Ted Hamilton
Helmet Painter / Racer
Another thing to consider would be a freewheel hub on the brake side (rear) so that it acts like an open diff. Cons -- 1 wheel drive traction.... pros -- easier to push around and tighter turning radius (without scrub) at slow speed. If it's going to be >35mph course, that's what I'd do. [EDIT: And on a kart, 35mph will feel like 55mph if they've never been that low to the ground...]