Abstract: A sled for use in tractor pulling contests, and the like, comprising a frame supported on front and rear wheels, a ballast mass supported by the frame, a pan adapted for sliding frictional engagement with the ground, and an articulated linkage mechanism for transfering the weight of the ballast from the wheels to pan. As the sled is pulled, the linkage mechanism, which is driven by rotation of the rear wheels, progressively shifts the weight of the sled from the wheels to the pan, by lowering the pan relative to the frame. The suspension springs for the rear axle have a greater vertical stroke than those for the front. Therefore, although the front wheels may ultimately be completely lifted from the ground during the weight transfer, the rear wheels always contact the ground with a force sufficient to drive the linkage mechanism. suBACKGROUND OF THE INVENTIONTractor pulling contests have become increasingly popular.