Well, I went out with my new bike pump today to test out the effect of tire pressure on rolling resistance. Tire pressure for the first test was 32 psi, and for the second test, it was 37 psi. I used a big spring scale for measuring grain that I inherited from my grandpa, a Kansas farmer.
Either time, the force required to get the car to move was 58 pounds. I know flat tires make a car harder to push (enough to feel the difference), and I also know the top end should be less dramatic. I'm anxious to try pressure out when I'm back to making repeated trips to and from school every day, since there was no effect here.
Maybe there's another way to test this...
Lifetime Fuel Economy: 39.49 mpg
View my fuel log here: http://ecomodder.com/forum/em-fuel-log.php?vehicleid=717