I spent many hours years ago working on designs that grew the wheels to 17, 18, 19 and 20 to a much better visually correct proportion. You will find most of the approaches grew only one area and in one case made the raised rib around the single hole thinner only increasing the hole size. The 17s and 18s looked good but the 19s and 20s became a bit to cartoonish. I ended opening up the 19s and 20s so they had the original design "flavor". Would the new 18" wheels be cast?