What are Struts? | Revv.ly Glossary

What are Struts?

Now, I realize this might seem rather fundamental, but the distinction between a strut and a shock absorber is one of those things that car enthusiasts often gloss over, and it's actually quite important. A strut isn't simply a shock with a different name--it's a fundamentally different structural component that serves multiple purposes simultaneously.
A MacPherson strut, named after American engineer Earle S. MacPherson who developed the design in the 1940s, combines the functions of a shock absorber and an upper suspension arm into a single unit. The key word there is "structural." While a traditional shock absorber merely controls damping and can be removed without the wheel falling off, a strut is an integral structural component. Remove it, and the suspension geometry collapses entirely.

The Mechanical Reality

The strut serves several simultaneous functions:
Damping -- Like any shock absorber, the strut controls the rate at which the suspension compresses and rebounds. Internal valving restricts oil flow to manage movement speed.
Structural Support -- The strut body provides the attachment point for the wheel hub and steering knuckle. It essentially replaces the upper control arm found in double-wishbone designs.
Spring Location -- The coil spring wraps around the strut body, using it as a guide. The spring perch at the base and the strut mount at the top sandwich the spring in position.
Steering Axis -- On front struts, the strut angle and offset define part of the steering axis, affecting caster and steering feel.

Struts vs. Shocks: The Practical Difference

This distinction matters when modifying your suspension:
In a strut suspension: The entire unit must be removed for spring changes or damper replacement. Coilover conversions replace the complete strut assembly. Camber adjustment requires camber plates or modified strut mounts because the strut position directly determines wheel angle.
In a shock-and-spring suspension: These components are typically separate. Springs can be accessed without removing shocks, and shock replacement doesn't affect suspension geometry. Camber adjustment happens through control arms or eccentric bolts rather than at the shock mounting point.

The MacPherson Legacy

MacPherson's design became dominant because of its simplicity and cost-effectiveness. With fewer components than double-wishbone or multi-link designs, it's cheaper to manufacture and requires less space--crucial for front-wheel-drive packaging where engine and transmission compete for room.
You'll find strut front suspension on:

• Most economy cars worldwide
• Many sports cars (Mazda Miata, Porsche 911 front, various hot hatches)
• Countless crossovers and SUVs
• Many performance sedans (BMW 3-series front, Audi A4, etc.)

The Limitations

MacPherson struts aren't without compromise. Purists note:
Camber Change -- As strut suspension compresses, camber changes more than with double-wishbone designs. This affects tire contact patch during hard cornering.
NVH Transmission -- Road impacts transfer quite directly through the structural strut. Isolation is harder than with multi-link designs.
Compromised Geometry -- Having one mounting point instead of two limits how precisely suspension engineers can dial in kinematics.
These are engineering trade-offs, not failures. For most applications, strut suspension works excellently. The cars that use double-wishbone or multi-link everywhere tend to be significantly more expensive.

Modifying Strut Suspension

Common upgrades include:

• Coilover Conversion -- Complete strut replacement with adjustable height and damping
• Strut Braces -- Connecting strut towers to reduce flex
• Camber Plates -- Adjustable upper mounts allowing camber correction when lowered
  Understanding that you're modifying a structural component, not just a damper, helps explain why strut modifications often cost more than shock changes and why proper installation matters so much.
  Explore suspension modifications with the Revvly community--where technical understanding meets practical application.
  Related: Coilovers, Camber Plates, Control Arms
  Strut Suspension Vehicles: Mazda MX-5, Ford Mustang S550, VW GTI MK7