Gas mileage observations

After changing to Goodyear Comfortreds about 45 days ago, I noticed that my MPG dropped about 2-3 mpg per tank of gas. Nothing dramatic since I've never been below 46 and 52 was the best tank numbers I have generated in my 15 months of ownership of an '05 package 5. Last week I noticed the tires looked under inflated. Sure enough each tire was down at least 5psi (I run 42-40 psi). After correcting inflation I drove 400 miles and the MFD shows 53.4 average MPG! Lesson learned: pay attention and pay le$$ at the pump!