Cold and wet here in the Pacific Northwest, so time to mess around with the bike!
I know a number of people have done these conversions. I just did this and thought I’d share the details in case it helps anyone. Plus I’d like to hear thoughts from those that have ridden these a while.

The Bike: Co-Motion coupled primera (2005). We love this bike and have travelled with it a number of times. The original setup was ultegra 9speed with v-brakes (tektro cx 8.4). It was quite nice, but I am fussy about the shifting which required constant attention.

The goal: wider and lower gear range, better shifting. We mostly credit card tour in hilly spots. I really like this bike and wanted to see what I could do with it.

What I did:
I put a 28T ring on the inner position of the original FSA gossamer triple. I put a 46t Wickwerks ring in the middle position. (I installed this in the correct orientation so the ramps would work, even though it’s meant as an outer ring. The bolt heads sit a bit proud, but do not interfere with shifting at any point.) Outer position left blank. Added a 2mm BB spacer on the right side, giving a front chain line of 47mm-ish.

I used an XT 11-40 cassette, which fits the original DT/Hugi hub. XT/Ultegra chain (w/114links if someone’s interested). This provides a gear inch range of 19-114 (600%). This compares to 545% with the original triple. The gaps are similar with 11 speed vs 9, and that doesn’t bug me. This gives us the low we want. Lower top gear. We spin out at around 35 mph, and I’m happy to coast past that.

For shifting, I had the luxury of being able to borrow some gear to test.
I tried sram etap red 11 speed. Not AXS, as I need to keep rim brakes and 11 speed. WiFli (A1) RD with a road link. This works perfectly. No more, no less. No issues in any combination.

I then pulled that off and put on Ultegra Di2 (rx805/8050). No roadlink. This too worked perfectly.

Even though I have had Di2 on my road bike for 8 years, I was still surprised at how much better the shifting was with either system. Both fronts shifted the 18 tooth gap without any issue. Both setups allowed full cross chaining without breaking anything, although we try not to do that. The braking was better, as both levers are simply better than the originals.

I have to choose one setup. I really want to like the etap. Clean and simple for travel. But I really prefer the shimano hoods and their shifting logic. Di2 wires mean external run (a bit ugly) or internal (pricey frame mods). Also, these items can be hard to source for a rim brake or mechanical disc setup. Shimano still produces Di2/rim brake levers. SRAM doesn’t make the levers anymore. Maybe some other minor pros/cons, such as battery life.

Curious about what folks would take as spares on a multi week tour? I’ve talked to people who take a set of shift levers and a rear derailleur, figuring those are the most likely to break.

Anyway, hope that info helps someone who is considering a similar change. I;d be happy to hear thoughts from those who’ve used these a bit, particularly etap.

Thanks,
Joel

I envy you guys that have been able to keep your triple chainrings and make them work for a double. I started down the rabbit hole of "I better find a tandem 11-speed double first" and now am committed to that.

I'm looking forward to Di2 but I'm not sure what spares I'd would want to bring along. For me it's been long shift/brake cables and a derailleur hanger. Having just completed external routing of Di2 on an aluminum tandem frame, those tiny little wires seem like they'd be a bit fragile. So maybe an extra wire or 2.

You’ll love Di2. It’s awesome.
Even internal routing leaves the wires exposed at the derailleurs and stem. I’ve not found them to be delicate at all.
Good thought on the hanger. I’ve that the road link can be fragile.

I thought about an 11 speed crank. Which did you get?

I was concerned that the 9 speed crank and rings wouldn’t work well, but they’re perfect.

Joel

I have the FSA bb392 tandem cranksets coming from Precision Tandems. The supply of those seems to be drying up. The “modular” nature of the crankset would seem to indicate that I should be able to dial in the stoker chain line for Shimano 12s. The spindle on my current captain’s FSA SL-K crankset is badly scored and creaking like crazy, so it needed replacing no matter what I ended up doing with the stoker crankset.

For the external Di2, I have the wire heat-shrunk to the rear brake housing so the only visible wires are at the derailleurs and the external battery.

