De Dion Suspension History
Originally patented in 1894 for use on de Dion Bouton steam-powered vehicles, this unique suspension design continues to be useful, well into the 21st century.
The latest company to adopt the De Dion design is Daimler-Fuso, in the rear end of its 2023 eCanter battery-electric truck. But long before this adaptation many, many automotive manufacturers have adopted variants of this clever design.
The De Dion suspension is technically a non-independent beam axle, but, instead of the half-shafts being located inside the axle tube, they’re positioned beside the axle. Also different is the fact that the final drive differential assembly is chassis-mounted and the half-shafts are fitted with flexible sliding joints where they connect to the final drive and at the wheel hubs.
The De Dion tube was named after Comte Jules-Albert de Dion, founder of French automobile manufacturer de Dion-Bouton, but the tube-based suspension was invented by co-founder Charles Trépardoux. He left the company in the following year, because he was convinced that steam was the future, while the other directors opted for petrol power.
De Dion suspension was developed to allow a rear-mounted steam engine and final drive to be connected to a leaf sprung beam axle. When de Dion Bouton replaced that with a single-cylinder petrol engine it was rear-mounted, so Trépardoux’s original suspension design was retained.
Contemporary vehicles used chain or belt drives that were eventually confined to motorcycle propulsion.
By the time Trépardoux’s patent expired, in 1910, de Dion Bouton was one of the world’s largest makers of automobiles and had followed the popular trend to front-mounted engine, radiator and transmission, with propellor shaft drive to a live rear axle, with differential gearing and internal half-shafts. The Trépardoux design wasn’t used again by de Dion Bouton, which was hit hard by post-WWI stagnation and the 1930s Great Depression. Car production folded in 1932.
In parallel almost with Trépardoux, German engineer Edmund Rumpler was also looking for alternative axle and suspension, when he came up with the swing-axle design in 1903. Rumpler was also an aircraft designer, so he was very busy during World War I and the swing-axle didn’t gain much traction until he displayed his revolutionary Tropfenwagen (water-drop) streamlined car at the 1921 Berlin Motor Show. This radical machine sported swing-axle rear suspension and caught the attention of several European car makers.
Rumpler Tropfenwagen – Detief Garbrecht
Best known for its weird behaviour in the rear ends of millions of VW ‘Beetles’ and US Army M151 Jeeps, the swing-axle was used by Tatra and Mercedes-Benz for many years and is still employed in Tatra off-road trucks. Swing-axle users included Hillman, Standard, Porsche, Renault and Triumph.
1925 Miller 122 – Writegeist
After WWI the De Dion axle appeared to have been relegated to automotive history, but, in 1925, the famous American constructor of Indianapolis track cars, Harry Miller, used a De Dion suspension in a front-wheel-drive racing car. This was the first use of a De Dion system in the front end of a motor car. He backed that up in 1931, with De Dion suspensions in the front and back of his V16 racer.
Miller-designed twin-cam racing engines doubtless inspired Ettore Bugatti in the design of his twin-cam Type 51 engine, but Miller’s use of De Dion suspension didn’t seem to have the same impact. However, by the mid-1930s the drivers of European racing cars were discovering the limitations of live axle and swing-axle rear ends – particularly those piloting the powerful Silver Arrows of Auto Union and Mercedes-Benz.
The Auto Union conglomerate was made up of Audi, Horch, DKW and Wanderer brands. Horch employed De Dion suspension on its eight-cylinder cars between 1936 and 1939. The only modification to the original design was the use of conventional universal joints instead of the De Dion type, which allowed telescoping action as well as angular action. To achieve the same effect Horch inserted a telescopic joint in each half shaft.
Mercedes-Benz took notice of the Horch design and in 1937 their Grand Prix car appeared with the De Dion rear axle. Torsion bar springs were used in place of multiple leaves, so radius rods had to be used to locate the axle. Also, the De Dion tube was designed in two halves, to allow one half to rotate slightly in relation to the other.
In 1938 Auto-Union abandoned the swing axles on their racing cars and used a De Dion system very similar to that used by Mercedes-Benz. Alfa Romeo did the same with the 158 Alfetta racer, adding a De Dion rear end to the car for post-WWII events, as did Bugatti with the Type 251.
