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Compact Chainset issues?

by we8ster
Fri, Jul 27, 2012 11:51
6

Hi,

I have a Cannondale CAAD10 105, with a FSA Gossamer compact chainset on. I love my bike, however, was wondering if anyone has experienced a problem with being able to use the smallest sprocket and the inner chainring without it rubbing the larger chainring? My derailers are all set up correctly, but can't seem to use the gear, without the rubbing!

Help and advise would be greatly appreciated!

Rob.

If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.

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6 comments

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Simon E | 12 years ago
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My Tiagra 9 speed triple copes OK on the middle (39t) ring, haven't tried it with the granny. But the 105 double on the other bike doesn't like top gear on the inner ring (39x12). I try not to use it anyway and never use the big-big combo.

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dave atkinson | 12 years ago
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The only groupset that's designed to work across the whole range of the cassette without trimming, so far as i'm aware, is Dura Ace 7900. And even to get that to do it is pretty tricky. And even then, it's still better to choose a straighter chainline.

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we8ster | 12 years ago
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Thanks guys, I generally keep straight chain line, however sometimes, just for short periods of descending Inbetween hills I'd like to be able to access that gear!

But just done a little bit more investigating, and it seems the chain isn't rubbing on the chainring, it is actually catching a couple of rivets on the larger ring, so looks like its a no go!

Thanks again,
Rob

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Paul J | 12 years ago
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It's fairly normal for the chain to rub when you're in extremely crossed gears (right chainring to left rear sprocket, and vice versa). Some shifters have "trimming" functionality that let you make a fine adjustment to the front dérailleur cage position to minimise rubbing - not sure if 105 has it (Ultegra at least does).

The best fix to very-crossed-chain gears and rubbing however is "Don't do that". Rather, change to a gear with a straighter position. E.g. the extremely crossed gear you're having problems with will be roughly equivalent to going on to your big ring and using the middle sprocket (the 5th one down from the biggest) on the rear. This will be more efficient for 2 reasons:

- the bigger sprockets means the chain has to bend around less, which minimises friction from the links turning.

- the straighter chain will minimise losses from rubbing, and side-loads.

Basically, when shifting gears, try choosing ones that keep your your chain straight. Also, learn where the overlaps in gear ratio are between your big and little rings.

Edit: Oh, and running very crossed gears regularly will probably shorten the life of your chain, because of the additional side loads on the links. Potentially increasing your risk of snapping the chain prematurely. Probably also cause faster wear on your sprockets.

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VecchioJo | 12 years ago
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crossing gears, small ring/small cog or large ring/large cog is generally considered 'bad form' and aside from rubbing can cause the rear mech to be too slack or (sometimes dangerously) too stretched, switching to the large ring up front and somewhere in the middle of the gears at the back will produce a similar gear to the one you're having issues with, without issues

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spongebob | 12 years ago
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Switch up to the larger chainring and it shouldnt rub any more.

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