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Double wishbone suspension

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A double wishbone suspension is an automobile independent suspension design using two parallel wishbone-shaped arms to locate the wheel. Each wishbone (or arm) has two mounting positions to the chassis and one at the wheel hub. The shock absorber and coil spring mount to the wishbones to control vertical movement. Double-wishbone designs allow the engineer to carefully control the camber angle of the wheel, and are commonly used in sports cars.

In mechanical engineering, it is also known as a short long arm, or SLA suspension, if it has unequal length arms.

A very similar arrangement, often using a single arm, is the A-arm suspension .

The suspension consists of a pair of upper and lower lateral arms, roughly horizontal, and of roughly similar length. Between the arms there is a spindle (with kingpin or hub) which carries the wheel.

In order to resist spin loads such as braking the arms have to have two bushes or ball joints at the body.

Double Wishbone Suspension
Double Wishbone Suspension

At the spindle end single ball joints can be used, in which case the steering loads have to be taken via a steering arm, and the wishbones look A or L shaped. For a rear suspension a pair of joints can be used, making the arms more H shaped in plan view.

In front view the suspension is a 4 bar link, and it is easy to work out the camber gain (see camber angle) etc, for a given set of bush locations.

The various bushes do not have to be on horizontal axes, parallel to the vehicle centre line. If they are set at an angle then antidive and antisquat can be dialled in.

The advantage of a double wishbone suspension is that it is fairly easy to work out the effect of moving each joint, so you can tune the kinematics of the suspension easily.

The disadvantage is that it is slightly more complex, and possibly less robust, than other systems like a MacPherson strut.

SLAs are very common on front suspensions for larger cars, and double wishbones are very common at both ends of racing cars.

Prior to the dominance of front wheel drive in the 1980s, many everyday cars used double-wishbone front suspension systems, or a variation on it. Since that time, the Macpherson strut has become almost ubiquitous, as it is simpler and cheaper to manufacture. Double-wishbones are usually considered to have superior dynamic characteristics, and are still found on higher performance vehicles.

Last updated: 05-07-2005 02:21:28
Last updated: 05-13-2005 07:56:04