Di2 Thread
 

I'm investigating Di2 for our tandem. I searched and found a few different threads that have found various debates the merits of Di2, some people's bike builds and a few other useful items. But was hoping to find the detailed specs - of course they are not all in one place. Also, some people have upgraded and/or changed their setups.

I was wondering if there would be an interest in providing your latest iteration of Di2. Feel free to add/change the list below. What am I missing? I am not a user, but am thinking about it. My hope is to have a source thread that users and prospective users can reference.

Chainring specs (i.e. 52-36)
Cassette specs (i.e. 11-36)
Deraileur specs (Ultegra xyz model & cage length)
Shifter specs
Battery specs & placement
Junction box(es)
Display?
Brakes
Cranks
Rear spacing

Any major issues with implementing your set up?

Any items that you intend to change (based on existing technology - not the hope for 3x road etc.)?

Thanks in advance for those who wish to contribute!!

Dan
Here goes with our setup We have been through a number of combinations and this is where we have ended up.
Bike Calfee Tetra with couplers with internal routing for wires.
Ultegra DI2 11 speed 6870
rear derailleur has K-edge cage on it but the med cage and a Road Link (Wolf components) accomplishes the same thing at a much lower cost
11-36 cassette for normal riding
11-40 XTR cassette for big mountain tours (simply replace the chain with a longer one no other adjustments needed)
50/34 Praxis chain rings on Lightning cranks
Seat post battery in stoker seat post
Front junction box is the XTR display
two other 41 junction boxes in the bottom tube so we can take the bike apart for travel one in front of the stoker BB and one behind the captain BB where the couplers are
RS 785 shift levers and hydraulic brakes
Goodridge brake hose ( very important with these brakes for solid lever feel and great modulation)
Brakes bleed with 9 mm thick bleed spacer instead of the normal 10 mm
Rear spacing is 142x 12 thru axle which is 135 spacing
System is flawless with at least 1000 miles before battery need charging.
Bleeding these brakes is a royal pain but once right they are amazing
180 mm rotors front and rear
semi metallic finned brake pads

At this point no desire to change anything it just works

Santana Team TI700 S&S
Dura Ace DI2 7960, external wiring.
50/34 Chainrings with Santanna carbon cranks (FSA)
11-32 normal riding (or 11-28 when visiting the flat areas)
11-36 with Road Link for mountain terrain (also swapped out the cage on the RD with an 6700 Med cage)
Rear 10" disc with Bengal caliper, Front cantilever.

Our setup - we're newbies to Di2:

Ultregra Di2 with Dura Ace caliper rim brakes
Gearing: 52t/34t front; 11t-36t rear. The front it beyond Shimano's spec of maximum 16t difference between chainrings. It shifts reasonably well but the jump from 52t to 34t is huge. We're pretty reluctant to go to a narrower range (like 50t/34t). We did a ride on Sunday where I wished we had a higher top end.
K-Edge arm on the rear derailleur.
Did not have display when we bought it but have since added it. I think this is very helpful.
We have not done any rides that would tax the brakes. Our old tandem had rim brakes & they were adequate for most every ride (including Mt. Evans).

I was skeptical of Di2 at first because it dictates only two chainrings and I found myself mis-shifting all the time compared to mechanical shifters. However, the more I ride it, the more I like it. I'm still not in love with it because of the compromises it enforces (note that I haven't said anything about the cost).

Maybe when they introduce synchroshifting, this will reduce my complaints about the big gear jumps.

We're using Ultegra ST-6870 shifters, FD-6870 front derailleur, RD-6870 rear derailleur (mid cage), SM-BTR2 internal battery, SM-JC41 Junction B, XTR Di2 display (in place of SM-EW90 Junction A). SRAM Red 50-34 chainrings, Shimano CS-6800 cassette (11-32T), and custom long eTube wire between XTR Di2 display to Junction B. We use Lightning Carbon cranks and carbon wheels with 145mm rear spacing.

