction.
(E) Rim Diameter
:Diameter of
the wheel in inches.
(F) Service Description
:The service description indicates
the load range and speed
rating of a tire. The load index
can range from 1 to 279. Speed
ratings range from A to Z.
Tire Terminology and
De nitions
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 5-51.
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.
5-48 Service and Appearance Care
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 Identi cation
Number (TIN), an alphanumeric
designator which can also
identify the tire manufacturer,
production plant, brand, and date
of production.
GVWR
:Gross Vehicle Weight
Rating. SeeLoading the Vehicle
on page 4-35.
GAWR FRT
:Gross Axle
Weight Rating for the front axle.
SeeLoading the Vehicle on
page 4-35.
GAWR RR
:Gross Axle
Weight Rating for the rear axle.
SeeLoading the Vehicle on
page 4-35.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.
Load Index
:An assigned
number ranging from 1 to 279
that corresponds to the load
carrying capacity of a tire.
Maximum In ation Pressure
:The maximum air pressure
to which a cold tire can be
in ated. The maximum air
pressure is molded onto the
sidewall.
Maximum Load Rating
:The load rating for a tire at the
maximum permissible in ation
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 lbs (68 kg).
SeeLoading the Vehicle
on page 4-35.
Occupant Distribution
:Designated seating positions.
Outward Facing Sidewall
:The side of an asymmetrical tire
that has a particular side that
faces outward when mounted on
a vehicle. The side of the tire
that contains a whitewall,
bears white lettering, or bears
manufacturer, brand, and/or
model name molding that
is higher or deeper than the
same moldings on the
other sidewall of the tire.
Service and Appearance Care 5-49