Swing axle

A swing axle is a simple type of independent suspension for the rear axle of rear wheel drive vehicles. Designed and patented by Edmund Rumpler in 1903, the then revolutionary invention in automotive suspension allowed powered wheels to follow uneven road surfaces independently. Along with better road contact and holding, each wheel's unsprung weight contributed to improved vehicle handling. The first automotive application was the Rumpler Tropfenwagen; another early example was the 1923 Tatra 11, later followed by the Mercedes 130H/150H/170H, the Standard Superior, the Volkswagen Type 1 Beetle and most of its derivatives, the Chevrolet Corvair, and the roll-over prone M151 jeep amongst others.

Many later automobile rear swing axles have universal joints connecting the driveshafts to the differential, which is attached to the chassis. Swing axles do not have universal joints at the wheels — the wheels are always perpendicular to the driveshafts; the design is therefore not suitable for a car's front wheels, which require steering motion. Nevertheless, a simplified variant, wherein the differential remained fixed to one of the halfshafts, was offered optionally on the 1963 Jeep Wagoneer's front axle, upon its market introduction.

Swing axle suspensions often used leaf springs and shock absorbers, though later Mercedes-Benz applications used coil springs and the VW beetle swing axle was torsion bar sprung.

One problem inherent in the swing axle concept is that it almost inevitably results in a very high roll centre which causes detrimental jacking effects and camber change when cornering and lateral cornering forces are applied. Its simple geometry limits design freedom to a great extent.

Swing axles can also be used as a low cost and durable independent suspension solution for non-driven front or rear axles, the Tatra 17 which had swing axles front and rear being an early example. It was also used in early aircraft (1910 or before), such as the Sopwith and Fokker, usually with rubber bungee and no damping.