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I just stumbled upon this photo of what appears to be a reasonably normal citybike, except it looks like it has a second set of pedals at the rear wheel.

one weird looking bike

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Anybody knows what it is?

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Those don't appear to be pedals but rather foot pads for someone to stand on while "hitching" a ride. Similar to the foot pegs you sometimes see on kids' BMX bikes. –  Daniel R Hicks Dec 11 '12 at 12:46
    
@DanielRHicks No, they're pedals and cranks. They even have a cog and chain attached. –  cmannett85 Dec 11 '12 at 12:50
    
@cmannett85 - Yep, looking at the photo yet again I see that you are right. The far-side chain angles down to a rear derailer, so that it's (barely) distinct from the "single-speed" chain on the near side. What's odd is the lack of clear provisions for a seat. There are bars on either side of the wheel but clearly insufficient to support a seat. But perhaps some additional hardware attaches. –  Daniel R Hicks Dec 11 '12 at 22:00
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1 Answer

up vote 11 down vote accepted

There are bicycles with a crankshaft that runs through the rear axle. The "Tur Meccanica Bi Bici" is such a bicycle:

Tur Meccanica Bi Bici

I can't tell from your picture if it's the same bike or not, but it certainly could be.

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Thanks. The photo is not mine, but it's taken in Florence, Italy, so it might very well be the same kind. –  Kenned Dec 11 '12 at 13:26
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It is worth noticing that the rear pedals are attached to a sync chain on the left side of the bike. This would make it topologically identical to most tandems: one normal crankside engages with the rear wheel with a regular set of chainrings and cogset, and additionally the "other drive side" contains equaly-sized chainrings connected by a chain to another, tandem-specific crank, so that the pedals move along sync'ed to each other. –  heltonbiker Dec 11 '12 at 19:02
    
That sounds useful, but in the original photo the cranks at the back are no longer at the same angle as the front ones, so they either accidentally came out of sync at some point (changing chain?) or someone wants them at 90 degrees. –  dumbledad Dec 12 '12 at 14:37
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@dumbledad - Some tandems are set up with the cranks about 90 degrees out of sync. I believe there are several "theories" for why this is a good idea -- easier starting, more constant power, less wobble, etc. What you generally don't want is the cranks about 180 degrees apart. –  Daniel R Hicks Dec 12 '12 at 16:08
    
I thought there might be, kind of like the oval chain rings discussions. –  dumbledad Dec 12 '12 at 17:48
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