14-8
If weight is not equally distributed around the wheel, unbalance centrifugal force by the wheel rotation
produces vibration. As the centrifugal force is produced proportional to the square of the rotating speed,
the wheel weight should be balanced even at high speed. There are two types of the tire and wheel
balancing: static and dynamic. Abnormal vibration may also occur due to unbalanced rigidity or size of
tires.
1) Static Balance
When the free rotation of the wheel is
allowed, the heavier part is stopped on the
bottom if the wheel weight is unbalanced and
this is called "Static Unbalance". Also, the
state at which tire's stop position is not same
is called "Static Balance" when the wheel is
rotated again. If the part A is heavier as
shown in the figure 1, add the balance weight
of a weight corresponding to unbalanced
weight from B to A to maintain the static
balance. If the static balance is not
maintained, tramping, up and down vibration
of the wheels, occurs.
2) Dynamic Balance
The static unbalance of the wheel creates
the vibration in the vertical direction, but the
dynamic unbalance creates the vibration in
the lateral direction. As shown in the figure
2 (a), if two parts, (2) and (3), are heavier
when the wheels are under the static
balance condition, dynamic unbalance is
created, resulting in shimmy, left and right
vibration of the wheels, and the torque Fxa
is applied in the axial direction. To correct
the dynamic unbalance, add the balance
weight of a same weight for two points of
the circumference of the rim, A and B, as
shown in the figure 2 (b), and apply the
torque in the opposite direction to the
torque Fxa to offset in order to ensure
smooth rotation of the wheel.
Center
A
B
a
a
Fxa
Fxa F
F
A
B
(a)(b)
[Figure 1]
[Figure 2]
3. WHEEL BALANCE
