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Old 06-04-11, 08:03 PM   #1
stilz
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Chain Knocking in Middle Chainring and Smallest Cog

Picked on my bike from the store today and took a ride, I noticed that when in middle chain ring and smallest cog the chain is knocking the cage of the front derailleur. Is that normal or poor adjustment?

Thanks
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Old 06-04-11, 08:11 PM   #2
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No, but maybe yes. In any position the FD cage can only clear chains coming from a limited range of angles. Normally the index system is trimmed so that on the outer ring it clears with the chain on the outer side of the cassette, the middle with the middle sprockets, and the inside with the inner sprockets.

The amount of non-rubbing sprockets depends on the width of the cage, how perfectly it's aligned, and the length of the chainstay. If all is good, each chainring should be able to be used (without rubbing) with all but one or two of the sprockets, but it varies bike to bike.
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Old 06-04-11, 08:20 PM   #3
stilz
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I guess I'll have the bike store take a look. Thanks

BTW, components are:
front: Tiagra
rear: 105
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Old 06-04-11, 08:39 PM   #4
Al1943
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On most Shimano triples there are two positions for the middle derailleur. Trim the derailleur over to the right when on the extreme right side of the cassette, and visa versa.
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Old 06-04-11, 11:35 PM   #5
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My wifes smallish frame Roubaix triple makes a tiny clank irregularly when pedaling in that exact combination. It has nothing to do with the derailleur. The chainline is fine per eyeballing. It might be off the tiniest bit...but the trouble of trying to shim things isn't worth it. The chain is touching the little buttons (dunno the actual terminology) on the chain ring. I doubt it will even be a wear issue and the noise it generates is minor. She'll end up just having to deal with it or change gears to the big ring.
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