Rim Size with Big Brakes?

So I just picked up a new runner, ('07 Limited 4x4) and it's got 18's on it right now. I haven't sold my 2wd yet, and have the same suspension setup, so I shouldn't have any issues clearing my old runner's tires. My problem, however, is that the 2wd has 17" rims, and afaik, big brakes won't get cleared by a smaller rim. What indicates the bigger sport brakes? Is there an obvious size difference at a glance? Do 18s clear the big brakes and 17s don't? Or is it 17's and 18's that do and 16's that don't? Probably a dumb question, probably gonna get chastised for not searching hard enough, but I literally just needed a break from studying Physics to write this lol.

Thanks in advance