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  1. #1
    Older than dirt CCrew's Avatar
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    47.5 versus 50mm chainline

    Looking to replace a cheapo Shimano M191 crankset that spec's at a 47.5mm chainline with a Shimano LX that spec's at a 50mm chainline. The M191 uses a JIS BB versus the Hollowtech II on the LX, so I really don't have the option of different BB widths. Is that 2.5 mm of chainline going to cause me issues and if so what should I anticipate?

    I'm swapping from 8 speed to 9 speed including shifters (LX Dual Control) and Front (XT) and rear (Ultegra) derailers at the same time if that matters.

    Thanks..

  2. #2
    Low car diet JiveTurkey's Avatar
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    See "Chainline Measurement" : http://sheldonbrown.com/gloss_ch.html#chainline

    MTB Triple is generally 47.5mm, but may be larger at 50.0mm if necessary to clear oversized seat tubes.

    According to Sheldon, 47.5 is preferred if the frame can handle it. In this case, Shimano has mandated a 50.0 chainline; I assume so it can be more universally compatible.

    Every other bike that has this--and similar--crank and bottom bracket combo work fine, so I imagine yours will, too. I doubt you'll notice anything.

    All that will happen is that each chainring will now be moved out just over one-half of a cog's worth (the center-to-center spacing between 9-speed cogs is 4.34mm) http://sheldonbrown.com/k7.html#spacing
    Quote Originally Posted by slopvehicle View Post
    Not wearing a helmet makes me more aware of my surroundings. I find myself anticipating the hardness of concrete 50 or 100 feet in front of me, it's almost a zen-like connection between my face and the pavement.

  3. #3
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    Quote Originally Posted by CCrew View Post
    Looking to replace a cheapo Shimano M191 crankset that spec's at a 47.5mm chainline with a Shimano LX that spec's at a 50mm chainline. The M191 uses a JIS BB versus the Hollowtech II on the LX, so I really don't have the option of different BB widths. Is that 2.5 mm of chainline going to cause me issues and if so what should I anticipate?

    I'm swapping from 8 speed to 9 speed including shifters (LX Dual Control) and Front (XT) and rear (Ultegra) derailers at the same time if that matters.

    Thanks..


    The only real issue ..... Depending on which rings you ride on most, a 50mm chainline may be better, or worse for drivetrain wear due to the angles of the chain.

  4. #4
    afraid of whales Mr IGH's Avatar
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    Because the external LX BB is made for both 68mm and 73mm, you can play with the washers to set the chainline to either 50mm or 47.5mm. If you have measuring calipers it's not hard to figure it out the correct combo.
    IGH's, Dyno Hubs, LED lights and old frames

  5. #5
    Older than dirt CCrew's Avatar
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    Quote Originally Posted by Mr IGH View Post
    Because the external LX BB is made for both 68mm and 73mm, you can play with the washers to set the chainline to either 50mm or 47.5mm. If you have measuring calipers it's not hard to figure it out the correct combo.
    Thanks. I found the Shimano Techdocs, looks like I do have some wiggle room. And yeah, have a nice set of Mitutoyo calipers

  6. #6
    Low car diet JiveTurkey's Avatar
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    Quote Originally Posted by Mr IGH View Post
    Because the external LX BB is made for both 68mm and 73mm, you can play with the washers to set the chainline to either 50mm or 47.5mm. If you have measuring calipers it's not hard to figure it out the correct combo.
    Bringing the right crank in will push the left crank out an equal amount, right? Is Hollowtech II centered already?

    If re-arranging washers does make the whole assembly off-center, I'd want to weigh that against getting the desired chainline.
    Quote Originally Posted by slopvehicle View Post
    Not wearing a helmet makes me more aware of my surroundings. I find myself anticipating the hardness of concrete 50 or 100 feet in front of me, it's almost a zen-like connection between my face and the pavement.

  7. #7
    Senior Member toytech's Avatar
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    I just installed a Truvative Stylo on my Bergamont, the chainline required me to tighten the fd cable and adjust the stops a little to compensate, but it works excellent. I did not want the cranks offset to one side.

  8. #8
    afraid of whales Mr IGH's Avatar
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    With a 2.5mm shift/offset and a seat height of 30" above the pedal, what's the angluar difference?...Using HS trig I get a angular difference of 0.4 degrees (87* on non-drive, 87.4* on drive side). I don't have an issues with high Q cranks, I suppose this is why the 0.4* isn't noticed at all by me (it is less than 0.5% difference).
    IGH's, Dyno Hubs, LED lights and old frames

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