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I have a 2015 Salsa Vaya 3, which comes stock with 3x9s Sora (74bcd 30/130 bcd 39/130 bcd 50 + 11-32). Since I'm weak, I've done the following to make biking Seattle hills easier:

  • Front chainrings 26/39/46
  • Rear 11-36, changed derailleur to Deore M592 SGS to accept 36 sprocket and increased tooth count

Chain has been lengthened appropriately.

My issue is that if I bring the front derailleur down to 3mm from the top 46t chainring, it rubs the 39t chainring when I shift into the top. So I'm forced to run it a bit high - like 15 to 20mm - too high to act as a guide. When I shift into the top ring, it (more often than I'd like) overshifts and falls off into my cranks. I'm locked to minimum 38t in the middle due to 130bcd. I've played with the high limit and have not found a sweet spot where I don't lock myself out of the big ring but also don't overshift out onto the cranks.

My question is whether I just need to bite the bullet on a new crankset (and associated costs for new chainrings) or whether there are other front derailleur options that have a shorter vertical profile that will allow me to use this setup while installing the FD "within spec".

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  • By my rough calculation you sound like you end up running the FD in the same place with the 46T ring as you would if it was 50T. I've got the same as your original setup and I would have said there was room to move a fair bit closer to the 39. I wonder if a 48 would be better, as you can swap individual rings
    – Chris H
    Oct 10, 2022 at 5:37

1 Answer 1

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It is possible to read on the internet a lot of parroting of the notion that front derailleurs are basically simple and their compatibility specs are more malleable than that of many other components.

This is a good case in point as to how that is just not true. You are running up against the spec that Shimano calls "Applicable top-mid tooth difference." They've changed the verbiage a little over the years, but the gist is the same. This number cannot be cheated by even one tooth without starting to cause the issues you describe.

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In the beginning of Shimano road triple from the late 90s, they were doing 30-42-52 as standard, and the FDs of that era had 10t for this spec with total capacity 22. They then moved into the more practical 30-39-50 and it became 11 with total capacity 20. Microshift makes 9-speed STI-compatible repair FDs that have the older 10t, 22t capacity spec, which relates to the cage shape and what it's contoured to work ideally with. You could think about getting one of those and going 26-38-48 on your existing cranks (38t is the smallest possible 130 ring). You could probably make that function, but the catch is that 130/74 ring sets in that combination that are made to play nice together vis-à-vis shift aid/ramp positioning don't really exist. You could probably get it a lot better than what you have though just using reasonably well-matched repair chainrings.

There is a lot to be said for cutting to the chase and getting 104/64 or 110/74 cranks with something like 26-36-48. Shimano makes various nominally "Trekking" type cranks of this sort, but they basically work with road triple FDs and STI. If you do that with the FD you have, you're cheating the total capacity by 2t, and the consequence of that is you will get chain/cage drag on some small/small crossgears, which is not a big deal for most on-road use since those are unimportant gears. With STI, it cannot be understated how much better the shifting performance is when it's a matched ring set like you get on a crank of this sort, compared to putting something together from parts. With other kinds of shifters that matters less.

It's very common for FDs that have gone through a lot of chain drop due to borderline non-functional setups to be in poor shape. If that is true for yours you might consider replacing it up front when making the above changes just to be done with the frustration.

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  • Thanks! Great in depth answer! For future readers STI = Shimano Triple Index; the Trekking series cranksets include (for 3x9) the Alivio T400 series and the Acera T3000 series.
    – heights1976
    Oct 11, 2022 at 13:59
  • I ended up getting the Alivio FC-T4060 in the 44-32-22 configuration which was compatible with my BB24 Hollowtech II setup. Out of spec at the bottom end so can't use the outer few cogs on the small-small end (the derailleur is fully relaxed), but these aren't important gears anyway. I'm considering increasing the 22 to a 26 but don't want to sacrifice performance of the matched triple, so might just leave it alone.
    – heights1976
    Oct 21, 2022 at 20:47

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