Di2 - can you intermix models and versions?

[tv_vt]

Have an Ultegra 6870 Di2 setup on a bike, with an SS rear derailleur (short cage). I'd like to swap in a medium cage rear derailleur, either a 6870 or a newer one - think the Ultegra model is 8070 GS RD, and run an 11-32 or 11-34 cassette for some climbs.

Can you mix and match Di2 components? They're all 11spd, so I'd assume it would it work. Electronics are compatible?

I am not seeing any medium cage 6870 RD out there, but there are 8070 GS models available, so that is what I'm wondering about.

Thanks for any info.

[BdaGhisallo]

As long as it's all 11sp, I think you can mix and match anything DI2 on the road side. Not so sure about mixing in XTR DI2, though.

[ikecycke]

Everything except the 1st generation of Dura Ace is cross-compatible, even the MTB stuff.

You just need to have the internal battery charger or another way to connect to a computer so you can get all the firmware on the same release.

[loxx0050]

Have you looked into a replacement GS cage instead? Wondering if that might be a more economical way to change it out. Or maybe a 6800 GS rear derailleur as a donor for swap.

Can anybody chime in with experience on if this is a feasible swap?

[dem]

You cannot mix road and mtb deraillers. Must be all road, or all mtb.

Shifters are fine either way:
http://e-tubeproject.shimano.com/pdf/en/HM-CC.3.3.3-00-EN.pdf

[DrSpoke]

Not an expert but do have some experience. The GS models are what I would consider medium cage but have the longest cage of the road derailleurs. The mtn bike derailleurs are, of course, longer. The 68xx series is the previous generation Ultegra and the current generation is R80xx. They made a RD-6870GS and is what I'm using on my gravel bike. Shimano rates it to 32t but I run it, as do most of my friends, w/a SRAM 11-36 cassette w/o any issues. Some have gone to an 11-40 though likely w/a Wolftooth RoadLink. The RD-R8070, the current generation, is rated to, I believe, 34t. So I'm sure you can go larger if needed.

You can use mtn derailleurs w/the road shifters but you must use both a front and rear together. That is, you can't mix a mtn bike RD with a road FD. This is a limiting factor for a variety of reasons. It doesn't make sense to me why they do this but that's the way it is . Finally, Shimano just introduced a gravel RD - it's basically an Ultegra w/a clutch mechanism similar to their mtn bike derailleurs. This increases chain tension reducing the chance of a dropped chain as well as reducing chain slap.

http://carltonbale.com/shimano-di2-everything-you-need-to-know/