after much testing and messing i cant make it work.
if i add any joints in the vehicle physics asset the wheels no longer work and the car will not drive.
also the body attached to the joint (a door for example) pings to 0,0,0 in the car as soon as the game starts, kinematic, collision on or off doesnt matter.
i found this and Ori mentions multi body vehicles being in the engine (4.2)
there some hidden tick box somewhere or something or did this not make it in at all?