After about 35,000 miles on my 2009 Prius Touring my dealer suggested that the car needed new tires. He had the Yokohamas on sale and a quick check on the web indicated that these should be good for the Prius so I agreed to have them installed. After they were installed I noticed an improvement in handling, but my gas mileage plunged about 10% or 4 mpg. I was stunned and called Yokohama customer service who said it might take 1-2K miles before the tires settled down. I now have about 2,500 miles on these tires and the gas mileage is still down between 5-10% depending on the type of driving. I'm wondering if the problem is the tires or something else. The dealer checked the inflation pressure and said it was exactly what Toyota recommended. He did not recommend increasing it above the factory spec. They also did an alignment when the tires were first installed and I'm wondering if they messed that up and it somehow had this effect on the gas mileage. If the problem can't be resolved I may ask for the dealer to exchange the tires for something else, even though I like the handling these tires provide. Has anyone had similar problems with the Avid Envigor or after a wheel alignment? Any suggestions on what I should ask for if they agree to exchange these tires?