I know this sounds wrong, but I just got back from my first longer drive with my winter tires (Michelin X-Ice) and got 27.9 MPG overall. This is my second winter with the car, and don't usually get over 25 or so on a highway trip in the winter, with winter gas that usually has ethanol in it. It was a 300 mile round trip, clear roads, no wind to speak of. The winter tires are 205/65s on a 16 inch rim, as opposed to the 225/55s on a 17 inch rim that is stock, and I have the winters up to about 38 psi. I really wasn't expecting it to be so good, actually wouldn't have been too surprised if it had gone down a bit. Maybe the pressure and narrower tread patch helped?