…..by which I mean can I run a Hope 183mm rotor on an Avid Juicy 7? Or are rotors somehow subtely different?

Try it and see.

ive got hayes rotors shitmano brakes, same wit avid brakes never had any problems tis only a piece of metal the brakes wont know the difference between brands..!

Well, the designs are subtly different but I’d imagine functionally identical. I’ve tried a few different discs with various brakes and not noticed much difference. I’d imagine the more drilled sections they have the more bite they’d have. Apparently they grooved profile on some discs is for better cooling.

hope rotors with shimano brakes and shimano rotors with hope rotors never had an issue

Anything will work in average scenarios. You might notice a difference on a 1.5hr decsent in the Alps. My advice is go for it. Worst case scenario is you waste £15. Try Woollyhatshop.co.uk

Thanks all. The reason I asked with Avids / Hope is that I have a spare Hope rotor! Cheers will give it a go.

the only reason not to use rotors from different brands is the width of the brake track. Shimano have a narrower braking surface than say hayes, so you shouldnt use a shimano rotor with hayes (you can but its not ideal) but you can use a hayes rotor with shimano as it will only use half the brake surface area. Think avid and hope might just work.

If it’s a floating rotor then be aware that the rivets will foul the pad’s backing plates when they start to wear. Also check that the pads don’t overlap the outer edge of the disc, if they do then the lips left after pad wear may butt together and stop the brake working properly.