Chainline Assistance, Please- Mtbr.com
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  1. #1
    mtbr member
    Reputation: badgermtb's Avatar
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    Chainline Assistance, Please

    Hello--

    Just purchased a new wheelset. Went with a Surly Disc rear hub, and will use White Industries thread on freewheels. 135mm rear spacing.

    The BB width on my Rig is 73mm. I run an XT crankset with external BB.

    I'd never thought much about the following issue until I saw some recent photos...BUT...will my chainline be WAY OFF if I leave everything as is with the drivetrain?

    My fear is that the chainline will be off, so much so that I won't be able to straighten it by messing with BB spacers. Especially seeing as how the rear freewheel/cog placement is fixed (no spacers).

    I'm new to this type or rear hub SS configuration, and went with it for durability's sake. The wheels are still being built, otherwise I'd figure this out on my own.

    Thoughts? Suggestions? Thanks!

  2. #2
    Chronic 1st-timer
    Reputation: lubes17319's Avatar
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    I ain't 2 smart, but I think it should be OK.

    I had Shimano Saint BB/cranks on my KM with Surly SS hub+WI freewheel & it slapped straight together.
    Trailwrecker at large

  3. #3
    mtbr member
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    Cool. Thanks. The KM has the same bb shell width as my Rig, so I think all should come together quite well.

    Went to SS for simplicity, and I've found a way to overthink this, too. ;-)

  4. #4
    achiever
    Reputation: redwarrior's Avatar
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    You are most likely going to need to shim your BB by 3.5mm. I have the same wheel/freewheel setup and it measures out to 53.5mm. I'm pretty sure that your crankset is designed to run a 50mm chainline so if you're off by 3.5mm, that's a lot. I have a 2.5mm and 1.0 mm spacer to get things right.

    Basically, this is how you measure for the front. Measure the tube diameter next to the chainring and dived that in half. Now measure from the tube to the center of your chainring. Add those together and you'll have your chainline measurement. Remember that you're shooting for 53.5mm. Here are some links to chainline measurement that should help. I find it easiest to use calipers...

    http://www.sheldonbrown.com/chainline.html

    http://www.parktool.com/repair/readhowto.asp?id=110

  5. #5
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    Reputation: chanorama's Avatar
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    Chainline clarification

    Hey just a quick FYI. When you measure the chainline, make sure to measure to the center of the teeth on the ring, not the inner or outer faces of the ring.
    It's your thing, Do what you want to do

  6. #6
    mtbr member
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    Thanks for this info...and being so specific.

    What is your BB width? I'm thinking that might come in to play here.

    I'm not opposed to running another spacer or 2.

    I'm also gonna check on the shimano site to see if I can find any info on the chainline for the XT cranks.

  7. #7
    mtbr member
    Reputation: chanorama's Avatar
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    As redwarrior said the XT crank gives you a 50mm chainline if you configure the spacers properly.

    On a 68mm Shell, it calls for 2 spacers on the drive side, and 1 on the non drive side. On a 73mm shell, It calls for 1 spacer on the drive side. The 68mm shell gives you a bit more chainline adjustment by swapping the spacers.

    Remember that you need to have the proper number of spacers for your shell, no matter what the configuration is.
    It's your thing, Do what you want to do

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