The Design Of A Racing Shock

We have been asked to present more basic information on subjects such as shocks. Sometimes, no matter what your level of understanding of a particular technology, it can be a good thing to be refreshed on the more basic information. So, we present a multi-part series on the racing shock.

I have heard claims by shock "experts" that all you have to do is bolt on their shocks and you will instantly be "bad fast," or three tenths quicker. While we do agree that gains in performance are possible and loss in performance often comes with running the wrong rates of shocks, the first order of business is to work out any basic chassis setup problems you might have before experimenting with shocks. Most shock experts will agree on that principle. Let's look at what shocks can do and cannot do.

What Shocks Will Not Do1. Shocks do not support the car.2. Shocks do not control the amount of load transfer.3. Shocks do not affect chassis balance at steady state mid-turn.4. Shocks are not a cure-all for basic handling problems.

What Shocks Will Do1.Shocks control (limit the speed of) motion of the chassis and the suspension.2.Shocks, with varying designs of resistance, allow more or less rapid movement of a suspension corner than opposing corners.3.Shocks regulate the amount of time it takes for a corner of the car, while in transition, to assume a new ride height. 4.Shocks can be used to redistribute the amount of load on the four corners of the car as it is in transition on corner entry and exit.5. And, shocks can be used to "tie" down one or more corners of the car, be that a good thing or a bad thing.

How Shocks Work Shocks resist motion by using a piston that must move through a fluid (thin oil) as the suspension moves, so that the fluid must pass through holes, valves and slots. Varying resistance is created when the oil is forced through different sized openings. The resistance is usually different for compression (inward motion) and rebound (outward motion).

All racing shocks are of two basic designs-twin-tube and mono-tube and can be either gas pressurized or "low" pressure. The twin-tube has literally two tubes, the inside tube is where the work is done and the outside tube is a reservoir that holds extra fluids and a flexible gas-filled bag.

Shocks are Spring Dampeners Shocks are installed in racecars, as in any car, to primarily control oscillations caused by the displacement of the springs, especially coil springs. If we place a load on an undampened spring, such as when they support the car, and then push and release on one corner of the car, the spring will compress and decompress in a series of diminishing oscillations over a relatively long period of time. There is no known advantage to this condition and many disadvantages, so we use dampers to control and slow down the movement of the springs.

In our racecar, both the shocks and the springs resist compression or bump at any one corner of the car. When that same corner tries to return to its normal ride height, the spring promotes that motion and the shock resists. The control of these two motions, compression (bump) and rebound (droop) is the primary function of the shocks.

Compression and Rebound The compression control side of what the shock does resists:1.The bump movement of a corner of the car when we hit bumps (rises in the track).2 The movement due to the transfer of load to the front end during braking/deceleration.3.The movement due to the transfer of load to the rear upon acceleration.4. And the speed at which the right-side springs compress when the lateral forces are applied as we deviate from a straight line and turn left.