To get the most out of Di2, use stiff 11sp chainrings with ramps and pins (eg. Sram Red or Praxis). Shimano Ultegra/Dura Ace chainrings are stellar but they don't work on tandem cranks. Although their chain pins are inconvenient, the Shimano Dura Ace HG901 chain has been very quiet with consistent shifting. There's no advantage in using KMC or Sram chains.

Forget about an external battery. The SM-BTR2 internal battery will fit in virtually any seatpost without modifications. Battery life is very long.

We're big fans of Di2 because the cost is justified by the higher consistency, precision, and reliability. What can make Di2 better is lower price, synchronized shifting, and slimmer hydraulic shifters.

Shimano has made Di2 more affordable by bringing most of the Dura Ace 9070 performance down to the Ultegra 6870. I run the full 9070 on my Giant TCR and its performance is virtually the same as Ultegra 6870. I only went with 9070 because I got a great deal.

Since synchronized shifting is coming in 2017, wait for the new Junction A and internal battery. These new components will work with 6870/9070 and the new R9150 components.

I don't like the Shimano R785 hydraulic shifters because they're bulky and heavy (about 500g). The new ST-9170 Di2 hydraulic shifters are supposed to slimmer and lighter (360g). Unfortunately, the ST-9170 will be expensive. To save money, wait for a sale on 6970 components, and mix-and-match Ultegra and Dura Ace where it makes sense.

As you know, with Di2 we now have the option of both road and mtn derailleurs, but only the XTR series has a triple. Gearing requirements should probably dictate how you should setup your tandem. Choice of components after that has been determined.

IMO, this current trend of super wide ratio cassettes is mostly driven by mtn bike single ring drivetrains and not the greatest thing for road efficiency. Swapping in a super big cassette for a one-off climbing tour might be passable, but otherwise not a preferable setup for everyday riding.

Also, synchro shifting does not solve anything as far as cog ratio gaps. The current XTR/XT implementation simply allows you to specify a predetermined mapping of where your chainring shifts will occur in relationship to upward/downward shift direction of the rear cogs. The upcoming DA synchro adds in a semi-synchro which allows you to force shift the front and have the rear happen in automatic fashion. Still, nothing that will solve huge ratio jumps that may exist in a wide ratio cassette.

Questions:

1. Do you care about cog spacing "jumps" (ie: require close ratio cassette, or don't care)?

2. What top end gear do you NEED (as apposed to think you need)?
Is the equivalent of 52x12 sufficient, or do you need 52x11, or bigger?

3. Likewise, what bottom gear range do you need for typical riding, and for epic/travel rides (ie: Ventoux)?

4. Do you or stoker have any special crank/Q-factor requirements, or can ride most any typical tandem crankset?

5. Are you stuck on, or against having a double or triple chainring setup?

We're currently specing out a new Macchiato to replace our aging Speedster. We spent a lot of time staring at gear charts trying to retain the existing gear range and jumps of the Speedster 3x9 drivetrain. Our first preference was to use a 3x10 mechanical drivertrain (XTR Di2 would sacrificed too much top end), but poor options for 165mm stoker cranks made 2x11 Di2 the best choice for us. Going Di2 will also better avoid obsolesce problems, as the 3x10 mechanical Ultegra drivetrain will be harder to find parts for as years pass.

Base specs are as shown on the Co-Motion website. Specific choices we made:

1) 50-34 chainrings, cranks TBD
2) 11-36 cassette, installation of Roadlink and/or replacement derailleur cage to be performed by LBS as necessary
3) Shimano Bluetooth compatible battery and transmitter to allow display of gearing on Garmin 510.

Anything I've forgotten or have wrong?


FYI- I've used a KMC masterlink with an HG901 for nearly 3 years on my Di2 equipped single without issue. I will likely also install on the Macchiato.

Looks like the Macchiato frame is Di2 compatible. However, check that the BB shells have slots that will allow the Junction B and the new internal wireless transmitter (EW-WU111) to pass through to the seat tube or boom tube.

I answered most of your questions above in Bold

For reference, we had previously ridden a triple set up (30-39-53 with 11x28 I think) and then when we ordered our new bike (3 years ago) I opted to try 2x to see how we would do with the different gearing and jumps. With the intent on likely moving to Di2 at some point. I guess it has not been a priority to make the change so far...

