Pontiac FIREBIRD 1972 Service Manual page 1243

10-6 1972 PONTIAC SERVICE MANUAL
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ADD BALANCE
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WEIGHTS HERE
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r--I
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CL
O F SPINDLE
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SPOT
WHEEL TRAMP
CORRECTIVE WEIGHTS
Fig. 10-6 Static Unbalance Correction
Each time tires are changed they should be inspected for
signs of abnormal wear, bulging, stones, nails, glass, etc.
WHEEL AND TIRE BALANCE
There are two types of wheel and tire assembly balance-
static and dynamic.
Static balance is the equal distribution of weight around
the axis of rotation (spindle) such that the wheel and tire
assembly has no tendency to rotate by itself, regardless of
its position, Fig. 10-6. Wheels that are statically un-
balanced cause a hopping or bouncing action called wheel
tramp as the tire rolls along the highway and, if severe,
will eventually cause wear and damage to the tire.
Dynamic balance is the equal distribution of weight about
the plane of rotation, Fig. 10-7, such that when the tire
spins, there is no tendency for the assembly to move from
side to side. Wheels that are dynamically unbalanced may
cause a vibration to occur while the car is turning.
Improper balance will cause objectional vibrations or
resonances in the vehicle and should always be checked
and corrected as part of a vibration diagnosis procedure.
Balance should also be checked when wheels, tires or
brake drums are replaced in service. Under normal condi-
tions, static unbalance has more adverse effect than dy-
namic unbalance.
Wheel and tire assemblies are balanced in production to
a static balance specification of 3 1/2 inch ounces (approx-
imately 1/2 ounce weight at wheel rim). In this procedure,
balance weights totaling a maximum of six ounces are
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WHEEL SHIMMY CORRECTIVE WEIGHTS
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Fig. 10-7 Dynamic Unbalance Corrections