For the past year, I lamented that the Di2 DuraAce derailleur would not support the Shimano Ultegra 11-32 cog cassette. That turns out to be erroneous. After hearing from two reliable sources that DuraAce + Ultegra 11-32 works, when I needed a new chain, I had the Shimano RD-9070 DuraAce Di2 derailleur installed along with it.
The first ride with the DuraAce upgrade tells the story: operation is flawless including 50 X 32 and over the range, and the shifts are noticeably snappier—a nice step up from Ultegra, and 51 grams lighter as well.
See additional notes at end of post.
Jonathan W writes:
I think without a mid-cage RD you might encounter issues in the extreme cross-chain gear combinations (i.e. 11x39 or 32-53). I know you probably won't use those gear combinations however I have heard 'it works!' too often without a disclaimer that certain gears won't work. Below is a link on YouTube showing a guy with a 11x32 and a short-cage RD. You can see at 00:40 the shift from 12 to 11 was very slow. This is because the chain is too long and there isn't enough tension in the chain. At 1:25 you can see the drivetrain just froze as the chain is too short in this gear combo.
Do you experience such problems? I've been following your blog for a long time and this my first feedback (I just found the link!) Keep up the good work and I'm glad you weren't hurt in your crash.
WIND: my Moots Vamoots RSL runs a 50 X 34 crankset (SRM 9000). The rear derailleur is the Shimano Dura-Ace Di2 RD-9070, purchased in May of 2015. And as far as I know there is only one length cage for 11-speed DuraAce.
Shimano specifications call out Max rear sprocket = 28 teeth for the Di2 Rear Derailleur 9070. That’s why I never ran it for the past year, assuming that was is true. And maybe it is true with a 53 X 39 or anything larger than a 50 X 34—I don’t know.
I’ve had nothing but fantastic snappy shifting in big ring and small (50 X 34), way better than Ultegra when I push those gear changes fast and under high wattage.
I was forced to cross-chain extensively during climbs at 50 X 32 during the 2016 Davis Double, because I lost front shifting after a collision at mile ~40. That is, only big ring for ~160 miles and 8000' of climbing. I was thus forced into 50 X 32 for any of the moderate to steep climbs.
Update 17 June 2016: two double centuries and a total of ~1000 miles of riding have shown no issues.
Not all configurtaions may work properly:
- The size of the chainrings almost certainly restricts things: 50 X 34 may be the only combo that works. There may be others, but it is very likely that the common 53 X 39 crankset does not work.
- Crank offset may be a factor (some bikes are asymmetric slightly).