[sperry]

Here's the way it works:

The truck is going 65. The car is going 75. The car's tires relative to the ground are gound 75. When the car hits the ramp the tires will have to slow from 75 to 10, relative to the ground/ramp their rolling on.

So, what you do is drive up behind the ramp closing at 10 mph. Just before you hit the ramp you push in the clutch (or shift to N). The car will hit the ramp and the tires will very quickly slow down to 10 mph, and the car should roll up the ramp (assuming 10 mph is fast enough to roll up the ramp).

Attempting to do this with the car powered means as soon as you hit the ramp, you'd have to slow the wheels from 75 to 10 before you hit the end of the truck. This probably wouldn't be all that hard to do... but things could get pretty squirely with the motor's inertia still spinning the wheels.

Edit: Aaron said it pretty well too.