Some car parts are named in ways that don’t exactly make it obvious to the noob as to what they are, like the header tank, planetary gears and banjo fittings. Multi-link suspension is not on that list. It’s suspension… made from multiple links.
Where a MacPherson strut setup only technically needs two controlling arms to keep it rigid, a multi-link needs a minimum of three lateral bars and one vertical(ish), or longitudinal. Each arm’s purpose is to limit and/or prevent the six degrees of an axle’s freedom; up and down, left and right and fore and aft. Sometimes some of the arms have ‘elbow’ joints along their length to achieve the necessary clearance around an axle while still achieving the proper angle of attack to fix to the hub.
Together they locate the wheel at the correct point and form a rigid frame anchored to the hub that prevents it from moving in any way it shouldn’t. Each bar is mounted on joints at both ends and is free to move vertically with the suspension travel – but nowhere else unless the arms themselves become bent or broken.
A multi-link design, usually with four or five arms, known as links, allows an independently-sprung wheel to combine both ride quality and handling. It’s laterally stiff so a car thus equipped won’t flop around through corners as much as with other designs, but it also allows smooth, independent movement of a wheel over even large bumps.
Not that multi-link setups are limited to independent suspension. Live axles often use multi-link setups bolstered by a sway bar, track (or Panhard) rod and, of course, the spring and damper units. Multi-link live axles are cheap and easy to put together – which is why they proved so popular in the US for so long.
One of multi-link’s key advantages is that engineers can alter a single suspension parameter without affecting anything else. On double-wishbone designs you’re always altering at least two, whether you like it or not. Multi-link can also keep the wheel more or less perpendicular to the road, maximising the tyre’s contact patch and grip.
Multi-link bouncy bits used to be too expensive to put onto everyday biffabouts, but in recent years costs have come down and various interpretations of this solution have found their way even into front-wheel drive hatchbacks; usually at the rear with (less expensive) MacPherson struts up front. For the most part these multi-link setups have replaced cheaper but effective trailing arms. Both offer the potential for maximised boot space, but multi-link back-end bounce is said to offer better ride comfort.
It can also be used at the front, where one arm is linked to the steering rack, but it’s still less common than a strut. Some BMWs use a type of multi-link system at the front and Hyundai has dabbled in the same thing with its Genesis. With the advantages it offers, expect to see it popping up in even more places in the future.