Selectively engagable auxiliary leaf springs (38 or 138) for vertically supporting a vehicle chassis (32) on an axle assembly (22 or 102) in parallel with main suspension springs (34 or 114). In three of the disclosed embodiments, both ends (38b,38a) of the auxiliary springs (38) are pivotally attached. In two other embodiments, one end (138a) of the auxiliary leaf springs (142) is pivotally attached and the other end (138b) is rigidly affixed in cantilever fashion. Actuators (56, 139 or 159) are employed to selectively enable or increase load supporting of the auxiliary leaf springs.