Is there data somewhere on optimal mph for fuel savings for the average sedan or by each car? I'm assuming it's basically the slowest you can maintain a decent rpm in the highest gear, but curious where that falls for different models.
In general your otto-cycle (diesel is different) engine is most efficient at full throttle near its peak torque. However, this is far more power than is needed at cruise.
So the lowest speed your highest gear can go?
Not quite. First, engines are so powerful that you’re probably well in a range dominated by aerodynamic forces. With modern 10 speed transmissions you are probably several speeds too high.
Like I said, it depends on the car, you’d have to test it on an empty flat country road. But I’d guess 50 kph or less.
I’m a pretty staunch Republican, but Jimmy Carter was a great president. And his 55 mph interstate speed limit is the most sensical fuel economy policy of any president.
Modern engines change the fuel air mixture if you go full throttle to give you extra power at the expense of efficiency. You really need to look at the engine spec to find the most efficient operations regime.
