So, about a year ago, I broke down and purchased a "new to me" Prius. A 2004 with all the bells and whistles from that year. Among these was a set of 17" rims that I was never really crazy about (I just didn't think they matched my car). So after a year of driving and getting low to mid 40mpg's, I told to my wife I wanted to swap tires with her car (also a Prius, but an '05) so I could test what the difference in MPGs would be. She said she didn't care, so I could do whatever I wanted. I swapped them between vehicles. My MPG went up, hers went down. I had half a tank with the 17's, and half with the 15's, and my MPG went up to 52mpg! She took a 1000 mile road trip, and her interstate MPG went down to 38 (normally mid to upper 40's)! Apparently the rolling resistance of those 17's was terrible.
She really hated the tires, and told me to give hers back, so I did... but not before I found a set of 15" Prius rims (from a 2010) and mounted some Bridgestone Ecopias to them :-). My first tank with the Ecopias came in at a whopping 64mpg! I am going to have to check a few more tanks, since it was a half tank (~250 miles) on account that we would be leaving on a trip. We currently have my car and are traveling on twisty, turney mountain roads in the middle of nowhere, so the next couple fill-ups may not tell much, but so far, EVERYTHING is better than it was. Road noise is reduced, acceleration in increased, tire mass is down, MPG is up (20% or more), the wife is happy, and I like the look of the new rims/tires on my car a lot better. If you are running 17's, just know, you could be paying an awful price for it!
