Can i use a PM to IS 203mm adapter designed for the front on the back?

Im not 100% sure that i can, but the front and rear calipers are identical post mount jobbies.

Cheers

Afraid not,same mount on front and back will require a 20mm bigger disc on the front.

…so you could with a 183mm rotor on the back to go with it. You’ve really go to be going some (and have fantastic rear tyre grip, else it just locks and skids like my 160mm one does) to need a 203mm rotor on the back too.

Already have a 185mm rotor, just thought i’d give it a try seeing as i have all the bits to do it now!