It avoids, as much as is possible, mounting errors, misalignment when mounting, wheel-rim imbalance and play. Compensation actually means, 'balancing' and refers to the mounting of the sensors on the wheels. An axle alignment may not deliver differing values simply because, e.g., the wheel is turned a half a rotation, or the vehicle is moved.Earlier, it used to function like this: A wheel was turned, and the mountings of the data-reader on the wheel rims were altered until the air bubble of the spirit-level in the data-reader no longer moved back- and forth. Thus, the data- reader was calibrated, and the "level position" of the data-reader was guaranteed.Nowadays, these differences are electronically determined and taken into account. Depending on the rotation angle of the wheels, (half, third or quarter) one differentiates between 2-, 3- and 4-point compensation. One must however, inform the wheel-alignment gauge, that one has carried out the required rotation. The whole process is an important pre-condition for the success of an axle alignment.

There are manufacturers who maintain, their pivot-points of the data-readers on the wheels are so precise, that no compensation is necessary. However, also here, a geometrical error or a certain amount of play can exist. Unacceptable play however, would have to be determined beforehand, and be removed. Who knows, what sort of strange things can happen to a vehicle? One can explain the information of the manufacturers only in such a way, that these vehicles do not, under normal circumstances, react sensitively to an alignment check without compensation.

What to do however, when a repair is to be repeated? As the above figure shows, there are quick-clamps for the wheel sensors, which make the moving of the vehicle impossible. One could raise the vehicle, but many manufacturers forbid this, for good reasons. Modern chassis are fitted with a number of elastic bearings. If one raised the vehicle, it would first have to be driven again for 15-20 minutes.

One solution is a clamping device, awkwardly fastened to the rim edge (see figure in axle alignment). This permits compensation without raising the vehicle. However, it takes longer, and would also have to be differently calculated for the customer. Nevertheless, this method is to be recommended in the case of stubborn errors in the chassis. The new 3D- axle alignment is without these problems. 07/08