Tire Stiffness Variation

In addition to balance and free runout, tire stiffness variation (loaded radial runout) can also cause a vibration. However, this is impossible to measure without a Tire Problem Detector (TPD) or a loaded radial runout buffer.

The TPD is a roller drum that slowly rotates the tire while under load and mounted on the vehicle. Tire stiffness variation causes wheel spindle movement which can be measured.

The loaded radial runout buffer slowly rotates the tire and wheel off the vehicle under load with a roller drum, and measures tire stiffness variation. It will then "match" the tire to the wheel by buffing off small amounts of rubber from the outer tread rows at the stiff spot. This procedure is usually effective, especially when used as a measuring device and for fine buffing only.

Use of the TPD and loaded radial runout buffer provides two methods to measure or correct tire stiffness variation, tire runout and wheel runout at the same time. However, the basic procedure of measuring free runout with a dial indicator, as previously described, is usually more practical, especially when the TPD or runout buffer is unavailable. The free runout of the tire will usually correspond with the tire's stiff spot.