- [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.