GMC 4000 Series Service Manual page 522

IMPORTANT: When servicing wheels, care
should be taken to prevent wheel discs, and rims
from becoming mixed. Rims should be tagged or
marked to assure assembly to correct disc. The
following chart is provided (fig. 7) to aid in a s­
sembling the correct rim to disc if they should
become mixed.
On vehicles with tires that are secured on
rim by a one-piece split lock ring, or by a contin­
uous side ring held in place by a split ring, con­
ventional methods are used to mount and dismount
tires.
WHEEL A N D TIRE BALANCING
It is desirable from the standpoints of tire
wear and vehicle handling ease to maintain proper
balance of front wheel and tire assem blies on all
models. All wheels intended for use on front of
vehicle, such as those switched during periodic
tire rotation and those installed as new or repaired
replacement equipment should be accurately bal­
anced. This may be accomplished by either of two
types of balancing system s in current use which
balance wheels either on the vehicle or off. The
"on-the-vehicle" type, however, is the more de­
sirable in that all rolling components (brake drums,
bearings, seals, etc.), are included in the balancing
procedure and thereby have any existing unbalance
corrected.
Wheel balance is the equal distribution of the
weight of the wheel and tire assembly around the
axis of rotation. There are two ways in which
wheels can be balanced — statically and dynam­
ically; wheels must be statically balanced before
they can be balanced dynamically.
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
manner that the assembly has no tendency to ro­
tate by itself, regardless of its position. For ex­
ample: A wheel with a chunk of dirt on the rim will
always rotate by itself until the heavy side is at
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 "flutter"
and quite often to wheel "tramp."
G M C S E R V I C E M A N U A L
DYNAMIC BALANCE
balance) means that the wheel must be in static
balance, and also run smoothly at all speeds on an
axis which runs through the centerline of the wheel
and tire and is perpendicular to the axis of rotation.
following precautions must be observed:
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.
should either be replaced or straightened before
being balanced.
if an eccentric or out-of-round condition exists.
Note that this condition, if severe, cannot be "bal­
anced out." An assem bly which has an out-of-round
condition exceeding 5/16" 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 over­
all ride quality.
ommended that the instructions covering the oper­
ation of the wheel balancer being used be closely
followed.
WHEELS A N D TIRES
D IM E N S IO N
----- A "
RIM
W h e e l S iz e D i m e n s i o n
20 x 5.0 5.0"
20 x 6.0 6.0"
20 x 6.5 6.5"
T-5634
Figure 7 — Rim Chart
Dynamic balance (sometimes called running
To ensure successful, accurate balancing, the
Wheel and tire must be clean and free from
Bent wheels that have run-out over 3/32"
Inspect tire and wheel assembly to determine
When balancing wheels and tires, it is rec­
Sec. 10
Page 511
DISC
A
T ire S iz e
7.00-20
7.50-20
8.25-20
8.25-20
9.00-20