a suspension system for a tractor - drawn mower used for crops for agricultural purposes is made up of parallel links , connected at a first end to a frame and to a mowing unit at a second end . a torsion spring assembly , similar to that used for torsion axles , is used to bear a portion of the weight of the mowing unit when the mowing unit is in a lower , mowing position . all torsional stress is removed from the torsion spring when the mowing unit is in a transport position . during mowing , the weight of the mowing unit is divided up between the torsion spring and the surface of the ground . the ratio of the weight supported by the ground to that supported by the torsion spring is adjustable by an operator .