We are currently riding 52-34 chainrings with 11-36 cassette. Giving us even wider gear range (with larger jumps) than we had on our previous bike. I realize that the large differential with the chainrings may be problematic with Di2. I'd think about going with a 50t, but don't want to give up the low. That said, maybe I'd rather go with 52-36 chainrings and do a 11-40 cassette?? Not sure...

Thank you everyone for sharing your specs. This is very helpful!!!

Ok, so my "experimentation" with running Ultegra Di2 long cage, 48/30 chainrings and cassettes 11-23, thru 11-36 (the latter with Roadlink), has no issues shifting those ranges. If your chainline is somewhat normal, then you should not have any issue with your current crank setup. If you are running a wider than normal chainline (ie: wide tandem cranks) then you might need a special FD mount to put it further outboard. Otherwise, you probably have a fairly easy derailleur, chainring and cassette setup.

If you have any interest in adding more shifters (TT bars, climbing buttons, etc) then you might want to get the 5-port junction A (EW90), otherwise a 3-port should do.

Then your decision on brake type will drive which levers to get... cable vs. hydraulic. I am running the rs785 levers and calipers, and while they work well for braking, the setup and style could be refined. This was Shimano's 1st gen Di2/Hydro combo. I'm looking forward to seeing the Dura Ace version & pricing.

Although the Ultegra front derailleur is rated for 16T differential, there's no harm in keeping your 52-34 and 11-36 drivetrain. If you're using a high quality chain and 52T ring (eg. Praxis Buzz, Sram Red), Di2 should shift much better than your mechanical setup. If the 18T gap is too large for your liking, go to the standard 52-36.

Excuse my ignorance on this topic as I'm looking to go to Di2 as well. What double tandem cranks are available? Can I use my existing FSA Gossamer triple cranks as a double? Have others done this?

I did that math and I see that the triple only gives us 2 extra gears so that's a lot of stuff for two gears. Nevertheless we definitely need those 2 gears at times as we frequently climb >12% grades. We also do fast flat so want the resolution. I'm still working on the ideal cassette/double chain ring combo.

I would really like to go with etap but I don't see that happening soon with max 28 rear cog.

edit: another question - what is the setup to use the mountain bike Di2 (triple) with road shifters?

My daughters boy friend manages a bike shop in the Tulsa area and he tells me that SRAM will have etap available that will accommodate a cog larger than 28. If I were to convert to electronic shifting I would use etap for the rear and keep my triple on the front. I would use the buttons to activate the rear derailleur and keep my existing brake shift levers.

Currently available double chainring tandem cranks:
- Lightning (~$1700 w/proprietary BB cups)
- DaVinci (~$1000 square axle with Ti BBs)
- Middleburn (~$850 for the newer RS8 type, ISIS 24mm axle and works with standard outboard bearings, ie: Shimano HollowtechII)

To use an existing triple (130/74mm bcd) as a double, mount the big ring in the middle position, keep granny. As a filler in the outer position you can add a chain guard/ring, or just Race Face crank arm tabs. Either of these are better than just using washers with your existing chainring bolts, but you can use washers if you wish.

Yes, other have done this. The standard Di2 road front derailleurs shift our 48/30 rings fine. Others use 52/34 rings with same results.

A triple is mostly about keeping the overall range while not having to resort to big ratio steps between cassette cogs. If you don't mind the steps in the wide cassettes (11-32, 11-36) then a double ring setup should be fine. For up to the 11-36, a $20 "Roadlink" extender is all that is needed. I have not tried running an 11-40, but some others may have. I believe that 40t is a bit too big for good chainwrap, and would only work well with the expensive K-edge rear derailleur cage add-on (instead of the Roadlink). Exactly what works and what doesn't sort of depends on the length of your RD hanger on the tandem.

