GRX825 di2 2x and 10-40 / 10-45 cassette?

[ccie6872]

I am currently running the new SRAM 13sp Groupset and while is is great, I am missing more range. Back in the day I had the prior gen GRX and was able to run a 11sp 10-40 cassette successfully. I haven’t seen people runing the new 825 di2 2x w/ a 12sp 10-40 cassette (or 10-45)…. Am I missing something?

[satanas]

The 11 speed cassettes were 11-40, not 10-40; such a thing doesn't exist AFAIK.

The only 12 speed cassettes >11-36 are Rotor 11-39/46 ($$, several alu cogs), Chinese 11-40/42/46 (Goldix/Sunshine/maybe others), SRAM 11-44 (Flat Top chain needed), SRAM 10-44 (XDR freehub and Flat Top chain needed), Ingrid 11-44 ($$$), Shimano 10-45 (Microspline freehub needed), and a very few MTB cassettes with <50T, like Garbaruk's 10-48 (XD).

Whether any of these will work acceptably with 2x is a matter of opinion, and trial and error. The 39/40/42T cassettes might be okay with the 2x12 RD, and the 44-45/46 might be okay with the 1x12 RD using SyncroShift to lock out problem gears, but few if any have tried yet. With 11 speeds, Shimano made suitable cassettes and they worked fine with their long cage gravel & road RDs.