This is a mystery frame that I got and built with a lot of spare parts I had. Can someone help we identify it? Also the rims are 700c. enter image description here

  • 4
    Can you post a picture of the headbadge ( the emblem above the front brakes)?
    – mikes
    Oct 16, 2015 at 22:56
  • Did the fork come with the frame? Are the decals the 'm's?
    – dlu
    Oct 17, 2015 at 0:31
  • 1
    Also it appears to be a track frame – based on the rear dropouts, I assume there is no provision for a rear derailer.
    – dlu
    Oct 17, 2015 at 0:32
  • 1
    @dlu agreed - the weird bent seat tube being so close to the rear wheel also supports your suggestion. Curious it has brake mounts though if its a track frame.
    – Criggie
    Oct 17, 2015 at 11:10
  • 1
    @Criggie the brake mounts weren't necessarily installed by the framebuilder. I've seen a few DIY mounts on rear seat braces that make me sympathise with builders who just don't put bridges on track frames, specifically to stop people drilling them for brakes they're not designed to take.
    – Móż
    Oct 25, 2015 at 6:59

2 Answers 2


It's a Mongoose Detain frameset. Originally retailed for around 200 dollars at Walmart as a complete bike.

Comparing the op's frame to the one above it's clear they're not the same if only because the backwards circle has a double seatstay sort of thing. Anyway, the frame matches a google image search so I'm 99% sure I'm right


Looks like a Backward Circle Fixie. It seems the previous owner swapped out the tires/wheels, possibly painted it and/or added a decal, which to me, made it seem like a GT, but I'm not sure if GT even manufactures fixies. I didn't dig too deeply to find and snap this off the Web. The crook in the frame is unmistakable.from the manufacturer's website

update to research the logo on the front in your pic is a dead-wringer for the logo on their site. if it's not a BC, then it is a damn-good knock-off (though I don't see the point in that crook other than aesthetic-value). plz note--detractors to my answer fail to explain the "Backwards" logo, seen on op's photograph -- if I am wrong, then someone went WAY overboard to make it LOOK like a BC (the logo is visible, as it is on most bikes in the front of the "handle" portion of the front-fork; just below the handlebar).

update to research pt. 2 "re-research" see comment (2) by ojd -- this crooked shanker design was apparently ripped off by other fixie manufacturers. Still I'm confident I've id'd this ride correctly., so I'm not changing/removing any portion of the answer, but I AM adding this notation; giving the writer credit and acknowledging that I might be wrong (sadly, it does happen sometimes).

OP - plz do inform us once you hammer this one down!

  • 2
    I think the point of the curved seat tube is to allow a shorter wheelbase while still preserving clearance for the wheel and the position of the seat.
    – dlu
    Nov 11, 2015 at 18:24
  • 1
    I'm sorry to spoil this, but Backward Circle uses different rear dropouts than OP's bike and all models have that slanted rear fork that is next to impossible to install brakes on. The crooked seat tube used to be common in track pursuit bikes (google "pursuit bike" for several examples) and many street fixies copy that design.
    – ojs
    Nov 11, 2015 at 18:33
  • @ojs thanks for the info - I concede that my answer might could be incorrect so I will notate that and credit you in my next update. Still I'd be remiss to withdraw the answer -- if perchance it is incorrect, ill do so. at min- the answer should lead op in the right direction.
    – Tapper7
    Nov 14, 2015 at 10:57
  • 1
    Actually, the crooked seat tube is copied from 80s track bikes from Pinarello, Moser and others. Backwards Circle is just as much rip off as everyone else. Also, the logo in OP's picture is different from the one on Backwards website.
    – ojs
    Nov 14, 2015 at 12:40
  • learn something new everyday. +1
    – Tapper7
    Nov 14, 2015 at 12:46

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