Quote Originally Posted by dc2r
You guys are from ClubRSX so I know you know a lot. (I'm from there too). I just watned to clear a few things about the tyre numbers and wheel numbers. I'll take my tyres and wheels as example. 195/55/15 tyres and 15x6.5 wheels (I think).

195 is the tyre width. 15 is the rim diameter. 55 is the aspect ratio, but what is this exactly? I know it is a percentage of the tyre width, but what does it represent? Is this the thickness of the tread?

For the wheels, 15 is the diameter size, 6.5 is....? Is this the rim width? Please help me out here. Thanks guys.
195/55/15 - 15/6.5

As you said above. The 55 is the sidewall height (which is a percentage of the tyre width (ie 195).

The 6.5 is the wheel width and basically determines how wide a tyre (eg 195,205 etc) you can fit on it. This is in inches.