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Old 04-02-2012, 11:47 AM   #11 (permalink)
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F.O.R.D - '87 Dodge Dakota LE

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Originally Posted by Sven7 View Post
Unless it's really gusting I don't really pay attention under the logic (?) that the MPG gained with a tailwind will be lost with a headwind, averaging the entire trip anyway. Is this true? If there is a 20mph wind going south and I drive north to the store at 50mph and back south at 50mph, wouldn't it be roughly the same average MPG as going 40mph up and 60mph back?
Assuming a no wind situation, absolutely not. As speed increases, so does the resistance produced by wind. This can be calculated if you know the drag coefficient and frontal area of your car. This, along with gear ratio, engine displacement, and RPM can be used to determine the absolute most efficient speed that you should travel. The average accross the United States is 55MPH, which is why it has been proposed to once again lower the speed limit on interstates to 55 - to save gas as a nation. However, there are those small cars, like a honda civic, or toyota corolla, that have a maximum efficiency at 67MPH, and the Ram 3500's that should be going 35. This broad range equals 55, but is not compatible with everyone.
The point is, that 40mph may be too low for you, and you are losing efficiency due to rolling resistance, but 60 may be too high, and efficency is lost in air resistance. Unless you have the specific numbers, a little bit of common sense can be used, but not to the point of 100% accuracy. 50MPH both ways is most likely the best route, but 40, then 60 is not the same at all.

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