Two types of springs :
Progressive and Linear
Progressive is the type of coil spring where the spring rate has varying rate of compression within the spring. If u see a spring that is coiled up with lower diameter from where the spring sits on the spring perch to larger diameter on way up....that is Progressive.
In this case, when the spring is compressed, the higher diameter characteristics provides a better level of comfort and the compression gets harder as the spring is fully compressed.
Hence it is fair to generalize that progressive spring is more comfortable. In terms of handling, it's not as sharp and induces some sort of roll still.
Most main stream names coilvers made by KW and Bilstein for road car applications run on prog rates and usually, u cant really specify the spring rates you prefer.
Now Linear springs...
As the name suggests, it means the rate of compression is linear throughout the travel. So visually, u see the spring has same diameter from lower coil to upper coil.
Not as comfortable as the prog almost for certain but it provides a much shaper cornering and reduces body roll. The steering feedback also improves.
Track/race cars usually use this and normally, the springs can be customized to your specification..
Just fyi, depending on specific makes, some V2 runs on different type of springs on different cars. Eg . Full prog in E9X front and rear But in previous model Z4, the front runs on linear and rear on prog.
For EVO X, i think it's linear springs front and rear and the rear is also on coilover, unlike most BMW models where the strut and spring are independent.
Cant help ya on what spring rates used...Maybe u can write to KW direct.
I'd imagine ard 550-600 lbs per inch is decent enough for daily cum occasional track days.
