This is an ultegra front derailleur, mounted on my Trek. This is mounted as low as possible on the bracket attached to the frame. I would like to fit a smaller front chainring, but would need to move the derailleur down. Is anyone aware of an adaptor I could use that would enable this. Thanks
Adapter to allow a smaller chainring to be fitted.
- Thread starter Trickedem
- Start date
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Big John
Guru
Don't forget you'll still need to clear the big ring without fouling it. If you drop the front mech further than it already is will it still clear the big ring? What combo have you already got and what ware you planning to swap it to? There are limits as to what size you can drop down to depending on the BCD of the rings.
numbnuts
Legendary Member
- Location
- Gone over the hill and far away
I'm running a 48 38 22 without doing any moving of the derailleur, but I had to fit a Dog Fang Chain Catcher to stop the chain falling off as it is a big drop from 38 to 22
Ajax Bay
Guru
- Location
- East Devon
Pretty sure the OP is trying magically 
to fit a smaller large chainring, not a smaller small ring (am assuming a compact or double).
Each tooth less is 2mm lower (12.7/2pi).
The issue is that the braze-on FD, designed with a cage curvature for a 52t ring btw, can't be slid any lower so even over the large ring there's too much gap between the teeth and the cage, leading to inaccurate shifting up and an almost assured regular dropping of the chain, outwards.
I have no solution, short of removing the braze-on and procuring a band-on FD. I wonder whether a triple FD design might reach lower?
ETA: Thinking about this (braze on as is), a maybe 2mm thick steel strip with the right curvatures and drilling might be inserted and bolted to the braze-on. The FD can then be bolted to that, acknowledging that the cage profile would have been moved to the rear those 2mm, with unknown effect on shifting. The forces on the attachment are vertical (the pull of the cable) and with only a ?20mm of distance from the pivot (braze-on point) so the moment is small and an adaptor as described would be well strong enough for purpose.
to fit a smaller large chainring, not a smaller small ring (am assuming a compact or double).Each tooth less is 2mm lower (12.7/2pi).
The issue is that the braze-on FD, designed with a cage curvature for a 52t ring btw, can't be slid any lower so even over the large ring there's too much gap between the teeth and the cage, leading to inaccurate shifting up and an almost assured regular dropping of the chain, outwards.
I have no solution, short of removing the braze-on and procuring a band-on FD. I wonder whether a triple FD design might reach lower?
ETA: Thinking about this (braze on as is), a maybe 2mm thick steel strip with the right curvatures and drilling might be inserted and bolted to the braze-on. The FD can then be bolted to that, acknowledging that the cage profile would have been moved to the rear those 2mm, with unknown effect on shifting. The forces on the attachment are vertical (the pull of the cable) and with only a ?20mm of distance from the pivot (braze-on point) so the moment is small and an adaptor as described would be well strong enough for purpose.
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presta
Guru
It's not clear what you're trying to do, are you reducing the size of the small ring alone, or the whole chainset? If it's the former, you can't just move the derailleur down, you'll need one with a bigger capacity: check the specifications. If you're reducing the size of the chainset as a whole, I doubt you find any adapters, there would have to be too many different varieties to make it economical. I think your best bet would be to remove the braze-on, unless you can find one that places the clamp in a position that doesn't foul.
roubaixtuesday
self serving virtue signaller
There are widgets that can be bought for this, but I've no experience of them so can't comment on how effective or not. Looks to be a couple of different designs at least.
Google "front derailleur adapter" shows some options.
Google "front derailleur adapter" shows some options.
cyberknight
As long as I breathe, I attack.
- Location
- Land of confusion
wouldnt it be easier to fit a larger cassette ?
fossyant
Ride It Like You Stole It!
- Location
- South Manchester
New Bike of course !
Pretty sure the OP is trying magically
Each tooth less is 2mm lower (12.7/2pi).
The issue is that the braze-on FD, designed with a cage curvature for a 52t ring btw, can't be slid any lower so even over the large ring there's too much gap between the teeth and the cage, leading to inaccurate shifting up and an almost assured regular dropping of the chain, outwards.
I have no solution, short of removing the braze-on and procuring a band-on FD. I wonder whether a triple FD design might reach lower?
ETA: Thinking about this (braze on as is), a maybe 2mm thick steel strip with the right curvatures and drilling might be inserted and bolted to the braze-on. The FD can then be bolted to that, acknowledging that the cage profile would have been moved to the rear those 2mm, with unknown effect on shifting. The forces on the attachment are vertical (the pull of the cable) and with only a ?20mm of distance from the pivot (braze-on point) so the moment is small and an adaptor as described would be well strong enough for purpose.
That is exactly what I'm trying to do. Unfortunately it isn't a braze on. It's a carbon frame and the attachment appears to be rivetted on.
Thanks. You put me on the right track. This looks like it could work
https://kidsracing.co.uk/products/croder-mechanical-front-derailleur-extender
Just need to work out what options I have for a smaller double chainset.
roubaixtuesday
self serving virtue signaller
There was a long thread on the subject recently in another place https://forum.cyclinguk.org/viewtopic.php?p=1729654#p1729654
Again, I've no personal experience of doing this.
Ajax Bay
Guru
- Location
- East Devon
Great thread - @Trickedem jump to p4 to get past the guff.
