Chainline, what can you get away with?-
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  1. #1
    mtbr member
    Join Date
    Feb 2014

    Chainline, what can you get away with?


    So I'm building up my fixed gear Krampus with a Paul Components 142 fixed hub. The threaded side is within 1/2 a millimeter of my crank's chainline of 52mm.

    I'm going to be only running a front brake, and am planning on running a 6 bolt cog on the disk side of my hub as a sort of emergency gear in case I need something lower. The idea is that I'd seldom if ever use it, but have it just in case.

    The chainline for that cog is 53.5mm. Can I get away with 1.5mm of deviation from crank to cog? It's a bit more than I'm comfortable with, but it also seems to run fine when in the stand (not any more noisy or anything like that). Sighting down the chain looks straight, but the measurements don't lie.

    Ironically, if I watch the chain on the cog, the teeth line up toward the inside of the narrow links on the chain. As if the cog is too far inboard rather than outboard. But again, the measurements are what they are.

    If I had a front wheel, I'd just go ride the bike around, but I don't so here I am.

    Thanks for any input.

  2. #2
    Downcountry AF
    Reputation: *OneSpeed*'s Avatar
    Join Date
    Oct 2013
    Probably ok, though like you said it's not ideal. How big is the cog? A bigger cog will retain the chain a little better. Also probably important to use a cog with tall teeth.

    Too bad it isn't off in the other direction, you could just shim it out a little.
    Rigid SS 29er
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    Stop asking how much it weighs and just go ride it.

  3. #3
    mtbr member
    Join Date
    Feb 2014
    Yeah, I thought the same thing. I have rotor shims but they are doing me no good.

    The cog is a 19 tooth and my chain ring is 28 teeth. The cog is a problem solvers bolt on cog.

  4. #4
    Reputation: Cotharyus's Avatar
    Join Date
    Jun 2012
    In practice, it should be fine. If the chain gets a little loose and develops some bounce going through rougher stuff, it may be more of a problem than it would be on a perfect chain line, but I don't think you're going to have any world shattering problems out of 1.5mm of spacing.

  5. #5
    mtbr member
    Join Date
    Feb 2014
    I'm going to double check my measurements today. I just realized that I might have a .7 mm bb spacer that will work on my bb. That will probably give me what I need to split the difference between my two chainlines.


  6. #6
    mtbr member
    Join Date
    Feb 2014
    I've remeasured with calipers and it looks worse than I thought. On my threaded cog, I'm within 1/2 a millimeter. Chainline on the crank is 51.5 and on the cog it's 51. With the disk cog it's 53.5 so I'm actually trying to cover a 2.5mm variance.

    I might still try a bottom bracket spacer. If I add my .7 mm spacer I will be within ~1.2 mm on the cog that I plan to use the most. On my back up cog, I'll be within ~1.3mm.

    So I can either have not perfect chainline on both cogs, or perfect chainline with my current cog and ditch the back up.

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