I always wondered about this from wheel set to wheel set. Not old vs. new but just the efficiency of a wheel altogether. I ride with a group at times and I notice that on coasting downhill some of my bikes seem to go faster than my other riding partners. On other rides some of my bikes go slower on a freewheeling downhill. Would be an interesting competition at Cirque to have a downhill race without chains to see which bike would be most efficient. I suppose you would have to factor in weight of the rider but that does not seem to matter in my unofficial experiments. I also know that tire to pavement surface area has an impact, still I think this would be a fun event.
Ray Homiski
Elizabeth, NJ