I saw this at Corner Carvers and found it quite informative.
http://www.motoiq.com/MagazineArticles/ID/3974/How-to-PROPERLY-select-and-size-TIRES-for-PERFORMANCE.aspx
chr
http://www.motoiq.com/MagazineArticles/ID/3974/How-to-PROPERLY-select-and-size-TIRES-for-PERFORMANCE.aspx
chr