12-8
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
