Thread: GRX Di2
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Old 09-02-20, 03:15 AM
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Quirks and issues with RD RX817 2 x setup

Hi and great to see all this helpful info. I too am setting up (or trying to) an RD RX817 in a 2 x configuration, but with an ultegra FD R8050 front derailleur. I have encountered some issues not mentioned in this string.

- Alignment: I don’t know what frame specs the 817 is intended for, but the intended limits on movement (physical, not electronic) are way inboard of a standard setup. I have a 142mm OLD back end, which should be standard for this mech - but low screw has to be way in, stopper on body doesn’t even touch high screw. I had to put a washer between derailleur link and hanger, just to get guide wheel outboard far enough to run on smallest sprocket. Sounds mega-crude but given that Di2 limits are essentially set thru shift adjustment (I know the screws are there but I can see no reason why it wouldn’t function without a hard high limit in place) this could potentially fly I guess. Not very elegant tho, to say the least. And perhaps risks of chain jam, without hard stop. Any explanation of why this derailleur would be designed this way? I am using an SLX 11-40 cassette with a 1.85mm spacer. Removing the spacer would help but would mess up chain line and perhaps bring jockey cage uncomfortably close to spokes.

- This is what happens when you shift from big ring to small: click 1: jumps 2 at rear; click 2: jumps another 2; click 3: changes ring. This leaves you on 5th smallest sprocket. It will then allow a shift to 4th smallest = smallest useable sprocket when on small ring. I guess this is Shimano’s way of being flexible enough to allow use of their ‘1 x’ mech in a 2 x setup?? Or is it due to the GRX-Ultegra derailleur mix??

I connected to E-Tube app (on laptop not phone) and tried to over-ride the small-small lockout in the usual way (long story if you don't know how). This crashed the app and initially bricked the system - nice. Luckily when I rebooted the app and reconnected the system it came back up. At some point I got a pop-up message about non-compatible derailleurs. So not possible to over-ride small-small lockout.

Funnily enough tho, losing all those gears doesn’t matter that much as they are duplicated on the big ring (ran the numbers).

One reason why Shimano may lock out the smaller sprockets (if they thought about it this hard): the standard cage on the RRX817 is pretty short, wouldn't allow sufficient wrap for a wide range 2 x setup.

Incidentally and for info - and I can't see how this would cause any of the issues I've mentioned - I modified the RX817 by fitting the longer cage from an RD M8000 SGS (mechanical), in order to get more chain wrap. The cages will swap OK, with some minor issues which I can explain if anyone's interested. The cage sits in exactly the same position as the original cage so this can't be causing the alignment issues mentioned above.

I was a bike mechanic in a former life so any basic or obvious solutions are unlikely to work. Thanks for reading / responding ...
pduncanj is offline