I would guess you need to 'tilt' the cars in MED, as the real cars look to be "shaped" with that tilt.
And getting the rotation to be affected by the off-center mass, cant you just position the mass away
from the center of the car model?
Probably toward the 'high' point of the car, so it is a bit more reactive and "swingy".
(remember I am next to useless with physics)