In this weeks technical article I will discuss the concept and history of the MacPherson Strut – what is now the most popular mode of suspension on cars today – front suspension that is, because it is connected to the steering. The rear suspension is similar but called a Chapman Strut after the founder of Lotus, Colin Chapman, took the concept and reworked it for the rear.
Earle Steele MacPherson was the inventor of this type of suspension and he was born in a suburb of Chicago in 1891. He spent most of his life in the auto industry, firstly with the Chalmers Motor Company in 1915 prior to their merger with Maxwell and ultimate conversion to Chrysler.
After the end of the First World War, he joined the Liberty Motor Car Company when they were bought by Columbia, he jumped ship to Hupmobile where he spent 10 years before being poached by General Motors and quickly became the head of design at Chevrolet.
It was at Chevrolet that he developed the first design of his new independent suspension. Most American cars still used older style suspension units with the high end European brands showing advances in technology including the suspension. After World War 2, Chevrolet and Ford were developing their own “light car” projects. The Chevrolet design, called the Cadet, was an early candidate for the MacPherson Strut but senior management disagreed, favouring a live axle and beam suspension. At the last moment before launch, GM pulled the plug citing economic reasons and the availability of raw materials.
MacPherson’s idea for the independent suspension was influenced by designs coming out of FIAT in Italy and he patented a new design that was significantly more superior. With the Cadet design cancelled, MacPherson felt that his time at GM had ended, so he jumped ship to Ford who also had a light car program. However, after Chevrolet cancelled the Cadet, Ford also cancelled their competitive car in the US, but the French division at Ford was looking for a new model and took the design and called it the Vedette, releasing it in 1949 with MacPherson’s suspension.
Ford in Europe clearly saw a good thing as the design was then added to the Consul and Zephyr in the UK and the Taunus in Germany. MacPherson was clever enough to take out several patents for his design!
The idea was simple enough: remove the wishbones commonly used and make something that would be much smaller but more efficient. He replaced the upper wishbone with a tube that the wheel hub was mounted on. The upper end of the tube was bolted to the car’s body. The tube had a shock absorber built in with a coil spring attached as well. He retained the lower wishbone concept and replaced it with a thinner control arm and a torsion bar, which acted as an anti-roll bar.
What MacPherson had done was simplify the suspension by making the components do two jobs and this meant fewer parts and therefore it was ultimately cheaper to manufacture. These struts work best when the body is of a unitary construction design so that the load is spread out although a space frame chassis is also a good mounting structure to support the loads for the same reason. After the patents expired in the early 1960s, engineers in Europe really developed the concept much further making the design even more efficient. Ford developed the RevoKnuckle and GM Opel produced the HiPer Strut, both highly advanced evolutions of the concept designed to allow more power to be transmitted through wheels that steer.
The rear strut concept developed by Colin Chapman from MacPherson’s design is almost identical except for the fact that the strut is rigid – it can’t swivel like the MacPherson version. It also uses the half shafts as lower control arms, doubling up their work.