How does the hight of a ramp affect the speed of a car?

The higher the ramps incline in affects how much work the engine has to put out. climbing up an average driveway requires very little from and average car. Going off-roading and going up steep hills means that the engine has to be able to put a lot more force on (FWD/RWD/AWD/4WD) to get up the hill. That means the engine needs to pump faster so that the wheels can push/pull the weight of the car up. As far as what causes the need for the extra work, that would have to be gravity. Gravity keeps cars down, and not down on any incline, down FLAT. Gravity does that to everything.