It means (or should mean) that the length of top tube (center of head tube to center of seat tube, measured along top tube axis) is 22.5" (57 cm) and length of seat tube, from center of bottom bracket to center of top tube, measured along seat tube axis) is 23.5" (60 cm). Most people "size" bikes by seat tube measurement, but many feel that top tube length is a more important feature for proper "fit." A lot of this has to do with a person's ratio of limb length to torso length, which does vary quite a bit from "neonate" to "octopus"
Depending on how much seatpost you like showing, and how low you're willing to have your bars relative to saddle top, a 60 cm frame might fit someone from 5'-9" to 6'-2" tall. In earlier decades, people tended to ride taller frames, and then later shorter frames were more popular. The big issues are: a) how stretched-out will the top tube make you (can be adjusted somewhat with seatpost setback (change seatpost or move saddle back or forward) and stem extension (change the stem); and b) while the other is how long a seatpost do you have, and how comfortable are you straddling the bike when stopped (in most cases, I find that I never truly "straddle" but stand on one leg, with the other still clipped to opposite pedal).
Did I win the "most parentheses in one post" award?
Last edited by Charles Wahl; 07-11-09 at 09:26 AM.