I know many saw Shimano’s announcement of the new Shimano XTR Di2 11 speed component group. At the time of announcement, there was wide speculation that this new system would allow the owner of a road bike equipped with Di2 electronic shifting to install the new XTR rear derailleur, thereby enabling the use of a cassette with a largest cog of up to 36 teeth. To the best of my recollection, Shimano was mum on the subject. K-Edge has offered to convert Di2 rear derailleurs to allow the use of cogs of up to 36 teeth, and we have quite a few clients avail themselves of this option. However, the possibility of using Shimano’s own mountain bike rear derailleur for those wanting low climbing gears still has its attraction and we had several clients looking forward to the actual availability of these derailleurs.
As with most new product announcement in the bike industry, it took months for these components to actually begin to flow into the supply chain. Product has now begun to trickle out, and of course people immediately tried this conversion. Unfortunately, early results show that you cannot mix the new XTR Di2 rear derailleur with any of Shimano’s road front derailleurs. It appears that Shimano has programmed the system to not allow this combination of components – mechanical or electronic, mixing mountain and road components within Shimano’s current line remains a “game over” equation.
This problem is similar to another problem that cropped up with Shimano back in August. Before that, you could convert your 10-speed Di2 bike to 11-speed by simply replacing the rear derailleur and the cassette. In August, without any forewarning, Shimano released a firmware update that looked to see if the front and rear derailleurs were, in their view, compatible (i.e. 10 and 10, or 11 and 11), and if not, it simply wrote the battery out of the system. The result, of course, was a completely non-functional shifting system. It seems that the problem with the XTR rear derailleur is also a software problem that prevents the road front derailleur from working with the mountain rear derailleur. Why, you ask? Good question. One I do not have an answer beyond knowing that Shimano has never been a fan of allowing for consumer creativity.
This all being said, if you have Di2 and want to get that low 36T climbing gear, you still have options: either have us install a K-Edge long cage derailleur cage on your current Di2 derailleur to work with cogs up to 36 teeth, try the inexpensive Wolf Tooth RoadLink hanger extender, or use both a new XTR rear and front derailleur (with the associated compatible front chainring combinations).