I rotated the Schwalbe Marathons on my single speed. They were formerly on my commuter and the rear tread was more visibly worn than the front. So I put the worn one on the front of the SS and the one with more tread on the back. There's still plenty of rubber on both, but I just want to get them both worn down. the front wears much more slowly than the back, especially down the center. The (worn) front tire, though, is nowhere near being worn through though.