yeah that's why I'm talking about a single wheel object, not a car object.
This wheel would produce the info needed to apply the proper force to the car body, which in turn would drag the wheels.
It's complex but not hard pretty well documented and I studied it at some point.
I just gotta start working on the SDK.
One thing that could be annoying is weight. The wheel needs to know how much weight its supporting, but if I get this info automagically from a physics car body (based on body weight and relative position and assuming all wheels are at the same height) then you don't get to create multi-part articulated wheeled vehicles (8-wheelers, bycicles, etc) or to model suspension.
But suspension and weight distribution aren't trivial to calculate, doing so in events would make a physics wheel behavior really difficult to use.
Perhaps the behavior could have utility expressions to calculate those things. Hmm.