ive got a 3.5 inch tyre on the stock rear rim and 2.5inch on the front. its good. noticably easier to wheelie and has big nobs on the edges so you can put up a nice roost. some people say a fat tyre takes longer to pick up speed but i havent noticed it. i run 88cc cylinder with stock head.
Yeah that's the size of the dunlops i'm running on my stocker. The bike is way more stable when i'm doing wheelies and it hooks up really good in the dirt.