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      06-10-2013, 08:46 AM   #54
ajsalida's Avatar

Drives: 95 M3, 02 R1150GSA, 09 335xi
Join Date: Aug 2010
Location: SW USA

iTrader: (2)

Shock dyno plot (off Koni's website) for Sport shocks with adjustable rebound. Also called force-velocity curves, just to give folks an idea of what the sports are doing. Velocity is piston velocity (inside the shock body), or how fast suspension is moving in rebound or compression You'd need motion ratios to figure wheel rates but in the industry they use piston velocity. Force is the force opposing motion. Note OEM curve vs full soft.

So this is not explicitly off our 335xi shocks but probably represents Koni's philosophy on a street performance rebound-only adjustable. Note compression is very close to OEM, maybe a little stiffer at low piston velocities.

At higher piston speeds there are internal blow off valves which prevent too much force being generated, this is why the curves roll over. Quite a lot of design goes into shaping these curves for various applications by the various manuf.

Point here is pick a piston speed at the lower end of the X-axis, and move up to the first green line. That is how much force is resisting weight transfer (unloading of that corner). Now move up to middle or higher point along the same x-point vertically. That is how much force is resisting weight transfer 1 turn. We don;t know units but it is clear full stiff could be 3-4 times as much force as stock. Also these are not linear (I have been told) WRT turns so you may be full stiff by 1.5 turns.

So imagine you'd cranked the rears to 1.5 off full soft, have Eibach pro kit (same spring rate as stock) but 3-4 times the force resisting extension of the shock for weight transfer, and maybe 2-3 times for keeping the tire in contact. No wonder other bits in the chassis flex first.

Last edited by ajsalida; 06-10-2013 at 08:59 AM.