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A torsion beam suspension borrows its design from a trailing arm suspension and is used primarily on small to mid-sized front-wheel drive vehicles. It utilizes a coil spring mounted in close proximity to, or over, the shock absorber. The torsion beam suspension is able to forgo the anti-roll bar due in part due to its ability to flex each side independently of the other when encountering a twisting force. Although not considered a performance suspension package, the torsion beam suspension has been used with success on vehicles marketed as limited performance vehicles such as Volkswagen's Golf GTI. Popular among automobile designers for not intruding greatly into the rear foot wells of the passenger compartment, the torsion-type suspension system is inexpensive to produce and easily manufactured.
The major difference between a torsion beam suspension and a torsion bar suspension is the spring utilization of each component. The beam uses a coil spring-mounted in conjunction with a shock absorber to cushion the ride of the vehicle. In a torsion bar suspension, the torsion bar is, in fact, the spring and is engineered to flex and twist as the vehicle demands, effectively cushioning the ride. The torsion bar suspension also manages the vehicle's ride height by utilizing an adjustable "key" that is raised or lowered, effectively raising or lowering the stance of the vehicle. This torsion bar suspension system is used on passenger vehicles from sports cars to off-road trucks.
A torsion bar suspension is crafted of a solid-spring steel, allowing the bar to flex and twist without breaking, whereas a beam suspension is commonly created by welding stamped steel components together in order to create a suspension system. The suspension is able to flex slightly due to manufacturing tolerances, however, the system is not created with the flexing ability factored into the design. With the coil spring and shock absorber taking care of the bumps in the road, the flexing ability of the beam is an unexpected bonus for the most part. When required due to damage from an accident or other reasons, the torsion beam is typically replaced as a singular unit and replaced with a new assembly.
Unlike a straight axle that mounts the wheels on a single axle suspended by a typical set of leaf-type springs, the torsion beam suspension uses an H- or C-shaped assembly mounted to the vehicle's chassis. This assembly is accompanied by coil springs to dampen the rough spots in the road. The shape of the assembly contributes to its flexibility.
Which one is better: A coupled torsion beam axle with a coil spring or an isolated trailing link with a coil spring, or a semi-independent twist beam coil spring?