You are correct. Howevera 16-inch stock tire on a new Civic has as aspect ratio of 55 or 60, so my comment about aspect ratios below 45 holds true, even on a newer Civic. For these Civics, you can probably upsize to a 17without needing an aspect ration below 45. 18s are getting into the kidney-pounding range.

 

yeah, according to discount tire direct, a 17 inch rim on my car will use a 205/50/17. it has a better appearance than stock, but doesn't lose as much ride quality.