Selectively engagable auxiliary leaf springs (38) for vertically supporting a vehicle chassis (32) on an axle assembly (22) in parallel with main suspension springs (34). Forward and rear ends (38b,38a) of the auxiliary leaf springs are pivotally attached to the vehicle chassis and the axle assembly, and pivotal movement of the forward ends (38b) is inhibited or prevented by engagement of actuator assemblies (56 or 100 or 170) to engage the auxiliary leaf springs. A control system automatically engages the actuator assemblies in response to load added to the vehicle and/or vehicle steering movement and/or rapid vehicle acceleration.