Best fuel economy speed
What speed are you folks seeing your best mileage ? When I was towing it was not always the low end of the range.
Forum Discussion
Airstreamer67 wrote:
Mr. Mark's data follows the physics involved: the faster you go, the more fuel you use. After about 45 mph, it's the wind resistance and related aerodynamics of the vehicle that determine the fuel economy differentials.
Right. But this is still very interesting. At any reasonable speed highway speed, mileage decreases as a function of speed. Lots of data are available for cars (e.g. here: https://www.fueleconomy.gov/feg/driveHabits.jsp). Since a major part of the equation is wind resistance (drag) (Drag = 1/2 * density * area * drag coefficient * speed-squared), one would think the mileage-versus-speed effect would be even greater for big boxy vehicles like a motorhome. Based on the posts above (Mr.Mark shows about .5 mpg decrease for each 5 mph above 55; tyoungs reports Cat and Cummins as .1 mpg loss for every mph, both of which agree), though, the speed penalty works out to about 1.4% decrease per mph at the low end to 1.7% per mph at the higher end. If my math is right, that's only about double the speed penalty reported for cars (which is 0.6% to 1% over the same range). I would have thought it would be more than that, but the data indicate otherwise. Very interesting.
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