I will spare you the details, but I had to replace all my tires and wheels on my 2010 Prius "V" package. I was at the tire dealer and didn't have time to do research here at PriusChat or TireRack beforehand, so I had to reply on the salesperson to recommend a tire. All I knew was that I wanted Low Rolling Resistance because I had glanced at forum posts in the past. I went from the 17 inch factory stock rims and OEM tires to 16 inch Goodyear Assurance tires. I immediately took a 300 mile round trip trip that was 85% flat interstate. I kept the speedometer cruise control on 60-65 most of the time. Air conditioning on. Three people and luggage. I watched the trip computer move as high as 55.1 MPG. I got home, and it was 53.9 mpg and average speed of 54 MPH. I am astonished because I make this trip all the time and previous trips averaged between 43 to 47 MPG at the best. Up to now, I had NEVER broken 50 MPG average. Granted, I did drive steadier and slower than usual. But I have *never* gotten such good mileage. So, I have concluded that there must be something to these tires. I wonder how much of the increase is attributable to the size (diameter) of the tires versus the tire design. Anyway, I was just so happy about my mileage that I wanted to share the news with you.