Quote:
Originally Posted by Grovsnus
75 mph is also far above the maximum speed that the EPA tests are done with, and will incur higher fuel consumption than lower speeds. I'm surprised you got as good results as you did.
A non-car-specific EPA estimate is that if you get 32 mpg doing 50 mph, you'll only get 23 mpg doing 75 mph.
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I think that's very old math. Many years ago, Road & Track calculated the ideal cruising speed for each car, based on drag coefficient, frontal area, gearing and the power curve. I used the calculated 72 mph for my CRX Si to justify plenty of speeding back in the day.
Having had access to a car fleet in Germany, I can say that an E39 525i got 22 mpg at 130+ mph and not much better when staying under that speed. It took ages to get there, but I was always surprised that it returned decent mileage at such high rpm. It would have never achieved over 30 mph like that chart shows, so the taper to 130 on that chart would have you expecting about 1 mpg at 130.