Jules-Albert de Dion

Comte Jules-Albert De Dion was a French Noble and founder of the¬†automobile manufacturer De Dion-Bouton. Although the name of the manufacturer has long since passed into history the name de Dion has been immortalized in a suspension system used in a few select performance cars. De Dion, however, was not the inventor of the suspension system that bears his name; that was invented in 1894, for use in the companies' Steam Tricycles, by the co founder of the De Dion-Bouton company Charles Trepardoux. As a concept the de Dion system, sometimes known as a de Dion tube, is a step above the solid (or 'live') rear axle, swing axles (ask an original VW Beetle or Chevelle owner) or the Hotchkiss drive, but is generally considered inferior to a true independent rear suspension (IRS). The system typically consists of a tubular beam that connects the two rear uprights and keeps the rear wheels parallel, as the tube carries no drive torque the system is sometimes referred to as a 'dead axle'. The system employs a chassis mounted differential and drive shafts and is located by various links. Its major advantage over a live axle is a significant reduction in the unsprung weight of the suspension due the chassis mounting of the differential and elimination of any requirement for universal or constant velocity joints in the main drive shaft. This gives a major improvement in handling if engineered correctly without the complexity of a fully independent rear suspension. As originally conceived by Chapman the Seven had a live axle and for many years after the Caterham assumption of the program this was sourced from the old Morris company; it was the unit used in the eminently forgettable Morris Ital, a car so bad it was sold by Morris into license production in Iran. In late 1983 it became clear that production of this unit was going to cease and several management and engineering personnel, in true British tradition, discussed their choices at a local pub, the King & Queen. The production live axles available that could conceivably fit within the dimensions required, even when modified, were minimal; and not promising from an engineering standpoint. Those present pondered the inevitable conclusion that to continue production of the Seven they would have to abandon the live axle. Adoption of a true independent rear suspension was discussed, and several present pushed for the idea, but the consensus was that development of an IRS would be a major undertaking for such a small company. One of the engineers, Reg Price, suggested the de Dion solution and, as he had worked out that the cost of such a system would be around 100 Pounds Sterling less than a true IRS, the idea was agreed by all present over a pint of beer. There were some historical precedents for the de Dion, some early Lotus Sevens had been fitted with the system and some racing Sevens had been converted, so the idea seemed to fit. Price and another engineer spent several months developing the system and the first production Caterham with a de Dion rear suspension debuted at the 1984 Birmingham Motor Show. The system is now standard on all Caterham's except the Superlight CSR, and certainly works very well, ask anyone who has driven the car. So the name of a French Count, who didn't invent a 120 year old suspension system, lives on in a Caterham ...