Rick's Free Auto Repair Advice

Difference between shocks and struts

What’s the difference between shocks and struts

Car owners are often confused as to the difference between shocks and struts. I’ll show you how the two system works and cover the advantages and disadvantages of each system.

What is a shock absorber?

A shock absorber is an hydraulic unit that dampens a vehicle’s spring oscillations. It’s entire purpose is to eliminate bounce and keepthe tires on the road to improve traction and vehicle control. The shock itself is similar to a doctor’s syringe where the plunger is connected to the body of the vehicle and the body of the shock connected to the wheel. The shock contains valves that control the rate the plunger can travel through the fluid and the rate at which it can return to its normal position.

Most modern shocks also contain nitrogen gas to prevent “cavitation” and air bubbles which can accelerate wear in the valve assembly.

What is a strut?

A strut is really just a shock absorber that is attached to structural components.

Image of fully loaded strut assembly showing new strut, new coil spring, new strut mount and new strut bellows

Fully loaded strut assembly

Older cars used an upper and lower control arm. These triangular shaped suspension components connected the steering knuckle to the frame of the vehicle. An upper and lower ball joint at the peak of the But it’s not quite that simple. Car makers use struts as part of the structure of your car. They support the entire wheel assembly of your car. You can drive without a shock absorber. You cannot drive without a strut. Because a strut is actually part of the support structure. A strut piston is usually more than twice the diameter of a shock piston. The strut housing is sturdier as well because it supports the spring. That’s why struts are usually 25-50% more expensive than shocks.

control arm type suspension

Control arm suspension uses an upper and lower control arm and an upper and lower ball joint in addition to a shock absorber and coil spring

strut style suspension

A strut suspension eliminates the upper control arm and upper ball joint. The strut assembly rotates in turn using the bearing inside the strut mount at the top of the strut.

Difference between a shock and strut

A shock does not include a coil spring or spring mount/a strut contains the shock absorber, spring mount, coil spring and a strut mount.

 

Advantages of a control arm suspension using a shock absorber

Smoother ride: The control arms move up and down with variations in the road surface.

Advantages of a control arm suspension using a shock absorber

Smoother ride: The control arms move up and down with variations in the road surface.
Less costly to maintain. Replacing a worn shock is a minor repair and the shock itself is far less expensive than a strut.

Disadvantages of a control arm suspension using a shock absorber

Far more costly to manufacture: More components. Vehicle manufacturer must install frame mounting points for upper control arm and upper ball joint

Softer and mushy response: Vehicle tends to “float” on the road and roll in turns. Not as responsive as a strut suspension

Advantages of a strut suspension

Stiffer sportier feel: Less body roll provides a European sports car feel.
Less costly to manufacture: Fewer components

Disadvantages of a strut suspension

Replacing worn struts is costly. Replacement requires removing the strut assembly from the vehicle, disassembling the strut assembly, installing a new strut, reinstalling on vehicle and performing an alignment.

©, 2019 Rick Muscoplat

Posted on by Rick Muscoplat



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