Are internal combustion engines really most efficient at 55 MPH?

Factual Questions
21

[QUOTE=Una Persson]
My Mustang can cruise comfortably at 35 mph in 5th, unless I hit a steep hill…
[/QUOTE]

Manual or auto?
I doubt that your auto would be in 5th with the torque converter locked up at that low a speed.

22

[QUOTE=Exapno Mapcase]
Most states had at least a 65 mph speed limit at the time. The change was dramatic, but not strictly political. It was a sound conservation move that would be as important today.
[/QUOTE]

And yet, in later years, rather than saying that it saved fuel, they kept trying to force it down our throats because “55 saves lives!” (Nevermind that automotive fatality statistics have been steadily dropping no matter what the speed.)

23

55 didn’t make sense for those who live in the big square states, though - and was widely ignored, but making de facto criminals out of virtually everyone. To add insult to injury, the federal government used the “carrot and stick” approach to this, refusing to return tax dollars to the states unless they complied.

24

Since the cars have to be tested by the EPA to determine fuel mileage, won’t the manufacturers deliberately design cars that can ace the tests? I don’t know the EPA’s testing regime, but I assume that the highway portion is driven at 55mph because that’s the Federal limit.

25

[QUOTE=Una Persson]
My Mustang can cruise comfortably at 35 mph in 5th, unless I hit a steep hill…
[/QUOTE]
Maybe it can generate enough torque to do it, but it is probably not the most fuel-efficient gear for that speed.

26

Anecdotally speaking, I seem to get better gas mileage in my 2003 Neon SXT at higher speeds than 55 mph. Data averaged over several trips seems to indicate that I get the following:

Typical commute to/from work: ~25mpg
Typical visit to/from parents, avg. speed 55mph: ~30mpg
Typical long road trip, avg. speed 70mph: ~33mpg

The automatic transmission in my Neon won’t hit overdrive/4th until I’m cruising at 65mph+ on a level roadway, could that account for the differences?

These averages are over about 5000 miles worth of me paying attention to gas mileage on trips.

Any thoughts?