1 x GRX rear mech with non Shimano 1 x chainset.

I am using an older Cannondale xc frame and attempting to put together a 1 x adventure/gravel setup without bodging it too much.

With SI cranks and Woltooth 1 x chainring on the front, am I okay using the 1 x long cage GRX mech to help me get a bigger cassette on than a standard cross setup? The worry is that Shimano have changed the chainline with the GRX chainsets by a couple of mm.

This for instance:

https://www.sigmasports.com/item/Cannondale/SuperX-GRX-Disc-Cyclocross-Bike-2020/MVPI

sticks with the older Ultegra RX mech. Is that purely because a bigger cassette isn't required, or because a GRX mech wouldn't work correctly? People that usually know better than me have said it should be okay.

Thanks

This for instance:

https://www.sigmasports.com/item/Cannond­ale/SuperX-GRX-Disc-Cyclocross-Bike-2020­/MVPI

sticks with the older Ultegra RX mech.

That's a GRX derailleur in the picture though. Either the picture is wrong, or the description is off.

Weirdly the same mistake can be seen on Cannondale's own website:

https://www.cannondale.com/en-nl/bikes/road/cyclocross/superx/superx-grx

GRX derailleur in the picture, Ultegra RX in the specs.

Anyway, the GRX chainline change only really affects the GRX double crankset, since you need the accompanied GRX front derailleur to make it work. Using the 1x GRX rear derailleur with a non-GRX 1x crankset shouldn't be an issue.

If your doing shifters at the same time i dont see a problem the 812 rear will cover up to a 46 with no hanger extension required . Merlin have grx discounts this weekend again.

If your doing shifters at the same time i dont see a problem

GRX is cross compatible with road groupset components of the same speeds (apart from having to pair the GRX double crankset with the GRX front derailleur). But besides, this isn't relevant to OP's question.

Chain line will be fine.

Thanks all.