For short term, special case use, we have used both 11-32 and 11-36 cassettes and had a blast climbing steeper longer stuff, but afterward I reinstall the 11-28 or smaller cassettes because we prefer closer steps. Especially, my stoker has trouble trying to push bigger gears at slower cadences, so big jumps in cogs is problematic for us.

Turbotandem has posted lots of info in his "Gravel grinder" and "Di2 XTR Triple" threads. Read those.

The XTR M9020 triple crankset specs are a 40/30/22 (an 18 tooth diff), but Andy has a 44/32/22 setup working. There are some reports of Santana trying to get a 52/39/30 working with a FD shim added in, but I'm not sure how good that shifts IRL. Both of those chainring setups are a 22 tooth diff. The two main issues with the XTR FD triple is max ring size and chainline. First, this FD has a fairly short cage and a sharper curve, so it doesn't match up great with rings larger than around 48t. Second, it needs a chainline of at least 48.5mm (its spec is something like 50mm), so a narrower setup is problematic. Luckily for most tandems their triple chainline is pretty wide at 50mm or more.

FWIW, I am in the process of setting up our Calfee as a triple (Lightning cranks), and swapping out the Ultegra Di2 derailleurs for the XTR Di2 triple front (FD-M9050) plus the long cage rear (RD-M9050 SGS). My base target chainring setup is a "trekking" range of 48/36/26 (may try stretching that to a 24t granny if possible), but some FD modification may be needed. My desire to go with 48/36/24 rings is for targeting use of a tighter 11-25 cassette 90% of the time, then 11-28 or even 11-32 cassettes the remainder for more wicked climbing stints. From what I have tested so far (48/36/26 x 11-25), the cage tail/bottom needs to be a bit wider to eliminate rub in all the gears I want to use, but the length seems fine. TBD.

I recently commissioned a new Calfee Adventure tandem frame and we are going to put XTR DI2 triple on it. We presently have Lightning cranks with double chainrings on our road tandem. They are great cranks but I don't like the proprietary bottom brackets that we have had to replace more frequently then I would expect. For this reason I am using the new RS8 Middleburg cranks that are very modular and we can use Chris King BB. The nice thing about these cranks is they are very modular 1x 2x or 3x different spindle lengths for 68,73,or 100mm BB's etc. Our new frame will have 68mm BB's but XTR is designed around 73mm so Chris King makes neat spacer sets to use 73mm cranks with 68 bb's. I will weight them when I get a chance but I think there will be significant weight penalty but I like the fact that I can go into any bike shop in the world and find a shimano 24mm BB for replacement if needed.

Rick at HouseofTandems.com has got the bigger cassettes with the eTap. It looks like he's using the Road Link.
SRAM eTap for tandems - House of Tandems - Houston Texas - Gulf coast tandems

You guys are lucky you can ride a cow sized fat bike (ie: super wide Q-factor) without ending up in the hospital.

I was oh so close to getting the Middleburn RS8 cranks instead of the Lightning. Alex Nutt (mtbtandem.com) came up with some Q numbers and chainline numbers for a narrow triple setup, but he didn't have all the pieces to confirm. Ended up with the Lightning set, but sort of a custom one (158mm Q-factor) at that. Tim was very helpful.

Good information from everyone. Gotta make a spreadsheet to keep it all straight. Interesting about etap. I might wait for that.

I too strongly prefer small gear steps - I really dislike not have a 16 between 15 and 17 on our cassette. Perfect cadence is key when riding in a fast paceline. I'm planning to build a second set of wheels and might be useful to have 2 cassettes and just swap wheels - as long as it's close enough that I wouldn't have to change chains (technically should be done) or mess with the brake caliper adjustment.

Since you like strenuous climbs (12% or higher) and fast rides, you should consider the trade-off of these electronic shifting options.

Option 1. Ultegra 6870 Di2 using 52-36 and 11-36 cassette
-double tandem cranks are expensive.
-double crank will have bigger gear jumps. The gearing works for us (and virtually all single bikes) but some teams don't like it.
-double cranks are lighter and have better chain lines.
-this setup has the same high (4.7) and low gear (1.0) as your FSA Gossomer (52-39-30 w 11-28 cassette).
-get synchronized shifting for programmable sequential shifting, eliminate cross-chain.

