I’m attempting to change my ultegra to Hope Rx4 and failed at the first hurdle.
I ordered two front flat mount callipers, not really noticing the word ‘front’.
The rear frame mounts are much closer together and look like it might need the post mount, could this be right?

If it’s post mount, the holes in the frame will be threaded.

I might be misunderstanding but I don’t think there’s any such thing as a post mount Ultegra caliper, they’re all flat mount.

With the Hopes you need front and rear specific calipers.

Yes of course, just looked at he diagram on Hope website, the one that is just ‘flat mount’ not front, looks correct.
Good point about the threaded post mount, so it isn’t that.

Lots of Al road bikes have mini posts but take flat mount callipers, which always look wrong! On my carbon road bikes the flat mount calliper is just that, totally flat against the frame.

There are 4 different Hope RX4+ callipers:

1. Post mount
2. 160mm front flat mount
3. 160mm rear flat mount
4. 140mm flatmount for front and rear.

The last can be used with adaptors to get you where you want in disc sizing.

Thanks Daffy

The replacement came this week and fitted. It is spot on thanks all. I was obviously concentrating so hard getting it right I ordered purple. I like it, it’s snazzy and it screams upgrade.
I did find a tiny brass washer at the end though, hopefully it’s not crucial.
Not ridden yet though as the dog is ill.

If the tiny brass washer is actually a copper washer, chances are it’s supposed to fit between the hose-barb and caliper fitting to provide a seal. Leave it out and you’ll probably end up with no brakes/fluid everywhere.

Shit on it.