The obvious answer here would be, “shock absorbers exist to absorb shock,” but the truth is, the name is quite misleading. The shock absorber actually exists to control the vertical motion of your vehicle’s wheels, affecting suspension travel and rebound, with the job of the shock absorption actually being handled by the springs.
Indeed, on their own, shocks don’t really do all that much. They don’t provide any lift and they would not technically be necessary in a standard vehicle as long as you were driving on a smooth surface, in a straight line. Once you tried to brake or turn a corner though, you’d certainly notice something was up.
This is why fitting replacement shock absorbers to a vehicle with worn-out springs will over-work your new shocks and lead to reduced performance or premature failure.
Conversely, upgrading only your springs but retaining worn-out shock absorbers can lead to insufficient spring control and body roll.
In a 4X4, in practice, shock absorbers are effectively hydraulic pumps that smooth out your ride and ensure your tyres remain in contact with the ground at all times. They don’t actually support the weight of the vehicle, which is another common misconception.
Types of shock absorber
There are two basic types of shock absorber: mono-tube and twin-tube, with the majority of 4×4 upgrade shock absorbers falling into the twin-tube category.
Twin-tube shocks – These are made up of two separate cylinders with the outer cylinder set inside the shell case and the inner cylinder containing the piston valve.
In this design, there’s no piston or barrier between the oil and gas in the outer cylinder. These shocks are cheaper to produce and can operate with lower gas pressure, which explains why they are more popular.
Mono-tube shocks – Here, all of the internal components are contained within a single tube, with a piston used to separate the oil chamber from the gas chamber within the shell case.
Mono-tube shocks use higher-pressure gas and have a larger oil capacity, which provides more efficient temperature control for improved performance in harsh conditions.
They also generally have an improved life cycle, as the oil and gas are separated by the piston so they can’t combine and foam or degrade.
Even premium shocks from brands like Old Man Emu and Terrain Tamer will (generally speaking) be of a twin-tube design but make up for this with high-quality outer casings and internal components. Indeed, twin or mono is far from the only factor to consider when researching shock absorbers.
Besides component quality and casing thickness, shaft diameter, type of valving and type and quality of end-fittings are all important considerations.
What about bypass shocks?
Very much the new kid on the block, at least in terms of the 4WD market, these shocks are more commonly used in cycle and motorbike racing.
These use a hose (or something similar) to attach a second cylinder or reservoir to the main body to allow for improved cooling and increased oil and gas capacity.
These premium products are recommended for punishing environments, competition use, or for obtaining the best ride quality and handling within the design limitations of any given suspension setup.