Put the massive sprocket on the engine, and the small engine sprocket on the wheel. Easy, and if you can get it to move with you on it, it'll go like Hell! lol
Anyway, you want around 1:6 (up to 1:9) or so ratio for good all-around speed versus power. So, if the engine sprocket is say 1 inch, the wheel sprocket would be 6 inches.
You'll probably need a jackshaft setup, so it might be a little more complicated. However that ratio should be your final drive ratio.