A MacPherson strut is one of several common automotive suspension systems. It typically consists of a single control arm that connects to the bottom of the wheel hub and a strut that is installed between the top of the hub and the body of the vehicle via a bushing. When the wheel is turned from side to side, the entire strut typically turns against the bushing. This fixes the wheel in place while allowing it to move up and down as the vehicle is driven.
The strut component of the MacPherson strut serves the dual purpose of a shock absorber and one of the two contact points that fix the wheel in place. A typical shock absorber only damps shock input from the road when driving, but a strut combines this with the function served by the upper wishbone in a dual-wishbone suspension. The strut housing that is typically responsible for substantial lateral stresses will usually include both a shock absorber insert and a coil spring on which the weight of the vehicle actually rests.
Some MacPherson struts will include a variable camber adjustment. While most struts simply bolt up straight, these applications will include two bolting points wherein the strut mounts to the hub, one of which will be on an eccentric. This typically allows the angle at which the strut is mounted to be adjusted before the bolts are tightened, resulting in a serviceable camber adjustment. A camber angle is simply a measure of whether the top of the wheel tilts toward the vehicle or away from it.
MacPherson strut suspensions were first seen in vehicles in the late 1940s and early 1950s and continue to be popular. While the competing double-wishbone suspension may provide certain performance benefits, the MacPherson strut is typically less expensive and takes up less space. The MacPherson strut is incorporated into some vehicles to reclaim space in the engine compartment, as vehicles have become smaller.
A double-wishbone suspension will often take up more space and may be more expensive due to containing more components. Rather than the single wishbone that mounts to the bottom of the hub, this suspension includes a second wishbone that connects to the top of the hub. This takes the place of the strut in directing the wheel. A shock absorber is then typically used to serve the same purpose as the shock insert found in a strut.