2001 GMC ENVOY wheel

4-25 Driving Across an Incline
Sooner or later, an off-road trail will probably go across
the incline of a hill. If this happens, you have to decide
whether to try to drive across the incline. Here are some
things to consider:

A hill that can be driven straight up or down
may be too steep to drive across. When you go
straight up or down a hill, the length of the wheel
base (the distance from the front wheels to the
rear wheels) reduces the likelihood the vehicle will
tumble end over end. But when you drive across
an incline, the much more narrow track width
(the distance between the left and right wheels)
may not prevent the vehicle from tilting and rolling
over. Also, driving across an incline puts more
weight on the downhill wheels. This could cause
a downhill slide or a rollover.

Surface conditions can be a problem when you drive
across a hill. Loose gravel, muddy spots, or even wet
grass can cause your tires to slip sideways, downhill.
If the vehicle slips sideways, it can hit something
that will trip it (a rock, a rut, etc.) and roll over.
Hidden obstacles can make the steepness of the
incline even worse. If you drive across a rock with
the uphill wheels, or if the downhill wheels drop into
a rut or depression, your vehicle can tilt even more.
For reasons like these, you need to decide carefully
whether to try to drive across an incline. Just because
the trail goes across the incline doesn't mean you
have to drive it. The last vehicle to try it might have
rolled over.
CAUTION:
Driving across an incline that's too steep will
make your vehicle roll over. You could be seriously
injured or killed. If you have any doubt about
the steepness of the incline, don't drive across it.
Find another route instead.
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4-27 Driving in Mud, Sand, Snow or Ice
When you drive in mud, snow or sand, your wheels
won't get good traction. You can't accelerate as quickly,
turning is more difficult, and you'll need longer
braking distances.
It's best to use a low gear when you're in mud
-- the
deeper the mud, the lower the gear. In really deep mud,
the idea is to keep your vehicle moving so you don't
get stuck.
When you drive on sand, you'll sense a change in wheel
traction. But it will depend upon how loosely packed the
sand is. On loosely packed sand (as on beaches or sand
dunes) your tires will tend to sink into the sand. This has
an effect on steering, accelerating and braking. You may
want to reduce the air pressure in your tires slightly
when driving on sand. This will improve traction.
Hard packed snow and ice offer the worst tire traction.
On these surfaces, it's very easy to lose control. On wet
ice, for example, the traction is so poor that you will
have difficulty accelerating. And if you do get moving,
poor steering and difficult braking can cause you to slide
out of control.
CAUTION:
Driving on frozen lakes, ponds or rivers can be
dangerous. Underwater springs, currents under
the ice, or sudden thaws can weaken the ice.
Your vehicle could fall through the ice and you
and your passengers could drown. Drive your
vehicle on safe surfaces only.
Driving in Water
Light rain causes no special off-road driving problems.
But heavy rain can mean flash flooding, and flood
waters demand extreme caution.
Find out how deep the water is before you drive through
it. If it's deep enough to cover your wheel hubs, axles or
exhaust pipe, don't try it
-- you probably won't get
through. Also, water that deep can damage your axle
and other vehicle parts.
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4-28
If the water isn't too deep, then drive through it slowly.
At fast speeds, water splashes on your ignition system
and your vehicle can stall. Stalling can also occur if you
get your tailpipe under water. And, as long as your
tailpipe is under water, you'll never be able to start your
engine. When you go through water, remember that
when your brakes get wet, it may take you longer to stop.
CAUTION:
Driving through rushing water can be dangerous.
Deep water can sweep your vehicle downstream
and you and your passengers could drown.
If it's only shallow water, it can still wash away
the ground from under your tires, and you could
lose traction and roll the vehicle over. Don't drive
through rushing water.
See ªDriving Through Waterº in the Index for more
information on driving through water.
After Off-Road Driving
Remove any brush or debris that has collected on
the underbody, chassis or under the hood.
These accumulations can be a fire hazard.
After operation in mud or sand, have the brake linings
cleaned and checked. These substances can cause
glazing and uneven braking. Check the body structure,
steering, suspension, wheels, tires and exhaust system
for damage. Also, check the fuel lines and cooling
system for any leakage.
Your vehicle will require more frequent service due to
off
-road use. Refer to the Maintenance Schedule for
additional information.
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4-36
Highway Hypnosis
Is there actually such a condition as ªhighway hypnosisº?
Or is it just plain falling asleep at the wheel? Call it
highway hypnosis, lack of awareness, or whatever.
There is something about an easy stretch of road with
the same scenery, along with the hum of the tires on
the road, the drone of the engine, and the rush of the
wind against the vehicle that can make you sleepy.
Don't let it happen to you! If it does, your vehicle can
leave the road in less than a second, and you could
crash and be injured.
What can you do about highway hypnosis?
First, be aware that it can happen.
Then here are some tips:

Make sure your vehicle is well ventilated, with a
comfortably cool interior.

Keep your eyes moving. Scan the road ahead
and to the sides. Check your mirrors and your
instruments frequently.

If you get sleepy, pull off the road into a rest,
service or parking area and take a nap, get some
exercise, or both. For safety, treat drowsiness on
the highway as an emergency.
Hill and Mountain Roads
Driving on steep hills or mountains is different from
driving in flat or rolling terrain.
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4-39
What's the worst time for this? ªWet ice.º Very cold
snow or ice can be slick and hard to drive on. But wet
ice can be even more trouble because it may offer the
least traction of all. You can get wet ice when it's about
freezing (32F; 0C) and freezing rain begins to fall.
Try to avoid driving on wet ice until salt and sand crews
can get there.Whatever the condition
-- smooth ice, packed, blowing
or loose snow
-- drive with caution.
Accelerate gently. Try not to break the fragile traction.
If you accelerate too fast, the drive wheels will spin and
polish the surface under the tires even more.
Your anti
-lock brakes improve your vehicle's stability
when you make a hard stop on a slippery road. Even
though you have an anti
-lock braking system, you'll
want to begin stopping sooner than you would on dry
pavement. See ªAnti
-Lockº in the Index.

