Originally Posted by keavze
now back to 'business'...
what's the difference or how will the car be affected if you use a hard spring with thin shock oil or soft spring with thick oil?
example: 1.8mm spring with 300oil vs 1.4mm spring with 700oil.
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.
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).
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.
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 under dampened situation helps, 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.
The job of the spring is to hold the weight of the vehicle above the ground and control the movement of the suspension.
The stiffness determines how much force is required to compress the spring.
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.
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.