I’m getting increasingly confused about Shimano GRX lever compatibility!

This page from Shimano says:

Fully Compatible Parts
As long as you maintain your current drivetrain speeds (10-speed versus 11-speed), the following GRX components are fully compatible and interchangeable with your existing parts: Shift levers, chains, brake calipers, bottom brackets, cables and housing, and Di2 batteries and accessories.

I’m going to replace my Ultegra 10 speed levers with GRX400 levers as the cheapest way to fit hydraulic brakes on my (post mount) gravel bike. Based on that comment from Shimano I had assumed that I could just stick some XT callipers on the end of the hose, but having read multiple threads on here it seems it’s not quite that simple, if only because of a possible mismatch with brake hose. In light of what appear to be contradictory replies to previous threads does anyone have any actual experience of doing this, and if so do I just need to get BH90 hose?

I’m doing this because of arthritic thumbs which make braking difficult, so I’m keen to get the most powerful brakes I can to minimise the force needed to operate them. So if there are any recommendations on the best available callipers that would be great. Hope RX4 seem to get the thumbs up, and if they’re materially better than XT I’d be prepared to pay the difference.

And anything else I need to be aware of?

Many thanks!

Those levers need to be used with either an RD-RX400 or a Tiagra 4700 rear mech. They won’t work with an Ultegra 10 speed derailleur.

Thanks (even if that isn’t what I wanted to hear!)

any input on the brakes question gratefully received…

any input on the brakes question gratefully received…

You can use any shimano caliper

Either BH59 or BH90 brake hose will work, you just need to make sure that you use the right barb for the hose type, as the inner diameter is different. The olives are interchangeable.

The thing to watch out for is the connecting bolts. The XT calipers will probably be banjo connectors. If you buy a banjo hose, it’ll come with an M8 hose bolt for the other end, and the levers need an M9 bolt which, if you buy levers only, won’t come with the levers, so you’ll end up paying another £6 per bolt:

https://www.sjscycles.co.uk/brakes/shimano-smbh90-flange-connecting-bolt-unit-m9-for-str9120r9170-y8rd98010/

If you go for a non-banjo caliper, you might be able to buy a hose the comes with the right bolts in the first place (M8 at caliper end, M9 at lever end) but I’ve not checked.

The cost of hoses and bolts quickly adds up quickly. For GRX 810 it would have been cheaper to buy a lever + caliper set and bin the unwanted flat mount calipers than to buy parts separately.

I find the GRX810s with Shimano calipers very powerful. Definitely a step up from the RS685s on my road bike.

Many thanks both, really helpful. I’ll order the relevant hose and connectors from SJS…

Thought I’d update this in case anyone else is trying the same kind of thing. The GRX-400 levers and rear mech are excellent, really crisp, positive shifts. Turned out I also needed a new front mech as the levers only work with GRX or Tiagra – I got a Tiagra 4700 as the GRX ones run on a different chainline.

It was very straightforward to set up some old Deore calipers, which worked well, but I’ve now swapped them for a pair of Zee four-pots I had knocking around. Complete overkill for normal people, but with my arthritic hands they’re just the improvement I needed.

Thanks for the help guys! @pdw you were spot-on about the M9 brake bolt. If I’d gone straight to the Zees I’d only have needed two of them and a couple of BH-90 inserts and olives, as I was able to reuse the Zee hoses.