I have read that for every 10 degree F drop in temperature, aerodynamic drag increases by 2%.
Jaeger, I find it hard to believe that you see little or no difference between winter/summer fuel economy.
Do you not drive in slushy roads, use winter tires, use the electrical systems more in winter eg:lights (less daylight, rear window defroster, heater blower motor, heated seats/mirrors , windshield washer pump , or warm your car.
I read that just bad road conditons (snowy/slushy) can effect FE as high as 50%, and cold temperatures effect FE up to 13%.
You got some amazing tips on wintertime FE you can share?