(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 illustration, it would mean that the tire’s sidewall
is 75% 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”.(A) Light Truck (LT-Metric) Tire:The United States
version of a metric tire sizing system. The letter “LT” as
the rst two characters in the tire size means a light
truck tire engineered to standards set by the U. S. Tire
and Rim Association.
(B) Tire Width:The three-digit number indicates the
tire section width in millimeters from sidewall to sidewall.
(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 illustration, it would mean that the tire’s sidewall is
75% as high as it is wide.Light Truck (LT-Metric) Tire
5-70
(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”. The light truck tire size example
above shows dual or single tire con gurations.
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 In ation 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. SeeIn ation - Tire Pressure on page 5-74.
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.
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Tire Pressure Monitor System
The Tire Pressure Monitor (TPM) system uses radio
and sensor technology to check tire pressure levels. If
your vehicle has this feature, sensors are mounted
on each tire and wheel assembly, except the spare tire.
The TPM sensors transmit tire pressure readings to
a receiver located in the vehicle.
When a low tire pressure condition is detected, the TPM
system will display the CHECK TIRE PRESSURE
warning message on the Driver Information Center
(DIC); and at the same time illuminate the low tire
pressure warning symbol. For additional information and
details about the DIC operation and displays seeDIC
Operation and Displays on page 3-51andDIC Warnings
and Messages on page 3-62.
When the tire pressure
monitoring system warning
light is lit, one or more
of your tires is signi cantly
under-in ated.
You should stop and check your tires as soon as
possible, and in ate them to the proper pressure as
indicated on the vehicle’s tire information placard.Driving on a signi cantly under-in ated tire causes the
tire to overheat and can lead to tire failure.
Under-in ation also reduces fuel efficiency and tire tread
life, and may affect the vehicle’s handling and stopping
ability. Each tire, including the spare, should be
checked monthly when cold and set to the
recommended in ation pressure as speci ed in the
vehicle placard and owner’s manual.
The Certi cation/Tire label or the Tire and Loading
Information label (tire information placard) shows the
size of your vehicle’s original tires and the correct
in ation pressure for your vehicle’s tires when they are
cold. SeeIn ation - Tire Pressure on page 5-74. For
the location of the tire and loading information label, see
Loading Your Vehicle on page 4-50.
Your vehicle’s TPM system can alert you about a low
tire pressure condition but it does not replace normal tire
maintenance. SeeTire Inspection and Rotation on
page 5-78andTires on page 5-65.
Notice:Do not use a tire sealant if your vehicle is
equipped with Tire Pressure Monitors. The liquid
sealant can damage the tire pressure monitor
sensors.
5-75
{CAUTION:
Rust or dirt on a wheel, or on the parts to
which it is fastened, can make wheel nuts
become loose after a time. The wheel could
come off and cause an accident. When you
change a wheel, remove any rust or dirt from
places where the wheel attaches to the vehicle.
In an emergency, you can use a cloth or a
paper towel to do this; but be sure to use a
scraper or wire brush later, if you need to, to
get all the rust or dirt off. See “Changing a Flat
Tire” in the Index.
When It Is Time for New Tires
One way to tell when it’s
time for new tires is to
check the treadwear
indicators, which will
appear when your tires
have only 1/16 inch
(1.6 mm) or less of tread
remaining. Some
commercial truck tires may
not have treadwear
indicators.
You need a new tire if any of the following statements
are true:
You can see the indicators at three or more places
around the tire.
You can see cord or fabric showing through the
tire’s rubber.
The tread or sidewall is cracked, cut or snagged
deep enough to show cord or fabric.
The tire has a bump, bulge or split.
The tire has a puncture, cut or other damage that
can’t be repaired well because of the size or
location of the damage.
5-79