Torsion beam suspension, also known as twist beam and torsion bar, is a vehicle suspension system. One end of a long metal bar is attached firmly to the vehicle chassis; the opposite end has a lever, perpendicular to the bar, that is attached to the axle of a wheel. As the wheel travels up and down it "twists" the bar along its axis to provide the spring force. This system was used extensively in European cars as well as by Packard in the 1950's and Chrysler throughout the 1960's.
The main advantages of torsion beam suspension are durability, easy ride height adjustability, and a smooth ride. One major disadvantage is the lack of a progressive spring rate which can lead to sloppy handling.
Some vehicles use torsion bars to implement automatic leveling with sensors and motors to dynamically adjust the torsion in each bar in response to changing loads and road conditions.
The more commonly used coil spring is merely a torsion bar formed into a helix.
