i know what the numbers means when they say 245/45 18" etc etc.
but i don't get when they do this 18"/8.5
it's hard to explain.. i know what it is..

but what i would like to know is.. 18"/'8.5' what does this 8.5 mean, like what is the limit of the wheels that can go on? does it have to do something with the 245mm? what is the maximum limit of the mm to go on a 8.5.

please give me a quick lesson, me very new at this.
say for 18"/8.. what would be the maximum tire size?
please teach me

 

The 8.5 is the width or the "fatness" of the rim. So that would be 8.5 inches wide. A rim that is 18x9.5 would be 9.5 inches wide.

 

There is none. Tire manufactures recommend various size tires for various size wheels.