What are Torsion Bars?

Torsion bars, also known as torsion beam suspension or torsion spring suspension, are simply springs that compose the vehicles’ suspension systems. A torsion bar is piece of material which when distorted tries to return to its original position. One end of the long torsion bar is attached to the vehicle chassis. The opposite end, which is fastened to a pivot perpendicular to the bar, terminates in a lever that is attached to the axle of the suspension arm. The bar’s torsion resistance neutralizes vertical motions caused by the wheels as it rotates along its axis. The flexibility of a steel bar or tube, twisting lengthwise of torsion bar suspension provides spring action. The length, diameter and material of the torsion bar are the determinants of effective spring rate.

Torsion beam suspensions enable easy configurability of ride height. It is durable and small profile along with the width of the vehicle. Unlike leaf spring systems, torsion beam suspension provides longer travel and takes up less of the vehicle’s interior volume compared to coil springs. However, it cannot provide an increasing spring rate, forcing designers to bargain between handling and riding quality. Though progressive torsion bars are available in the market, these types have a tendency to crack where the diameter of bar changes – therefore losing durability.

Torsion bars were first incorporated on some vehicles to provide automatic leveling that respond to changes in road conditions. The early prototypes of Volkswagen Beetle, prior to World War II, incorporated tension bars to compensate its traverse mounting style. This system was applied to many war vehicles and was used extensively in European cars.
Torsion bars are installed both front and rear parts in the vehicle and interconnects them to improve riding quality.

Trucks and SUV’s from Ford, General Motors and Dodge currently use torsion bar suspensions to balance between lighter and heavier engine packages and allow adjustment of the ride height.