|DMR STS Tension Seeker|
I've done quite a few single speed conversions in the last few years, and I've tried a handful of tensioners for vertical dropout bikes: The On-One Doofer, The On-One Other-Doofer and a Surly Singulator. All did the job, but none really did it well.
|Tensioner in "push down" mode|
|Tensioner in "push up" mode|
Ideally, one would want a frame with horizontal (or "track") dropouts for a single speed set-up. Sliding dropout frames work very well, too. But when you're converting a vertical dropout frame, you must tension the chain one way or another*. And, for efficiency, the less chain wrap, the better.