The MacPherson Strut Suspension (3 key insights)

In this brief article, we will discuss the MacPherson Strut suspension, its design features, advantages and applications.

What is a MacPherson Strut Suspension?

A Macpherson Strut suspension’s main component is the Coilover shock absorber. The Coilover Strut’s lower mount is securely bolted onto the Knuckle. The Coilover Strut’s top mount has a bearing that allows the strut to rotate simultaneously with the knuckle. The MacPherson strut is relatively simple as compared to the Double wishbone with lesser number of components and joints and also occupies comparatively lesser space.

Why is the Macpherson strut suspension called so?

The MacPherson Strut suspension was first seen on the Chevrolet Cadet Prototype. The name MacPherson strut is in remembrance of Chevrolet’s then Chief Engineer of the famous Chevy Cadet Light car Project, Earle MacPherson. The Chevy Cadet was the first car to feature the unique and compact suspension design approach which later came to be known as the MacPherson Strut.

The History behind the MacPherson Strut Design

The Double wishbone suspension with upper and lower control arms had always been the standard independent suspension setup for any car from the post World War II era.

The Chevy Cadet post-war Light Car Project had the ambitious objective of producing a new mass-market car that was ‘Compact’ and fit within a $1,000 price tag. As a result, the Chevy Cadet’s Chief Engineer, Earle MacPherson tried out several unique space-saver design innovations. One of the many aspects he looked into was the design of the front independent suspension.

Even though the Chevy Cadet Prototype was successfully built, project fell through in its last stages and never saw production. However, Earle MacPherson joined Ford subsequent to this and saw through the implementation his MacPherson struts on the Ford Verdette, Consul and Zephyr. The Verdette, in 1949, became the first ever production car with MacPherson struts.

MacPherson Strut Design Features

Earle MacPherson’s Strut design drew inspiration, most probably, from Aircraft Landing gear strut design and some designs by FIAT from the mid-1920’s. 

The Double-Wishbone suspension, as the name suggests, consists of 2 wishbones, upper and lower, that are connected to the chassis. The upper and lower wishbones are connected to the Knuckle (or wheel carrier) through an upper and lower ball joint respectively.

The Basic construction approach of the MacPherson Strut is: 

  • To take the Double-wishbone front suspension and eliminate the Upper Control Arm. 
  • Replace The Upper Control arm with a Shock absorber Coil-over Strut that is securely bolted on to the Knuckle. 
  • Replace the Double-wishbone’s Upper Ball-joint with a bearing at the Coil-over Strut’s top Chassis mount.

Advantages of the MacPherson strut

  • The biggest advantage of the MacPherson Strut was space. The MacPherson Strut’s top mount occupied less of space, that would have otherwise been occupied by the engine bay
  • Another advantage was the reduction in the total number of major suspension components, namely the Upper Wishbone and the Upper Ball Joint
  • With the elimination of the Wishbone and Ball-joint came the reduction in the cost associated with replacement due to wear out issues of the upper control arm and the upper ball-joint
  • The MacPherson Strut design allows easy tuning of the suspension parameters for optimizing ride and handling performance.
  • In some vehicles, a MacPherson Strut is used in rear independent suspension systems as well. This approach would eliminate the need for an upper control arm and thus result in a packaging advantage

What vehicles use a MacPherson strut?

  • In the initial years of the post-war era, the MacPherson strut was used primarily in compact cars where overall size vs. packaging space was the challenge.
  • In the later era, as cars moved from the body-on-chassis approach to the more compact and efficient Monocoque design, the MacPherson struts were the preferred choice since 
    • Monocoques provided higher rigidity between the strut mounting points,  
    • MacPherson struts were more cost-efficient, and
    • MacPherson struts help in maximizing the packaging space advantage that monocoque design offers
  • Nowadays, apart from only compact hatchbacks, the MacPherson strut has seen more widespread application in mid-size sedans as well
  • Over the years, the MacPherson struts application has only widened across the spectrum of car categories. Between 80-90% of all passenger cars sold worldwide have a MacPherson strut suspension.
  • Contrary to the general impression that the MacPherson strut is a compromised design meant for economy class, several performance oriented cars have MacPherson struts on them. 
  • A few of the notable examples of performance car models with MacPherson struts are the Porsche 911 GT3, the Audi A4, the Ford Mustang GT350 and BMW 1,2, and 3-series.

Is a MacPherson strut a shock absorber?

Yes, a MacPherson strut is a shock absorber,  meaning, it deos the work of Damping road vibrations that come in through the tires. The MacPherson Strut is a Coilover, which means that the shock absorber and spring are both mounted within a load bearing column called a Strut with spring mounts inbuilt. Apart from being a Shock Absorber, the MacPherson also performs two other functions of-

  • Absorbing road loads through the coilover spring
  • Providing a Steering axis to the knuckle through the Strut Top mount bearing

Conclusion

In this brief article, we have discussed the MacPherson Strut  suspension, its design features, advantages and applications.

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