a guy on supermotojunkies.com mounted up some 17 inch knobbies on his husky sm wheels. they are a 100-100-17 rear on the front, and a 5.10-17 on the rear, both IRC Volcanduro VE-33's he says he has never ridden anything better in the sand/loose dirt.
http://www.limsynch.com/husky/side_view_bike.JPG