That “floating” behavior is most probably perceived as unrealistic because of the environment, and not the physics itself: car speed & acceleration, scenery scale, etc. When everything fits into real-world scales then the perception is more realistic.
However, for this kind of arcade games the best workaround is increasing global gravity as Paulo suggested, so the perception is more realistic on jumps. The increased gravity should help as well with the slow rolls, but I’d also try adjusting the car’s physic material for more friction.