Short Long Arm suspension

Short-long arm suspension, almost always abbreviated to SLA, is a particular execution of the double-wishbone layout in which the upper control arm is deliberately made shorter than the lower one. It exists because suspension engineers want to control not just how far a wheel moves, but how its angle relative to the road changes throughout that movement. By choosing the lengths and mounting angles of the two arms independently, the designer can dictate the path the wheel follows as the suspension compresses and extends, which is something a simpler layout cannot easily achieve.

Mechanically, the wheel hub is held by two roughly horizontal arms, each hinged to the chassis at its inboard end and to the upright at its outboard end. Because the upper arm is shorter, it swings through a tighter arc than the longer lower arm as the wheel rises. The geometry is arranged so that the top of the wheel is pulled inwards relative to the bottom as the suspension is loaded, producing progressively more negative camber. A coil spring and damper, often a coil-over unit, react the vertical loads, while the arms and a separate tie rod handle the lateral and steering forces.

The practical payoff comes during hard cornering, when the body rolls and the loaded outer wheel is forced upwards into its bump travel. The camber gain built into the SLA geometry counteracts the roll, so the heavily loaded outer tyre stays close to upright and presents its tread squarely to the tarmac. The result is a larger, more evenly loaded contact patch, more consistent grip and more predictable handling, which is why the layout is favoured on performance cars, many front-engined sports cars and competition machinery.

The SLA is a refinement of the broader double-wishbone family and is closely related to multi-link designs, which split the arms into several separate links for even finer control. Historically, unequal-length wishbones became widespread once independent front suspension replaced beam axles, and the layout has appeared on everything from 1960s grand tourers to modern supercars and the front of many pickup trucks. The exact arm lengths, pivot heights and bushing rates are tuned to suit each vehicle's mass, ride height and intended use.

The trade-off is complexity and cost. An SLA uses more individual components, joints and chassis pick-up points than a MacPherson strut, occupies more space within the wheel arch and adds weight, all of which makes it more expensive to manufacture and to repair. Bushings and ball joints wear over time and a knock can disturb the carefully set alignment, so periodic geometry checks matter. For packaging-sensitive or budget vehicles the strut remains the pragmatic choice, but where ultimate grip and handling are the priority, the short-long arm arrangement is hard to beat.