(relaxing music)
- [Narrator] Why do we balance wheels?
We balance to cancel out the uncomfortable vibration
that can be felt when an unbalanced wheel
is traveling at speed, but balance is not the only cause
of wheel and tire-induced vibration.
A vehicle may have four perfectly balanced wheels
and still experience vibration.
Vibration can also be caused by a bent rim.
How the tire fits on the rim.
Or by construction characteristics of the tire.
These factors contribute to road force,
which is the change in force acting
on a wheel assembly as it rolls.
Fortunately, road force is easy
to correct if you can measure it.
Road force balancers emulate driving conditions
by pressing a roller against the tire.
The roller measures the road force for an assembly,
and the balancer suggests corrections
to minimize or eliminate the road force vibrations.
The most common corrective actions are,
match mounting, the process of rotating the tire
on the rim to reduce road force. Bead massage,
a technique of exercising the new tire
to better fit the rim. Or placing higher
road force assemblies in less sensitive wheel
positions on the vehicle, like the rear.
Balancing is always required to eliminate vibrations,
but eliminating all wheel and tire-induced vibration
requires measuring and correcting road force as well.