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From a Truck Nut.
All of you are close to the answer. Part of the FE of a big rig is the frontal area to mass ratio. That part was dead on. The other item to consider is gearing. When you look at horsepower to weight, a typical semi has fewer horses per pound than a car but with 18 to 24 sppeds, the gearing lets them run the engine near its optimum specific fuel consumption rpm at any speed. Once they are up to speed and rolling, the engine is running near optimum rpm and very highly loaded for the engine size.
The penalty for that is, naturally, very poor accelleration. 0-60 in 25 seconds is pretty slow by comparison to any car.
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Truck Nut
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