I think if you look on the info below, which I stole from ORB, at this link
https://www.e90post.com/forums/showp...1&postcount=10
You see the difference between the M3 oem spring rates and the e9x non M 335, (Orb did not include the M-sport versions (eu/us) but it's somewhere in this forum).
You see a big difference in spring stiffness. Also front - rear ratio is significant different, M is almost factor 4.
Anyhow, to be honest I'm not completly sure why M went with both stiffer springs and sways. Stiffer springs I can imagine. But the more heavy sways, I can only guess, it might be a good fit for our chassis.
I'm also not sure if they are progressive or linear.
The message from Orb:
The motion ratio for the car:
Front: 0.96^2
Rear: 0.563^2
Calculation for wheel rates:
Coil spring rate * Motion ratio = Wheel spring rate
Stock 335i example.....
E.g. 145lb/in * 0.96^2 = 134 lb/in
E.g. 460 lb/in * 0.563^2 = 146 lb/in
Spring rates:
Stock 135i:
Front: 120 lb/in
Rear : 350 lb/in
Stock 335i e92:
Front: 145 lb/in
Rear: 460 lb/in
Stock M3 e92:
Front: 160 lb/in
Rear: 550 lb/in
335i KW v3:
Front: 260 lb/in (progressive average)
Rear: 570 lb/in
335i KW Clubsport:
Front: 400 lb/in
Rear: 570 lb/in
M3 KW v3:
Front: 285 lb/in
Rear: 630 lb/in
M3 KW Clubsport:
Front: 508 lb/in
Rear: 800 lb/in
335i Bilstein PSS10:
Front: 385 lb/in
Rear: 615 lb/in
Orbs 335i:
Front: 336 lb/in;
Rear: 672 lb/in;
To scale the OEM suspension frequencies you can use this formula to get a rear spring rate.
(New front spring rate/OEM front spring rate) * OEM rear spring rate = new rear spring rate
E.g. (265 lb/in /145 lb/in) * 460 lb/in = 840 lb/in
If you do the calculation you will see the rear spring is really soft in these performance setups. Soft ass end means more understeer! Kind of makes one wonder if anyone is telling the truth that thier car is all that great!
End of copy...
------------------
I'm still looking for the exact m-sport spring rate and sways. Will get back to that one.