BB. Chase and face that rascal while you're in there if it hasn't been done. Also, if you're way light, maybe consult with some other smaller people to see what they like and upgrade your tires (mini-rant: rider weight should be mandatory along with PSI in all tire threads). You might even do well on 20's if your normal rides are pretty good pavement. But ask someone else, I weigh over twice what you do.