I got the chance to check out Sturmey-Archer's new 3-speed fixed drive train. Pretty cool stuff. Sheldon would definitely be into it. I think a lot of people would agree that it kind of takes away from the simplicity that makes riding fixed so enjoyable to begin with, but it definitely will make sense from some- especially those living in hilly terrain.
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Naturally, they will come in all the standard anodized colors.
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Shifting is controlled with a single lever that can be used as either a bar-end shifter (above) or as a downtube shifter (below as shown on a custom Retrotec).