What motor do you plan to use? 2-stroke, 4-stroke, make/manufacturer ? Are both your primary drive and final drive going to be belt? or just the final drive to the rear wheel? I'm assuming you are planing on using a v-belt for the final drive, but you also mention a camgear in your post, does this indicate that the primary drive is going to be automotive timing chain or metric timing belt? You might want to look at the belt drive trains used by Whizzer's They use v-belts and you can purchase parts from various Whizzer dealers around the country. They have a large dia. rear sheave 17in.-18in. I believe that comes with a mounting system for the rear spokes. I think they are pretty reasonably priced?
ocscully