SethAZ 

BLUF: the E-Tube program doesn't list all of the cassettes Shimano actually sells, so when setting up synchro shift, if you have an unlisted cassette, you can do the math, make your own gear ratio table to identify the shift points, and then set those shift points in the program using some other cassette as a placeholder.

Question: the E-Tube program was up to date. Is there any workaround for making it list all cassette options, or else manually specifying custom cassettes via updating some settings file?

Background: I just swapped out the 11-32t cassette that came with my Lynskey for a 12-25t* cassette. I wanted to set up synchro shifting, so I got the e-tube software up and running.

While setting up synchro shift, I was given the option to set which chain rings and which cassette I was using, so that the software could show me a table with the gear ratios listed for each cog for each of the two chain rings so that I could specify the transitions that I wanted.

Here's the rub: the drop-down list that the e-Tube program shows for choosing cassettes only had like four cassette options listed, and the 12-25t wasn't there. This is an Ultegra 6800 12-25t cassette, so it's the same generation as my Di2 6870, and I can't for the life of me figure out why Shimano's own program doesn't know about it's own cassettes that they sell.

I ended up setting it to the compact chainrings up front, and I chose 12-28t for the rear cassette, which was the closest fit to what I actually have on there now. With pencil and paper I created the same table that the program shows, filling in all of the values of gear ratio for the 34t and 50t chainrings and for each cog on the cassette. They were the same all the way up to 17t. My cassette has an 18t that the 12-28t doesn't have, and everything above that is shifted by one place, so I did the math and filled that in.

After drawing the transitions that I wanted on paper using my own table, I set the transitions in the e-Tube project by cog number. It looks nonsensical since the gear ratios displayed aren't the ones that are really on the bike, but that's OK. The Di2 has no idea what the real gear ratios are, it just wants to know when it gets to such and such a cog and shifts up or down, switch change ring and automatically shift over to some other cog.

I tested it and it does seem to be shifting automatically to the cogs that I specified, so I think I'm all set. I'm just mildly surprised that I had to hand-jam this table and set up the shifts using a bogus placeholder cassette because they don't even list all the cassettes that they sell.

*where I live it's very flat, with a few hills, and I seldom do hard mountain climbs. On my old bike I had a 13-25t cassette, and the 25t was sufficient for all my usual rides. By putting a 12-25t 11-speed cassette on this new bike I get 1-tooth shifts from 12-19t and then 2-tooth shifts at 21, 23, 25. This gets me nice, tight, 1-tooth shifts for probably 95% or more of the typical riding I do. I saved the 11-32t cassette and the chain that fit it properly off to the side, and can swap it back on the next time I plan a worthy mountain ride.