Smaller calipers on bigger rotors?

[Pavetim]

I'm gonna do a disc brake conversion with some stock parts on my obs. I was wondering though can i use a caliper from a 305mm rotor on a 345mm rotor or is the caliper actually bigger? Not sure if the actual pad contact area on a bigger rotor is bigger or just overall diameter.

[casey23]

almost anything works.. get the correct parts for the caliper and install them on the rotor and see how it sits... may have to adjust a little.. just dont want to to be to shallow. and only use half of the rotor...