Shocks and struts are both components in the suspension system that dampen and control body motion. They prevent excessive up-and-down bouncing or side-to-side rolling of a vehicle while it drives. This is necessary to create comfort for occupants. Both terms are sometimes used to mean the same thing. However, shocks and struts are two distinct and very different parts.
Struts and shocks are not interchangeable and cannot replace one another. Every modern vehicle has either shocks or struts at each wheel. Most modern vehicles actually use struts at the front and shocks at the rear.
What Is a Shock?
A shock, or shock absorber, is a non-structural component designed to control body movement by absorbing motion. It’s a hydraulic piston, with gas or liquid inside, that allows for dampened movement. In technical terms, shocks convert the kinetic energy of a car’s motion into heat energy that’s dissipated by hydraulic fluid. This up and down movement is controlled via hydraulic compression. Most modern shocks are dynamic. They use valves to allow different amounts of rebound depending on vehicle speed or conditions.
Unlike a strut, a shock does not support the body weight of a vehicle. A shock is used for vehicle body control, but is simpler in design. Because they don’t have to support weight, shocks are often used in heavier vehicles. Large body-on-frame SUVs and trucks typically use shocks, though many modern SUVs, pickups, and crossovers use struts in the front.
The tight space constraints in the front of a vehicle mean that the spring and shock are typically integrated. Up front, a shock is placed with the spring, attached to the upper control arm. However, they don’t have to be mounted together in the rear. The engine, transmission, and steering don’t affect the layout. For example, a rear leaf spring setup can use a shock absorber that is separate from the spring.
Pros and Cons of Shocks
Even though some think of shocks as more "floaty," they do a good job controlling body motion for large or off-road vehicles. Plus, they’re often used with the rear wheels of many modern vehicles. They do take up more space, however.
Shocks Pros and Cons
|Pros of Shocks||Cons of Shocks
|Less expensive to replace
||Take up more space
|Easier to swap
||More expensive to manufacture
|Better for off-roading
What Is a Strut?
A strut is a structural part of the suspension system that acts as a damper and also a support between the wheels and the vehicle body. It’s a hydraulic piston that allows up and down movement. Struts also control alignment and connect multiple suspension parts together. The strut integrates the vehicle’s spring into the assembly. A car could be driven without shocks (with a very uncomfortable ride), but not without struts. It would simply collapse onto the wheels.
Since it does absorb vehicle motion, a strut is technically also a shock (but not the other way around). You can think of a strut as a shock that provides dampening but also has the additional task of supporting the vehicle’s body. They’re still two distinct components though.
A strut consists of a coil spring, which sits on the strut seat. The spring is sometimes covered with a coil spring boot. Struts take the place of upper control arms and actually support the weight of the vehicle. Because of this, a strut setup only has a lower control arm.
Even without the spring, struts are constructed more robustly than regular shock absorbers to support the weight of the vehicle. Because they mount to the body and support it, struts are used with unibody vehicles.
The MacPherson strut system is by far the most common strut setup in modern vehicles. It’s especially prevalent in the front of FWD cars. The use of fewer parts, while still maintaining low unsprung mass and good ride comfort, make it optimal for most passenger vehicles.
Other types of independent suspension use shocks, not struts. Examples are the double wishbone (including SLA), as well as the less common leaf spring and multi-link suspensions. The double wishbone setup is still common today, but usually in the rear of vehicles. It can be found on the front wheels of larger vehicles like trucks and SUVs.
Pros and Cons of Struts
Struts have gotten popular because of their efficient packaging, specifically for the front wheels. However, they are expensive to replace.
Struts Pros and Cons
|Pros of Struts||Cons of Struts
||More expensive to replace
|Take up less space
||More complicated to replace
|Cheaper to manufacture
Struts vs Shocks vs Coilovers
Coilovers are a third option for vehicle damping, specifically for performance vehicles. They work in a way that combines a strut and the spring. Coilovers can go in cars with struts, but not in those that use shocks.
The term “coilovers” is often used to refer specifically to aftermarket, adjustable strut assemblies. The adjustability of coilovers for different suspension tuning makes them popular for performance cars. The driver can alternate between more comfortable settings for daily driving and stiff settings for the track.
Sources: The Differences Between Shocks, Springs, and Struts, It Still Runs | What Are Struts on a Car?, J.D. Power | How Suspension Works, Donut Media | How Car Suspensions Work-Springs vs Shocks, Engineering Explained
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