As an experiment, I have recently converted my SS Carlton to fixed gear using a spare wheel. Owing to having a cold, I haven't rode it all that much but one thing is bovious to me. Nothing has changed on the bike apart form the absence of the freewheel but the Wrights "B17 clone" saddle which has been unbelievably comfortable for several thousand miles gives me a sore arse very quickly when I ride it fixed. If I put my other wheel with the freewheel back in, it is comfortable. How can this be? FWIW, the gear ratio is the same in both cases.