Usually one would run the front tire an inch larger diameter than the rears. Smaller diameter lowers the quad say 18 or 20" for flattrak motocross. Less sidewall flex faster stearing, little ground clearene harder ride. Taller tires best for desert or trail. I have 22" on rear and 23'ss Razer ll up front on 9" rims. It gives me clearence and some cush in the tusch--i ride desert. It all depends on where you ride. you can change gearing easy enough so get the tire that suites where and hoow you ride then gear up or down acordingly