The torsion bar adjusting device comprises a frame structure defining a collar with a slot in its lateral wall. Within the collar are first and second torsion bar end receiving sockets each having integrally radially outwardly extending arms passing through the slot in the collar. These arms may be individually moved to impart a rotation to the socket portion within the collar over a given number of degrees within the confines of the width of the slot. The arrangement is such that a center section of the housing for the torsion bars associated with the left and right rear wheels respectively in an automobile suspension system can be cut out and the adjusting device substituted for the section with the inner ends of the torsion bars being received in opposite ends of the collar to be secured to the respective torsion bar end receiving sockets. Individual movement of the radially extending arms will then impart a further twist to the associated torsion bars and thereby enable quick adjustment of the "stiffness" of the suspension system.