Option 2. Ultegra 6870 Di2 with FSA 52-30 crank w 11-28 cassette
-save money by using existing FSA triple crank.
-the 22T gap is much higher than the rated 16T jump. You can probably get acceptable shifting with 18T gap (52-34) but you're pushing your luck with 22T jump.
-synchronized shifting is almost impossible with such a large gear jump.

Option 3. XTR Di2
-the gearing is low enough for virtually any type of trekking or off-road use.
-slightly cheaper than double tandem crank.
-the XTR is only rated for 10T gear jump with a 40T limit for the big ring (40-30-22).
-some teams have tweaked the front derailleur to use 48-36-26 rings.
-if you're willing to push the limit with a 48T big ring, keep in mind that your higher gear is only 4.4 (48x11). This is almost the same as a 52x12 combo.
-if you stay with the specified 40T big ring, your top gear is only 3.6, or about the same as a 52x15 combo.

Option 4. Sram eTap (rear only)
-like option 2, you can save money by keeping your FSA crank.
-don't have to worry about internal cabling.
-will need Sram left & right eTap shifters (for rear shifting) & mechanical front shifter.
-can't do electronic front shifting, which is the biggest advantage of Di2 or eTap.
-mechanical front derailleur can't auto-trim, shift quickly and consistently, or do synchronized shifting.

These long cage rear derailleurs have such a good capacity that I haven't needed to modify the chain length when switching between 11-23 up to 11-32 cassettes (min chain length set to 32t cog). For the 11-36 I just add 2 link pairs (3 chain links + an additional KMC Missinglink), which was enough for the 36t and good chain wrap.

We can definitely ride a 173mm bottom bottom bracket however the fat tire tandem is not a all day long ride situation so we may have issues on a very long ride and many times we ride flat pedals on it so there is lots of movement. We can also accomplish more of a narrow Q factor by pedal choices with different pedal spindle lengths. The nice thing about these cranks is the variety of choices i.e. if the triple does not work out we can change to a double very easily with just a new spider. The spider is more robust which I like for an adventure tandem. Alex at MTBtandems is great and I have also had good service from Tim at Lightning.

Thanks for the analysis, @mtseymour.

We would have to leave our ego at home to go with anything less than 4.7 (52-11). We originally only had a 12 highest gear cog on the cassette and would get dropped by single bikes because we were spun out. We like to ride fast downhill so 4.7 is a must. Plus, those single cyclists depend on us to pull fast on the downhill (we are too light to rely on weight).

It's sort of amusing to think we like >12% grades. I suppose we do in a masochistic sort of way, but reality is that these grades are a part of the every-day rides that we do. 15% is not at all unusual.

I think a triple is necessary for us for the best resolution in shifting.

I do like the idea of keeping our FSA cranks as I've looked at the others and too many drawbacks as far as I can tell (questionable BB with Lightning and I'm no fan of proprietary gear; old-fashioned looking cranks with daVinci though I would seriously consider them as I actually don't mind square taper axle and weight seems good; what's with Middleburn's website?? what little I can find on them is not impressive.)

I also prefer more choice of double tandem cranks but the market is probably too small for Shimano or FSA.

Despite my initial skepticism, the Lighting's BB has proven to be reliable and quiet. the installation was straightforward. Lightning apparently holds the patent on the Hirth joint, and has licensed the design to Specialized for their S-Works carbon cranks. The Hirth joint is light but strong, and is used in some aircraft crankshafts. The major drawback is the price.

https://en.wikipedia.org/wiki/Hirth_joint

If you're counting grams, the Lightning BB is lighter than my Shimano Hollowtech or Cannondale Hollowgram BB with similar reliability.

US sales... mtbtandem.com (Alex Nutt). Don't be shy to call him.

Alex is the man! He is ALL things MTB tandem and just an all around good guy. I think he's the primary US distributor for Middleburn.

Sounds like lots of possibilities with these cranks! I like having another option that is NOT square taper.