How a Shock Absorber Works
The shock absorber, or more correctly, damper, is a hydraulic or pneumatic device that operates up to 1900 times per mile to stabilize a vehicle's handling and generate as much contact between the road and tires as possible.
Without a shock absorber fitted, your springs would contract and expand continually till the energy stored in them is dissipated. This would make for one hell of a bouncy ride, with handling that is completely unpredictable.
A brief history of the Shock Absorber
Early cars were fitted with friction disc dampers, which were incredibly basic and shook passengers to the core. These were made up of interconnected arms that were separated by a leather friction material, helping to bring spring movements under control.
The Gabriel Suspension company claim to have invented the worlds first hydraulic shock absorber in 1918. By the 1930's, hydraulic dampers became standard equipment.
Technically speaking, shock absorbers are a form of a linear dashpot mechanism.
How does a shock absorber work?
Shock absorbers come in a number of different formats, such as:
- Twin tube
- Gas-filled monotube
- External reservoir
These two are available in many different shapes and sizes, as struts (McPherson), traditional telescopic dampers and cartridge types. Damper bodies have numerous different fixings that vary from vehicle to vehicle, with bayonet and ring mounts, integral bushings and bar mounting fittings to name just a few.
All dampers work around the same basic principle. As the control arm or wishbone moves to accommodate differences in the road surface, those initial shocks are cushioned by the spring. The spring technically is doing the shock absorbing. The compressed spring now has a store of kinetic energy and the tension of the coil causes the spring to expand, then contract and so on, with this process repeating until the energy has faded away.
The damper turns the kinetic energy of the spring into heat. This is achieved by a filling the cylinder body with oil and having a piston that has a plunger fixed to the end. At the end of the plunger are a number of holes that control how much oil flows between the two chambers in the damper.
This brings the spring oscillations under control, the resistance within the damper creating heat. The heat is then passed from the body into the atmosphere and the conversion from kinetic to thermal energy is complete. After driving on a rough surface, you may notice that you shock bodies are actually warm to the touch.
What else does the suspension system do?
Not only does the suspension system keep the wheels firmly in contact with the ground, it also performs a number of other important roles:
Braking Nose Dive Control
As weight transfers forwards due to momentum under braking, the suspension helps to resist this shift and balance the weight transfer.
Left unchecked, a body would lean away from the direction of travel. This shifts weight and reduces grip. The suspension system helps support the body and resist the rolling motion.
Powerful track cars will experience what is essentially the opposite for nose-diving, where the front end lightens and raises under acceleration. The shocks will help counter this force.
Traction loss can happen for a number of reasons, but one bumpy road, the suspension forces the tires into contact with the ground, increasing grip.
On cars with low ride height, you may experience scraping or bottoming out, where the cars body or tub comes into contact with the track. The suspension will help prevent this.
Types of Shock Absorber
Twin-tube on the right, Monotube on the left
Twin Tube Shocks
Generally, twin tube shocks are the most cost-effective and common shock style. You will find them fitted on many light cars and trucks. These shocks are made up of two interlocking tubes, an outer body and an inner cylinder that houses the piston. Tiny holes in the piston work with valves that are designed to control the movement of oil between the inner and outer tubes.
These shocks do suffer from overheating. This will be most noticeable on rough terrain or bumpy tracks. The constant movement can cause the shock oil to become churned up into a foam that causes erratic and irregular compression of the shock. This translates to a wallowy ride and increases the chance of losing control of the vehicle. OEM dampers are usually not serviceable.
Monotube shocks can help reduce the heat build-up problems we see in twin-tube shocks. Because there is only one tube that the piston moves up and down in, there's less material to insulate the shock and to hold onto heat. These shocks are less likely to overheat on washboard roads, however, they will generally be more expensive than a twin tube damper as the manufacturing costs and requirements are higher.
Gas Filled Shocks
To prevent the shock oil from foaming, called cavitation, a pressurized gas is used inside the damper. This gas prevents the oil from mixing with air in the oil chamber and forming bubbles that give unpredictable wheel motion control.
Gas-filled dampers are less likely to have faded from overheating or cavitation and are used by off-road and rally driving teams. Typically, Nitrogen gas is used as it is inert and compressible, behaving in a predictable manner.
External / Remote Reservoir
External reservoir dampers further reduce overheating problems and are used in performance and motorsport applications. The shock body is lightweight and more compact, as part of its oil capacity is stored within the reservoir. The reservoir is connected to the shock body via a high-pressure hose line. External reservoirs shocks are used because they can be easily adjusted, installed in small spaces and provide optimal oil cooling (you could duct air over the reservoir for example). A variation on this concept is piggyback dampers, where the reservoir is fixed externally to the shock body.
We hope you enjoyed this post on how dampers work, let us know what you think in the comments below.