What is a Strut Suspension?

In this brief article, we will discuss the Strut suspension, the different types of strut suspensions and the vehicles that have Strut Suspension.

What is a Strut Suspension?

A Strut suspension is a suspension in which the main structural load bearing member is a Strut. A Strut is a Coilover shock absorber that combines a spring and a damper. There are are 2 basic types of strut suspension:

  • MacPherson Strut Suspension
  • Double Wishbone 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. 

A Double Wishbone Strut suspension is very similar to the MacPherson strut suspension, the only differences being that:

  • There is an upper control arm in addition to the lower control arm
  • The coilover strut’s top and bottom mounts are eye-type, meaning they are free to rotate

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.

What is a Strut?

By definition, a strut, is a structural member that resists compression i.e., it is being pushed from opposite ends. In the context of the Automotive chassis, a Strut is a load bearing member of the suspension that is a combination of a spring and a damper and serves as a connection link between the wheel and the car chassis or body (whichever is the case).

The primary purpose of the struts is to support the weight of the vehicle while also absorbing surface impacts and ensuring a smooth ride.

What is the difference between a strut and a Shock?

A Strut, also called a ‘coilover’, is a load-bearing member that also contains a damper. So a strut takes up road loads coming through the wheels and also dampens the road vibrations.

A Shock absorber, on the other hand, only dampens road vibrations. It does not contain a spring or load bearing element.

Is a MacPherson strut a shock absorber?

Yes, a MacPherson strut is a shock absorber, meaning, it does 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

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 Suspension strut

  • The biggest advantage of the Strut is space. The Coil spring and shock absorber are both packaged between the same two mounting locations. 
  • The Coilover is a more efficient approach as opposed to a separate spring and damper which both require space for separate top and bottom mountings.

What vehicles use a strut Suspension?

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.

Double Wishbone Strut

  • In the past, Double-wishbone suspensions had the spring and damper on separate mountings. 
  • A majority of the Recent cars and SUV’s with front suspension as Double wishbone have Coilover struts 
  • Some well-known and high selling cars had or still have double-wishbone front suspension are:
    • Mazda Miata MX-5
    • Honda Accord
    • Toyota LandCruiser, Prado, HiLux
    • Nissan Titan/Armada/Xterra/Frontier/Pathfinder
    • Ford F-Series: F150, F250, F350

Conclusion

In this brief article, we have discussed the Strut suspension, the different types of strut suspensions and the vehicles that have Strut Suspension.

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