No matter what design of suspension a vehicle uses, there are certain components that it will always include in some form. This page is a very general description of these, as more detail will be given later.

Springs

  A spring is a device for storing energy. When you deform it from it's original state, you put energy into it. The spring then uses this energy to return to it's original configuration when you remove whatever load was applied to it. In car suspension, we are normally concerned with using this property to absorb changes in terrain that try to move the car around: When you hit a bump, the energy that would normally go into jolting the car is absorbed by the spring as the suspension compresses, and then released again as the suspension extends afterwards. For a pothole, the spring releases energy as the suspension extends to drop the wheel into the hole, and then reabsorbs energy as it compresses again.

  A spring's energy storage is measured in terms of how much force is required to deflect it a given amount, called the spring rate - usually in the sense of applying a given weight to compress it down due to the earth's gravity acting on a certain mass. So if we had a spring that compressed by one inch in height when a mass of 100lbs was placed on top of it (with the earth's gravitational pull trying to work against the resistance of the spring), we would say that the spring's rate was 100lb/in - it will move one inch (or part thereof) for every 100lbs (or part thereof) loaded onto it.

  This is called linear, or fixed-rate, behaviour. Some springs required the force applied to them to be increased in order to deflect them more - e.g. 100lbs to compress by one inch, a further 150lbs to compress by another inch after that, and so on. This is called rising-rate behaviour, because the spring's rate increases as it is compressed. A rising-rate spring allows for quite large deflections under small loads, but without necessarily compressing the spring fully under high loads. For example, the spring discussed above would be compressed one inch by a 100lb load, but a 300lb load would not compress it by three inches - rather, it would move by a little over two inches.

  This kind of behaviour can be extremely useful for automotive applications, especially in situations where there is likely to be a large difference in the highest and lowest loads a suspension system will need to deal with. A linear system would be required to be stiff enough to cope with the heaviest load, but this may result in it being stiffer than desired when lightly loaded.

Dampers

  Dampers are used to slow (damp) the movement of a suspension system. A given force applied to a damper will cause it to move at a certain speed - but unlike a spring, it will keep moving until either the force is removed, or it reaches the limit of it's travel. Also, when the force is removed, the damper will remain in that position, not return to it's original state. In a car, the suspension damping controls the dynamic peformance of the suspension; Applying a load to the suspension will compress it a given amount (determined by the spring rate) no matter how much damping is used - the damping determines how quickly the suspension compresses under load, and how quickly it returns to it's nominal state when the load is removed.

  The primary use of damping is to prevent oscillation in the suspension: A sudden load dropped on a spring will compress it further than the spring rate would do if simply loaded by the same amount, and the spring then bounces back past the static-loading condition as it returns, trying to work off the excess energy stored in it. Eventually, having to work against friction in the suspension system dissipates the energy, and the spring holds itself in the compressed position - but we could really do with it doing this as quickly as possible.

  That's where the damper comes in - providing a measured amount of resistance to try and make sure the suspension doesn't over-react to sudden loadings, and stop the car from bouncing around uncontrollably every time you hit a bump. Obviously, the suspension still needs to react quick enough to do it's job, so you don't want the damper giving too little resistance (underdamping) or too much (overdamping). Ideally, you want the spring to reach it's nominal position as quickly as possible without going past it - termed critical damping: The graph on the right gives a simplified representation of the principle. Whether this ideal situation can be obtained all the time is another matter - one that we will discuss later.

Suspension Arms & Linkages

  The various components of a suspension system are linked together by a variety of designs of arms and links, but they all perform the same function - holding everything in place, and providing support and leverage as required. These components can vary from simple pieces of tube to complex pressed, cast, or welded assemblies, depending on the application. Their purpose is not to actually do anything, but rather to make sure that the other suspension components are able to do their job properly. Their design is critical to creating a suspension system that operates as intended, and in most cases linkages are intended to be as stiff as possible to eliminate unwanted movement.

Pivot Points

  Joints between moving components need to be able to rotate freely in the desired way, and have minimal movement in others. There are two basic types used in car suspensions: Rubber or plastic bushings, which allow for a certain amount of misalignment, and help prevent transfer of vibrations, and metal spherical bearings (also called Rose joints). These are much more expensive, and give a very stiff, solid joint, at the expense of also being stiffer to the end of transferring more vibration. Broadly, you are unlikely to find these on production road cars, where the vibration-absorbing properties of rubber bushings are preferred. A later section will go into more detail on this area.

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