(i)

Solutions

Several engineering options can limit swing axle handling problems, with varying success:

1. Anti-roll bar: As a design option, a front anti-roll bar which can ameliorate the swing axle car's handling—shifting weight transfer to the front outboard tyre, considerably reducing rear slip angles—thereby avoiding potential oversteer.
2. Single-pivot point: Mercedes-Benz addressed the handling issues by producing swing axles with a single-pivot point located under the differential, thus well below the axle. This configuration markedly reduced the tendency to "jack-up" and the later low pivot swing-axle equipped cars were praised in contemporary publicat

   Several engineering options can limit swing axle handling problems, with varying success:

   1. Anti-roll bar: As a design option, a front anti-roll bar which can ameliorate the swing axle car's handling—shifting weight transfer to the front outboard tyre, considerably reducing rear slip angles—thereby avoiding potential oversteer.
   2. Single-pivot point: Mercedes-Benz addressed the handling issues by producing swing axles with a single-pivot point located under the differential, thus well below the axle. This configuration markedly reduced the tendency to "jack-up" and the later low pivot swing-axle equipped cars were praised in contemporary publications for their handling. The low-pivot swing-axle remained in production with Mercedes-Benz W108 280SE and 300SEL until 1972. It was fitted to the 300SEL 6.3, which was during the early 1970s the world's fastest production sedan. AMG-modified 6.3s were also raced with the stock swing axle.^[1]
   3. Tyre pressure differential: The Renault Dauphine, Volkswagen Beetle and first generation Chevrolet Corvair (1960–1964) used a tyre pressure differential strategy to eliminate oversteer characteristics of their swing axle suspensions—specifically low front and high rear tyre pressure—which induced understeer. The tyre pressure differential strategy offered a significant disadvantage: owners and mechanics could inadvertently but easily re-introduce oversteer characteristics by over-inflating the front tyres (that is, to typical pressures for other cars with other suspension systems) or by inflating all four tyres to the same pressure. The effectiveness of this option was criticized in lawsuits in the US during the 1960s.^[2]
   4. Z-bar and roll-inducing springs: Mercedes-Benz introduced, to help their low-pivot swi

      Ralph Nader in his 1965 book Unsafe at Any Speed detailed accidents and lawsuits related to the shortcomings in 1960–1963 models of the first generation Chevrolet Corvair's swing-axle design. Nader identified a Chevrolet engineer who had fought management after the management had eliminated a front anti-roll bar for cost reasons. The 1964 models were fitted with a front anti-roll bar as standard equipment, in addition to a rear transverse leaf spring, thus improving stability during emergency maneuvering. Second-generation Corvairs (1965–1969) used a true independent rear suspension (IRS) system.

      The Hillman Imp designers learned from the problems with the Corvair, having crashed^[3] one at a relatively low speed, and they designed their rear-engined car with a semi-trailing arm suspension at the rear. To attain correct handling balance, they actually used swing-axle geometry at the front, with the steering pivots mounted at the outer ends of single swing wishbones. These caused too much understeer and uneven tyre wear, and modifications were made to reduce the positive camber of the front wheels by lowering the swing-axle pivot points.^[4] Aftermarket kits were also available to do this, and an inexpensive alternative was to insert a tapered shim to change the inclination of the kingpin carrier relative to the wishbone.

      Replacement

      Swing axles were supplanted in general use by de Dion tube 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 de Dion types are virtually unused today.

      One exception is the Czech truck manufacturer Tatra, which has been using swing axles on a central 'backbone' tube since 1923 (model Tatra 11) instead of more common solid axles. This system is claimed to give greater rigidity and better performance on poor quality roads and off-road. There the inherent reduced stability on roads is compensated by an increased stability on rough terrain, allowing for higher off-road speeds, all else being equal. This is especially manifested in long 6+ wheel vehicles where off-road chassis twisting can be a major issue.

      Twin I-Beam

      Another use of the swing axle concept is Ford's "Twin I-Beam" front suspension for trucks. This system has solid axles, and may transmit power in four-wheel-drive versions, where it is called "Twin Traction Beam". Though it is an independent suspension system, as each tyre rises and falls without affecting the position of the other, the parallelogram action of the A-arm suspension system is not present. Each tyre moves in an arc, but, due to the longer arms, camber changes are proportionally smaller than in powered swing axles for the rear wheels listed above. The pivot point of the axles is lower and located not in the center of the car, but nea

      The Hillman Imp designers learned from the problems with the Corvair, having crashed^[3] one at a relatively low speed, and they designed their rear-engined car with a semi-trailing arm suspension at the rear. To attain correct handling balance, they actually used swing-axle geometry at the front, with the steering pivots mounted at the outer ends of single swing wishbones. These caused too much understeer and uneven tyre wear, and modifications were made to reduce the positive camber of the front wheels by lowering the swing-axle pivot points.^[4] Aftermarket kits were also available to do this, and an inexpensive alternative was to insert a tapered shim to change the inclination of the kingpin carrier relative to the wishbone.

      Swing axles were supplanted in general use by de Dion tube 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 de Dion types are virtually unused today.

      One exception is the Czech truck manufacturer Tatra, which has been using swing axles on a central 'backbone' tube since 1923 (model Tatra 11) instead of more common solid axles. This system is claimed

      One exception is the Czech truck manufacturer Tatra, which has been using swing axles on a central 'backbone' tube since 1923 (model Tatra 11) instead of more common solid axles. This system is claimed to give greater rigidity and better performance on poor quality roads and off-road. There the inherent reduced stability on roads is compensated by an increased stability on rough terrain, allowing for higher off-road speeds, all else being equal. This is especially manifested in long 6+ wheel vehicles where off-road chassis twisting can be a major issue.

      Another use of the swing axle concept is Ford's "Twin I-Beam" front suspension for trucks. This system has solid axles, and may transmit power in four-wheel-drive versions, where it is called "Twin Traction Beam". Though it is an independent suspension system, as each tyre rises and falls without affecting the position of the other, the parallelogram action of the A-arm suspension system is not present. Each tyre moves in an arc, but, due to the longer arms, camber changes are proportionally smaller than in powered swing axles for the rear wheels listed above. The pivot point of the axles is lower and located not in the center of the car, but nearly on the opposite beam of the chassis, so the effect is far less hazardous.^[5]

      References