We’ve all heard of a MacPherson strut setup, but what is it?
Over the years, automative suspension setups have had many different options and iterations. Automakers like to strike the delicate balance between comfort, safety, cost, packaging and road-handling into the suspension setup they are designing.
One of the most successful and still most commonly used setups is the MacPherson Strut.
When we talk about MacPherson struts, we are typically describing a setup on a car with independent front suspension (meaning each wheel has its own independent movement over terrain). Any type of independent suspension tends to offer better comfort and road-holding than non-independent setups such as leaf springs. With setups such as leaf springs when one side moves under force, the other side will also be affected.
MacPherson strut arrangements can differ slightly between cars, but in its most simple form you find the strut itself (containing the spring and damper arrangement) is mounted to the vehicle’s body, via the top mount. The lower control arm (often referred to as a track-control arm) is also mounted to the car body or more commonly the engine cross-member. This allows the suspension assembly to move up and down with the hub when the car goes over uneven terrain . The setup also consists of an anti-roll bar which not only stabilises the set up, but also provides for a better ride, as when the suspension compresses on one side of the car, the roll-bar twists and forces the suspension to compress in a similar manner on the other side – helping the car to stay flatter when cornering.
So the core principle of the MacPherson strut set up is to “triangulate” the suspension using generally an anti-roll bar, track-control arm, and then the actual body of the car. MacPherson struts became commonplace as cars began to move to a monocoque all-steel body construction, as the actual body of the car provided enough rigidity to form one side of the triangle required for the MacPherson strut arrangement (as seen in the image above).
Hmmm, it’s annoyingly clever – who came up with it?
A bit of history for you, Earle S. MacPherson was the Engineer who designed the setup. He was born in the USA in 1891 and after a few roles in the car industry he worked his way up to “Chief Engineer of truck design and passenger cars” at General Motors. The vehicle his team worked on was a ‘Light Car’ concept (known internally as the Cadet). This vehicle was the first to feature his revolutionary suspension design, and though the Cadet never actually came to market – the suspension technology developed here went on to feature in millions of cars!
The final part of the recipe – dampers and shock absorbers.
Typically, the “spring” component in a MacPherson set up is a shock absorber (which converts the cars body and wheel oscillations into heat energy), and a coil spring which helps alleviate movement of the shock absorber by ‘fighting back’ on each bump in the road, resulting in less movement.
There are two main types of shock absorbers, single and twin tube. Both have their advantages and disadvantages.
There are two main types of shock absorbers, single and twin tube. Single tube has a sealed piston, which is connected to a rod. Liquid in the piston is then compressed as a result and a compression valve opens to allow a proportion of the pressurised liquid back through the piston. A pressurised ‘compensation chamber’ then acts as a second pressure reliever for a steadier damping effect when a car goes over bumps.
The single damper setup can be mounted in any orientation depending on use, with performance cars having almost horizontal setups, and this also allows for easy adjustment. The combination of a “spring and damper” however does make the setup longer, making it difficult for smaller design and packaging requirements in some cars.
A twin tube damper setup involves a second tube surrounding the main tube. The second outer tube acts as a fluid reservoir; this setup removes the need of for a compression chamber (as found in the single tube damper) as valves are used instead to release the compressed liquid into the outer tube as a result of the inner piston compressing. The benefits of a twin tube damper include a better response to the road surface, as the friction of the seals is less than a single tube; grit and debris doesn’t risk damaging the damper, as the outer tube protects the inner tube containing the piston and lastly, the twin tube setup can be much shorter than a single tube as the compensating chamber is next to the piston, not beneath it.
A twin tube setup has its limitations, these include a higher exposure to overloading and therefore ‘cavitation’, which essentially means bubbles are produced in the liquid when the damping is needed at a very high rate, removing the effects of damping altogether. Also, the damper can only be installed in certain orientations, because of its design.
One of the first modern-day modifications that cars undergo is the installation of lowered ‘coil overs’, which are part of the MacPherson Strut setup, and result in giving the car a hugely adjustable ride-height which (when done right) can make it handle better and of course give the car the desired stance.