Abstract: A supplemental suspension and method of supplementing the suspension in a vehicle having an axle, wheels rotatably disposed on the axle, a frame and an existing leaf spring suspension system for mounting the axle onto the frame. The supplementary suspension system includes first and second suspension arm members having front and rear ends, a cross member for connecting the two arm members, hanger means for pivotally suspending the rear ends of the arm members from the frame of the vehicle, mounting means for mounting the front ends of the arm members on the axle, and air suspension means for operably connecting a portion of the suspension arm members disposed between the front and rear ends of the members to the vehicle frame. The air suspension means further includes air bags, wherein the degree of suspension of the suspension means can be adjusted by altering the amount of air in the air bags. The arm members preferably have a generally "U" shape when viewed from a side of the vehicle.