mxv

Greetings. I've been poking around this forum and the web getting ideas to rebuild my family bike. It's been a while since I had a nice off-road bike, an XTR equipped Klein, then I had kids and now they're big. I considered buying a gravel bike but thought it might be more fun to rebuild my Fuji with nice components and then pick up a new frame down the road when I have a better idea which way I want to go. I'll stick with what I know best, Shimano, GRX for this build. My question is about the RX810 brakes. My Fuji has IS tabs and I believe the RX810 calipers only come in flat mount. I'd like to hear your thoughts on using adapters, but of equal interest is the possibility of using XT four-piston calipers. Do any of you know if there would be any problem with that? Thank you in advance

srode1

I have not seen any adapters that allow using flat mount calipers on a post mount frame, only the other way around - using post mount calipers on a flat mount frame. Is that your question?
I was just looking at this because I'm debating moving my post calipers over to a new flat mount frame instead of buying new calipers.

mxv

Thanks for the reply srode1. I was inquiring about the possibility of using either adapters or pairing other calipers with the GRX levers. I found the Shimano products compatibility guide, section c-499 specifically. The only post or IS tab compatible calipers with the GRX ST-RX810/BL-RX810 levers were the BR-RS785 2-piston Ultegra 6870 series, so I just ordered them along with the levers and plenty of other bits and pieces to update my bike. Everything I read about these calipers looks good, certainly good enough for my needs.

I thought it would be good/beneficial to get the 4-piston XT brakes but my local shop recommended against it. They said those calipers might perform poorly, too touchy as I would have it configured. I don't know either way, but I think I'm heading in an interesting direction and time will tell how it all works out.

Now I need to find some new QR hubs for my 11-speed cassette, preferably center lock. I'm open to suggestions.

jan nikolajsen 

I'm using Deore MTB calipers with GRX levers on a frame that does not take flat mount. Just fine. I had them in the parts box. Were I to start with new stuff I would like you chose 6800 Ultegra instead.