COPIED FROM MY OLD POST A COUPLE DAYS AGO.
"To help you understand tire sizes, let me give you my example
My toyo at2 is 285/70/17.
1- This is the width of the tire in millimeters. The conversion is 1"= 25.4mm so for our example: 285/25.4= 11.22" width.
2 - This part is the "aspect ratio" of the tire and is a relation of the tire's width to the sidewall height of the tire. My example is '70'. This means the sidewall height is 70% (.70 in calculation) of the width of the tire. (this part of the math i don't know lol)
^edit: 11.22 x .70= 7.85
3 - Your wheel size. (i say wheels...since rims are on motorcycles...its like when people say headers when theres only 1...my pet peeve)
In conclusion, a 285/70/17 equates to 11.22 wide and is (7.85x2)+17"= 32.71" tall, or basically equivalent to a 33x11.50R17 if we can call it a standard size.
BUT.....the real measurement takes place once the tire is on the wheel and set to psi. then you could use a measuring tape. mine came up to 32 tall, and a lil over 11 wide taking real measurements for my procal setting."