New GRX 12S Di2 Groupset?

[VonPG]

"Maddy Nutt was running 1× GRX Di2 with a 40t chainring and a 10-50t cassette on her ‘Stone Edition’ Ribble Gravel SL with Parcours Ronde wheels"
It seems that she used new grx di2 groupset.
Because it is impossible for Shimano to give firmware to old GRX.

[damond]

that's the current GRX di2 with a garbaruk cassette and cage.

[Pottermouse]

Sorry to semi-hijack, but I have the shorter version of the 11sp GRX Di2 rear mech (so 815). Max 34T. If i changed the cage could I do this too... or are there other differences with the 817 version?

[pdlpsher1]

The cage on the 815 is actually longer than the one on the 817. But the cage length isn't the only difference between the 815 and 817. Cage length determines the chain wrap capacity, which is higher on the 815 (hence longer cage) to facilitate 2x which requires a higher chain wrap capacity. Besides the difference in cage length, the 815 and 817 have different upper pulley offsets, which allows the upper pulley to track the cogs with minimal b-gaps (distance between the cog and upper pulley) on 1x vs. 2x cassettes. The 815 has a standard non-offset upper pulley. The 817 has an offset pulley. You cannot use 815 on a wide range cassette bigger than a 11-40 (official spec. is 11-34, but 11-40 works). The 817 is spec'ed up to a 11-42 and 1x only, but could work on a 10-50 (as shown in the pic). Your best bet is to get the 817 RD (or potentially retrofit a 815 with the offset pulleys and cage from a 817) and use a 11-42 or 11-46 Shimano cassette, or a Garbaruk 10-50 casseette. But keep in mind that this is all 1x only. I assume your bike is a 2x since you have the 815. There's currently no way to run a 10-50 in a 2x. The RD in the pic. is very likely a 817, not a 815. Or if Garbaruk makes an offset pulley cage, the RD in the pic. could be a 815 with the special offset cage.