Originally Posted by
nat3r
but how do i find out if it will fit in my frame?
That one, actually, is more of a trial and error type thing. A lot of the time it will have to do with your brakes more than your frame, and even then the actual size of the tire assigned to a given number can vary from one manufacturer to another. Just in general, I'd say most bikes will at least be able to clear a 28 or so. You should be fine with anything at or below that. As a rule, thinner = higher pressure = less rolling resistance but harsher ride, whereas wider = lower pressure = more rolling resistance, but more cushy. I prefer 23's, and they're more or less the standard for racing, but plenty of folks opt for the comfort of a slightly bigger tire. It's all a matter of personal preference.