Virtual Pivot Axle

Assignment

What the constructors would really have liked, was to have had the pivot axle in the wheel. This is the reason why, e.g., in some modern double-wishbone-suspensions the upper ball-head does not lie next to the swiveling wheel, but above it. To see this, click on the lower button. The four-link suspension is a brilliant contribution to this theme. When turning the steering the wheel turns around a so called virtual steering axis. This is now, no longer the connection of the upper- and lower ball joints, but can be construed from the intersections of the strut extentions.

Function

Unfortunately, in the above picture, the second lower strut is not visible. To make things easier to understand, the sub-frame and parts of the engine have been cut away. If each strut has its own ball joint, the pivot axis can be be moved very far outwards and, in addition, can change with the turning angle. Depending on the arrangement and the length of the two wishbones, the camber-, kingpin- and caster changes, the precise matching to the spring compression is possible.
Both the front axle constructions shown in the above pictures make an important contribution to the reduction of the interference force radius. This is the distance of the tyre center to the pivot axis at the height of the wheel hub. A high interference force radius conducts the accelerating and the decelerating forces to the steering. The further the pivot axis is shifted into the wheel, the lower these influences are. 12/10