Braze on front mech with sub-compact chainrings (46/30)

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  • Hey LFGSS, i was wondering if anyone would be able to help with a question i've got about installing sub-compact cranksets with braze on mounts. I've been digging around online have hit a dead end.

    I've just picked up a Cannondale CAAD12 off here and absolutely love it (now it's got my brooks on...), but I think need to gear it down a bit for the longer distance riding I do.

    My plan is to install sub-compact 46/30 chainrings (this guy) and new ultegra front mech, along with a 11-34 cassette on the back (with ultegra mid-cage mech) which would give me a 30-34 as lowest gear for spinning up big hills with kit on the bike

    I've checked out the max capacity and compatibility on the shimano pages and it all checks out for these parts with my STI shifters. My only concern now is that the bike has a braze on mounting for the front mech. I was wondering whether anyone had any experience of swapping chainrings with braze-on mounts and whether there would be any issue with using a 30T chainring with a ultegra braze on front mech? My concern is that the braze on mount might not allow me to position the mech in the right place for the 30T chainring.

    Any help would be amazing! I'm open to other ideas as well, which would give me a low gear (at least 1:1) without having to buy a new front and rear mech, chainrings and rear cassette...



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  • IRD (Interlock Racing Design) has a sub-compact braze on front derailleur­uct/60110-ird-front-derailleur-sub-c-bra­ze-on-2351?search=derailleur

    I have used it with a VO Grand Cru crankset with similar chainring combo 46/30. The FD cage is quite stiff and up-shifting is fine considering the huge gap of 16T between chainrings.

  • Thanks @Greasy_Paws - is the advantage of the IRD derailleur that it has a bigger range of movement vs something like the ultegra?

  • Range of movement is the same as this is defined by the H and L stop screws. The cage is the main difference as I understand it; the inner plate (The one that pushes the chain from the smaller to the bigger ring) goes a bit lower than standard road FD, it's shorter for less flex and has slightly minor radius for smaller inner chain ring.

    However, try first with your current FD as it'll probably work. Shimano indicates max tooth capacity of 14T for their FD but you may get along with bigger 16T gap.

  • Making a wild suggestion without experience to back it up.
    Would it be worth trying an earlier generation triple derailleur to see if it could accommodate. Braze on 5703 or 6703.

    I believe 5703 was designed around 50/39/30. Some have been successful running it with an even smaller inner giving 50/39/24.

    I probably have a spare if you wanted to try before you buy.

  • Thanks @Greasy_Paws and @wot - I reckon I might be able to get it to work with a wolftooth and an 11-40 cassette. Will give it a go and drop you a message about the triple if it doesn't pan out!

    Thanks again

  • For anyone wondering - it looks like a 46/30 could work on road bikes with braze ons - see pics here

  • Install it carefully and if you can't get the derailleur low enough return it. The joys of online shopping.

  • For anyone with this issue/who's interested, the front mech wouldn't go low enough for the 46. I spoke to IRD and they said that for 11speed to get one of these. Seems a lot for a little bit of metal, but hopefully will work

    So I'll hopefulle end up with ultegra front and rear mechs with 46/30 and 11-34 cassette. Will ping a pic up if I get it working as I can't see one of the droppers in use online anywhere apart from the ird website


  • Hi Beams. Did you get this working? I'm in the exact same situation, trying to get an Ultegra R8000 front derailleur to play nicely with my Rotor 46/30 crankset on a frame with a braze-on mount.

  • I meant to ask, did the IRD adapter work?

  • Hey - was a bit of a faff, but all good now. The IRD dropper didn't work as it got in the way of the bottom of the braze on - I messaged IRD about it and they didn't have a solution (see image for issue).

    I then bought this which works perfectly as it allows free movement of the derailleur. I'd say if it's a small drop you need, then I'd go for the FSA, but if it's a large drop the IRD would give you more room for movement.

    I got my IRD from SJS cycles and the FSA widget direct from FSA (cost around 40EUR).

    The ultegra mech works perfectly with that set up

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  • Also - the dura ace FD didn't work (am running the ultegra one)

  • Which ultegra one is it you're running?

  • R8000. Links to parts in the first post

  • @Beams thanks for the quick reply. I came to the same conclusion with the IRD adapter - too low for a 46 outer ring. Do you have a photo of your current setup, with the Ultegra derailleur and the FSA adapter? Cheers!

  • Here you go

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  • Thanks so much. I completely forgot that I have one of those adapters from another project. Here's mine fitted - problem solved!

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  • There's one final piece of the puzzle. You can install a wedge between the front derailleur and the braze-on mount to drop the tail of the derailleur cage closer to the chainring. This is what I have done on my other bike.

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  • You need to check that you have sufficient clearance between the tail of the derailleur cage and the chain stay.

  • Ah so thats what those are for - kept coming across them whilst trawling the net.

    I’m properly pleased with the 46/30. Perfect set up for days with tired legs + kit


  • Think they are intended for frames with steep seat tubes, like TT bikes? Worked a treat on my Colnago!
    I'm loving these lower gears down here in hilly Cornwall. Means I can spend more time in the big ring on the rare flat stretches.
    Thanks for your help - ride safely!

  • Great thread and some really useful into here. I too am looking to make the change from compact to sub compact 46/30 but there's just one issue I'm having that I haven't been able to solve - maybe someone can point me in the right direction!

    On my tricross (2012 model) I can't move the fd down to the correct position for the 46 chainring as the bottom of the cage hits the chain stay. Can anyone recommend a short cage fd that may work please? It's a 9 speed sora set up I'm afraid... Thanks in advance.

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Braze on front mech with sub-compact chainrings (46/30)

Posted by Avatar for Beams @Beams