Y'all are talking about two different tires. The Spitfire is the cheaper of the two, the BT45 is a more expensive tire. I put a BT45 on the back of my K75S, and I really like it. It has a wider, flatter profile than the Metz and so I don't get that "falling" feeling going into a turn anymore. I am still running a Metz Lasertec on the front, no real beef with it.