Alfa Romeo is probably the highest-volume adopter of this technology, using it on the Alfa Romeo Alfetta, GT, GTV, GTV6, Giulietta, Alfa 6, 90, 75/Milano, and SZ/RZ.
Other production vehicles that used this suspension include: Lancia Aurelia and Flaminia; first and second generation Prince Gloria; the original Mazda Cosmo; Volvo 300-series; Rover P6; Chrysler all-wheel-drive minivans from 1991 to 2004; DAF 46 and 66; all Iso cars; early Bizzarrini 5300 GT Stradas; several large Opels, including the 1969 Opel Diplomat B; all Aston Martins from 1967 to 1989; Ferrari 375 and 250TR; first generation Maserati Quattroporte; Smart Fortwo and Smart Roadster; Mitsubishi i kei car and the Lotus Seven derived Caterham 7.
De Dion pros and cons
The original design of the De Dion suspension was to satisfy the need for a rear engine to power a rear axle, by means of a chassis-mounted final drive and half shafts with flexible connections at both ends. The cross-tube ensured that the wheel ends remained parallel to each other, as with a conventional ‘live’ axle, while leaf spring packs provided longitudinal and lateral axle control.
When the popular layout of vehicles became front engine and transmission, with rear live axle drive, the De Dion suspension was comparatively complicated and expensive. It offered lower unsprung weight than a live axle and better control of acceleration and braking forces, but that was of little concern to vehicle makers, considering the generally low engine power and braking abilities of most vehicles in the between-World War periods.
Vanwall racing car De Dion rear suspension
The De Dion suspension re-emerged firstly in racing cars in the pre-WWII era and was then adopted post-WWII in racing and performance cars. Initial applications were relatively simple, when suspension was by leaf springs, but the move to coils or torsion bars saw the need for radius rods to control longitudinal axle location and torque absorption and Panhard rods or Watt’s linkages to control lateral movement.
Eventually, in the 2000s, most car makers moved to wishbone-style rear independent suspensions for rear-wheel-drive applications.
Walter Snow Fighter – Histruckorps
However, the attraction of the De Dion design for some leaf-spring applications remained. For many years after 1935, New York based Walter Snow Fighter plough trucks used De Dion axles with portal gear hubs front and rear. A portal hub is ideal for a De Dion installation, because the entry point into the wheel hub by the half shaft is well above the stub axle centre line.
Because they were chassis-mounted, Walter’s large differentials could be designed for durability without increasing unsprung weight or reducing ground clearance. Forged steel beams were used instead of tubes.
A US pick up with De Dion suspension coupled with leaf springs was the battery-electric powered Ford Ranger EV. It was produced in limited numbers from 1998 until 2004. The original model had carbon-fibre leaf springs that provided inadequate lateral control, so it was subsequently fitted with a Watt’s linkage to provide lateral control of the axle tube. Later models had conventional steel leaf springs and the Watt’s linkage wasn’t required.
However, for its high-performance Raptor pick ups in the post-2000s, Ford went back to live axles, with coil spring suspension and Watt’s linkages.
By 2020 it appeared that the De Dion system was finally obsolete, but an unforeseen need for it emerged with the advent of ‘eAxles’ in some electrically-powered trucks. While most new-generation battery-electric trucks and fuel-cell electric trucks use a live axle with an electric motor and final drive unit bolted to where a diesel truck’s differential ‘nose’ would be mounted, this is not an elegant engineering solution.
That location significantly increases unsprung weight, which isn’t such a huge issue for heavy trucks, but there is a risk of vibration damage to the electro-mechanical components if the vehicle is driven on rough roads. (Try finding a road that isn’t rough in Australia!)
Daimler-Fuso’s solution to the eAxle vibration issue is a return to the De Dion design, in the case of the 2024 eCanter. As with the Walter snow plough trucks, the De Dion tube is replaced by a forged steel beam. Because the standard eCanter’s dual-rate leaf spring suspension is heavy-duty, it has plenty of longitudinal and lateral axle location capacity.
De Dion lives on!