A crossmember is a structural section, usually of steel, usually boxed, that is bolted or welded across the frame rails of a vehicle, to support the vehicles motor. For the suspension of any vehicle to operate as it should, for proper handling, and to keep the body panels in alignment, the frame has to be strong enough to handle the loads applied to it. It must not deflect, and it has to have enough torsional strength to resist twisting.