I have a gravel bike with GRX 11spd Di2 1x. I find the gear ratio range isn’t great for me, mostly on the high speed end as I’m spun out on almost every ride. So, questions about going to 2x:
Do I need to change out the rear derailleur? For cyclocross I have just popped an 11-34 cassette and new chain on. Never had a problem even though stated minimum is 40T. I’m sure the shorter cage would be better, but any concerns using this long term?
I have a Stages L power meter. Can I use my current 1x left crank with the same crank length as the new 2x crankset. Would obviously save a ton to not get a new power meter?
I have double Di2 shifters so would just have to reprogram left shifter to new 2x setup.
Based on a bikeforums.net post, there is a limitation with using the RD-RX817 with 2x. According to betershifting.com, using that derailleur for 2x is not officially supported by Shimano.
The 817 RD does limit one feature of Di2, synchronized shifting. Without the matching front/rear 815 derailleurs, the system will not allow you to program the sync shifts. Not sure if anyone has found a work around for this yet but for now I can just shift the front as needed. Not a deal breaker for me but it may pose issues for those that use Di2 on multiple bikes and like that feature. The auto trim feature still works just fine so no worries about chain rubbing on the front derailleur cage.
You’ll need the required wiring to connect the front derailleur, so I imagine you may need a junction to connect the front end wires to the rear end wires (battery, rear derailleur, and front derailleur).
Your shifters will be fine. There is no 1x only shifter for 11 speed di2.
You will need to buy them rear derailleur for 2x. The 1x uses an offset upper jockey wheel which will not work with the different effective chain length when you have two different sized chainrings.
You probably don’t need to buy a new crankset. Rather just the 2x chainrings and install them on your current crankset. You definitely don’t need a new powermeter. The non drive crankarm will be interchangeable.
You will have a junction a box in your bar end or attached to your stem. You need to determine if you also have a junction b box inside your frame. If you do, all you need to do is get an extra wire to run from that to the front derailleur.
Parts list
shifters (existing)
Junction a box ( existing)
Junction b box (likely existing, but check)
Battery (existing)
Front derailleur (new)
~600mm di2 wire for front derailleur (new)
Other di2 wires (existing)
Rear derailleur (new)
Crankset (existing)
Chainrings (new)
Cassette (existing if you already have 11-34)
Chain (new to accommodate bigger chainring)
Bluetooth unit (optional to allow gear data on Garmin and wireless updates)