The Perfect Chainline

Discussion in 'Motorized Bicycle General Discussion' started by 5-7HEAVEN, Feb 26, 2017.

  1. 5-7HEAVEN

    5-7HEAVEN Well-Known Member

    Aug 2, 2008
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    "The instruction is for SS (single sprocket?) conversion from geared cassette and having the front chainline as the constant, meaning that the chainring is fixed and the cog will be the one to follow/adjust.

    1. Measure your front chainline. This is the distance between the center of the frame/tube and the chainring. It's a bit tricky to find the center of the frame, look for bottle mounts. I gave mine as an example, 50mm.

    2. Measure your rear hub spacing. Most mountain bikes have 135mm rear hub spacing, when in doubt, measure from locknut to locknut. Image courtesy of Sheldon Brown.

    3. Reminisce grade school.

    135mm / 2 = 67.5mm, this is your imaginary center of your rear spacing.

    I think you know what next. Subtract your front chainline to the center of rear spacing.

    67.5 - 50 = 17.5mm

    17.5mm is your "perfect chainline", measure this from your locknut to your hub similar to figure 2. Take note that the center of the cog must fall into this measurement.

    Congratulations! I promise you that there will be no more skipping, no more guessing, no more headaches."

    Cut and pasted from, June 25, 2008.

    This will help me and others find the perfect chain line, so that our chain doesn't fall off at the bottom bracket (BB).

    My new project will have a Sturmey Archer 8-speed internal hub. With this information, I'll know EXACTLY where to place the chain ring sprocket on the BB! dance1
    #1 5-7HEAVEN, Feb 26, 2017
    Last edited: Feb 26, 2017
  2. Tony01

    Tony01 Well-Known Member

    Nov 28, 2012
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    Haha my frame has been crashed so many times and fixed and braced, there is some imaginary center but only in my imagination...
  3. curtisfox

    curtisfox Well-Known Member

    Dec 29, 2008
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    Another simple way. Take straight edge, put on flat surface of sprocket,then line the second sprocket to the straight edge. So they both touch and lay flat. ............Curt
  4. Amarion1

    Amarion1 Member

    Sep 15, 2012
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    I use a 2 foot aluminum keystock. Looks straight the the eye and works wonderfully

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