The simple way to turn a geared frame into a singlespeed.
Got a geared bike that you want to run as a singlespeed? Decided your commuting bike needs the fuss-free reliability of hub gears? The On-One Doofer chain tensioner takes up the slack with a simple sprung arm and jockey wheel. Screws into the gear hanger. Adjustable side-to-side for chain position.
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