I have a quadmaster 500 and i just love that thing. My only complaint is the crapy dunlops it came with. I do alot of mountian riding in Utah with lots of snow/mud. Are 27 in tires good for mountains and can i still use my stock wheels with them.

 

You will have no problem putting 27" tires on the bike. They will fit fine, with out rubbing anything. You have pleny of power to turn the 27" tires. I have 27" blackwater XT's. Huge difference over the stock dunlops. They are great on rocks, trails, stumps, roots and mud. If however, you are planning some serious deep mud riding, go with 27" vampires. I am changing to the vampires in the spring. Blackwaters are a great all around tough tire, but I usually ride in a lot of swampy areas where you may be in 14" of mud or deeper. That calls for the vamps.
27x10-12 fronts and 27x12-12 rear will fit your stock wheels just fine.

 

Although I don't own a Quadmaster, my buddy has one with 27" Blackwaters, much better than stock.

P.S. nice quad...

 

I'm not happy with the Dunlop quality either. Patched holes 5 times in the last year; got me wondering about ply strength and tread design (too much open and un-protected space between treads??). I was also wondering what the impact on power and top speed is with 27" wheels and if anyone had tried 26" as a compromise.