That’s exactly what I did. I had to climb the hill first, increasing my gravitational potential energy.
I did subsequently convert that gravitational potential energy to kinetic energy (adding to my speed), but fortunately I was never in free fall. That would have involved riding off of the edge of a cliff. 
Somewhere in the 60s MPH. Good downhill, paved highway, cranking as hard as my 10-speed would go. Guy next to me in a car shouting out the speed!
Good times. No helmet, either. About 17 years old.
When I was a kid we built a bonfire one year. A bunch of us rode up to the rubbish tip, halfway up Black Mountain, to get tires to put on the bonfire for additional smoke. Don’t ask me why. We all had crappy 1960s bikes; no gears, back pedal brakes. We each hung tires on our handle bars and set off back down the mountain. None of us was a physicist and we had not contemplated the speeds at which we would travel downhill burdened with many pounds of dead weight over our front wheels with only braking inadequate for an unladen bike down a hill that steep. How fast did I go? Terrifying per hour I think.