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Chain rub

by Danno
Wed, Jul 20, 2016 21:47
4

I've noticed that the front derailleur rubs when I'm in bigger gears  and pressing on. the crankset appears to be flexing. I ride a cannondale synapse alloy sora.

Is this a problem? Does it waste significant watts to warrant upgrading?

A club member has offered to sell me their as new ultegra group set as has moved to sram etap. Note this would also mean upgrading my stock wheels as they are not compatible with an 11 gear cassette.

All advice great fully received.

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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4 comments

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Danno | 8 years ago
1 like

Yep, have got rid of the chain rub. Looks like I'll need a better excuse to get that upgrade past the wife.

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Jack Osbourne snr | 8 years ago
1 like

Agree with both above.

Check cable and test.
If it's not that, check limit screws are properly set.
If it's not that, check derailleur alignment and height.

A front mech rarely goes wrong itself. Almost always you can resolve issues by resetting cables, stops or alignment.

You're unlikely to NEED that Ultegra mech, but you could use it as an opportunity to upgrade your bike as a whole... just don't fit it until you can afford new wheels.

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Simon E | 8 years ago
1 like

It's quite likely that the cable has stretched so the STI click-stop does not put the front mech in exactly the same spot as previously. This will be more obvious when on the bigger gears (smallest cogs on the cassette).

Shift to the inner ring so cable tension is at its lowest, then undo the pinch bolt and pull a few mm through (I use pliers as the cable slips through my fingers). Tighten up the bolt then go for a test ride.

If this is the cause then the adjustment should also make shifting onto the big ring a little easier.

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TypeVertigo replied to Simon E | 8 years ago
1 like

Simon E wrote:

It's quite likely that the cable has stretched so the STI click-stop does not put the front mech in exactly the same spot as previously. This will be more obvious when on the bigger gears (smallest cogs on the cassette).

Shift to the inner ring so cable tension is at its lowest, then undo the pinch bolt and pull a few mm through (I use pliers as the cable slips through my fingers). Tighten up the bolt then go for a test ride.

If this is the cause then the adjustment should also make shifting onto the big ring a little easier.

Agreed. Seems like backing out the barrel adjuster along the front mech cable run will do the same thing.

If it's still not resolved by increasing cable tension, you could try repositioning the front derailleur for parallelism against the big ring. I noticed that chain rub tends to happen if there's a bit of yaw in the cage position.

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