I'd imagine that they're using whatever the real cars are using.. By
progressive/linear/digressive, are you referring to how the shock axis angle
changes with wheel travel? I don't think they're doing that, as I'd heard from
someone that Kaemmer is still considering doing a full suspension model
(meaning it would be linear and is not done yet in N4)... i.e., there isn't
really one there yet, but it's close enough so you can't tell anyway... I
could have misinterpreted/be remembering incorrectly.. Still though, with that
type of system, you can approximate the other two very closely as well, at
least as closely as dynamic camber is being done..
The real answer is, of course, that I don't know :-) Just speculating.
Todd Wasson
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Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://PerformanceSimulations.Com
My little car sim screenshots:
http://performancesimulations.com/scnshot4.htm