Even though the terms “shock” and “strut” often appear interchangeable, they are actually two different vehicle parts and thus can’t be used in place of one another. Nevertheless, that doesn’t mean they don’t serve similar functions.
Both shocks and struts are responsible for keeping vehicles controllable and reducing body roll and tire movement. Without shocks or struts, handling, braking, and wheel alignment would be impossible. In other words, they keep cars from bouncing on their soft springs by mitigating the “up and down” actions that would otherwise make cars feel like trampolines.
While shock absorbers have only one function, struts serve several:
1. Shock Absorbers
True to their name, shock absorbers are solely responsible for keeping spring and suspension movement in check and thus ensuring that tires are always planted on the ground. They operate thanks to the compression of hydraulic fluid via a piston. Whenever an impact causes the shocks to compress, that fluid offers resistance at a fixed rate in order to maintain a comfortable and stable ride.
Struts do contain shock absorbers, but they are far more comprehensive in their function since they are structural units. In cars with shock absorbers, the springs and steering knuckles are separate parts. In struts, those parts are contained within one unit.
Why Use Struts Vs. Shocks?
As mentioned above, struts combine shock absorbers and coil springs into a single item, so manufacturers can keep costs down by avoiding having to spend on multiple parts. Struts also save on space and make replacements potentially easier.
As for why an automaker might choose to use separate shocks, it might make sense to offer a more interchangeable part. Perhaps the shock is in a sports car that can have multiple types of shocks swapped out depending on the type of ride the owner wants. In addition, shocks can be used in several vehicle types, while a strut would be more specific to a single vehicle style or size.
Replacing Struts and Shocks
If you notice your handling is suffering, your steering response is poor, and your braking is unstable, your shocks or struts might be due for replacement. Your specific vehicle will have a replacement interval specified in the owner’s manual, which can range anywhere from 50,000 to 100,000 miles.
Replacing struts or shocks should be done with great care. Suspension springs are under a lot of tension, so if you accidentally loosen the wrong item, it can cause the spring to come loose with great force. When in doubt, leave the job to your local shop since they can also perform an alignment afterward.
Summary: The difference between shocks and struts is subtle but important. Struts contain the coil springs and steering knuckle, while a shock absorber is a single-function item responsible for taming spring rebound.