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  1. #1
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    Fatbike Q: Is it possible to space a Rohloff cog out a few mm?

    I'm thinking of trying to build a low Q fatbike. This would have elevated chainstays, so the only things that would have to clear the tyre down low would be the cranks (no problem) and the chain. Rear spacing would preferably be 135mm, symmetrical. The bike would be unlikely to see much if any use on snow, so super-wide rims and tyres (>4") are not required, and it's more likely I'd use 47mm rims and ~3.7-3.8" tyres.

    The standard Rohloff chainline is 54mm, so the inside of the chain would be at ~50-51mm, enough for a Larry, but perhaps not quite enough to clear a Nate or BFL.

    Is there any reason why it shouldn't be possible or reasonable to put a fairly thin (1-3mm) spacer under the cog so the chain just clears?

    There is a 13T cog available, with a 58mm chainline, but using this would require a smaller than easily possible chainring to get a useful gear range.

    If the cog cannot be spaced out, there are other options, like offsetting the dropouts a few mm to the RHS, but it'd be simpler to avoid this.

    Suggestions?

  2. #2
    will rant for food
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    Yo... I think that Nate would clear. Want me to check? I have some 47mm rims sitting dormant in my garage.
    Latitude: 44.93 N

  3. #3
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    If you could do that it would be extremely helpful indeed, and would help me decide on whether to proceed before buying any spendy wheel bits! :-)

    FWIW, I'd probably make any frame from some sort of (cheapish) steel, as I have some expertise there, and know others with more. Your bamboo frames look excellent, but I know nothing about composites and have no idea if any suitable frame tubing is available here in Australia. I've only ever seen one fatbike, and have never ridden one, but have been curious for some years. So far I've not bought anything due to doubts about what might happen to my knees with a Q factor of ~200 mm, and use very low Q (and old) cranks due to bio-mechanical issues from an old break.

    Any suggestions about how much tyre to chain clearance is necessary would also be helpful. I'm guessing no less than 3 mm, but that 5 mm+ would be way better.

  4. #4
    will rant for food
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    Right on - I'll get a measurement to you soon.
    Latitude: 44.93 N

  5. #5
    will rant for food
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    Derp, I forgot to do so last night. Will make myself a note.
    Latitude: 44.93 N

  6. #6
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    ^ No worries, and no hurry. Any time you can get around to it will be fine by me. Thanks again.

  7. #7
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    Nates on 47mm rims clear fine on a Rohloff, both with chain and in belt configuration:


    IMG_0265 by Michiel Kuit, on Flickr

  8. #8
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    ^ Thank you for that Michiel, but can you please tell me if the frame is offset, and if so how much? (I'm guessing it is as the pictures seem to show a lot of overhang past the BB shell, making me think there's an 83 or 100 mm BB and thus an offset rear end.) Thanks again! :-)

  9. #9
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    No its not off-set and uses a 68mm BB-shell (BTW, rear tire in the pic is a Knard 3.8, but have run Nates at the rear as well)

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