Page 310 of 402

When It Is Time for New Tires
Various factors, such as maintenance, temperatures,
driving speeds, vehicle loading, and road conditions,
influence when you need new tires.
One way to tell when it is
time for new tires is to
check the treadwear
indicators, which 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 new tires 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
cannot be repaired well because of the size or
location of the damage.
The rubber in tires degrades over time, even if they are
not being used. This is also true for the spare tire, if
your vehicle has one. Multiple conditions affect how fast
this aging takes place, including temperatures, loading
conditions, and inflation pressure maintenance. With
proper care and maintenance tires will typically wear out
before they degrade due to age. If you are unsure about
the need to replace your tires as they get older, consult
the tire manufacturer for more information.
Buying New Tires
GM has developed and matched specific tires for your
vehicle. The original equipment tires installed on your
vehicle, when it was new, were designed to meet
General Motors Tire Performance Criteria Specification
(TPC spec) system rating. If you need replacement tires,
GM strongly recommends that you get tires with the same
TPC Spec rating. This way, your vehicle will continue
to have tires that are designed to give the same
performance and vehicle safety, during normal use,
as the original tires.
GM’s exclusive TPC Spec system considers over a
dozen critical specifications that impact the overall
performance of your vehicle, including brake system
performance, ride and handling, traction control,
and tire pressure monitoring performance.
5-70
Page 313 of 402

Uniform Tire Quality Grading
Quality grades can be found where applicable on
the tire sidewall between tread shoulder and
maximum section width. For example:
Treadwear 200 Traction AA Temperature A
The following information relates to the system
developed by the United States National Highway
Traffic Safety Administration (NHTSA), which
grades tires by treadwear, traction, and
temperature performance. This applies only to
vehicles sold in the United States. The grades are
molded on the sidewalls of most passenger car
tires. The Uniform Tire Quality Grading (UTQG)
system does not apply to deep tread, winter-type
snow tires, space-saver, or temporary use spare
tires, tires with nominal rim diameters of
10 to 12 inches (25 to 30 cm), or to some
limited-production tires.
While the tires available on General Motors
passenger cars and light trucks may vary with
respect to these grades, they must also conform
to federal safety requirements and additional
General Motors Tire Performance Criteria (TPC)
standards.
Treadwear
The treadwear grade is a comparative rating
based on the wear rate of the tire when tested
under controlled conditions on a specified
government test course. For example, a tire
graded 150 would wear one and a half (1.5) times
as well on the government course as a tire
graded 100. The relative performance of tires
depends upon the actual conditions of their use,
however, and may depart significantly from the
norm due to variations in driving habits, service
practices, and differences in road characteristics
and climate.
Traction – AA, A, B, C
The traction grades, from highest to lowest, are AA,
A, B, and C. Those grades represent the tire’s
ability to stop on wet pavement as measured under
controlled conditions on specified government test
surfaces of asphalt and concrete. A tire marked C
may have poor traction performance.
Warning
:The traction grade assigned to this
tire is based on straight-ahead braking traction
tests, and does not include acceleration,
cornering, hydroplaning, or peak traction
characteristics.
5-73
Page 319 of 402
The following information tells you how to use the jack
and change a tire.
Removing the Spare Tire and Tools
If you have a cargo van or a passenger van, the
equipment you will need is located in the passenger
side rear corner of the vehicle.
Remove the retaining wing
bolt and lift it off of the
mounting bracket.
If you have a van with the 15-passenger seating
arrangement, the equipment you will need is secured on
the rear floor of the passenger side of the vehicle.
5-79
Page 320 of 402
To access the equipment, remove the retaining wing
bolt and lift it out of the mounting bracket.The tools you will be using include the jack (A), jack
handle extension (B), jack handle (C), wheel wrench (D),
and the ratchet (E).
The spare tire is stored underneath the rear of your
vehicle. You will use the wheel wrench (D) and the
ratchet (E) to lower the spare tire from the vehicle.
5-80
Page 321 of 402
To lower the spare tire from the vehicle:
1. Attach the wheel
wrench and ratchet,
with the DOWN side
facing you. The wheel
wrench has a socket
end and a flat chisel
end. Note that there is
an UP side and a
DOWN side on the
ratchet.
2. Put the flat chisel end of the wheel wrench on an
angle through the hole between the body and the
bumper. Be sure the flat end connects into the
hoist shaft.3. Turn the ratchet counterclockwise to lower the
spare tire to the ground. If the spare tire does
not lower to the ground, the secondary latch
is engaged causing the tire not to lower. See
Secondary Latch System on page 5-90.
5-81
Page 322 of 402
4. When the tire has been lowered, pull the tire toward
you so you can reach the tire retainer and pull it up
through the wheel opening.
If you have a vehicle which was completed from a cab
and chassis, refer to the information from the body
supplier/installer.
The spare tire is a full-size tire, like the other tires on
your vehicle.
Removing the Flat Tire and
Installing the Spare Tire
If your vehicle has plastic wheel nut caps, loosen them
by turning the wheel wrench counterclockwise. The
wheel nut caps are designed to remain with the center
cap. Remove the center cap.
If the wheel has a smooth center piece, place the chisel
end of the wheel wrench in the slot on the wheel and
gently pry it out.
1. Do a safety check before proceeding. SeeChanging
a Flat Tire on page 5-78for more information.
2. With the DOWN side facing you, use the ratchet
and wheel wrench to loosen all the wheel nuts.
Do not remove them yet.
5-82
Page 325 of 402
{CAUTION:
Getting under a vehicle when it is jacked up is
dangerous. If the vehicle slips off the jack you
could be badly injured or killed. Never get
under a vehicle when it is supported only
by a jack.
{CAUTION:
Raising your vehicle with the jack improperly
positioned can damage the vehicle and even
make the vehicle fall. To help avoid personal
injury and vehicle damage, be sure to t the
jack lift head into the proper location before
raising the vehicle.5. Raise the vehicle by turning the ratchet clockwise.
Make sure the UP mark faces you. Raise the
vehicle far enough off the ground so there is enough
room for the spare tire to fit.
5-85
Page 330 of 402

Secondary Latch System
Your vehicle has an underbody-mounted tire hoist
assembly equipped with a secondary latch system.
It is designed to stop the spare tire from suddenly
falling off the vehicle if the cable holding the spare tire
is damaged. For the secondary latch to work, the
tire must be stowed with the valve stem pointing down.
SeeStoring a Flat or Spare Tire and Tools on
page 5-93for instructions on storing the spare tire
correctly.
{CAUTION:
Before beginning this procedure read all the
instructions. Failure to read and follow the
instructions could damage the hoist assembly
and you and others could get hurt. Read and
follow the instructions listed next.To release the spare tire from the secondary latch:
{CAUTION:
Someone standing too close during the
procedure could be injured by the jack.
If the spare tire does not slide off the jack
completely, make sure no one is behind you or
on either side of you as you pull the jack out
from the under spare.
1. Check under the
vehicle to see if the
cable end is visible.
If the cable is not
visible, start this
procedure at Step 6.
2. Turn the wrench counterclockwise until
approximately 6 inches (15 cm) of cable is exposed.
5-90