Context: I'm designing a drivetrain for a touring triple-tandem that I'd like to have a very wide gear ratio.

I plan to use the Shimano Di2 derailleurs (long cage RD-M9050-SGS and 3x11 FD-M9050) to limit cross chaining so that I can (hopefully) safely fit a wider cassette and a wider range triple crankset within the capacity of the long-cage rear derailleur.

I've read that Shimano's e-tube project software lets you pick from a limited set of supported chainring and cassette configurations. I'm looking at cranks (E.g. 44/33/22) and cassettes (e.g. the SRAM 10-42) that may not be in the Shimano dropdowns.

I know that some people on the internet suggest picking "similar" ones in the software and that you can customize the shift map when you use the right shifter in full-syncro mode.

What I don't know is:

1) Whether there are options like 44/33/22 in the crankset dropdown, and

2) If there's aren't super close options, can I manually enter my chainrings?

3) If necessary, can I ask the software to lock out EXTRA small sprockets on the cassette when in the smallest chainring?

To be specific, based on the quoted capacities (41-45 teeth) of the long-case derailleur, I've made the following chart of what I believe is safe:

Chart of safe chainring and sprocket combinations

My concern is that I understand that even if I enable full syncro-shift with a custom shift map that does protect unsafe gearing combinations, there will be a way to use the left shifter to get down into the lowest chainring while still in a low enough sprocket that the chain is too loose-- UNLESS I can ensure the derailleurs fully prevent those unsafe red-combinations.

More broadly, will I be able to set these components up in a way that Di2 prevents the unsafe cross-chaining in my desired drivetrain?

I tried playing with the software myself, but it wouldn't let me into the customize menus without having first bought all the Di2 components, which I have not yet.

Thanks so much.

  • I have always gone with the low tech solution of listening for chain rasp and giving a glance back to the cassette every so often. Its pretty rare that I ever find myself in an extreme cross chain, by sound alone its pretty noticeable. Is this worth all the setup hassle? – Rider_X Nov 2 '18 at 19:47
  • Well it’s on a triple tandem, so I’m far from the drivetrain. I also want to keep it extra safe as my stokers are two young children. Also the gearing combination I posted above is pretty aggressive. I might make changes to the cassette or chainrings if I learn I can’t lock out certain combinations electronically. – John McD Nov 2 '18 at 23:40

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