How do you measure wheel width of AMG's?
 

Can anyone advise as to the correct measurement points for measuring the width of my 18 inch 5 spoke AMG 230's?

I want to find out if I can go from 255 / 225 set up to a 265 / 235 set up and still use my existing rims.

You measure from where the bead of the tire seats against the rim.
Kinda hard to do accurately with the tire already mounted.
I don't see a problem increasing the sizes ( front & rear ), by only 10 mm. :)