A trailed vehicle has at least one beam axle (but perhaps two with or without load sharing coupling) with the wheels independently suspended on leading or trailing arm members. The axle is mounted to the chassis or body so that in bump or positive roll conditions when a wheel on one side and the body or chassis move closer together, the axle moves forwardly at that side resulting in the steering of the wheels in a direction to counter the effects of the displacing force acting on the trailed vehicle and thus undesirable effects exerted by the trailed vehicle on the towing vehicle. A ''''bolt-on'''' suspension unit has a torsionally resilient beam axle, a primary torsion suspension for the arm members and a secondary suspension allowing forward movement of either side of the axle about one of a pair of transversely aligned pivots in reaction to torque imposed on that side of the axle under bump or positive roll conditions.