From your equation it follows that you get the largest contact patch with a flat tire, but that's not the same as "optimum". Maybe one of those tire and wheel outfits can help, like:
http://www.tirerack.com/tires/index.jsp
Enter "tires" into
www.google.com and you'll get lots of sites to try. You could email your question to them, and please post what you find out.