Originally Posted by BarryC
Hey guys - well apparently I trashed the note with the specific rates for the Eibach and OEM. My memory is the following approx. numbers:
Front: Stock 154 Eibach 170
Rear: Stock ~500 Eibach ~600
Big spread front to rear....
I measured and computed the rates for stock E92 springs. Wheel rates front and rear are about 200# per inch (my front wheel calculation disagrees with the one above, and it might be wrong - it's based on wire and coil diameter and number of coils, etc).
The rear spring is much stiffer but it's the spring rate measured at the wheel that matters. Because the rear spring sits about half-way between the lower control arm pivot and the wheel, the spring is compressed about half as far as the wheel moves. That means the effective spring rate at the wheel is about a quarter of the actual spring rate - the reduction is the square of the lever ratio.
My exact calculated wheel-effective rates were 202 pounds per inch at the front, 195 at the rear.