WIth a need to replace the wheels on the Passat searching for information on how wheel size influences fuel economy is my new pastime. Tire Rack has an article suggesting that "upsizing" to performance tires may cause an increase in rolling resistance. This seems to be logical. There is also the trade off in weight. Low-profile tires are lighter but the wheels they mount on are heavier than their 15-inch brethren.
If low-profile did better in the lab would not the Ford Focus have standard 17-inch wheels instead of 12- or 13-inchers? Another article from a trucking publication says "When low profile tires first came out, they were about 4 percent more fuel efficient." It concludes "With today's new tires, there is virtually no difference in mpg due to tire size." I'm leaning towards believing this. Apparently it is true for large trucks and if anything it seems smaller wheels may provide better economy. Certainly when it comes time to buy new tires the standard-sized option will be significantly cheaper. Added to the extra shock-absorbing and the possibility that the next pothole won't require a new set of rims and the idea looks pretty good.