That bike should have come with 6 inch wheels. The Bonanza MX models did come with 8 inch wheels, and some people have even put 10 inch wheels on bikes similar too your's. Build it however you like! but try and keep in mind the gear ratio with the sprockets, 6 to 1 is considered ideal, but it depends on how you ride/how big you are. I'm sure others will comment.:thumbsup: