Quote:
Originally Posted by curtludwig
Your example has NOTHING to do with the rotational speed of the engine and EVERYTHING to do with the force needed to push the car through the air. Force required cubes with the square of speed. Less speed = less force, less force = less fuel. Your mileage will rise significantly at 65mph vs 75-80 mph.
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Your statement ignores the point of the question and fact that the efficiency of an internal combustion engine is dependent on RPM. Try to go cross country in 3rd gear .
My attempt is to optimize MPG at a given commuter speed of 75MPH. This speed is probably higher than what the vehicle was optimized for. (Probably 60 or something).
Since a 5th gear to lower RPM is out of question, the only remaining option is the overall gear ratio. After more than 3000 miles I know now that 12% taller tires help about 2-3%. on my MPG.