How does this work, exactly?

[ImaCynic]

It’s a converted single speed. My guess is that the front chainrings are swapped to maintain better a chainline with a lower ratio. No rear change is possible unless the rear dropout can be adjusted.

[jrenaut]

If you pedal SUPER-fast, the chain heats up and expands and switches to the big ring automatically. Slow down and it cools and shifts back.

[huskerdont]

@ImaCynic 205278 wrote:

It’s a converted single speed. My guess is that the front chainrings are swapped to maintain better a chainline with a lower ratio. No rear change is possible unless the rear dropout can be adjusted.

That’s certainly the case, and it’s a pretty clever solution. Instead of installing a rear freewheel or fixed cog, this person just kept what was there and was able set it at the ratio he or she wanted by swapping the rings around.

[ImaCynic]

@huskerdont 205321 wrote:

That’s certainly the case, and it’s a pretty clever solution. Instead of installing a rear freewheel or fixed cog, this person just kept what was there and was able set it at the ratio he or she wanted by swapping the rings around.

Well, ratio can’t be changed without altering the chain length. If it has horizontal dropouts, it might be able to do one change.

[huskerdont]

@ImaCynic 205323 wrote:

Well, ratio can’t be changed without altering the chain length. If it has horizontal dropouts, it might be able to do one change.

They would have altered the chain length when they did the configuration–to get rid of all the slack from no longer have a rear derailleur or needing the big ring. The dropout is visible in the pic.

[ImaCynic]

@huskerdont 205356 wrote:

They would have altered the chain length when they did the configuration–to get rid of all the slack from no longer have a rear derailleur or needing the big ring. The dropout is visible in the pic.

Didn’t have the pic available when I replied, and just realized SteveO had already described the dropouts. (Sorry Steve!) Now one just need to carry a Park SS-15 for on-the-fly gear change, but this thing has bigger issues…

[EasyRider]

@Steve O 205276 wrote:

I passed the bike parking at National Airport on my way to get a Capital Bikeshare bike. If I’m there, I usually look at the skeletons and the 1-2 actual being-used bikes, just out of curiosity. Someone had parked their bike and a Burley trailer (the trailer was not locked), which made me nervous. Hopefully they were not leaving it for any length of time.

Anyway, that’s neither here nor there. What really caught my eye was one of the skeletons had this:
[ATTACH=CONFIG]22712[/ATTACH]

Two chain rings in the front, reversed, and five in the rear, no derailleur.
So this is being ridden as a single speed (actually, it appeared to be abandoned, so it’s not being ridden at all). To switch gears without a derailleur requires moving the rear wheel in the dropouts to maintain chain tension, not something one can do on the fly.
Has anyone ever seen anything like this before?

White Industries made (still makes?) a two speed freewheel. Closely spaced, just a couple teeth difference. A bike with long enough track or horizontal dropouts can keep the chain taut in either gear by moving the wheel forward or back. I guess it’s possible that they could get 2 usable gears out of this setup.

I’d have thought most big rings would strike the chain stay if moved to the inner position of the crank. I’d guess the big ring is there at all because the owner didn’t know or care enough to buy shorter chainring bolts, or use spacers.

[Judd]

That bike was there at least two years ago when I first bikes to take a flight. There’s a couple of other bikes that were abandoned the last time I was there. It’s something I’d like to eventually work on addressing along with getting some upgrades to the bike parking and signage at the airport.

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