De Dion tube
A de Dion tube is an automobile suspension technology. It is a sophisticated form of non-independent suspension and is a considerable improvement over the alternative swing axle and Hotchkiss drive types. A de Dion suspension uses universal joints at both the wheel hubs and differential, and uses a solid tubular beam to hold the opposite wheels in parallel. Unlike an anti-roll bar, a de Dion tube is not directly connected to the chassis nor is it intended to flex. In suspension geometry it is close to the trailing beam suspension most recently seen on the front wheel drive Chrysler "K-cars", but without the torsional flexibility of that suspension.
The benefits of a de Dion suspension include:
- Reduced unsprung weight compared to the Hotchkiss drive since the differential is connected to the chassis.
- Unlike a fully independent suspension there are no camber changes on suspension unloading (or rebound). Fixing the camber of both wheels at zero degrees assists in obtaining good traction from wide tires and also tends to reduce wheel hop under high power operations compared to an independent suspension.
There are costs, however:
- If coil springs are used then a lateral location link (usually either a Panhard rod or Watt's linkage), plus additional torque links on each side (five link suspension) or a combination of lower trailing links and an upper transverse wishbone are required. None of these additional links are required if leaf springs are used.
- Sympathetic camber changes on opposite wheels are seen on single-wheel suspension compression. This is not important for operation on improved surfaces but is more critical for rough road or off road use.
- Compared to a fully independent rear suspension the ability to refine the dynamic response of the vehicle is somewhat limited.
De Dion tubes are generally considered exotic and are rarely used. The Smart Fortwo micro-compact car produced by DaimlerChrysler, Mitsubishi i kei car produced by Mitsubishi Motors and the Caterham 7 (a version of the Lotus Seven) produced by Caterham Cars are the only cars currently in production that utilize this arrangement, as well as some kit car companies. In addition the original Mazda Cosmo, Alfa Romeo GTV6, and Rover P6 are examples of production vehicles using this suspension.
A recent production vehicle using this suspension using an aluminum tube with leaf springs was the Ford Ranger EV. The earliest production used carbon fiber leaf springs which required the use of a transverse locating linkage of the Watts type. Subsequent production used steel leaf springs which were sufficiently rigid to perform the transverse location function. Rather than only a differential, an integrated drive component consisting of an AC electrical motor, 3:1 reduction, and differential action was mounted to the chassis.