Quote Originally Posted by jbhondatech
every 10mph over 60mph = a 4% reduction in fuel economy due to air resistance in the front and the vaccume effect in the rear. This is why racecars draft each other. Playing with your ignition timing can also increase fuel economy at certin rpms but reduce it in others this trick is realy only good for highway driving

More information on drag coefficients and such.

Realistically, the more important factor is how deep your foot is into the pedal through the course of the trip and how often you spend accelerating. If you want the best idea for saving gas: Get behind a big 18-wheeler, RV, or bus and shadow it. When you lose it and it turns off, find another. Oh, and try and drive at night, but make sure to get plenty of sleep and be well rested!