Shocks and struts, while commonly interchanged in everyday speech are actually two different suspension components that indeed do serve the same purpose. The goal of both components is to smooth out the ride of the vehicle and dissipate energy absorbed by shocks of the road. The main difference between them is that a strut, which usually contains a spring coil assembly also is a structural part of the vehicle. A shock is an individual component and usually works in conjunction with another spring assembly such as a leaf spring. Since struts serve as pivot points for the steering system, an alignment is always recommended after a strut replacement. Some vehicle setups require a strut assembly in the front and a shock assembly in the rear or vice versa.
Shock absorbers can come in many different configurations, each with unique components that serve a different purpose. Their main function is to dampen the vertical motion and feedback from the road, these are sometimes also called dampers and do exactly that. Vehicles riding on just a spring assembly would quickly shake themselves apart if they didn’t throw you out first. Shocks serve two very important purposes in a vehicle. They absorb vertical travel and shock from the road to make for a much smoother ride than without them. As with springs, the stiffer your setup the less travel is allowed which in turn reduces comfort because the shock doesn’t absorb a lot of that force, instead transferring more to the chassis and driver. The second function of springs is to provide adequate downward force at all times to keep your tires planted on the road. For those who track their cars the sacrifice is comfort in return for a stiffer ride to keep your wheels planted during hard cornering by getting stiffer shocks or dampeners in conjunction with stiffer springs also.
Twin tube shock designs are the cheapest and most commonly used shocks. The twin tube design consists of two individual cylindrical chambers, separated by a valve that regulates the flow of oil between chambers during compression and decompression.
Electronically controlled dampers
Electronically controlled dampers work exactly the same and usually come in the same twin tube design as traditional oil filled shocks. The benefits of electronically controlled dampers is that the travel of fluid between the two chambers is managed by an electronically controlled valve that responds to shocks in the road as opposed to natural compression.
Gas filled Dampers
Gas filled dampers consist of two individual chambers in the shock assembly. One chamber is filled with traditional oil and the other chamber is filled with a high pressure gas. Since the rod moving during compression is passing through two high pressure chambers, one with oil and one with gas, the compression and rebound of the shock is much more controlled and this is the preferred variation for high performance and racing applications.
The magnetic damper system consists of a standard twin tube shock assembly and functions essentially the same. Instead of oil filling the reservoirs of the shocks there is a fluid with tiny magnetic particles dispersed all throughout. Attached to every damper is an ECU that controls the magnetic current running through the dampers which is applied via magnetic coils at either end of the damper. When a current is applied the magnetic particles align in the cylinder, stiffening the fluid and causing a dampening effect. The strength of the current determines the dampening effect the shock has. When there is no current applied the shock is at it’s softest setting and as more current is applied, the shock gets stiffer. The benefit of magnetic shocks is the almost instant dampening effect they have as opposed to traditional dampers which stiffen as the fluid inside of them is compressed under pressure.
Coilovers usually come in one piece assemblies consisting of a shock and a spring assembly. Coilovers resemble struts in appearance but usually have much smaller and tighter wound spring assemblies than your average strut assembly. Coilovers are usually used in high performance and racing applications because of their adjustability in vehicle height, stiffness and the overall improved handling over stock. The downsides of custom coilovers is that their dimensions sometimes have clearance or rubbing issues with other OE parts such as stock sway bars or having to re-reroute fluid lines depending on the vehicle and application. Most coilovers or “coils” come with adjustable spring plates to adjust the spring stiffness and a damping valve to adjust the dampening effect of the built in shock. Some modern coilover units also come with external reservoirs to be mounted outside of the initial assembly to help with space and dimension constraints.
What makes a strut different from just a shock or coilover assembly is that a strut has numerous suspension components built into one unit as opposed to a coilover system which would just be a coil spring and shock assembly that attaches to the rest of the suspension assembly. A Strut assembly wraps up the coil spring and shock, but also spring seats, strut bearings and steering knuckles all into one piece. The benefit of a strut over a coilover system or stand alond spring and shock assemblies is the convenience of it’s structure. Having all of these components in one makes strut assemblies much cheaper than coilover or custom assemblies but as a trade off struts don’t offer the wide range adjustability that coils do. Structurally the strut connects the upper strut to the lower ball bearing at the bottom of the strut to allow it to pivot during vehicle motion.