What choices do I have in balancing a wheel?
As the word static implies, the tire will be balanced when at rest. For example, if an unmoving assembly was centered on a cone and was balanced, it would be statically balanced. A “bubble balancer” is designed to statically balance a tire/wheel assembly.
Static imbalance is where there is one amount of weight located in the center of the tire/wheel assembly causing an imbalance. As the weight rotates, centrifugal forces are created causing the wheel to lift as the weight reaches top dead center. This lifting motion causes the tire/wheel assembly to move “up and down” creating a bounce to be felt. This static imbalance condition is evident by a “jiggle” or up-down movement of the steering wheel. These vibrations may also be apparent in the body, with or without steering wheel shake.
A statically imbalanced tire driven for an extended period may cause “cupping” in the tire's tread, create vibration, and adversely effect handling.
Static balancing alone is a seldom-recommended procedure that balances the assembly using only a single weight plane. For example, a single weight is commonly placed on the inner clip weight position for cosmetic purposes. This is not a recommended practice and usually insures the assembly is not properly dynamically balanced. The assembly may then experience side-to-side imbalance while in motion, causing a shimmy condition and objectionable vibration.
Dynamic imbalance in general terms is defined where one or more locations of the tire/wheel assembly are heavier causing an imbalance force and/or an imbalance wobble. Shown below is a tire/wheel assembly with two heavy spots of equal weight which are located 180 degrees radially from each other on opposite sides. As this assembly rotates, centrifugal forces cause a large imbalance wobble to be created, but the imbalance force (as well as the static imbalance) will be zero. A wheel with this condition will cause a wobble or shimmy to be felt in the steering wheel. Excessive dynamic imbalance of this type creates a shimmy that transfers through the suspension components to the occupants of the vehicle, especially at higher speeds.
Modern “dynamic” balancers spin the wheel in order to measure both the up and down imbalance force and the wobble or shimmy related imbalance (side-to-side). Dynamic balancers direct the operator to place correction weights on the inside and outside correction locations of the rim so that both imbalance force and imbalance wobble will be eliminated.
Static and Dynamic Imbalance Sensitivity
As a general rule of thumb, to achieve the best balance on an average sized tire and wheel assembly:
A small amount of residual dynamic imbalance is preferred over a similar amount of remaining static imbalance.
In general, it takes much more residual dynamic imbalance to cause a vibration than the same amount of static imbalance.
The larger the diameter used for weight placement, the smaller the amount of correction weight is required.
The wider the distance between the two weight placement locations, the smaller the amount of correction weight is required.
If static balance is the only option, always verify that the remaining dynamic residual imbalance is within acceptable tolerance.