marciero

Considering Di2 for our Cannondale. I know that if I want to retain the triple chainrings I can use XT fd and rd with road Di2 shifters. Or, I could go with a double and use road throughout. But since my issues are mostly with the shifting on the rear I am wondering if I can just do the rear as Di2 and keep my 105 6703 front cable shifter. Is the front needed to complete the circuit or otherwise necessary?

TerryDi2C

Sure, you can do that. Keep in mind that the levers (left/right) will feel different though.

The only requirements in a Di2 system are:

• Battery
• Junction A
• 1 shifter*
• 1 derailleur*

(* the system will probably work without a shifter or derailleur.. but it'd be a bit pointless )

marciero

Thanks-good to know in case I go this route

Chris_W

I rode such a setup before: Di2 rear derailleur and mechanical front derailleur to make sure that the battery lasted a complete ultra-distance event and so that I had some gear options even if the Di2 completely failed.

It works well but you do lose a lot of the advantages of Di2 including automatic trimming of the front derailleur based on RD shifts. Plus, you need 80% of the parts that you would for a full Di2 group, so it's a heavier setup than a full mechanical or full electronic group.

I didn't keep that setup for long. I now have spare batteries and trust Di2 enough to run it front and rear for even the longest events.

DubT

Check out X-shifter. https://www.sportcrafters.com/products/xshifter

oldacura

There have been lots of discussions about this. I was in the same boat several years ago when we got a new tandem. Most everyone that had Di2 loved it. I wanted the electronic shifting but wanted the wide range of our old 3x8 drivetrain. The only option for Di2 at the time for a front triple was XTR which limited you to a 46t big ring in front (I recall). This wasn't tall enough for pedaling much above 30 mph.

We would up going with a road Di2 Ultegra. 52t x 34t up front and 40t x 11t in the rear. It works pretty well but there are compromises. We don't have quite the range as on our 3x8. We ride the bike mostly on the big ring with the small front ring used as a bail-out. Most of the shifts are quick & crisp except for the drop from the 52t to 34t. This is a huge drop and it is really important to inform my Stoker before I do this shift. If I forget, she is not happy.

I understand that some shops are now doing a 3x11 road Di2 setup (Tandems East and maybe House of Tandems). I don't know the cost or difficulty in doing this. However, it would be much better (cheaper) to make this decision upfront rather than try some hybrid system.

Good luck.

tandem rider

In 2018 I got a new tandem with Di2 50/34 chainrings and 11 - 34 eleven speed. It was not geared low enough for us on steep hills and the 50/34 would sometimes require frequent shifting. In July of 2019 my wife and I took the tandem to Tandems East, a 1300 mile drive round trip. Tandems East put on a new FSA triple 52/39/30 crank set, an XTR front and rear derailleur, a new front derailleur hanger and 11 - 36 cassette. We also replaced the Di2 brains with the XTR although the Ultregra was working. I find the XTR brains much easier to use. The XTR works much better for us, we ride on the 39 chainring most of the time and it is geared low enough for the steepest hills in Indiana. It was well worth the drive and cost.

act0fgod

We bought another tandem and this is exactly what I want to do, but looking online there is repeated mention of a special shim that is required for the front derailleur hanger. One thread says there is a thread on bikeforums talking about making the shim with a washer. I can't seem to find that thread. Could you provide a picture of your front derailleur hanger. Also are you using an SGS rear derailleur or something like a wolf tooth?

tandem rider

The derailleur hanger was made by Tandems East. I'll try to post a picture. Tandems East said the wolf tooth would not work and replaced the SGS rear derailleur with an XTR.

tandem rider

oldacura

Just be sure I understand: Your XTR front derailleur will handle your 52/39/30 chainrings? I had been told (some time ago) that the maximum chainring for XTR was 46t.

tandem rider

Yes, the chainrings are 52/39/30. By modifying the derailleur hanger, the XTR can shift larger chainrings. The picture reminds me that I need to clean the chain.

marciero

There is a countour/lip on the wolf tooth that did not clear the lower edge of the derailleur hanger on our Cannondale when I went to put an 11-40 cassette on there. But five minutes with the file on the wolf tooth in the vice took care of that and it works fine with an Ultegra mid cage derailleur.

That's interesting regarding the chainring capacity for XTR triple and modification. Typically the limitations with triples (or even doubles) have to do with chainring differences rather than raw size (contour of the plate matching the chainring radius notwithstanding.) Mechanical Shimano derailleurs were often optimized for either a 10 or a 14 tooth difference from middle to big, but were not as sensitive to differences in small to middle.

act0fgod

​​​​​​​Thanks for posting the picture. Appreciate it.

oldacura

We have exceeded the recommended maximum chainring size difference from Shimano for our Ultegra Di2 setup. The recommended maximum difference is 16 teeth. We are at 18 teeth (52 - 34). The shift between the two works fine but it is a huge jump. I would have preferred a 3 ring setup but it wasn't available for the road at that time. I still want the wide range but would prefer smaller steps. Tandems East quoted $2500 to convert our 2x to a 3x but this seems like a lot.

marciero

I think exceeding the max can be more forgiving than not having enough of a difference. In the latter situation the inner cage can foul the middle ring when in the largest ring unless the derailleur is mounted higher than optimal. From what I've read some of the other threads here the shim that people are using is to address the fact that the outer cage on the XTR is radiused for smaller ring, with the shim tilting the derailleur. If so this still sounds like a less than ideal hack to me but apparently is working fine for people. But for $2500 I would expect a newly fabricated cage.

sch

The needed Di2 XTR triple FD is now quite scarce, which scarcity developed precovid and now the uncertainty is whether
Shimano will still be making it as triples are passe or worse on ATB singletons which is a much larger market than tandems.