I'd like to put the narrowest (with the least tred) tires I can on the bike I have right now using the rims that are already there. How do you determine what that size would be? Is there a formula? a chart? I have already gone down one size narrower and I remember the guy showing me an even narrower tire (I think my response was ...eeeek!....at the time, but I'm ready now) I'm also ready to do this myself. Also, any recommendations on online sites to buy tires from? - I'm just trying to get a little more speed and less friction for now. Shopping for a new bike - don't want to rush the decision. thanks so much.....