Swing axle

A swing axle is a simple type of independent suspension first used in early 20C. aircraft, Sopwith, Fokker et al, 1910 or earlier usually with rubber bungee and no damping..

Much later motor car rear swing axles have universal joints connecting the driveshafts to the differential, which is attached to the chassis. They do not have universal joints at the wheels - the wheels are always perpendicular to the driveshafts. Swing axle suspensions traditionally used leaf springs and shock absorbers. Pre 1967 Volkswagens used torsion bars as their spring.

This type of suspension was considered better than the more typical solid axle for two reasons:

1. It reduced unsprung weight since the differential is mounted to the chassis
2. It eliminates sympathetic camber changes on opposite wheels

However, there are a number of shortcomings to this arrangement:

1. A great amount of single-wheel camber change is experienced since the wheel is always perpendicular to the driveshaft
2. "Jacking" on suspension unloading (or rebound) causes positive camber changes on both sides
3. Reduction in cornering forces due to change in camber can lead to oversteer instability and in extreme cases lift-off oversteer

These problems were evident on Volkswagen up until 1967, the Mercedes-Benz 300SL, the early versions of the Porsche 356, the Triumph Herald, Vitesse and Spitfire, Tatra T603 and others.

Swing axles were supplanted by deDion axles in the late 1960s, though live axles remained the most common. Most rear suspensions have been replaced by more modern independent suspensions in recent years, and both swing and deDion types are virtually unused today.

The First Production (1960-1964) Chevrolet Corvair used this design. The alleged unsafe behaviour of the Corvair was described in detail by Ralph Nader in his book Unsafe at Any Speed. Second Production Corvairs (1965-1969) used a true independent rear suspension system.

Swing axle suspension characteristics: Camber change on bumps, "jacking" on rebound

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