[MikefromOhio]

I have 4 months of driving nearly 75 miles one way to work every day through both a 55 MPH construction zone and normaly 65 MPH highway zones that would show you otherwise.....it surprised me too. There is not much of a difference......

[Paladin2]

If it's a gasoline engined vehicle with an auto trans, the difference may be relatively small as the engine operation with more throttle is more efficient which tends to mask the extra energy necessary to push the air out of the way faster.

If the energy fraction used for things other than pushing air out of the way is relatively large (A/C on, fat tires, disk brake drag at all four corners, heavily preloaded bearings, power steering and automatic hydraulic pumps, heavy vehicle, etc.), then the percentage effect is also reduced.

[Paladin2]

If it's a gasoline engined vehicle with an auto trans, the difference may be relatively small as the engine operation with more throttle is more efficient which tends to mask the extra energy necessary to push the air out of the way faster.

If the energy fraction used for things other than pushing air out of the way is relatively large (A/C on, fat tires, disk brake drag at all four corners, heavily preloaded bearings, power steering and automatic hydraulic pumps, heavy vehicle, etc.), then the percentage effect is also reduced.

[rkhampton]

The only thing that I can possibly suggest is that in going through the construction zone at the lower speed, you are constantly accelerating and decelerating, somewhat. What I said only holds true at constant highway speeds. If that doesn't explain it, than like you, I am rather surprised at your results, because at a 20 mph difference, the air resistance would definitely affect things.