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I have replaced the freewheel on my bicycle with a singlespeed. However, the chain line appears to move inwards from the rear to the front. picture

I have measured the rear frame spacing as approx. 127mm. picture I then measured the distance from the center of the freewheel (teeth) to the inside of the rear fork, which was 25.4mm. picture As per Sheldon Brown's website, the rear chainline measurement calculates to 38.1mm. I have measured the distance from the teeth of the chainring to the middle of the seat tube which is approx. 42mmm. Does the difference between the front and rear need to be within 1mm?

I think the only way I can achieve a straighter chainline is by removing the bottom bracket cartridge ring and placing a 2.5mm BB spacer from eBay between the ring and the BB shell. But I'm not sure this would work.

Alternatively, could I add a slightly longer spacer to the rear axle on the freewheel side, a shorter spacer on the non-drive side to move the rear chainline inwards and then redish the wheel?

  • I can't speak for freewheel to single speed conversion but on cassette to single speed you use a number of spaces on the free hub for alignment. – paparazzo Nov 7 '14 at 18:25
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Could you move the chainring on the crank arm? I can't tell from your picture if it used to be a double or not? I have an old schwinn that I converted to fixed and had the exact opposite issue (chain line moved away from the bike). I wanted the 52T large chain ring to stay so I moved it to the inner ring position. This is probably not ideal, but I've had no issues in 10 years on it. pic

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  • It's just a single chainring (should of mentioned this). I'm not sure how I could move it outwards unless I spaced the bottom bracket. dropbox.com/s/8zgahl67qnhxe3g/… Thanks, though. – Chris Nov 7 '14 at 20:46
  • Oh, okay. The picture almost looks like it used to be a double? (just looking at the crank arm). If it was me, I would try to remove the ring and see if it fit on the outside of the arm (but that might move the chainline 3-4mm, maybe more than you want). Hope you find an answer! – Shed Hider Nov 7 '14 at 21:14
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In the end I purchased a new Tange bottom bracket with a 127mm axle/spindle. My old BB was 113.5mm. Installed the new Tange BB and it has improved the chainline a lot. Relatively cheap solution.

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