I was giving actual numbers reported by my SGII...12 and 16 horsepower at 60 and 80 mph respectively, which fit a similar curve to the Prius on the chart.
Maybe I'm missing something, but I think most of the horsepower used at 60 mph is just keeping the engine up to speed, with only a few additional needed to overcome rolling resistance and aerodynamic drag at that point, so you're starting with maybe 3 or 4 horsepower in the equation, not 12.
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