I built a go cart a couple years ago. Used a lawn tractor for steering and drive parts. A comet centrifugal clutch. The gear ratio was to high the thing would do about 45 mph and was really hard to get moving so I used the shaft from a 510 Massey combine straw chopper which has woodruff keys every couple inches and made a gear reduction for it, my boys had a blast on it. Made it low and wide. I had fun building it they had fun trying to destroy it.