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CHASSIS SUSPENSION
WHEEL BALANCE
6-27
SECTIO'~
6-D
WHEEL
BALANCE
AND ALIGNMENT
CONTENTS OF SECTION 6-D
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6-26
Wheel and Tire Balance
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6-27
6-27
Static and Dynamic Balance
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6-27
6-28
Wheel and Tire Balancing Pro-
cedure
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6-28
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6-29
Front Wheel Alignment Factors.
6-30
Front Wheel Alignment Pro-
cedure
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6-30
Bulletin No.
Page No.
SERVICE BULLETIN REFERENCE
SUBJECT
6-26 WHEEL AND TIRE BALANCE
Wheel and tire balance is the equal dis-
tribution of the weight of the wheel and tire
assembly around the axis of rotation. Wheel
unbalance is the principal cause of tramp and
general car shake and roughness, and contrib-
utes somewhat to steering troubles.
All wheel and tire assemblies are balanced
when assembled at the factory. Tire casings
and tubes are assembled with the valve stem
located in line with a red mark on the sidewall
of the casing, so that the weight of the valve
is placed on the light side of the tire. When
assembled in this manner the off-balance of the
tube tends to counter-balance any off-balance
of the tire. After installation of tube and tire
on the wheel, the assembly is further corrected
for balance,
if necessary, by installing balance
weights on the rim of the wheel.
The original
balance
of the tire and
tube as-
sembly may change as the tire wears. Severe
acceleration, severe brake applications, fast
cornering and side slip wear the tires out in
spots and often upset the original balance con-
dition and make it desirable to rebalance the
tire, tube and wheel as an assembly. Tire and
wheel assemblies should be rebalanced after
punctures are repaired.
It
is recommended that wheel and tire assem-
blies be checked for balance every 5000 miles.
6-27 STATIC AND DYNAMIC BALANCE
a. Static Balance
Static balance (sometimes called still bal-
ance) is the equal distribution of the weight of
the wheel and tire assembly about the axis of
rotation in such a manner that the assembly
has no tendency to rotate by itself, regardless
of its position.
For example: A wheel with a chunk of dirt
on the rim will always rotate by itself until the
heavy side is a.t 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, commonly known as wheel
tramp, which will also develop into wheel
shimmy.
b. Dynamic Balance
Dynamic balance (sometimes called running
balance) means that the wheel must be in static
balance and also run smoothly at all speeds on
an
axis which
runs through the center line of
the
wheel
and tire, and is perpendicular to the
axis of rotation.
To explain the principle of dynamic balance,
let us first consider what happens when we
swing a weight attached to a string.
If
we start
to swing this weight slowly, it is apparent that
the weight swings in a sharp angle with refer-
ence to the axis of rotation (the hand)
.
But if
the speed is increased, the weight climbs until
the weight mass is at right angles to the axis
of rotation. Now, let us apply this principle to
a spinning wheel.
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