<HTML>What you should use, is a $29.95 Wal-Mart kids scooter. This has a fairly large tire on the back (compared to a skateboard), that can be replaced by a rear tire from a small kid's bike. This will give you the sprocket you will need to drive the rear wheel. I would suggest mounting the engine above the rear wheel, to give more room to stand. A break lever would be a perfect throttle. Just remember, on any 2 wheeled vehicle, 2/3 of your breaking power is in the front, consider that in your design. Now all you really have to do is figure out how to mount the engine.