Most RWD drive cars have a 50/50 weight distribution give or take these days. Also when a car moves foward the torque of the rear wheels reacts against the body to tip the car up at the front so transfering weight to the back and thats increased with the rear suspension being compressed. Of course in reverse the reverse happens so don't bother trying to reverse up a snowy hill in RWD as I've seen a couple of people try in the past. It don't work.