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      01-11-2010, 10:13 PM   #35
rzm3's Avatar

Drives: E92 M3
Join Date: Aug 2007
Location: USA

iTrader: (18)

Originally Posted by lucid View Post
rldzhao, if the stock spring preload compression is indeed 2" (JAJ's numbers suggest that is more like 0.8"), then that creates even more room for using shorter and stiffer aftermarket springs, and would explain how H&Rs are stiffer and result in 1" drop. I haven't taken any measurements on any of this, so I'm going with what you guys have posted here so far. All I can measure is the natural length of the stock springs as they are in my basement. I believe the fronts are ~11.5".
From my fresh measurement:

Stock front spring: ~12"
Front spring (mounted) perch-to-perch distance: ~8"
Preload compression: 12"-8"=~4"

Which means that the front suspension experiences a preload of roughly:

147 lbm/in * 4 in = ~588 lbm

Now, this number may be slightly high because the spring stiffness during the initial 20% of travel is less than 147 lbm/in, which means the preload will be <588 lbm.