Changes to damping for new spring rates
I've done a forum search and I couldn't find a concise answer:
I've just lowered my spring rates from 440f/900r to 250f/440r (I was actually recommended to use 450 on the rear, but I happened to have these 440lb/in springs lying around you see :) ).
Should I be softening the damper rates as well?
I've got these really nice, triple-adjustable Penske 8760s, but very little idea of how to adjust shocks, as my last car had non-adjustable Bilsteins.
If I go out in practice with the shocks set as they are, and I do need to change the damping, what am I looking for to tell me?
What I thought I would do is carefully count each adjuster from its current position to fully closed before returning them to the original value for the first session, but if anyone has a good rule of thumb for such a large change, I'd love to hear it.
Alan
shocks, springs, and set up
Some general guidelines:
Use preload to set the desired droop (I like to have about 1/4 inch at the shocks for most tracks.....a bit less if very smooth track)
Use only the push rods to adjust ride ht.
Measure the motion ratiio. You have to know it to do anything.
Set wheel rates (motion ration squared x spring rate) at some multiple of corner weight. ( for FF, same as corner weight is a good starting point.......winged cars higher.......up to about 1.5 x corner wt for FC).
Shock damping should be about 70% of critical damping. Several formulas are available to calculate critical damping. You can find them via google.
Have the shocks dynoed......and rebuilt if they don't match.......and/or they are way off the damping you need.
Use good springs that also match at the same installed ht.
When scaling the car.....level the front of the car......make sure bellcranks are at same angle......then adjust ride ht and corner wts. Driver wt in the car will help in the beginning.......until you know what the change is from driver to no driver.
Use rake and springs for initial ball park tuning......then go to bars and shocks for fine tuning.
If it is a winged car, adjust the wings for high speed corner balance.
Enjoy the process......the challange is part of the fun.
Jerry Hodges
JDR Race Cars