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Cannondale Tandem Conversion to DI2 11 Speed

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Cannondale Tandem Conversion to DI2 11 Speed

Old 07-29-21, 12:39 PM
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ARe you thinking of using an external battery (SM-BTR1 + BM-DN100), or the external-mount-for-internal-battery (SM-BTC1), or something else?
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Old 07-30-21, 11:49 AM
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External battery mounted where bottle cage is
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Old 07-31-21, 11:15 AM
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Small-small or in our case, middle-small is not an interesting or very useful gear. We also run large cassettes on our tandem. I'm much more inclined to stay in the big ring as long as I can than to run the middle ring with smaller cogs. There are 2 reasons:
1) Big ring and large cogs gives closer gear spacing than does middle ring and small cogs.
2) The more teeth touching the chain, the longer the rings, cogs, and chain lasts.

I usually don't run further up the cassette than the 3rd largest cog using the big ring. That leaves me with 1 more cog if I need it. My chain is a tiny bit too short for big-big. If I screw up and try to shift the cassette one cog too many, it just doesn't quite go, no damage. Because we run a 24T granny, this chain length works better for us. As we've aged, that granny has gotten smaller and smaller and the cassette larger and larger.

The above is with cable shifting, If I were running DI2, I'd have set the chain to be able to run big-big.
Results matter
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Old 08-01-21, 08:58 AM
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I ran my conversion with the external battery mount on the rear seat tube waterbottle mounts. My specific tandem had a long distance between the rear seat tube and rear wheel so I used some aluminum angle that I cut and ground to rotate the external mount 90 degrees and put it more rearward. below are a couple of picts.
I also have the bike setup to run both small/small and large/large. Meaning, physically it can get to those gears without breaking anything. Though, this is much easier with the DaVinci setup because the difference between my 13t granny and 29t top gear on front is only 16t instead of the equivalent 26-x-58 triple that has a 32t difference. Chain wrap concerns are much lower. I'm also only running a 11-34t on the rear I think, again decreasing chain wrap concerns. For the DI2 those gears are locked out as I have shifting setup automatically. They simply aren't needed and I don't like cross-chaining for the stress on the system.

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Old 01-30-23, 10:25 AM
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Fergp I know this is an old thread, but tandem electronic shifting information is kind of slim and un organized. I would like to take our Cannondale Tandem (2009 model) to a 2x electronic shifting system and tried to look at your photos but the links don't work any longer.
Could you share them again and possibly update your build list from the below?
• I built the configuration around the 11-40 XT Shimano cassette since it is one the few 11 speed cassettes that work with a 10 speed wheel. This bike has DT Swiss 540 hubs and can't use a normal 11 speed road cassette.

• I used a Wolf Tooth Road Link to extend the Ultegra 6870 GS rear derailleur to 40 tooth capacity.
• I moved the 52 tooth chainring to the middle position and found a 38 tooth 74 BCD chainring on eBay to replace the granny gear. I then added a chainring guard to the outer position to make it look cool!
• I added the D-Fly DI2 wireless module, so I see the current gear selection on my Garmin display. The Garmin also shows the DI2 battery charge level and pops up a warning when the charge goes below 20%.
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