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Vehicle Care 369
(5) Tire Inflation:The
temporary use tire or
compact spare tire should
be inflated to 420 kPa
(60 psi). For more
information on tire
pressure and inflation see
Tire Pressure 0372.
(6) Tire Size
:A
combination of letters and
numbers define a tire's
width, height, aspect ratio,
construction type, and
service description. The
letter “T”as the first
character in the tire size
means the tire is for
temporary use only.
(7) TPC Spec (Tire
Performance Criteria
Specification)
:Original
equipment tires designed
to GM's specific tire
performance criteria have a
TPC specification code
molded onto the sidewall. GM's TPC specifications
meet or exceed all federal
safety guidelines.
Tire Designations
Tire Size
The example shows a
typical passenger vehicle
tire size.
Passenger (P-Metric) Tire
(1) Passenger (P-Metric)
Tire
:The United States
version of a metric tire
sizing system. The letter
"P" as the first character in
the tire size means a
passenger vehicle tire
engineered to standards
set by the U.S. Tire and Rim
Association. (2) Tire Width
:The 3-digit
number indicates the tire
section width in millimeters
from sidewall to sidewall.
(3) Aspect Ratio
:A 2-digit
number that indicates the
tire height-to-width
measurements. For
example, if the tire size
aspect ratio is 75, as
shown in item (3) of the
illustration, it would mean
that the tire's sidewall is
75 percent as high as it
is wide.
(4) 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.
(5) Rim Diameter
:
Diameter of the wheel in
inches.
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370 Vehicle Care
(6) Service Description:
These characters
represent the load index
and speed rating of the
tire. The load index
represents the load
carrying capacity a tire is
certified to carry. The
speed rating is the
maximum speed a tire is
certified to carry a load.
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 kPa (kilopascal) or psi
(pounds per square inch).
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 kPa
(kilopascal) or psi (pounds
per square inch) before a
tire has built up heat from
driving. See Tire Pressure
0 372. 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
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 Vehicle
Load Limits 0242.
GAWR FRT
:Gross Axle
Weight Rating for the front
axle. See Vehicle Load
Limits 0242.
GAWR RR
:Gross Axle
Weight Rating for the rear
axle. See Vehicle Load
Limits 0242.
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388 Vehicle Care
Warning (Continued)
it has been driven may be
unknown. It could fail
suddenly and cause a crash.
When replacing wheels, use
a new GM original
equipment wheel.
Caution
The wrong wheel can also
cause problems with bearing
life, brake cooling,
speedometer or odometer
calibration, headlamp aim,
bumper height, vehicle
ground clearance, and tire or
tire chain clearance to the
body and chassis.
Tire Chains
{Warning
If the vehicle has 235/60R18
or 245/45R20 size tires, do
not use tire chains. There is(Continued)
Warning (Continued)
not enough clearance. Tire
chains used on a vehicle
without the proper amount
of clearance can cause
damage to the brakes,
suspension, or other vehicle
parts. The area damaged by
the tire chains could cause
loss of control and a crash.
Use another type of traction
device only if its
manufacturer recommends
it for the vehicle's tire size
combination and road
conditions. Follow that
manufacturer's instructions.
To avoid vehicle damage,
drive slow and readjust or
remove the traction device if
it contacts the vehicle. Do
not spin the wheels. If
traction devices are used,
install them on the front
tires.
Caution
If the vehicle is equipped
with a tire size other than
235/60R18 or 245/45R20,
use tire chains only where
legal and only when
necessary. Use low profile
chains that add no more
than 12 mm thickness to the
tire tread and inner sidewall.
Use chains that are the
proper size for the tires.
Install them on the tires of
the front axle. Do not use
chains on the tires of the
rear axle. Tighten them as
tightly as possible with the
ends securely fastened.
Drive slowly and follow the
chain manufacturer's
instructions. If the chains
contact the vehicle, stop and
retighten them. If the
contact continues, slow
down until it stops. Driving(Continued)
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