That site is great . I also like to check the specs on the tire manufacturers site also cuz the actual size differs brand to brand. Plus the usually give rim width guide and mounted width on suggested width rim. What size wheel is on the front again? And for Pittsburg kid. The first 3 numbers on a metric tire is the section width from the widest point of the outer sidewall to the widest point of the inner sidewall. The next 2 numbers the aspect ratio are measured from rim to tread giving the sidewall height but the number 30 , 35, 40, 45. Ect are a the percentage of the first number (section width)