Vauxhall Workshop Service and Repair Manuals

Geometric driving axis

The rear axle decides the tracking axle of the vehicle. Therefore all measurements on the front wheels relate to the geometric driving axis. The vehicle drives "straight ahead" on the geometric driving axis.

The geometric driving axis (1) arises from the bisectors of the total toe (4) of the rear wheels. It is therefore determined by the toe variation of the rear wheels divided by two. The diagram shows the ideal case. The axis of symmetry and the geometric driving axis coincide. The individual toe values (2, 3) of the rear wheels in this case have the same positive value, e.g. rear left/right +0° 10'. But this ideal case also applies with the same negative value.

If these axes deviate outside the tolerance given by Opel/Vauxhall, the toe of the rear wheels must be adjusted. If the toe cannot be adjusted, the rear axle must be adjusted or aligned using the corresponding special tool.

If adjustment/setting as specified is not possible, the rear axle body must be replaced or the fixing points of the rear axle checked for damage on the vehicle subframe.

An anti-clockwise deviation of the geometric driving axis ("pulling" to the left) results in a negative and a clockwise deviation ("pulling" to the right) produces a positive angle.

During electronic chassis alignments, the geometric driving axis is automatically determined as a reference line for the toe measurements on the front wheels. The reference measurement is a vital requirement for correct measurements on modern Opel/Vauxhall vehicles.