What is MacPherson Strut Suspension?

Take a look at the technical specifications of most modern day cars and the chances are that the description of the suspension type will be 'MacPherson Strut'.

MacPherson Strut is an extremely common type of passenger car suspension but what or who is MacPherson, and why is this design so common?

The MacPherson Strut is named after its inventor, Earl MacPherson. In the 1940's British born MacPherson became a renowned engineer while working for General Motors in France. He moved to rival company Ford, and it was there that he developed a new suspension system that became known as the MacPherson Strut.

In 1949 the French-built Ford Vedette became the first production car to use the new system. This was closely followed by several Ford cars built in Britain. Through the 1960s the design was adopted by many of the mainstream manufacturers and was more commonly used on the front of the vehicle.

So what makes the MacPherson Strut suspension such a popular system for modern cars? Well, like all popular systems, the MacPherson strut is simple and cheap.

MacPherson struts are unique because all of the suspension components are part of one single assembly. The main part of the assembly is the damper unit which is contained within the strut case. A coil spring is carried on the assembly with the strut passing through its centre.

At the top of the strut is the mounting to the car bodyshell (at the top of the inner wheel arch), and at the base of the strut there is a bracket which secures the strut to the steering knuckle or upright.

The struts are installed vertically in the car making the total suspension assembly extremely compact. The whole strut assembly pivots as the wheels are steered and the assembly becomes a structural part of the car, carrying the vehicle's weight and guiding the wheel and hub assembly as the suspension becomes compressed.

Locating the steering knuckle, hub, etc to the car body is the job of a single A-arm or wishbone which controls the lateral and longitudinal position of the wheel.

The simplicity of eliminating any upper control arm not only makes the system efficient in using less parts but also allows for more space to be utilized within the engine bay. For this reason the MacPherson strut is extremely popular in front-wheel-drive vehicles in which transverse engine mounting is very common. 

Although the MacPherson strut is more commonly used as a front suspension system it is also equally effective for rear suspension. Several European cars used MacPherson strut rear suspension in the 1980s including the rally icon Lancia Delta and today the Subaru Impreza still uses this configuration.

The design does however have some slight disadvantages. There is a certain amount of camber angle change as the suspension is compressed, which in some cases can have a negative effect on the vehicle handling. The direct mounting of the strut to the car bodyshell can give a slightly harsh ride and can also amplify road noise and vibration in the cabin compared to other popular suspension systems.

Despite the disadvantages the design is still very popular with many manufacturers, and will continue to be so with the consumer's hunger for cheap compact cars getting stronger.