January 2010 Tech Tip: The Role Of The Hydraulic Shock Absorber.

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The primary function of the shock absorber is actually not to absorb shocks at all - this role is carried out by the spring. Its ultimate role is to keep the tyre in contact with the road surface.

The shock absorber is a hydraulic device that resists any unwanted motion of the spring that can result in reduced wheel traction. It does this by controlling the oil flow as the unit extends and compresses.

When the car passes over a bump in the road the downward motion of the car’s unsprung mass creates an energy that is primarily absorbed by the spring.

During this compression stroke the oil inside the shock absorber flows from the pressure tube through to the oil reservoir.

As the coil rebounds it releases the energy it has built up through compressing and the shock absorber must control this recoil to maintain the tyres contact with the road and provide stability to the body of the car. It achieves this by reversing the oil flow back into the pressure tube with the rate of flow controlled by valves.

Gas charging the shock absorber puts the oil under pressure, providing a more responsive action and consistency in oil flow. Other benefits can include a longer shock life.

When you replace your vehicles springs you should consider shock absorber replacement as well, with the following in mind:

- The age of the existing shock absorbers

- The rating of the existing shock absorbers – are they valved appropriately to control new heavy-duty springs?

- Ride comfort - worn shock absorbers can cause loss of tyre contact with the road surface and excessive body roll

- Suspension travel – for lowered or raised spring kits are there shorter or longer shocks available to maintain appropriate travel?