The torsion bar spring suspension should absorb road imacts through a metallic connection between the car body and (as a rule) the lower part of the wheel suspension. It has a very prominent inventor, namely Ferdinand Porsche. In contrast to the coil spring, it saves space. (e.g., for the usable boot width)
The torsion bar spring is frequently used as a stabiliser and is often integrated into the wheel suspension. An L or U profile provides, in connection with e.g., two trailing arms, for a simple rear-axle construction. While normally a simple solid, round steel bar or tube has to cope with the torsion-stress, in the torsion bar suspension other forms, or even packages of flat steel are also found. A multiple interlocking or a lever with a stop-bolt allows the setting of the preliminary tension. This makes the altering of the 'vehicle-to-road' height possible, (e.g., when lowering the vehicle) without having to exchange any components. The torsion bar suspension can neither be progressive, nor does it have the self-damping properties of the multiple leaf spring.
Unfortunately nowadays, the torsion bar springs have become extremely rare in motor vehicles, if one ignores the ubiquitous stabilisers.This used to be different. The VW-Beetle and it's offspring were famous for their torsion bar suspension. Ever since the appearance of the Golf 1, almost unwillingly, or so it would seem, have they gone over to the coil spring. The torsion bar suspension was, at that time, found even more frequently in French motor cars, at least in the models up to the mid-range.
Shown above are four typical representatives. The rear axle of the VW-Transporter (identical in construction to the Beetle) has two short torsion bars, which are installed side-by-side, in one axle tube. In the above picture, the most modern design with a double-jointed axle can be seen. The Peugeot axle is completely different. This only required little effort, because this is not a driven-axle, it simply hangs on.This counts for the following two constructions as well. They however, are a bit more complex, because due to the higher suspension-comfort, longer torsion bars had been used. Two solutions emerge: Renault placed the two torsion bars one in front of the other and used equally long trailing arms, which gave the R4 or R5 differing wheelbases (!) on the right and on the left. Simca's construction was more elegant, they placed the torsion bars crosswise in the available space. This way, they did not disturb each other and the right- and left wheelbases could remain the same. 09/11