Alan D. wrote:Maybe I need a 4 inch helper spring and a shorter main spring. I have a short ( 8 inch I think) main spring, rated at 90 pounds. I wonder what this would be like with the 60 pound helper spring?
Alan
I think that would be going the wrong way and you will end up with a 90lb/in spring rate again, with the helper spring flattened.
If I have followed the thread correctly, then your problem is getting ride height with the softer 75lb/in spring.
The softer the spring the greater the deflection under static load, roughly around 4 inches with the 75lb/in spring. The 90lb/in spring would deflect less - around 3.33inches.
The helper spring will probably be coil bound (or near to it) under the static load - the corner load is around 300lb, which would deflect a 60lb/in spring by 5inches, but it is only 2inches to start with, so it follows that it is coil bound. That is okay because it is only there to keep the main spring seated under droop. However, if you have wound the spring platform up to raise the ride height you may have created preload such that the helper spring won't actually be called upon.
One answer would be to start with a longer 75lb/in spring - you get the same 4 inch static deflection, but the ends sit further apart. But thinking about it further that doesn't help, you still end up winding in pre-load to raise the ride height. You would get the same effect if you inserted a spacer sleeve between the coil end and the spring seat. The length of the coil just needs to provide enough travel to accomodate the static deflection - 4 inches - and then the free travel of the damper from the static loaded position - probably another 4 inches. So that's a total deflection of 8 inches, which sounds feasible with a 12 inch coil.
So if spring length isn't the answer what is? Well, logically you need to adjust the height at the top of the damper. That is, raise the body with respect to the top of the damper. As I mentioned before, if you preload the coilsprings to take out all of the static deflection you will have raised the top of the damper to its full extent. You won't get any more ride height and additional preload will just make the springs appear solid until the dynamic load overcomes the preload. Unfortunately, the scope for raising the ride height is limited by the length of the thread at the top of the damper. To gain more adjustment an extension piece would be required, something that would not be beyond the capability of someone who is handy with a lathe.