Allow greater following distance on any
slippery road.

Watch for slippery spots. The road might be fine
until you hit a spot that's covered with ice. On an
otherwise clear road, ice patches may appear in
shaded areas where the sun can't reach: around
clumps of trees, behind buildings or under bridges.
Sometimes the surface of a curve or an overpass
may remain icy when the surrounding roads are
clear. If you see a patch of ice ahead of you,
brake before you are on it. Try not to brake while
you're actually on the ice, and avoid sudden
steering maneuvers.
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4-42 Two-Wheel Drive Vehicles and Vehicles
with the Electronic Shift Transfer Case
Tw o-wheel-drive vehicles and vehicles with the
Electronic Shift Transfer Case should not be towed
with all four wheels on the ground. These transmissions
have no provisions for internal lubrication while being
towed. To properly tow these vehicles, they should be
placed on a platform trailer with all four wheels off the
ground. Towing with all four wheels on the ground
should be avoided.
In rare cases when it's unavoidable and your vehicle
has to be towed with all four wheels on the ground,
the propeller shaft to axle yoke orientation should be
marked and the propeller shaft removed following
the applicable service manual removal/installation
procedure. See ªService and Owner Publicationsº in
the Index.
Dust or dirt can enter the back of the transmission
through the opening created by removing the propeller
shaft if proper protection is not provided. Also, check
the transmission fluid level before driving the vehicle.
Four-Wheel-Drive Vehicles
(Automatic Transfer Case)
Use the following procedure to correctly tow your
vehicle on all four wheels:
1. Firmly set the parking brake.
2. Place the transmission in PARK (P).
3. Securely attach the vehicle being towed to the
tow vehicle.
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4-43
4. With the engine running, shift the transfer case to
NEUTRAL. See ªFour
-Wheel Driveº in the Index
for the proper procedure to select the NEUTRAL
position for your vehicle.
CAUTION:
Shifting the transfer case into NEUTRAL can
cause your vehicle to roll even if the transmission
is in PARK (P), for an automatic transmission,
or if your vehicle is in gear, for a manual
transmission. You or others could be injured.
Make sure the parking brake is firmly set
before you shift the transfer case into NEUTRAL.
See ªFour
-Wheel Drive (Automatic Transfer Case)º
in the Index.
5. Release the parking brake only after the vehicle
being towed is firmly attached to the towing vehicle.
6. Turn the ignition to OFF. The OFF position unlocks
the steering column and reduces battery drain.
Unlocking the steering column will allow the proper
movement of the front wheels and tires during towing.
Loading Your Vehicle
The Certification/Tire label is found on the driver's door
edge, above the door latch. The label shows the size of
your original tires and the inflation pressures needed to
obtain the gross weight capacity of your vehicle. This is
called the Gross Vehicle Weight Rating (GVWR). The
GVWR includes the weight of the vehicle, all occupants,
fuel, cargo and trailer tongue weight, if pulling a trailer.
The Certification/Tire label also tells you the maximum
weights for the front and rear axles, called Gross Axle
Weight Rating (GAWR).
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4-50 Weight of the Trailer
How heavy can a trailer safely be?
It depends on how you plan to use your rig. For example,
speed, altitude, road grades, outside temperature and
how much your vehicle is used to pull a trailer are all
important. And, it can also depend on any special
equipment that you have on your vehicle.
The following chart shows how much your trailer can
weigh, based upon your vehicle model and options.
VehicleAxle
Ratio Max. Trailer Wt.
2
-Wheel Drive,
2 Door
Auto. Trans.3.08
3.424,700 lbs. (2 133 kg)
5,700 lbs. (2 587 kg)
2
-Wheel Drive,
2 Door
Manual Trans.3.42 4,200 lbs. (1 906 kg)
2
-Wheel Drive,
4 Door
Auto. Trans.3.08
3.424,500 lbs. (2 043 kg)
5,500 lbs. (2 497 kg)
4
-Wheel Drive,
2 Door
Auto. Trans.3.08
3.42
3.734,400 lbs. (1 997 kg)
5,400 lbs. (2 451 kg)
5,400 lbs. (2 451 kg)VehicleAxle
Ratio Max. Trailer Wt.
4
-Wheel Drive,
2 Door
Manual Trans.3.42 3,900 lbs. (1 770 kg)
ZR2
Auto. Trans. 3.73 4,800 lbs. (2 179 kg)
Manual Trans. 3.73 4,300 lbs. (1 952 kg)
4
-Wheel Drive,
4 Door
Auto. Trans.3.08
3.42
3.734,200 lbs. (1 906 kg)
5,200 lbs. (2 360 kg)
5,200 lbs. (2 360 kg)
4
-Wheel Drive,
4 Door
Manual Trans.3.42 3,700 lbs. (1 679 kg)
Maximum trailer weight is calculated assuming the
driver and one passenger are in the tow vehicle and it
has all the required trailering equipment. The weight of
additional optional equipment, passengers and cargo in
the tow vehicle must be subtracted from the maximum
trailer weight. The weight of the trailer tongue also
affects the maximum trailer weight. See ªWeight of the
Trailer Tongueº later in this section.
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