How is it much more fuel efficient to travel at say 50 mph for longer than 70 mph for a shorter period of time. Like if I was going a set distance, if I drive slower I’m using the car longer so why isn’t it the same fuel being used.
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To add to what others have said, not only does air resistance scale exponentially with speed, but also engines have an optimal RPM efficiency, generally they’re the most efficient when the car is in the highest gear (giving the most mechanical advantage, and most distance traveled per engine revolution) and the lowest (or on the lower end) RPM to maintain the torque to stay in that gear. Balancing all of this, most cars are at peak efficiency when traveling at 50-60mph because they can be in the highest gear, and going faster would have much more air resistance.
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