Saw this posted on Motoiq.com this morning, and found it quite useful on how to choose the right size tire: http://www.motoiq.com/MagazineArtic...LY-select-and-size-TIRES-for-PERFORMANCE.aspx
Hopefully it'll be of use to some of you as well!
To sum it up, the author recommends choosing your tires before choosing your wheels so that you purchase wheels which are the same width as your tires or up to 0.5 inches narrower than your tires.