We went through the mental exercise about 8 years ago when it was time to upgrade. We also wanted to retain disk brakes, so the calculation was a bit different than OP. By the time I was done thinking about the full list, it became clear that it made more sense to replace the bike, not the components.

We ended up getting another coupled bike, this time a Co-Motion. Etap seemed a better choice because of cables and disassembly. But, I've been in the Shimano universe for a long time and the Di2 is pretty bullet-proof. We chose Ultegra level based on what was available then. Even though we've always had a triple, the doubles give enough range now. I've always been irriated by the constant trimming required with traditional triple set ups on a tandem. That's all gone - now just set, trim once and forget.

Connecting the wires when reassembling is a non-issue; only requires a little more time than connecting the cables on your current bike.

We got straight off-the-shelf gearing - 50/34 and 11/34, since those are easy to find and replace. When we're planning a hilly tour, we switch to an 11/40 cassette, requiring a longer chain and Roadlink. That's enough to get us up the double-digit grades. And I have to reprogram the cassette settings in the the app so the Garmins are correct. But not difficult or time-consuming.

We've been happy with this set-up. Assuming we do one more tandem before hanging it up, I'll probably do a 1x12 (or maybe 1x13 by then).

edit - you asked about what spares to take on a tour. Since you’ve toured with mechanical systems and already know what to take generally, I assume you’re only talking about the electronics.

I’d say it depends on the kind of tour.

I wouldn’t take electronic shifting on any long self-supported tour. But I have done a half-dozen organized / supported tours with Di2 and not taken anything different than I did with the mechanical bikes. (I do carry a spare Gates belt, and a few different things but they're not related to this discussion.)

My winter project bike is a 2009 vintage Cannondale Street. I’ve got a lot of Di2 components laying around…coincidentally I have a set of ST-R8070 I took off of a bike that was “upgraded” with 11-speed GRX a while back (4 years??), I’ve got an RD-RX805, and I have the XT 11-40 cassette ready to mount on the rear wheel with a DT Swiss hub. As far as I can tell, my only option is to put that RD-RX805 on (or potentially an RD-RX815 from the GRX line), as the XT RD-M8050 won’t function with a road FD-which I need to use due to the FSA SL-K double crankset on the bike.

That's lot of words to ask- how did you get that RD-RX805 to work, just a b-screw adjustment? How about chain wrap, did you use synchro shift to prevent chain combos that the capacity wouldn’t actually allow (such as big-big or small-small)?

I've got friends with lots of gear, so I've been able to try a number of configurations.

Re the rx805, it works perfectly on our comotion primera. No road link. The B screw is almost all the way in (I don't think it would accommodate the 11-42). I believe, but can't confirm that the GRX 815 would work too. The standard manual shift mode locks out the last two small cogs when on the small chainring. That works great as I have the chain sized to use the big-big, which I sometimes use, and avoids a slack chain in gears you'd never use. Chain wrap looks fine throughout the range and no shifting issues at all. I haven't played with full synchro mode enough yet to look at lockout, but it doesn't seem necessary. I do think frame specifics including derailleur hanger shape and chainstay length along with chainline can impact the success of this setup. Working great for us!

One thought: if you have the RD-M8050 RD, I'd consider buying an XT M8070 FD. I have tried this specific combo ( again, borrowed stuff) and can confirm it works perfectly with our 8050 road levers, 11-40 XT cassette and 28/46 chainring combo. That specific derailleur is on closeout at universal cycles for $50 currently, which is a screaming bargain.

I specifically shied away from the MTB FD only because I was unsure if I could get it adjusted inward enough to shift into the small ring. I was also considering that the official Shimano capacity for that FD was 10t, but of course Shimano are notoriously conservative in their published specs. Seeing you tested it with an 18t difference, 16 in theory should pose no issues for us. I may just go ahead and purchase it with the FD905-L clamp, since I was already eyeing the Bottle cage mount for using one of the spare internal batteries I’ve got on the bench and eliminating the Junction B box.

