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Old 05-20-09, 04:33 PM   #1
efranko
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new bike derailleur adjustments

I just completed a build of a gorgeous Cannondale Six13 with an ultegra/dura-ace mixish. This was my first time with a nice road bike let alone putting one together myself, and I think I did a pretty decent job. My only problem is with installing the shifter cables, which I assume is the hardest part. I calibrated the rear derailleur correctly (or so i thought), but for some reason the chain from the chainring to the cassette isn't straight and everytime i turn the pedal the chain rubs on the chainring. I'm guessing it has something to do with small adjustments, front or rear derailleur, any advice would help greatly as i have no idea. I also watched those videos on bicycletutor and they didn't help much... thank you!
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Old 05-20-09, 04:47 PM   #2
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More info needed. When the chain rubs on which chainring? Exactly which chainring and cog is the chainring on when the rubbin occurs? If the chain is on the inner ring of a double when it rubs on the side of the big ring this is normal if the chain is cross-chained small to small. Otherwise you may have a chainline problem. This cannot be cured by adjusting the derailleurs. Exactly what bottom bracket do you have? How long is the spindle? Or is it an outboard bearing type? Is this a double crankset or a triple? Is the cassette 10-speed, 9-speed, or what?

Last edited by Al1943; 05-20-09 at 04:50 PM.
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Old 05-20-09, 05:48 PM   #3
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And, naturally, photos speak volumes and are very welcome.
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Old 05-20-09, 07:02 PM   #4
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i can't really get clear photo's right now but it's a double crankset 10 speed drivetrain. ultegra cassette 12-25t and a 105 crankset with hollowtech 2 bb. the chain rubs when the cranks is on the small ring and the casette is on the smallest. there's a posibility that i installed the crankset wrong but i cant imagine there are too many ways to do it (i basically slid it through and tightened the left arm). i also haven't really adjusted the front derailleur too much but i don't think that's the problem. if still necessary i can provide pics but i dont really think they'd show much.

lemme know if any more info is needed...

p.s. when i look from the back it appears that the chain bends slightly from the front to the back.
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Old 05-20-09, 07:09 PM   #5
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That's called being "cross-chain"

Quote:
Originally Posted by Sheldon Brown
Try to avoid the gears that make the chain cross over at an extreme angle. These "criss-cross" gears are bad for the chain and sprockets. Especially bad is to combine the inside (small) front sprocket with the outside (small) rear sprocket. This noisy, inefficient gear causes the chain to wear out prematurely.
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Old 05-20-09, 07:20 PM   #6
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that makes a lot of sense but i can go small to small on my other bike with no problem... it doesn't seem to be a rub its like a full on push against
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Old 05-20-09, 07:22 PM   #7
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It's possible that you could improve the situation if your FD isn't properly aligned, but ... typically ... if you look at the actual gear-inches of the combinations you have available to you ... there's usually a better gear combo you can access that avoids the whole thing.

Conventional wisdom dictates ... avoid big-big and little-little. I'd betcha' most of us do.

[EDIT: Thanks again, Sheldon!]

Gear inches calculator: http://www.sheldonbrown.com/gears/
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Old 05-20-09, 07:30 PM   #8
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Quote:
Originally Posted by efranko View Post
that makes a lot of sense but i can go small to small on my other bike with no problem... it doesn't seem to be a rub its like a full on push against
Al's got some good questions about whether or not your chainline's set up properly.

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Otherwise you may have a chainline problem. This cannot be cured by adjusting the derailleurs. Exactly what bottom bracket do you have? How long is the spindle?
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Old 05-20-09, 07:32 PM   #9
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the way you explain it and I understand it:
you may have to change out the Bottom bracket for a longer one that make the chain rings align better.
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Old 05-20-09, 07:38 PM   #10
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i don't exactly have an answer to that, it's an english threaded ultegra hollowtech 2, i wasn't aware of different lengths... under what circumstances would a longer bb be necessary, i can't imagine my setup is unusual...
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Old 05-20-09, 07:41 PM   #11
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I bet your older, not rubbing crank is a 52/42 and your new 105 is a 53/39 right? The greater difference in chainring diameter makes the chain rubbing in small-small quite common. The cure? Avoid small-small.

Since your 105 is the new Hollowtech II, you can't do anything to change the soindle width or chainline as the spindle is part of the carnk arms and all of the bb cups are the same. Live with the rubbing or avoid it by staying out of the small-small combination.
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Old 05-20-09, 11:00 PM   #12
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The only time either of my bikes is using small - small is when it's parked for the day. The wisdom being that this will place the least amount of stress on the cable and prolong it's life.

I have since learned this is doing nothing - so to speak - but I keep doing this anyways. It was the thinking at the time I learned.

Good luck!
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