Missed this thread from before, but here is some information for you based on previous posts by Gene Fryman and discussions we've had in the physics forum.
All mods use the same bump rubbers.
The bump rubbers produce a maximum force of 179 pounds/800 newtons when fully compressed and are adjustable from .5 to 2.5" in the player setup menu. The bump rubber comes into play at this length before the maximum suspension travel of 19 cm/7.5" is reached. So if you set a 2.5" bump rubber length, it starts adding force to the wheel/spring force beginning at 5" of suspension compression.
The force is not linear but varies with the cube of the compression distance. The formula is:
Force = Resistance * Compression ^3 / Bumper Length ^3
where Resistance is 179 pounds/800 newtons
Compression is how much the bump rubber is compressed
Bumper Length from the setup menu
For example, if a 2.5" bump rubber is compressed by 1", then it only adds a force of 11 pounds. At 2", the force will be 92 pounds. And at full compression of 2.5", the maximum force of 179 pounds is applied.
GPL's springs are different. In the real world, the wheel rate and the spring rate are normally different and vary in relation to each by the mechanical advantage afforded by the suspension geometry. So in the real world, 1" of wheel travel does not necessarily equate to 1" of spring travel. In GPL, the wheel rate and spring rate are the same which is why in the setup menu, you are adjusting not only the wheel rate, but also the spring rate by the same amount.
As the suspension compresses in bump, the wheel/spring force is added linearly. So each inch of compression increases the spring force the same as the prior one. In other words, GPL does not have progressive springs.
When the bump rubber comes into play, its force is added to the spring force for the total force acting downward on the wheel.
One of the issues we've found with the upcoming sports car mod is that there really isn't a limit on the maximum amount of suspension travel. There is no equivalent of a mechanical stop as real world cars have. Although the normal suspension travel is 19 cm/7.5", under extremely heavy load the suspension may compress even more than this. It's not completely clear what GPL does for spring/bump rubber force at this point.
If you are experiencing chassis bottoming, the only way to prevent this is to raise the ride height, increase the wheel rate, and/or increase the bump rubber length.
Hope this helps.
Edited by Lee200, Jul 30 2010 - 07:00 AM.