Springs -

The job of the spring is to hold the weight of the vehicle above the ground and control the movement of the suspension.

Preload:

Preload is actually a misnomer. Preload is actually the method of determining the ride height of the vehicle. If a spring is shorter than the shock is at the desired ride height you add preload to allow the spring to hold the correct ride height and allow the spring to work at full length. Preloading does not gain any force in the spring, if you compress the spring further than the natural weight of the vehicle you are reducing the travel of the suspension.

Stiffness:

The stiffness determines how much force is required to compress the spring. This is usually rated in pounds. A higher stiffness will require m ore weight to compress the spring than one with a lower stiffness. The stiffness of a spring has a tremendous affect on how a vehicle will respond to the surfaces that it travels across and how the tires will react.

Springs:

There are two distinctly different types of springs that can be used on vehicles, linear and progressive. Linear springs are of a basic type, they hold a constant stiffness throughout its compression. Progressive springs change their force throughout the compression process. Usually a progressive spring will provide less stiffness through the first stages of compression and gradually increase in stiffness as the spring continues compressing.

Springs in Relationship to Dampening:

Since shocks control the spring and springs control the car, the relationship is fairly simple. The dampening is there to keep the car from oscillating (or bouncing) which reduces the contact of the tires to the road. It is essential to match the shock oil with the particular stiffness of spring that is to be used. If this is not accomplished the car will either be over or under dampened. To find the optimum you must make sure that the car can traverse bumps in the track without oscillating continuously after the initial bump. If an oscillation occurs, the spring that you are using is too stiff or your dampening is too low. A car that is set-up correctly should have no oscillation yet have a very quick reacting suspension.

Tuning:

Springs and Ride Height:

In setting ride height it is essential to use a springs that will the vehicle weight above the ground without major compression in the spring. Usually the spring should compress 1/8th of the length or less. If the spring compresses more under the natural weight of the vehicle you should use a stiffer spring. This is the minimum stiffness spring that you can use.

Springs and Straits (general settings):

When using a linear spring it is much easier to determine what oil should be used since there is no real change in spring rate of the shock shaft under a quick heavy load. This however does provide a smaller window of error which can cause some problems as well. The problem with a linear spring is that since it keeps stiffness it will not be able to take large irregularities in a surface effectively. Larger bumps than that which the vehicle is tuned for can cause the cars chassis to hit the ground and cause a loss of stability

A progressive style spring solves the major problems of the linear spring in that it can change stiffness throughout itıs travel. This change allows the spring to compensate for a unexpected bump that may be larger than the norm by stiffening further as the suspension travels, hopefully avoiding the chassis hitting the ground. The disadvantage (or an advantage depending on how you look at it) to the progressive spring is that the dampening becomes a compromise due to the shock shaft changing speed constantly. Progressive springs can be tuned to be over or under dampened depending on suspension travel. This means that Progressive springs have a range of dampening possibilities leaving a larger window to tune within.

Graph showing Linear spring and Progressive spring to oil weight range to come

Springs and Corners:

In setting up the spring and shock combination, all of the concerns of a straight set-up have to be taken into consideration. The set-up for the corners does differ from a straight set-up though. The most major way is that you are turning, this action causes the outside tires to have more weight (Gıs) on them than the inside tires causing them to grip better. There is a limit to this grip and it is determined by the tire and suspension geometry. If the weight on the tire exceeds what the tire can handle then the tire will loose grip causing the car to slide. The over-taxing on the tire is caused by the chassis rolling to much or leaning toward the outside of the corner. To achieve maximum grip for the tire that is used you must limit the roll so that there is not as much weight being put on the outside allowing the tire to do the job required at itıs optimum. You can have to little roll in a vehicle as well which will also limit the grip that the tire provides by not putting enough pressure on the tire. Normally to adjust the roll of the vehicle with the shock and spring combination you will use stiffer springs and the corresponding dampening.
Suspension Geometry and further set-up will be covered under the heading of Suspension Geometry. Tires will be explained more under the heading of tires.

Suspension (Shock and Spring) Set-up and Road Conditions:

Set-up for road conditions is a compromise between set-up for the straights, and maximum cornering grip. Suspension set-up for the in a perfect world have the straight set-up and the cornering set-up exactly the same with no degradation in either area, this however does not usually happen.

If the road that you are dealing with is bumpy you would tend to choose a softer set-up for the shocks and springs. This will allow the car to be more stable over the bumps by not transferring as much force into the chassis. However sometimes the degree to which the suspension is softened will cause the vehicle to roll more than what is desired. This added roll will transfer more of the cars weight to the outside tires causing the cornering grip to be reduced. The reduction in cornering forces require the use of additional stiffening by using anti-roll bars.
Anti-roll bars will be explained further under the heading of roll bars.

Smooth roads are a much easier set-up problem than a bumpy road. The reason for this is the cornering set-up can be much closer to the straight set-up. Simply put the suspension can be tuned for the corners and it will work well on the straights also.

On a surface that is wet or dusty a set-up a little softer than the normal will usually work well. Dusty and wet surfaces are unpredictable at the least so tires have more than a major role to play. Since the surface is unpredictable a comfortable (more stable) set up is desired over a quick set-up.
Tires will be explained more under the heading of tires.

It is usually better to set-up a car to obtain maximum grip in the corners over straight. The closer you can get suspension set-up to provide maximum of both straight and cornering grip the better the car will handle.

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