I don’t know much (OK, anything, lol) about disc brakes, so can someone answer the following. People seem to talk about fitting bigger rotors, but what I can’t get my head around is if the calliper is mounted on the same mounts, then how come the bigger rotors don’t foul / miss the pads, as the braking surface would be further from the axle, but the callipers / pads would remain the same distance from it, if you see what I mean.

That’s what brake adapters are for

For a bigger rotor you use an adapter that moves the caliper further out.

different mounts for bigger/smaller discs

Aha, that makes perfect sense. I’d never seen these before, I’d seen IS to post type of adapers, but not ones for different rotor sizes. Thanks!