Originally Posted by
Cdst
The reason I was looking at used was to find carbon wheels.
Wanting to pair a rim brake bike with carbon wheels in this day and age is an odd purchase criterion when you'd literally be wearing through a structural component of the wheels (and if you intend to buy the wheels used, they probably already are worn, woohoo). Besides the restriction on tire size that many have already pointed out, the choice also limits your inner tube options (no latex if you want to avoid the risk of a blowout from overheating) and tubeless (which works better at higher volume, lower pressure). I guess if you never plan to brake or are OK with treating your wheels as disposable, knock yourself out. Not exactly as "maintainable" as you seem to imagine pursuing deprecated bike tech to be, though.
I'll probably run 25s but having the option for 28s would be nice as I don't think I would get a wheelset that could fit something that narrow for the gravel bike.
Uhh, what? Literally any 700c disc brake wheelset with the right hub spacing for your gravel frame would fit, and there are an enormous amount of options for road wheelsets -- anything with internal rim width under 23mm which was nearly every road wheelset in existence until wider rims got popular in the last few years.