Watts Linkage

The Watts linkage is an automotive rear suspension designed in the early twentieth century as an improvement over the Panhard rod as a means of locating the rear axle of an automobile relative to the body and preventing relative movement side to side. Whereas the Panhard rod is pivoted at both axle and body forcing the axle to move in an arc, thus introducing a sideways component into the vertical movement of the axle, the Watts linkage ensures pure vertical motion.

It consists of two almost symmetrically arranged long rods mounted one at each side of the chassis and running parallel to and behind the rear axle, where they attach to the ends of a short vertical bar whose center is mounted to the center of the axle and which is free to rotate in the plane at right angles to the automobile's longitudinal dimension. As in the Panhard rod, the sideways arms themselves are free to pivot vertically at either end. Thus, each sideways member acts as a shorter Panhard rod mounted to the center vertical member providing lateral location. In contrast to the Panhard rod's action, however, the sideways components of the motion of the two arms as they pivot around their outboard mountings cancel each other in their effect on the axle, and are instead taken up by the center member's rotation about its axis.