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Vehicle Care 279
(5) Tire Ply Material:The type of cord
and number of plies in the sidewall and
under the tread.
(6) Uniform Tire Quality Grading
(UTQG)
:Tire manufacturers are
required to grade tires based on three
performance factors: tread wear,
traction, and temperature resistance.
For more information see Uniform Tire
Quality Grading 0290.
(7) Maximum Cold Inflation Load
Limit
:Maximum load that can be
carried and the maximum pressure
needed to support that load.
Compact Spare Tire Example
(1) Tire Ply Material:The type of cord
and number of plies in the sidewall and
under the tread.
(2) Temporary Use Only
:The compact
spare tire or temporary use tire should
not be driven at speeds over 80 km/h
(50 mph). The compact spare tire is for
emergency use when a regular road tire
has lost air and gone flat. If the vehicle
has a compact spare tire, see Compact
Spare Tire 0298 and
If a Tire Goes Flat 0293.
(3) Tire Identification Number (TIN)
:
The letters and numbers following the
DOT (Department of Transportation)
code are the Tire Identification Number
(TIN). The TIN shows the manufacturer
and plant code, tire size, and date the
tire was manufactured. The TIN is
molded onto both sides of the tire,
although only one side may have the
date of manufacture.
(4) Maximum Cold Inflation Load
Limit
:Maximum load that can be
carried and the maximum pressure
needed to support that load. (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 0282.
(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.
Chevrolet Trailblazer Owner Manual (GMNA-Localizing-U.S./Canada-
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280 Vehicle Care
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.
(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 Pressure0282.
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.
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292 Vehicle Care
Wheel Alignment and Tire
Balance
The tires and wheels were aligned and
balanced at the factory to provide the
longest tire life and best overall
performance. Adjustments to wheel
alignment and tire balancing are not
necessary on a regular basis. Consider an
alignment check if there is unusual tire wear
or the vehicle is significantly pulling to one
side or the other. Some slight pull to the
left or right, depending on the crown of the
road and/or other road surface variations
such as troughs or ruts, is normal. If the
vehicle is vibrating when driving on a
smooth road, the tires and wheels may
need to be rebalanced. See your dealer for
proper diagnosis.
Wheel Replacement
Replace any wheel that is bent, cracked,
or badly rusted or corroded. If wheel nuts
keep coming loose, the wheel, wheel bolts,
and wheel nuts should be replaced. If the
wheel leaks air, replace it. Some aluminum
wheels can be repaired. See your dealer if
any of these conditions exist.Your dealer will know the kind of wheel that
is needed.
Each new wheel should have the same
load-carrying capacity, diameter, width,
offset, and be mounted the same way as
the one it replaces.
Replace wheels, wheel bolts, wheel nuts,
or Tire Pressure Monitor System (TPMS)
sensors with new GM original equipment
parts.
{Warning
Using the wrong replacement wheels,
wheel bolts, or wheel nuts can be
dangerous. It could affect the braking and
handling of the vehicle. Tires can lose air
and cause loss of control, resulting in a
crash. Always use the correct wheel,
wheel bolts, and wheel nuts for
replacement.
{Warning
Replacing a wheel with a used one is
dangerous. How it has been used or how
far it has been driven may be unknown.
(Continued)
Warning (Continued)
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 225/60R17 or 225/55R18
size tires, do not use tire chains. There is
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(Continued)
