Shocks and springs are an integral part in the set-up of a vehicle. These parts are what help keep the tires connected to the road and allows them to do their job. A well thought out and set-up shock and spring combination will allow a vehicle to maintain contact (through the tires) with the road under all circumstances. If it is not correct the tires will not be able to do their job effectively.

Shocks -

Oil:

The oil determines how fast the shock shaft moves, this is also referred to as dampening. If low dampening is desired you would use a lower weight oil to facilitate a higher speed. To raise the dampening (slow the speed) you would need to use a heavier weight oil.

There are two types of oil, synthetic and natural, there are also blends of these. Whether or not to use a certain type of oil is a concern in a shock. Natural oils are cheap to purchase but are affected adversely by temperature. Synthetics are not as affected by temperature but usually cost more. Environmental conditions and the pistons traveling through the oil generate heat which cause degradation in natural oils. Due to this degradation synthetic oils work better for use in shocks, however, it is not always a rule and natural oils can be used effectively.

Pistons:

Pistons control what speed the oil flows from the lower chamber of the shock to upper chamber and visa-versa. A larger hole, more holes, or a combination of both in the piston will give a faster flow which will give a higher shaft speed (lower dampening), smaller holes or less holes in turn will slow down the shaft (higher dampening). This is effectively the same as using lighter or thicker oil but there are less concerns about oil contamination (two different oil weights being mixed).

One advantage to using pistons as a tuning source for the shock absorber is that you can fine tune the placement and size of the holes in the piston to precisely match the dampening to the spring being used and the reactions wanted in the vehicle. The downside to this is that you must rebuild the shock each time that a change is to be made.

Some shocks are made with adjustable pistons. These shocks will allow changes to be made in the dampening effect from the outside the shock without actually having to rebuild it. These shocks accomplish this by uncovering larger, or smaller holes during adjustment.

The pistons in a shock absorber can be specially tuned to provide a slower movement in one direction over the other, these pistons are known as Two-Stage. Two-Stage pistons are more complex than a normal piston but allow further fine tuning to the dampening rate of the shock.

Piston Hydrodynamics:

A pistons shape and weight also effect the performance of the shock. Since the piston is a moving device through a liquid, hydrodynamics play a small part. It is desired to have a smooth transition of the oil from one chamber to the other. The smoother this transition the better. A consistent pressure on the entire piston will yield less binding in the shock due to a better flow of the oil from one chamber to the other. This is a very minor concern but the results will be a more consistent set-up.
Simple terms: It is better to have two smaller holes than one large one.

Picture showing two holes in a piston to one to come.

Bladders:

A bladder is a pressurizing system that compensates for the airspace that is left inside the shock to accommodate a fully compressed shock shaft. Modern shocks will use a pressurizing system to keep the oil solid and bubble free throughout the shaft travel. Highly advanced shocks will use nitrogen or some other gas to accomplish this task.

Air:

Air is a bad thing in a shock, plain and simple. Air in a shock allows the oil to foam up (drastically thinning out) causing the shock to lose itıs effectiveness in controlling the spring movement. If air is in the shock you must rebuild and re-bleed the shock
Bleeding a shock - the process of removing all the excess air from the shock to allow for consistent dampening.

Shock limiting:

This is a common method to keep a vehicle from bottoming out or the suspension from becoming over extended either by unseating the spring or stressing the drivetrain. The less limiting of the shock that you do the better since you are allowing the suspension more freedom to deal with changing road conditions. The limiting should have no effect on the natural compression of the spring by the cars weight. (It should not preload to the spring in any manner).

Tuning:

The shock dampening should be tuned to the fastest movement that the shock shaft will encounter. This is done to allow the shock to have consistent and quick reaction without causing a back-up in the transition of the oil between the chambers (see piston hydrodynamics). If a back-up occurs the dampening will have a negative effect on handling of the vehicle because it will not allow the spring to start and complete itıs job effectively.

If the dampening is to high the shock will act as a secondary spring or spring bumper which will not allow the vehicle to transition through rapid changes in direction easily. Over dampening will smooth out the ride of a vehicle over minor bumps by making them almost invisible to the springs. Major bumps will cause the vehicle to become unstable. The major of concern of over dampening is that the car will become sluggish through chicanes and in avoidance maneuvers.

The newest shocks "4-way" have a system by which they will allow a lower dampening to be achieved in the initial hit of a larger bump, but provide heavier Dampening at all other times to produce a more stable vehicle and overcome the major instability concern of having a highly dampened system.

If the dampening is to low the shock will not be able to control the spring causing the car to oscillate (bounce continuously) causing a loss of grip over any bump. Transitions in a low dampening situation will be extremely quick, most of the time too quick. The main concern of this situation is that the car becomes extremely unstable under any situation. The one thing that an underdampened situation help is that it is able to absorb large bumps with ease.

It is better for the car to be over dampened than under dampened because an unstable car is uncontrollable. The optimum dampening should be just enough to stop the spring from oscillating.

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