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Chain rubbing on large chain ring.

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Chain rubbing on large chain ring.

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Old 06-19-10, 07:08 PM
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Pockymonster
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Chain rubbing on large chain ring.

I have this bike running a stock drive train http://www.bikepedia.com/QuickBike/B...&Model=Roubaix

When I'm riding in the small ring (34T) up front and I gear into 12 13 14 or 15 the chain rubs on the larger ring (50T). Now I don't expect to be able to use 12 or 13 as that would be some serious cross chaining but being able to use 15 or maybe even 14 would be great. The crank is a compact crank.

It seems no matter what setting I have for the front derailleur it doesn't matter because it's rubbing on the chain ring. Is this normal?
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Old 06-19-10, 07:50 PM
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Torchy McFlux
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No, it's not normal.
What crank do you have, and are you sure you're using the correct BB spindle length with it?
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Old 06-19-10, 07:56 PM
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I don't know anything about BB spindle length. It's all stock as far as I know. I got the bike used. FSA Gossamer Mega Exo Compact, 34/50 teeth
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Old 06-19-10, 08:00 PM
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I wouldn't call it normal but it's common.

When I had a bike with a compact crankset I installed a 2 mm spacer under the drive side of the bottom bracket.
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Old 06-19-10, 08:10 PM
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Did the 2mm spacer fix it? I guess I'd have to bring it to a bike store to get it done. Ugh already spent so much money on this bike.
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Old 06-19-10, 08:50 PM
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So in this chart here. The red highlighted ones are not usable. The 50T can shift into the 2 largest but it's severely cross chained so I don't want to use it. The 34T red highlighted, The smallest two are cross chained. The other two rub the front chain ring a little It's not a constant rub but every full rotation it maybe touches it once. Should I just not care and use it anyway. It makes an annoying sound but worse that can happen is the chain wears out faster and the ring gets scratched on the inside. Who cares right?


I have a gap between 3.9 gear inches and 4.6. It's a bit annoying because I'm either spinning too fast or too slow.

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Old 06-19-10, 10:03 PM
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Originally Posted by Retro Grouch View Post
I wouldn't call it normal but it's common.

When I had a bike with a compact crankset I installed a 2 mm spacer under the drive side of the bottom bracket.
This is an easy fix if the bottom bracket is a conventional type, you won't even have to break the chain. The spacer goes between the outer cup and the frame, and it will fix the problem. If you have an outboard bearing type bottom bracket you will probably need to replace it with a longer one.
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Old 06-19-10, 10:07 PM
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Originally Posted by Al1943 View Post
This is an easy fix if the bottom bracket is a conventional type, you won't even have to break the chain. The spacer goes between the outer cup and the frame, and it will fix the problem. If you have an outboard bearing type bottom bracket you will probably need to replace it with a longer one.
I only understood the words bottom bracket, break the chain, and spacer. I'm not sure what the rest of it means. LOL. Can you explain it to someone who doesn't understand that stuff? I looked online and my crank has an integrated BB or something.

It only rubs a tiny bit in the gear I want to use, only rubs maybe once every revolution like a slight tick sound. Could I just leave it and let it rub away?
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