I was having trouble running a wide range cassette on my GRX DI2 gravel bike. It is set up as a 2x drivetrain.
My local bike shop put on the roadlink DM, and I took the bike out for a quick spin and it seems to be working really well.
But then I went on the website and Wolftooth says the Roadlink DM is only for use with 1x GRX not supported for 2x , wondering why this is and if anyone has tried this?
What is the RD capacity?
With 1x you only need the capacity to match the cassette cog difference.
Example, 46 - 11 = 35.
With a 2x you need chainring difference plus cassette difference or you will have to avoid any gear combo that exceeds the chain length required to maintain tension for smaller cogs and accommodate the largest cog.
With a Shimano RD you can normally add 2T to the stated capacity as an achievable max.
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I am running GRX 600 2x (46/30) with road link and a 11-42 cassette in the back. Works fine, but chain is long, the clutch mechanism helps however.
Still, a lot less issues then with SRAM Eagly GRX 
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Hi dtom and others, hope you can help, sorry for long post!
Im running a GRX812 RD. I was running 1x11 with 11-42, but now gone to 2x11 48/31 with 11-34 and it works fine as my all round road/gravel bike.
However I need more gears as have a ride coming up in Andes riding up over 3800 metres. and will need the extra granny gears! 
GRX 812 has a capacity of 31T based on Max 42 (42-11=31)
GRX 810 has capacity of 35T based on Shimano Website:
- Maximum front difference: 17T
- Top sprocket: Max. 11T/Min. 11T
- Low sprocket: Max. 34T/Min. 30T
- Total capacity: 40T
Various youtube videos show 11-40 works with GRX 810
“With a 2x you need chainring difference plus cassette difference or you will have to avoid any gear combo that exceeds the chain length required to maintain tension for smaller cogs and accommodate the largest cog.”
For my understanding with 2x, the calculation is 48-31=17 and 40-11=29 so its 17+29=36T? Is this right calc?
Thus, is RD-810 better for 2x with 11-40?
Would Roadlink help with the RD-812?
Any thoughts would be appreciated.
Regards
Hugh
Not sure about the calculations but as 11 speed grx has a removable b link so a goat link would increase the gear range without adding potentially more slop into the mech.
I’ve used on for 1x grx to run a 46 MTB cassette and it’s reported to allow 50t ones.
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