Figure 8-41.Tire rotation diagrams.
When your tires wear out together, you can get a
new set of tires without being forced to change tires in
pairs. By replacing tires as sets, you will maintain the
original handling balance.
Figure 8-42.Dynamic imbalance.
Improper wheel balance is the most common cause
of tire vibration. Often a tire will appear to be round
and true when rotated slowly. However, when one side
is heavier than the other. centrifugal force tries to
throw the heavy area outward during operation. To
obtain maximum tire wear and a comfortable ride, you
should balance the wheels. The two types of tire
imbalance are as follows:
DYNAMIC IMBALANCE (fig. 8-42) lies on
either or both sides of the center line of the tire, which
causes the tire to vibrate up and down (wheel hop) and
from side to side (wheel shimmy). To be in dynamic
balance, the top-to-bottom weight and the side-to-side
weight must all be equal.
STATIC IMBALANCE (fig. 8-43), also called
wheel tramp or hop, lies in the plane of wheel rotation,
which causes the tire to vibrate up and down. For a
wheel and tire assembly to be in static balance, the
weight must be evenly distributed around the axis of
To static balance a wheel and tire assembly, add
wheel weights opposite the heavy area of the wheel. If
a large amount of weight is needed, add half to the
outside and the other half to the inside of the wheel.
This will keep the dynamic balance of the tire.
However. when dynamically balancing a wheel and
Figure 8-43.Static imbalance.
tire assembly, the weights must be added exactly
where needed (fig. 8-44).
A wheel-balancing machine is used to determine
which part of a wheel assembly is heavy. The three
types of balancing machines are as follows:
BUBBLE BALANCER (fig. 8-45) is the most
common type of balancer used by the NCF. This type of
balancer will ONLY statically balance a wheel