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Actually, if you do the maths, you'll see that preloading the bellevilles DOES have an effect. Within the displacement in which the bellevilles are preloaded (so if the preload is 1mm, then for the first 1mm movement) the roll rate is TWICE that of the stacks you choose. Beyond that displacement (i.e. once the preload is overcome, in this case beyond) then the rate is EQUAL to that of the stacks.
And that's just taking the rate of the stack as a single number. What actually happens is the single bellevilles become 'coil bound' first, which takes them out of the equation and makes the rate of the stack jump up.
Hence:
With a ><<>>< stack and 0.5mm preload
The overall non-preloaded rate is 363kg/mm
The preloaded rate is 725kg/mm
For the first 0.5mm the roll rate of the monoshock is 725kg/mm
Between 0.5mm and 1.126mm travel, the rate is 363km/mm
Between 1.126mm and 2.252mm the singles go coilbound and the rate jumps up to 1088kg/mm.
Beyond 2.252mm all the bellevilles have become coil bound, so it all goes infinitely stiff and bad things happen.
Good teams/drivers (I am not one of them) can play tunes, such that at turn in, mid corner, and corner exit the rate is different, with known and predictable switching points.
I have assumed a linear rate between unloaded and coilbound, which won't be the case, but is close enough for my needs.
Other than the friction of the system, there is no damping in roll other than what can be done via the warp of the chassis (i.e. the rear dampers).
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