I figured it out once, and the actually difference between a 170mm crank and a 175mm crank is something miniscule like .4"... I don't think it really makes as big a difference as some might lead you to believe. As for cornering clearance, if you are going hard into a corner, your inside leg is probably up anyways, so it doesn't really matter if you have 167's or 180's... they won't strike.