[Diesel_Dave]

I did a little more number crunching and found that the air density changes about 0.5% for every 2 degrees F. The aero drag is directly proportional to the density, so we can account for 1/2 of the change in fuel economy due to increased drag. The rest must be due to the longer warm ups, increased rolling resistance, and other factors.

Yesterday was the warmest day of the year here so far (66 deg F). I was giddy at the thought of being able to drive home! I smashed my evening commute record. My previous record had been 40.6 mpg on a 94 deg day. Yesterday I got 41.9 mpg, with the help of a 10 mph tailwind. Boy, I can't wait for summer!