Why does fuel economy get better on the highway, but EV range gets worse?
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Because combustion engines have a more efficient operating RPM, and the car is geared so that it operates near that ideal RPM at highway speeds.
For EVs, it usually isn’t necessary to have any transmission at all, so they burn more energy to beat the wind.
It’s a bit complicated, but there are three things that primarily affect the efficiency of combustion engines:
1. The inherent issues within combustion engines
2. Rolling resistance, which is more or less constant at all speeds
3. Wind resistance, which increases by the square of the speed. Thus the wind resistance at 50 m/s is 25 times greater than at 10 m/s, 112 mph and 22mph, respectively.
With EVs, the motor is more or less equally efficient at all speeds, so the wind resistance plays a huge role in lowering efficiency at higher speeds, whereas with combustion engines, the engine’s efficiency plays a larger role than wind resistance at highway speeds. In other words, you save more fuel by operating the engine at constant ideal ranges than you lose in fuel by beating the higher wind resistance.
It should be noted here that once you drive the car faster than the ideal operating range, you quickly become significantly less fuel efficient than the EPA rating on the sticker. Those tests are done in such a way that the car is tested at average highway speeds and that efficiency number doesn’t extend beyond that
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