I have found over time that my 4cyl 5 speed gets the best mpg at 50-55 mph. Cars like BMW and luxury cars nowadays have more gears in the auto trans and get better mileage at higher speeds (they also have better aerodynamics). I'm talking about highway driving of course. In stop-and-go traffic, you need to stay off the gas pedal. Accelerate slowly and anticipate red lights. You will infuriate many other drivers doing this though

 

There's usually a balance. In the city, it's very possible you can get WORSE mpg by accelerating too slowly. I'm talking crawling, so this isn't a justification for smoking burnouts...

 

I am not sure about the best speed, but I do know that traveling downhill with a tail wind always afford the best MPG... that is why I plan all my trips that are down hill... both ways..

(sorry, I couldn't resist)

But back on subject.. I think normally 55 to 60 is the best general speed for MPG.. over that the efficency to convert power of motion forward vs air drag that increases expontentionally with speed over 60

I have heard it takes twice as much engery to push thru air at 70mph compaired to 50mph

 

I am so glad that I don't worry nor really care what my gas fuel consumption is on my cars. As long as I can afford the cost of the gas is my only concern .

 

While the above is true, it ignores the fact that engine efficiency (as measured by Brake Specific Fuel Consumption or BSFC, lower is better) improves, to a point, as the output levels rise. So, while any given vehicle may well require more power to push through the air at 70 versus 50, it is also true on many vehicles, that engine efficiency is so much better at the 70 mph speed as to more than offset the extra drag.

 

My observations on a 2000 EX mt, is to keep the rpm's between 2.8K and 3.0K.

 

jet...I think that's the optiomal engine speed in most engines... I guess for engine speed optimal findings.. find the Horse power curve and the torque curve and there they interesct at the highest on the graph should be the best RPM effiency. (sorroy for spelling.. I am getting tired)
brian B