Found another way to save on gas.

[JanGeo]

I said this before - the diameter / radius from ground to center of the tire will increase when you add more air but that will not change the circumference of the tire. All you are doing is reducing the flat spot on the tire contact patch. The tire will still have to travel the same amount if it was under inflated or over inflated to make one revolution. The steel cords do not stretch with more air pressure.

Compensating for speedo error in my ScanGauge results in an odometer difference of about 11 miles in 400 miles traveled or about the 3% that I adjusted the ScanGauge speed by.