Castellian

According to Shimano, my GRX RD, (RX812) is only compatible with a 1x setup - max 11-42T / min 11/40T.


Has anyone had any experience or knowledge of use this RD with a 2x setup? I'm seriously considering it or trying a larger chainring to avoid spinning out on tarmac using my gravel bike.

Shadco 

I’m pretty sure we have a Look gravel bike with a GRX 800 of some type in the shop with a 2 by crankset I’ll check tomorrow.

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maddog34

Shimano also states that it''s specifically engineered for a 1x with a 11/40-42 Cassette.... chances are that you would run into the Max Wrap not being sufficient.... 31 teeth difference specified.... the location of the upper roller in relation to the pivot point plays into that spec.

Shadco 

Just checked the spec, it’s a GRX 810.

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grumpus

You could retain the current chainring size for the inner ring, and add a 10 tooth larger one for overdrive - just be sure not to use the two largest sprockets with the large chainring, otherwise crunch.

The other and possibly more correct solutions for this:
Increase your cadence.
Drag the back brake.

squirtdad

Bad Idea, you need to be sure any set up can run big big, if not and when you do shift to big big which will happen the results can hurt, depending on speed you are going

bottom line grx812 is not for 2x...... anything you do will be a hack and not shift well

grumpus

It could just refuse to shift and break nothing (including rider). It could break the frame, destroy the wheel and put the rider under a bus. Rider awareness would be a major factor in the outcome.
I don't see that there would be a problem with shifting as long as you avoided the evil sprockets of doom. Am I missing something?

squirtdad

rider awareness works until it doesn't I can say that from personal experience. I put a build together and chain was a bit tight....I knew i could not do big/big... not a problem I will be super aware because I want to ride my new frame. kid and dog cut in front of me on a mup and I do an emergncy shift.... crud am in big big and all stopped moving. I was going slow and was able to lean over and grab a fence and avoid a fall. At speed it would have hurt a lot

never setup where you can't do big/big

as to shifting in general, no hands on but plenty of other discussion about 1x rear being opimized for 1x and big sprockets.... pulleys etc. and in general experience of trying to make things work..... nothing work as well when used in a non designed for situation