Yes, forgot about the need for the separate proprietary mount for the XT FD. It worked on our bike. No issues getting far enough inboard and no problem with the 18t jump. That’s the most I’d ever want.

A couple of notes: I was able to use a 2mm BB spacer to push the stoker crank slightly to the right. And our large chain ring is 46t. The XT RD’d cage suits that well, but maybe not with a larger big ring. I haven’t tested it with our original 53t ring. I’d bet it would work, but perhaps not as well?

The bottle cage mount for the internal battery is pretty slick. You’ll like it.

Good luck and enjoy the project!
Joel

Similar setup on our Co-Motion Speedster tandem. 28/42 front rings on a road triple crank (74/130 BCD), with an 11-speed 11-40 cassette (we live in Switzerland). Rear derailleur is the GRX Di2 11-speed, and I believe the front der' is Ultegra (because the GRX FD is made for a wider chainline). It works perfectly and we're very happy with it. Multiple junction boxes means that it's easy to unplug when splitting the bike for transport.

I'm not a fan of SRAM in terms of ergonomics of the hoods, the fact that you need two hands for front shifts, keeping an eye on the charge level of 4 batteries instead of 1, and many other aspects of their design, engineering, etc.; other people don't seem to consider these to be drawbacks.

Joel,

I did a similar triple to double conversion also with a FSA gossamer triple crankset although not electronic shifting.
Put an Origin 8 46T chainring on the middle position and 30T on the granny gear.
Like you I tried reversing the the 46T chainring so the ramps were on the inside, but I could not get it to work because the chain would hang up on the chainring bolts.
I am wondering how you were able to get it to work. Maybe the Wickwerks chainring is thinner where the bolts hole are, or the bolts are lower profile?
Can you send me a picture of yours?
I am using a Force 22 FD and it still shifts pretty good but the adjustment is really finicky and it tends to throw the chain off the outside.
I am wondering if that is due to the ramps not being on the inside.

Thanks - Joel (we have the same name!)

Joel,
Ill try to post some photos when I get home next week.

I did not think the outer-as-middle ring would work, but it does.

it’s possible the wickwerks ring is thinner? My inner ring is 28, and I think the chain runs below those bolt heads. Chain line matters too. I used the Origin 8 single bolts. They’re steel and may be thinner than alloy? Lastly, are you using 11s? Obviously narrower than the original 9s.

it’s a way out of spec setup but it works great for us. Now that Campy offers a standard chainset as 29/45 I don’t feel as weird.

FYI I’ve gone back to testing the SRAM red etap stuff. It’s growing on me.

I ordered a long cage from Chinook cycles on sale (they’re closing their shop)that will allow more capacity if I want.

Yes I am using 11s, chain ring bolts are problem solvers stainless steel. I originally had a 28T granny gear but changed it to 30T so it might shift better and also not so much of drop in gears when shifting from big to small chainring.
Where did you get the Wickwerks chainring? When I look on their website they only sell them in pairs.

Thanks

I made some measurements and I have about 0.06" clearance between the chain and inside of the big chainring with the chain on the small chainring.
The bolts protrude about 0.08" so that will cause interference. I could counterbore the chain about 0.03" to get enough clearance but not sure if this will weaken it too much since there is already a counterbore on the other side.
Shifting as is is not that bad so I am not really motivated to change it.

Joel,
0.06” is about 1.5mm. For 11s, this seems very close.
I have attached a photo of our setup. It’s a bit hard to see, but the arrow marks one of the chainring nuts. I can fit a 2mm Allen key between the nut and the chain. Clearly the spacing between my chainrings is larger, although it’s hard to measure accurately. All the 11s front derailleurs I’ve tried shift these rings perfectly. You might consider experimenting with chainring spacers. These are cheap and come in several thicknesses. I would add a 0.8mm or 1.0mm spacer set to move the inner chainring inboard slightly.
(Interestingly, the machined ramps of the wickwerks ring protrude nearly as much as the nuts. )