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Double wishbone

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

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 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.

At the spindle end single 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 MacPherson strut.

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