Torsion bar suspensions use a special type of spring known as a torsion bar or torsion rod in order to resist the bumps and movement that a car or truck normally encounters on the road. Unlike the standard coiled springs that appear in shock suspensions, torsion bars are straight bars of steel or similar metals. Because of the manner in which the torsion rod is made and mounted within the suspension, it is able to give support similar to that offered by coiled springs.
Resistance to Torsion
When stress is placed on a torsion bar as the car or truck it is attached to goes over an uneven road, the force of this stress causes the torsion bar to begin to twist. This twisting, known as "torsion," is resisted by the metal that the torsion rod is made of. The metal is able to twist to a limited degree before the tension in the bar becomes greater than the amount of force that is being placed on it by the torsion. When this occurs, the tension within the bar is able to overcome the torsion, and the rod will twist back in the opposite direction to its original position. This twisting allows it to support the wheels and frame of the vehicle that it is attached to, preventing too much stress from building up within the suspension.
Transverse and Longitudinal Torsion Bars
Torsion bars are connected to the frame in one of two configurations. Transverse torsion bars are mounted across the width of the car or truck, connecting to the frame close to the centre of the vehicle. Longitudinal torsion bars are mounted along the length of the car or truck, connecting to the frame closer to the midpoint of its length. Regardless of where the torsion bar connects to the frame, it also connects to the wheel mount to provide suspension for the vehicle.
Adjusting Torsion Bar Suspension
Because of the torsion that torsion rods are subject to, they may require periodic adjustment in order to keep functioning properly. One of the most common problems that can occur with torsion bar suspensions is that the torsion rods in the suspension will begin to warp or sag slightly. This leads to the suspension not offering as much support for the vehicle as it once did and can result in an uneven ride and reduced gas mileage. Periodic adjustment of the torsion bars can eliminate this sagging and can also allow your mechanic to recognise excess wear in the torsion rods of your suspension so that you will know when the rods need to be replaced.