GRX rx810 and rx812 with 11-34 cassette?

[Aesch]

To make wheel swaps even easier between my two disc bikes I am looking for a single cassette that works on both derailleurs.
one is 1x gravelbike with an rx812 rear derailler (Top sprocket: Max. 11T/Min. 11T Low sprocket: Max. 42T/Min. 40T according to shimano). The other is an 810 with a max 34 size. I know this works with 11-40 since shimano is quite conservative but I was hoping it also works the other way around.
11-34 should be plenty since it's only for road application in that setting on the 1x anyway.

Any experiences running an 11-34 on both? or just the 812?

[andrzejg]

If that helps you, I use RX810 with a Sunrace MS8 11-36T and 2x compact crankset (50/34T). Everything works just fine. Unfortunately, I have no experience with this derailleur in a 1x drive.

[satanas]

Try it - there's a good chance it'll work.

FWIW, a few years ago I used a 12-23 10 speed road cassette with a Deore 9 speed MTB RD rated IIRC for 28T minimum. After I backed the B-tension right off everything was fine.

There were also no problems with an R8000 FD and RX800 RD with 42x27 rings and an 11-40 XT cassette; all the gears had acceptable chain tension.

IME you can usually get away with larger or smaller cassettes than Shimano say, within reason.

[CampagYOLO]

If it helps I use a 11-32 on a SRAM Apex 1 rear mech with no issues, just wound the b screw out.
SRAM don't seem to state a minimum cassette size unlike Shimano

[JMeinholdt]

I have an Ultegra RD-RX800, which I believe is almost identical to the GRX810 RD. I have it set up with an 11-40 XT cassette and it runs great in 1x. It can also be adjusted down to accommodate 11-34 as well.

I did try it with an 11-42 cassette as well. It did not work. Got a vid up on YT trying out the 11-42. I'll post a follow up with the 11-40.

[Aesch]

thanks for the replies, will report back as soon as i've tried !