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Struts, shocks, dampers, coilovers, springs, shock absorbers, monotube, twin-tube, inverted—sound familiar?
Whenever the topic of car suspension comes up, all of these terms are used to describe a similar type of suspension component, and they’re all widely used.
Because of this, many people often get confused by these technical terms. For the most drivers, this might not cause much trouble. However, for those who are interested in understanding the vehicle suspension system or planning to modify their cars, it can be a real headache. Especially when some manufacturers like to use fancy technical jargon to confuse consumers.
That’s why we’ve put together this guide—to help you make sense of it all. TGQ will explain and clarify what shocks and struts really are.
Why Do Cars Need Struts and Shocks?
Before diving into the difference between struts and shocks, it’s important to understand why vehicles need these components in the first place. Without any damping parts installed, a car would bounce around like crazy—imagine pushing a shopping cart over rough asphalt. It would be a jolting, uncomfortable ride, and your hands would go numb from all the vibrations.
To tackle this problem, automotive engineers developed two key components that work together to absorb the bumps and vibrations from the road, making the ride smoother and more comfortable. These are the springs and the dampers.
What Is Strut?
Strut is actually a multifunctional component that combines several important roles: damping, springing, suspension linkage, and steering support. There are many types of suspension systems around the world, but only one requires struts—the MacPherson suspension system, often called the strut-type suspension.
Since it’s a specialized part, why does it often get confused or mixed up with other components? The reason is simple: today, over 60% of passenger vehicles use MacPherson suspension. Over time, struts and shock absorbers have become almost interchangeable in everyday conversation.
In short, a strut is a multifunction chassis part that’s specifically used in MacPherson suspension systems.
What Is Shocks?
“Shocks” is just a shorthand for shock absorbers. And, as the name suggests, their main job is to absorb shocks. A shock absorber is a type of damper designed to reduce vibrations. Using a combination of gas, liquid, and a piston mechanism, it effectively softens the bumps coming from the road.
It’s important to clear up a common misconception: many people think shock absorbers carry the vehicle’s weight, but that’s actually the job of the springs. And remember from the previous section—struts can be considered a type of shock absorber as well.
What Is Spring?
Springs serve two main purposes: first, by using their natural ability to absorb energy, they help keep road vibrations from directly reaching the cabin, ensuring a smoother ride. Second, they support the vehicle’s weight.
Modern vehicles use various types of springs, including coil springs, air springs, leaf springs, and torsion bars. Among these, coil springs are the most common and familiar—you probably see them the most in everyday life.
What Is a Coilover?
From the previous sections, we know that shock absorbers and springs are two completely different parts. But smart engineers thought—what if we combined them into one unit? That way, we could free up more space for the cabin or other components.
This idea gave birth to the coil spring over shock absorber, commonly known as the coilover. For car enthusiasts and modifiers, adjustable coilovers are especially popular because they allow you to control the vehicle’s ride height by adjusting the length of the shock body, rather than messing with the spring itself (which is actually a pretty complex process).
And just to tie things together—struts can also be considered a type of coilover.
What Are Twin-Tube and Monotube Shocks?
Shocks are a type of damper, and depending on their internal design, they fall into two categories: monotube and twin-tube. Most shock absorbers you’ll find on cars today are twin-tube dampers. That’s because twin-tube shocks deliver performance very similar to monotube units, but come with a clear cost advantage.
Twin-Tube Shocks
A twin-tube shock consists mainly of an outer oil reservoir (the outer tube), a piston, an oil chamber (the inner tube), valves, and hydraulic fluid.
How It Works
When the vehicle hits a bump, the piston is pushed downward, opening both the valve at the bottom of the oil chamber and the piston valve. Part of the hydraulic fluid moves from the bottom of the oil chamber into the reservoir, while the rest flows above the piston.
Next, the shock absorber rebounds as the piston moves upward. At this point, the valve at the bottom of the oil chamber closes while the piston valve remains open. The fluid that moved into the reservoir can’t flow back due to the closed valve, and the fluid above the piston slowly returns to the oil chamber. This controlled flow creates the damping effect that smooths out vibrations.
Twin-Tube Shocks: Advantages and Disadvantages
When twin-tube shocks operate, a pressure difference forms between the oil chamber and the reservoir. For typical driving conditions, this pressure difference isn’t a problem. However, on rough or off-road surfaces, this cavitation can cause air bubbles inside the damper. These bubbles negatively affect the shock’s ability to absorb impacts. Additionally, twin-tube shocks use more material and weigh more, but they come with a lower cost.
Monotube Shocks
Monotube shocks have only one chamber and do not feature a separate oil reservoir. At the bottom of the shock is a gas chamber, topped by a separating piston. Above that lies the oil chamber, which the main piston divides into upper and lower sections. When the shock compresses, the main piston moves downward. Most of the oil flows through the valves on the main piston into the upper oil chamber, while a smaller amount pushes down on the separating piston, increasing pressure in the gas chamber.
On rebound, the main piston moves upward. Most of the oil flows back through the valves to the lower oil chamber, and the compressed gas chamber pushes the separating piston back up.
Monotube Shocks: Advantages and Disadvantages
The biggest advantage of monotube shocks is their ability to eliminate the issue of air bubbles. The gas chamber at the bottom controls rapid shock movement, reducing cavitation. Monotube shocks also use less material, making them lighter.
However, their complex design leads to higher manufacturing costs. For this reason, monotube shocks are mostly found on premium vehicles.
What Are Inverted Shocks?
Regardless of the type, most shock absorbers share two main components: the main cylinder (outer tube) and the piston rod. The main cylinder needs to hold oil and allow the piston rod to move inside, so it’s always thicker than the piston rod.
Typically, shock absorbers are designed with the thicker main cylinder connected to the wheel carrier, and the thinner piston rod connected to the vehicle body. Inverted shocks flip this arrangement: the main cylinder attaches to the body, while the piston rod connects to the wheel carrier.
This reversed setup offers a few benefits:
- Body rigidity: Since the body is heavier, having it supported by the thicker main cylinder improves overall chassis stiffness.
- Unsprung mass: With the heavier part attached to the body, the weight on the wheel side is reduced, lowering unsprung mass. Some argue this raises the vehicle’s center of gravity, but the difference is minimal.
While these advantages might be hard to notice during everyday driving, they’re critical for sports cars and rally racers. That’s why inverted shocks usually come with a higher price tag.
Traditionally, monotube shocks and inverted shocks were almost always paired together. However, in recent years, more monotube shocks have appeared without the inverted design. By the way, struts can also be designed as inverted type.
Conclusion
In this article, T.G.Q has outlined the most common terms related to dampers and springs, hoping to help everyone get a better grasp of what these components actually are. And if you’re able to clearly tell them apart by now, well—that’s even better.
References
- T.G.Q R&D
