I would guess and say you could stick some 31's under it, but you may have issues when it comes to flexing. You could use 30's without any issues.
Just me, but why not just drop the $150-210 for a 2" lift from Day star and go with some 30" mud or all terrains? If you plan on offroading, you may want to invest in a new set of shocks as well.
Here is a link that shows an install:
http://www.4x44u.com/pub/k2/am4x44u/...s/bwjor001.htm[addsig]