Ok, I've been a bit quiet on here lately. Back in November I posted a few things on this topic - since then I have been busy sorting out a few things. I've also done a lot of work on this, and with Dave Coopers help at Track Developments, have come to some sort of idea how to proceed.
I'm afraid Martin Clans calculations look a bit different to mine - sorry Martin.
I think were all agreed that collapsing a coil Mark's way is not ideal. BMW springs are also too stiff because the cars are much heavier.
The place to start is the wheel rate (WR) and a desired frequency for the suspension. Using the front spring rate of 300lbs and the front geometry, for mine, this is about 100lbs WR and freq approx 1.4 cps (dependent on the weight). Note that a BMW M3 coupe is 100lbs and 1.1 cps.
What we really need is a good estimate of the weight, that's why I have tried a few a times to get this before. My estimate is 900kg including driver and half tank of fuel!
Then using the rear geometry and wanting the back to be a little softer, say 1.3 cps, the rear springs will be about 250lbs.
But there are differences, mine is an E36 and heavier. Do you guys really have 7” between the rear spring seats at max – luxury mine are more like 5”
Hope this helps.
Cheers,
Martin
Keep up the good work.
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