Some sizes you only have a handful of LRR sizes and some quite a few more. One size in particular takes the cake with 43 different LRR models to choose from, the 205/55/16. I have seen these on the front end of a 911 to the front end of an Eclipse GSX which of course is much heavier, and is still in use on new cars decades later. Another thing to consider is tire cost, not just mpg, and when there is more to choose from the cost goes down. I guess there is something to be said about a tire size such a wide variety of engineers continually choose.
So like the heading questions, when you weigh in tire cost it may be more than the fuel savings.
http://www.tirerack.com/tires/TireSe...erformance=ALL