This question is always in my head and I cannot find a firm conclusion to it.

If I move a disc brake caliper from front to rear or vice versa, how do I adjust rotor size?

What I have tried to put a rear caliper design for 160mm rotor size and put it to the front. It ended up fitting a rotor of 185mm on front.

With calipers like Avid, I can change the adapter to fit it easily. But some calipers like Magura or Hope, you cannot esp if you want to go from large to small.

Has anyone tried similar things and have an answer to this?

I am thinking of putting a caliper design for 8" rotor (205mm) on front to the rear of a bike.

Thanks