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Chainline Challenge

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Chainline Challenge

Old 06-14-11, 11:13 PM
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tanguy frame
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Chainline Challenge

I have an old school steel frame with a 68mm BB shell, tapped for Italian threaded BB. I put a SRAM Apex compact crank on with Italian GPX BB, and no spacers. I measured the chainline and for the inner ring I got 42mm and the outer ring I got 46mm. This is close to the standard Shimano according to Sheldon Brown's page .

I'm running Campy 10 Speed rear, 130mm between the dropouts, and I made a combination of measurements and calculations to get the chainlines for each cog; from the inner cog out, the chainlines are approximately 6, 11, 16, 21, 26, 31, 36, 41, 46, 51.

I can hear the noise from cross chaining when I'm in the larger cogs in the rear.

Front derraileur shifting is sensitive. I keep fussing with the derraileur angle and height, and the limit screws. There's a tendancy to shift off the inner ring when shifting from large to small if I'm not super careful, and shifting up to the large chainring seems to take more effort than it should. The setup does not shift as fast and relaible as I like.

The frame was designed for 126mm hubs. I'm basically forcing the 130 hub in there each time; I didn't cold set it, no LBS has touched it. There's adequate clearance between the chain and the dropout in the smallest cog.

Any suggestion on how to correct the chain line? Ideally I'd like to see the middle range cogs with a chain line around 44, where the chainrings sit. Is there a way to pull in the chainring chainline? Maybe a 10mm anti-spacer?

I question the advisability of putting a 10mm spacer behind the cassette. I'd probably need to cold set the frame to 140(?) and re-dish the wheel. There must be a better way...

Thank you,
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Old 06-14-11, 11:26 PM
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ultraman6970
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Larger cogs and larger chainring ???? The chain is way too crossed if you do that. Dont cross the chain

If you arent crossing the chain and you have sound is maybe because the RD is not well adjusted, the jokey wheels are shot or maybe the RD hanger is not right.

Good luck but crossing chains is a pretty bad idea, that the combinations are there doesnt mean u have to use them, or ask to Andy Schleck about it, h can tell you his experiences with dropped chains and crossed chains for sure. The other factor is that u have an olde frame, the rear end is not what suppose to be... at least you got it running you know.

Large cogs with large chainwheel = big no no

small cogs and small chainring = no no

Good luck

Last edited by ultraman6970; 06-14-11 at 11:30 PM.
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Old 06-15-11, 01:50 AM
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Originally Posted by tanguy frame View Post
I made a combination of measurements and calculations to get the chainlines for each cog; from the inner cog out, the chainlines are approximately 6, 11, 16, 21, 26, 31, 36, 41, 46, 51.
you have the big cog 6 mm from the bike's centerline? That can't possibly be right. You couldn't build a wheel that would support that. Your measurements are off by ~20mm I bet
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Old 06-15-11, 04:07 AM
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Mark Kelly 
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Originally Posted by zzyzx_xyzzy View Post
you have the big cog 6 mm from the bike's centerline? That can't possibly be right. You couldn't build a wheel that would support that. Your measurements are off by ~20mm I bet
This.

If your rear end is aligned correctly the distance from centreline to smallest cog is always a shade under 60mm: by definition the distance from centreline to lock nut is 65mm and the usual distance from lock nut to smallest cog is about 5-6mm*. The spacing between cogs for C10 is 4.12mm, so the largest cog is 9 x 4.12mm (37.1mm) further in, giving a centreline to largest cog distance around 22mm.

Your 42mm chainline will normally line up somewhere between the 5th and 6th cog. If it doesn't, something is amiss. Given that you are trying to make this work in a space that wasn't designed for it, I'd start by checking how springing the rear end (to fit the wider hub) is affecting the alignment.

*If the outside of the lockring is 2-3mm from the lock nut. The distance from the outside of the lockring to the centre of the smallest cog is about 3mm, not coincidentally equal to half the width of the chain.

Last edited by Mark Kelly; 06-15-11 at 05:48 AM.
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Old 06-15-11, 08:28 AM
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Yes, I remeasured this morning and found the small cog is at 62 and the large cog is around 22, placing the center of the cassette around 42, which matches the chainring chainline, so the alignment is ok. I'll look elsewhere for front derraileur performance enhancement.
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