dvdslw

The time has come for me to decide which rear derailleur I'm going to use on my gravel bike and I can choose between XT, XTR, GRX 817, or GRX 815. So far I have a Sram XX1 cassette and a set of Ultegra di2 shifters. There seems to be some confusion with the rear derailleurs and their capacities and hoped that there were some actual users out there that could chime in on their experiences using any of the four I mentioned on a 1x setup.

So far my research hasn't come up with any solid answers about each derailleurs performance as a 1x along with a 42+ cog on the rear. Some say the XT and XTR derailleurs don't shift well and are slow compared to the road components but almost all have attributed that slowness to the syncro-shift feature where the front and rear derailleurs work together for optimal gearing. (seems less than optimal)

The GRX di2 derailleurs are also confusing where the 817 designed for 1x has a shorter cage than the 815 designed for 2x, wtf? The 817 is based of the XT mountain derailleur with a larger motor and clutch assembly where the 815 is based off the road derailleurs.

At the end of the day I want a 1x derailleur that will shift as well as my old road bike with Ultegra di2 but work with a 10-42 cassette. Which would you choose and why? Right now I'm leaning towards the XTR due to price because its $50 less than the GRX817 and also weighs a bit less too.

Thanks.

blazin

I ran 11-speed Di2 XTR RD for about two years with a e*13 9-46 cassette. Worked a charm. Didn’t notice it being any slower than my 6800 Di2 road bike. Eventually switched over to the AXS mullet, but that wasn’t due to any dissatisfaction with the Shimano set up.

shoota 

I'd go for the cheapest of the XT, XTR, and GRX RDs. Plenty of people using them with 11-42 cassettes around here on their gravel bikes.

base2 

In my experience working on a friends bike, the GRX di2 would not accomodate the 16 tooth jump in front chainrings. A 10 tooth jump was the limit & it was enforced by physical design stops.

Intentionally crippling the derailleur for reduced range to wedge in a product niche never sat well with me.

In the end, I stuck the di2 road derailleur back on with a new 11-42 cassette & told her junction box to avoid the big/big combination. (Even though the derailleur handled big/big fine, I just thought it best to avoid anyways.)

I really don't "get" GRX it seems so much like a solution looking for a problem.

XT/XTR would be where I'd look if I were looking for something new. Else, I'd first see how the road derailleur you have does on the workstand.

nagakuraruan

I have a spare XT di2 I used to use in a 1x set up. If you want it you can have it. DM me.