Cannondale Tandem Conversion to DI2 11 Speed
 

I just finished my winter project; converting our 2015 Cannondale Road Tandem 2 to DI2 11 speed! I received a lot of help from this form, so I wanted to share the result. Here are a few key points to this project:

• 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%.

We are waiting for nicer weather before we take our first ride, but shifting performance on the stand is quick, clean and precise. There is no hesitation on any shifts either up or down. My configuration exceeds the chain wrap capacity so I can’t use the 52 – 40 gear, but that is not a practical gear to use anyhow, so I’m not too concerned. Thanks for everyone’s help!

Looks awesome. Did you consider moving the timing chain to the drive side?

Nicely done! I am considering doing the same thing with my Co-Motion tandem, either with Di2 or Sram eTap wireless. I cannot tell from your photos where you installed the battery or the wire layout on the bike. Do you have any other photos showing that?

Here are a few more pictures. I fabricated an extension to the standard battery mount to make it fit the water bottle mount on the bottom of the down tube. I decided to stay with the old-style battery to match the other three DI2 setups we have in the family! This also meant that I could not use the newer Bluetooth version of the D-Fly transmitter due to compatibility issues. The old model (SM-EWW01) was hard to find. Also, the older style battery and wire harness are less expensive and keep me close to my $1000 budget for this project.
We now have about 8 rides on the new set up and absolutely love it! The shifting is crisp and precise at every position. I also like the simplicity of the double up front vs. the old triple!

Thank you, very helpful!

IMHO, Electronic shifting makes a huge difference on a tandem.

With the longer cable runs, and the torque of two riders, cable actuated shifting on tandems always leaves a little to be desired.

Di2 on a tandem shifts perfectly.

I'd resize the chain. Far better to have too much chain so it wont wrap in the small/small combination, than not enough to go in the big/big.

Someday you'll inadvertently shift into the big/big, and it can be a very expensive misshift.

I've always wondered exactly what would break if your chain is too short and you shift into big/big. Would the derailleur hanger snap? Would the chain itself break? Would the Di2 servos get damaged trying to move the chain into a gear it can't fit on? Not sure, don't really want to find out myself.

The chain jams as you force it into the too big gear. You're still pedaling, putting force to the jammed situation, until you realize what's going on. This is even worse on the tandem, where you've got double the force, and less than instant feed back to the captain. Worst case scenario, it rips the derailleur hanger from the frame ( or just bends the derailleur itself), puts the derailleur in the spokes, trashes the wheel, and you come to an unplanned screeching halt.

Yes, I understand, but when I'm in the small/small the chain is almost hitting the 2 pulleys and there is very little tension in the spring. I am afraid that adding one more link to the chain will create a problem at the other extreme.

The point is that it is better to have to stay out of the small/small, than the big/big

There's no reason that you need to use the smallest cogs, with the small ring. You've got comparable ratios available using the big ring and a different cog.

If you size for the big ring and you put it in the small/small combination, nothing really bad happens. It's noisy and sloppy and you realize don't use that combination.

If you size for the small/small, and inadvertently shift into the big/big under load you potentially: 1) trash a derailleur; 2) trash a chain; 3) trash the frame (by breaking the dropout/derailleur hanger); 4) trash the rear wheel, and 5) crash the bike.

Admittedly, the odds of all that happening are low, but it can and does happen. And the odds are fairly decent that eventually you'll forget, and at least f up an expensive Di2 derailleur.

If you don't have a derailleur with enough wrap capacity for the entire range, it is a dramatically better idea, when you consider the risks, to size for the big/big.

Just curious as to the approximate price that changing the Triple to Di2 cost you?

I'm hoping SRAM comes out with the 1x 12 speed system for road bikes with drop bars sooner rather than later. Then, I don't have to worry about electronic compatibility/batteries

Hello
What is the front dérailleur ?
Thx à lot
Stéphan

Moved to Tandem forum.

Where did you get the chainring guard?

Not sure if the OP will see this as it is from 2017 and moved from road cycling. That brand guard is readily available on Ebay and Amazon is the $30-40 range depending on size

It's an Ultegra DI2 11 speed front derailleur. I did end up changing the big ring to 50 tooth (still 38 small ring), to improve shifting performance. We have done about 3000 miles since the DI2 upgrade and still love it!

Ours was not a conversion but a new build Calfee Di2. I wanted the widest range we could get out of a 2x system. We're at 52t x 34t up front with a 40t x 11t cassette. It was set up with a K-Edge long derailleur arm. We didn't try the Wolf Tooth Road Link. I really don't know which is better.

The bike shifts fine despite the fact that we're beyond the recommended range up front (18 tooth difference).

My biggest complaint is that the drop from the big ring to the small is huge and I need to make sure that I notify my stoker about this upcoming drop. However, we do use the full range when climbing & descending big hills.

Chinook tandems sells a longer pilley cage which would solve your chainwrap problems. We're using a Digirit pulley cage on our eTap rear derailleur but a bit longer would be good

Does anyone know if the medium cage Shimano 8000 series Di2 rear derailleur can handle an 11-40 cassette? We currently have a 2016 Co-Motion Carrerra with Di2. At the time we bought it we had to get a 52-39 on the front and a K-Edge with 11-40 on the back. We'd like to change to the current Shimano 8000-series setup with 50-34 on the front if it can handle the 11-40 in the rear.

Just did a shakedown ride yesterday on a stokers new comotion steelhead running ultegra di2 Rd-r8050gs rear and slx CS-m7000 11-40 cassette. Front chainrings are the stock comotion 50/34. Shifting was flawless

We have a 2015 Calfee with Ultegra Di2. I wanted the biggest range possible. We're running 52t x 34t up front with 11t x 40t in the rear. We have a K-Edge long cage on the rear derailleur. This is probably far outside the operating limits of Di2. However, it shifts fine. My only complaint is the jump between the big & small rings is huge. Unfortunately, this is the consequence of a big range with only 2 chainrings.

How did your conversion work out?
 

Hi,

We're looking at something similar. Did you have issues? Have you kept this configuration?

Yes, we still love it! (had a great ride yesterday) I did change the big ring from 52 to 50. This this improved the shift up from the 38 tooth ring and helped with the chain wrap in the back in the rare times you ride the extremes (11-38 and 40-50).

Paul

My di2 potential setup need help
 

I only want 1 tandem and understand it will not be able to do anything perfect. I got a custom ti frame and fork and had problems with the initial build. 1. The tandem specialist in my area said a 50/34 and a 10-42 would not work (break the rear derraileur) so the made it a 10 and had it not shift into the 42. Should it have worked? The next thing is I did not put cables stops thinking I would run full housing. Shifting is delayed on rear and problem with front derraileur. I have now decided to go di2 . I do not plan to use a front derraileur I have a 2 sets of wheels road with a 10-32 to use with 50t and a 10-42 to use with mnt /gravel to prevent from ruining the derraileur. I bought di2 Ultegra shifters and xtr rear. I was thinking about putting the battery on the underside of the stoker toptube. What do you think? Any comments? I may try a front derraileur later

https://cimg1.ibsrv.net/gimg/bikefor...bc962b56d.jpeg
https://cimg5.ibsrv.net/gimg/bikefor...c95a72891.jpeg