I've got that mix too but it seems the CO2 is increasing ever so slightly each year!

My first full tank with the Michelin Pilot Exalto A/S tires came in at 52.03 miles per gallon, down slightly front the last tank's 52.86 and the previous tank's 54.72. The heat is on full steam in Denver, nearly 100 every day, so that too is contributing. Overall thus far the loss seems fairly minimal. The alingment done at the installation of the new tires showed both front and rear to be within tolerances, though they did align to bring them in a bit closer.

The install was done at Sears Auto Center in Westminster, Colorado.

1978 Plymouth Horizon - 165,527 miles, still the longest lasting
1985 Dodge Daytona - 62,500 miles and the transmission gave out
1991 Mazda Protoge - A very good car
1997 Ford Contour - This one saved my life in a driver side impact accident
2000 Pontiac Grand Am - I have a bulls eye painted somewhere, this one was rear-ended
2004 Civic Hybrid - My first Honda, My first Hybrid, ran 88,300 miles before the tax rebates came calling
2007 Civic Hybrid - Going strong and a joy to drive
___________________________________________

That is consistent with my experience. After about 3-4000 miles the mileage jumped up about 21%.

I was going to get the Michelin Exalto's but changed my mind after checking with Consumer Reports which rated highly on the Michelin X Radial as having excellent LRR. Got about 500miles on them and getting a few miles per gallon better than the old Dunlops, but I also had the rear control arms replaced so that might factor into the numbers. Tires are at 32psi, gonna bump it up to 38psi next week to see if I can squeeze out a few more mpg's. Tires are a lot quieter than Dunlops but they tend to break loss easier on turns after a stop. 80K mile warranty also is not too bad. $440 out the door from Costco, just missed their $60 off sale, which could of got me in for $380. The Michelin X Radial is only available at Costco and Sam's Club if anyone is interested.

I replaced my Insignia SE's with Goodyear TripleTred and mileage has not changed enough for me to notice. Still getting over 50MPG on my highway 46mi/day commute

I bought these to have good traction in the Winter.

based on my san diego driving environment and what i need from a tire, i'm going to replace my oem dunlops with the kumho solus kr21, which was rated #2 in standard touring all-season tires on tirerack. i was going to go with a costco tire, but all of the tires they offer are at least 3lb heavier.
http://www.tirerack.com/tires/tires....del=Solus+KR21

Note to Self: Stay out of assist!