34.8 Clamped-on front derailleur on 31.8 seat tube, possible?

Hi all,

Next week I'll probably buy a new frame to replace my creaking old one, but the Look I'm considering has a 31.8 mm seat tube and my front derailleur, still quite new, has a 34.8 mm clamp. Should I buy a new derailleur, or I should just fill the empty space with a rubber sheet? Will I find geometry or adjustment problems? Any experience or feedback about this case will be much appreciated...

I believe that Shimano makes/sells a shim for using a 34.8mm clamp on a 31.8mm seatpost ... I don't know how much it costs ... there may be generic shims available ... it should be less than $10(US). Check with your LBS.

Of course, the shim doesn't care whether or not you are using a Shimano front derailleur or one made by someone else.

Depending on your soon-to-be new frame, you may want to consider buying an E-mount front derailleur (presuming you are looking at a MTB) ... if you are referring to a Look ROAD bike, then you'll probably need a braze-on front derailleur.

Thanks a lot for your help :-)

Maybe I mistook "clamp-on" for "braze-on" since English is not my mother tongue. The frame I'm considering is a road Look 585; my front derailleur will be too wide for the new seat tube.

Campagnolo front derailleur from 2007 and older? You can swap clamps. shimano has shims for their clamp on front derailleurs, normally used for their one size clamp MTB FD but they will work for a shimano road FD clamp. Failing that, go to a hardware store and get an appropriate chunk of PVC pipe, cut a split in it, wrap around and clamp to that.

I'm not familiar with most of Look's framesets ...

A braze-on derailleur attaches to a TAB that is attached to the frame (in the past, the tab was brazed onto the seat tube, hence the name) ... the 585 may use a clamp on front derailleur.

If a braze-on tab is present on a(ny) frame, then a standard, clamp on front derailleur cannot be used because the tab will be where the clamp would be located.

The disadvantage of using a reducing shim should only be cosmetic.

Thanks both :-)

I see I used the proper word: there's no tab in the frame and so what I have is a clamp on derailleur. Before buying a 31.8 mm one, I'll try my 34.8 mm (2009) with the shim or pipe as you suggest.

Thanks again :-)

Suggest you simply buy an appropriately sized derailleur clamp and replace the one attached to your existing derailleur. Google "derailleur clamp".

You can do anything with anti-freeze and 40 wt. ball bearings. You can even make a too large derailleur clamp work.

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Oddly, this website says braze-on (but I don't see the braze) and it gives a clamp size of 31.8:

Look 585 Ultra Frameset from BikeBling.com

Personally when I purchase a new derailleur I always buy braze on, and I have the different problem-solver clamps (ok one Problem solver and one overpriced Campy one..) to make it work on different frames. The weightweenie crowd may cringe at the unnecessary grams, but it beats turing a $100 FD into a paper weight.