GMC 1982 Light Duty Truck Service Manual page 399

of the tire causes a small feather edge of rubber to appear on
one side of the tread and this feather edge is certain
indication of misalignment. The remedy is readjusting toe-
in, or rechecking the entire front end alignment if necessary.
Uneven Wear
Uneven or spotty wear is due to such irregularities as
unequal caster or camber, bent front suspension parts, out-
of-balance wheels, brake drums out of round, brakes out of
adjustment or other mechanical conditions. The remedy in
each case consists of locating the mechanical defect and
correcting it.
Cornering Wear
When a truck makes an extremely fast turn, the weight
is shifted from an even loading on all wheels to an abnormal
load on the tires on the outside of the curve and a very light
load on the inside tires, due to centrifugal force. This
unequal loading may have two unfavorable results.
the rear tire on the inside of the curve may be
First,
relieved of so much load that it is no longer geared to the
road and it slips, grinding off the tread on the inside half of
the tire at an excessive rate. This type of tire shows much the
same appearance of tread wear as tire wear caused by
negative camber.
Second, the transfer of weight may also overload the
outside tires so much th a t they are laterally distorted
resulting in excessive wear on the outside half of the tire,
producing a type of wear like th at caused by excessive
positive camber.
Cornering wear can be most easily distinguished from
ab n o rm a l ca m b er wear by the rounding of the outside
shoulder or edge of the tire and by the roughening of the
tread surface which denotes abrasion.
Cornering wear often produces a fin or raised portion
along the inside edge of each row in the tread pattern. In
some cases this fin is almost as pronounced as a toe-in fin,
and in others, it tapers into a row of tread blocks to such an
extent th at the tire has a definite "step w ear" appearance.
T h e only rem edy for cornering wear is proper
instruction of operators. Driving more slowly on curves and
turns will avoid grinding rubber off tires. To offset normal
cornering wear as m uch as possible tires should be
interchanged at regular intervals.
Wheel and Tire Balancing
It is desirable from the standpoints of tire wear and
vehicle ride and handling ease to maintain proper balance of
wheel and tire assemblies on all models. This may be
accom plished by either of the two types of balancing
systems in currect use which balance wheels either on the
vehicle or off. The "on the vehicle" type, however, is the
more desirable in that all rolling components (brake drums,
bearings, seals, etc.) are included in the balancing procedure
and thereby have any existing unbalance corrected.
Truck Wheel Balance Weights
All truck wheels equipped with a tubular side ring
(rolled flange rim) on the outboard side of the wheel rims
require special design weights to fit. Dynamic balancing can
be accomplished through use of these special balance
weights which are designed only for installations on the
outboard side of these wheels. Conventional weights fit only
the inboard side of these wheels.
Static Balance
Static balance (sometimes called still balance) is the
equal distribution of weight of the wheel and tire assembly
about the axis of rotation in such a m ann er th a t the
assembly has no tendency to rotate by itself, regardless of its
position. For example: A wheel with chunk of dirt on the rim
will always rotate by itself until the heavy side is a the
bottom. Any wheel with a heavy side like this is statically
out of balance. Static unbalance of a wheel causes a hopping
or pounding action (up and down) which frequently leads to
wheel "flu tte r" and quite often to wheel " tr a m p " .
Dynamic Balance
Dynamic balance (sometimes called running balance
means that the wheel must be in static balance, and also run
smoothly at all speeds.
To insure successful, accurate balancing, the following
precautions must be observed:
• Wheel and tire must be clean and free from all foreign
matter.
• The tires should be in good condition and properly
mounted with the balance mark on the tire, if any, lined
up with the valve.
• Bent wheels that have runout over 1/16" should be
replaced.
• Inspect tire and wheel assembly to determine if an
eccentric or out-of-round condition exists. Note that
this condition, if severe, cannot be "balanced o u t" . An
assembly which has
exceeding 3 /1 6 " on tire sizes through 19.5" is not
suitable for use on the front of the vehicle. Its use on the
rear should be governed by its general condition and
whether the roundness defect seriously detracts from
overall ride quality.
• When balancing wheels and tires, it is recommended
that the instructions covering the operation of the wheel
balancer being used be closely followed.
• When balancing truck type nylon tires, tires must be
hot (run for several miles) before raising vehicle to
balance so that flat spot is elimated. A tire which is flat
spotted will be incorrectly balanced.
• On 10 and 20 series trucks, do not attem pt to externally
drive the wheels with the transfer case in the neutral
position. Although, the transfer case will be uncoupled
from the transmission, the front and rear drive trains
will be coupled through the transfer case. For example,
attempting to balance a rear wheel on the vehicle will
cause one or both of the front wheels to also be driven.
The wheels may be dynam ically balanced on the
vehicle with the transfer case in the 2H position. The
transfer case neutral position should only be used when
it becomes necessary to uncouple the transmission from
the transfer case.
WHEEL INSTALLATION
Single Wheels
W hen installing the tire and wheel on the vehicle, the
following procedure should be followed:
After wheel nuts are put on loosely, turn the wheel
WHEELS A N D TIRES 3E-7
an out-of-round condition