|Tire/wheel balance is important for vehicle ride and
stability and for customer satisfaction as well. Tires are manufactured to close
tolerances for roundness and shape, but as a tire wears, the tire's mass may become
unevenly distributed, and the original rim/ tire balance may be affected.
A tire both rolls and steers. To provide smooth running, a tire's mass must be evenly distributed around both the rolling axis and its centerline. A heavy spot in the center of a tread can cause bounce. This is referred to as static imbalance.
An improperly mounted tire or a heavy spot in a sidewall
can cause wobble, or side-to-side shake. This is called dynamic imbalance. Any such
movement transmits itself throughout the vehicle. Wheel imbalance causes forces that
result in vibration through the vehicle's steering, suspension and body. Imbalance is the
cause of the majority of vibration complaints. Rims and poorly matched rim/tire
combinations are frequent contributing factors.
Static and Dynamic Imbalance
Off-car dynamic balancing is recommended because it balances the wheel/tire unit very accurately. However it cannot compensate for imbalance in the brake/hub assembly. Some vehicles may have imbalanced brakes. In this case, the brake/hub must be removed and balanced separately. This gives the optimum balance and allows for future tire rotation.
On-car electronic balancing includes the brake/hub assembly and the wheel/tire unit, making possible an accurate balance. It is difficult to perform a dynamic balance using this method, but it does balance the entire rotating mass as a unit. The wheel must be marked so it can be reinstalled in the same location (both position on the car as well as position on the hub) after future service work.
Wheel weights added to the inside or outside of the rim correct imbalance as indicated by balancing equipment. While balancing may seem a relatively simple operation, care must be taken to eliminate imbalance, since even a minor imbalance contributes to wheel wobble and poor ride and handling characteristics.