Originally Posted by Eurofordfan
In talking with a professional wheel / tire shop -- and the principal who I consider to be a pretty decent source of accurate info -- he said go out of your way to stay with the stock ET value. He had had direct experience, decreasing the ET value (i.e. decreasing the back-set) on his shop vehicle. It went from tracking really well, to a circumstance of very poor steering.
In my direct experience on my own cars, it only makes a huge difference in steering feel and tracking if you change the offset drastically. like changing your offset by 2 inches to get that hellaflush look.
Most folks would not even notice a difference if the offset changed 10-15mm. I havent done the math but im guessing the track width alone on all the new 2012 focus tire options varies by at least that much or more.
a little lower offset if you are upgrading wheels is not a big deal. You get a wider track width. If you are having tracking issues, check your alignment, it may be within spec but that hardly means its accurate or straight.