Even the first Ferrari featured a leaf-spring mounted rigid axle. Even the up-to-date model of the Ford Mustang has it. This design is exceptional for passenger cars though. It is used primarily, for (town) busses and other heavy utility vehicles. These vehicles mostly have a chassis (ladder-type frame) in which the axis can be integrated relatively simply and at a reasonable price. For heavy vehicles there is hardly an alternative to the rigid axle. It connects the wheels of an axis and holds the track and the camber consistent. This easy and stable construction is also suitable as a rear axle for front-wheel drive vehicles (figure 5) because of lower non-sprung masses. Real cross-country vehicles often feature a rigid axle because the axes interlock range is wider ('X' form).
Figure 4 shows a not driven, rigid rear axle, this time not combined with leaf springs , but with an air suspension. If one side is engaged, the opposite wheel is influenced. Rigid front axles make use of just one-pieced tie rods. The rigid part ends in case of non-driven axes in a fist, and for driven ones in a fork. Consequently, the name of the design. Figure 6 shows the production process of the pre-forge up to the state ready for installation.
Driven rigid axle tramples, only DeDion does not.
A driven rigid axle (figure 3) has large non-sprung masses, the final drive, the axle drive shafts (full-floating axles) and half the cardan shaft. It inclines to trampling and damps well only with a lot of sprung masses (e.g., trucks). The final drive of the De Dion rear axle and the cardan shaft are fastened completely to the vehicle floor and they are connected to the rear wheels through axle drive shafts. Through this rather costly expenditure, the advantages of the rigid axle (consistent track and camber) are preserved without having the disadvantages of the large non-sprung masses. With all other driven axes (independent suspension) drive shafts from the final drive to the wheels are necessary.
If rigid axles are not combined with leaf springs, e.g., with the aerial-sprung truck (figure 4), special guiding elements are necessary. In addition trailing arms can be mounted on both sides, one on top and another one below, to take up the tilting moment of the axis during the initial drive and braking. Also, precautions are in place against lateral running off of the axis. Figure 4 on top displays especially stable trailing arms. Alternatively a triangular wishbone (figure 7) in the middle, a Panhard rod, or a Watt linage. 12/08