BALANCING

Drivers of high-performance vehicles will be more sensitive to imbalance problems, but no driver is happy with an annoying vibration.

AN OUT-OF-BALANCE TIRE AND WHEEL ASSEMBLY

• Degrades ride quality and driver comfort.
• Shortens the life of tires, bearings, shock absorbers, and other suspension components. Vibration is the most noticeable effect of imbalance.
• It is dependent on vehicle speed.
• It often first becomes apparent between 64 and 72kmh and increases in magnitude with greater speeds.

HEAVY OR LIGHT SPOT IMBALANCE

There are two types of imbalance caused by heavy or light spots: static and dynamic.

STATIC IMBALANCE

Occurs when there is a heavy or light spot in the tire so that the tire won't roll evenly and the tire/wheel assembly undergoes an up-and-down movement.

DYNAMIC IMBALANCE

Occurs when there is unequal weight on both sides of the tire/wheel assembly centerline. The tire/wheel assembly has a side-to-side movement.

RADIAL OR LATERAL RUN-OUT IMBALANCE

This results from poor bead seating on the rim or the placement of components. Poor bead seating is usually the result of improper mounting or the use of improperly made wheels. A small degree of this imbalance is acceptable, but too great a run-out causes vibration and excessive tire wear.

RADIAL RUN-OUT

An "out-of-round" situation where vibrations are produced as the wheel spindle moves up and down.

LATERAL RUN-OUT

A side-to-side or wobbling movement of the tire and wheel. It is less common than radial run-out. Sensitivity of a vehicle to vibration from radial run-out is four to eight times that of wobble from lateral run-out.

SOURCES OF IMBALANCE

Two sources of imbalance occur in tires: heavy or light spots in the tire and radial or lateral run-out. Imbalance also can be caused by:

• Variations within the wheel, such as thickness and welds.
• Rotor and axle imbalances.

HEAVY OR LIGHT SPOT BALANCING

Achieved either statically or dynamically, depending on the type of imbalance that has occurred.

STATIC BALANCE

Achieved with a bubble balancer, but does not correct for dynamic imbalance.

DYNAMIC BALANCE

Achieved with a spin balancer where the tire/wheel assembly is balanced both statically and dynamically.

RUN-OUT BALANCING

Depends on whether it is radial or lateral run-out.

RADIAL RUN-OUT BALANCING

Achieved by rotating the wheel and tire assembly two stud positions on the hub or by rotating the tire 180° on the wheel. If run-out is still over specification, check wheel run-out and mark the low point. Rotate to match the high point of the assembly run-out with the wheel low point. If the assembly run-out is still too high and the wheel is within specification, replace the tire.

LATERAL RUN-OUT

Achieved by using a run-out gauge to check both the tire and wheel. Chalk-mark the highest point of run-out on both the wheel and tire. Replace whichever (wheel, tire, or both) is out of specification.