Just finished building my new 2009 BMC Fourstroke 02 with 650 B front end. We tried to get the 650B to work on the rear, but we came up about a 1/4 to 1/2 inch short, even with the Quasi Moto, the smallest tire we could find. The build still turned out great, FS bike that rolls obstacles well, accelerates and climbs like mad, and is still nimble in the tight stuff. I have been riding it for a week and the bike is awesome. Plenty of clearance for the 650 B Nevegal in the Fox RLC 120. Just waiting on my Quasi Moto to show up next week to drop some weight, the Nevegal is a great tire but a bit heavy. The Quasi should get the bike to the 25 pound build goal. For those considering the 650 B as an option, try it even if you can only get it on the front, you will see a noticable difference to the positive IMO. Her's ma few pics of the new sled!