If your bike ain't fixed, it's broken. Solve that problem with Surly's Fixxer Cassette Hub Converter Kit. This kit can transform most Shimano rear hubs into the perfect fixed gear rear hub in no time flat. It simply replaces the freehub body allowing the hub to accept a fixed gear cog and lockring (sold separately). A Fixxed wheel is perfect for track racing, spring training, commuting, messengering and anything in between.