Rim size

[Junny]

how do you measure it?
i measured my 18s and they ended up to be 20 when converted....
*flame suit on*

[Not_An_Abba_Fan]

Bead diameter.

Don't really understand your post though? Your 18's turned into 20's?

[chrism182]

Check out this page - How to Measure Tire Rim Size | eHow.com

[Not_An_Abba_Fan]

They are incorrect in what they say the 205 and the 40 stands for. 205 is the sectional width of the tread area, not the overall width at the sidewall, 40 is the aspect ratio, 40% of the tyre width, not the sidewall height in mm's. In a 205/40R16, the 40 would represent 82mm.