First fixie build
#26
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Well, every mm you deviate from that recommendation will theoretically move your chainline farther from being perfectly straight. That said, a deviation of 2-3mm probably wouldn't be that big a of a deal.
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Ok, so I just measured my bottom bracket shell and it looks like its 70mm. That means it is italian thread, correct?
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The only way to be sure what thread your bottom bracket shell uses is to check it directly. If it's Italian thread, a known English thread cup will fall into the shell without engaging any threads.
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Thanks for the info guys. I ordered an italian thread BB, so I guess we will see if it works!
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also, couldn't you just add spacers to the hub to correct the chainline? So my thought was it would be better to go a few mm wider and just add spacers if needed...
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No, because spacers sit outside of where the cog or freewheel threads on. You'd essentially make the axle wider, necessitating wider dropouts, without changing the position of the cog/freewheel or the overall chain line.
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Is that true? You can only add spacers after the cog? Is there no way to move the cog out? Am I better off buying wheels and having a shop dish them to correct the chainline?
#34
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if you buy a new set of wheels that are ‘track’ wheels, they will already have a centered axle and will require no dishing. If you can’t achieve a good chainline by moving the sprocket outboard a few multimeters, then you need to move your chainring or entire crankset inboard.
Last edited by seamuis; 01-07-19 at 08:02 PM.
#35
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thanks for clarifying. sorry it took so long for me to get back on here. been busy working on the old house. starting to look at wheelsets now. i think i'll be good to just get a track wheelset and space the cog out a bit.
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Umm, you're not going to be able to space out the cog very much on a track wheelset. Why are you committed to using a crank and bottom bracket that give you the wrong chainline?
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i'm not, just never done this before and i'm having a hard time understanding the mechanisms involved. i guess i need more learning.
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Did you find out whether your bottom bracket shell is Italian or English yet?
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Yes, it was italian. I got a Shimano Bottom Bracket BB-UN55, Square Taper 70x110mm and paired it with a ofmega crank and 46T chainring.
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Progress. What does your chainline measure with that?
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For my Peter Mooney fix gear project, I built up a wheel around a double sided track hub, spacing it from 120 to 126 with 4mm of dish. Had made for me a double cog "dingle" that I screwed onto the dished in side. Made up a triple crankset. Now I had a wheel with 3 cogs, each one lining up with one specific chainring, giving me three very different gears with the rear wheel moving in the dropout very little. This wheel rides rock solidly in all three gears. Yes, a true bastard, but a very happy one.
Ben
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https://sheldonbrown.com/chainline.html
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#44
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i'll have to measure that when i get home from work. thanks for the info! i'm guessing i'll need this info before i purchase my wheelset.
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Track hubs are almost always designed for a chainline of 42mm, that's why I try really hard to get 42mm at the chainring.
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good to know. i am also realizing that most hubs are around 120mm, and my rear dropout spacing is 126mm. i guess i may have to do something different, but i don't know what that is yet, lol.
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You can add a couple 3mm spacers on either side of the axle or cold set the rear triangle to 120mm. Easy breezy beautiful.
#48
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#50
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you wouldn’t actually need to do anything if you use a 120mm hub. I have a 126 conversion and it takes literally no extra effort to simply hand tighten the nuts down and take in the 3mm per side. I mean, there’s nothing wrong with dropping some cash on a couple of spacers, but it’s completely unnecessary.