Page 319 of 414

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.
5-73
Page 322 of 414

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.
5-76
Page 329 of 414
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.
5-83
Page 330 of 414
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.
5-84
Page 331 of 414
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 5-93.
5-85
Page 332 of 414
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 5-82for 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.
5-86
Page 335 of 414
{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.
5-89
Page 339 of 414

11. Use the wheel wrench to tighten the nuts firmly.
Turn the wheel wrench clockwise and in a
crisscross sequence as shown.
12. Put the wheel cover or the center cap and plastic
wheel nut caps back on. Remove any wheel blocks.
Have a technician check the wheel nut tightness of
all wheels with a torque wrench after the first
100 miles (160 km) and then 1,000 miles (1600 km)
after that. Repeat this service whenever you have
a tire removed or serviced. SeeCapacities and
Specifications on page 5-116for more information.
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 5-97
for 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.
5-93