What is the fuel efficient speed for a car?

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  • 1 decade ago
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    At low speeds, your fuel efficiency is dominated by the friction in running the engine. At high speeds, your fuel efficiency is dominated by aerodynamics.

    Therefore, your fuel efficiency starts at zero when parked with the engine running, rises rapidly at first, and begins to decline when aerodynamics and wind drag begin to dominate the resistance function. At very high speeds, fuel efficiency drops rapidly as a number of nonlinear factors collide to prevent increases in speed without massive increases in fuel consumption.

    The equation is even more complex, because your car is tuned to run well in a certain RPM band, and above a certain RPM level engine friction increases significantly, while below a certain RPM level your engine's combustion recipe may not be running optimally. Therefore, gear ratios and tire sizes come into it as well (as these affect the ratio of engine speed to vehicle speed).

    In the 70s, 45 mph was a typical speed for peak fuel efficiency. In modern cars 55-60 mph will be a typical number for peak fuel efficiency. If your car gives you real-time fuel efficiency, you can try several speeds on a flat road with little wind, and try to see where your vehicle configuration has the best fuel efficiency.

  • 1 decade ago

    The speed at which the fuel consumption is at a maximum for the power demands placed by the instantaneous driving conditions....

    Hard to do with regular autos with basic 3 or 4 speed transmissions. Adding a Continuously Variable Transmission (CVT) lets a car approach this condition over a broader speed range...

  • 1 decade ago

    The lowest speed consistent with the word "transportation". The air resistance to the auto's motion varies as the cube of the velocity. The faster the vehicle, the greater (by the cubic) the wind resistance, and the less mpg

    One should always drive down-hill with the wind coming from behind.

  • 1 decade ago

    It depends on the car, but ususally it is between 35mph and 55mph. My non hybrid Honda Civic HX (lean burn) seems to do the best between 40 and 50mph in 5th gear.

    Air resistance increases at the square of the velocity. That means a car going 80 has 4X the drag of a car doing 40.

    Hope this helps.

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  • 1 decade ago

    You need to refine the question. Do you mean mpg as the measure of efficiency or do you mean horsepower produced versus energy available in the fuel consumed?

  • 1 decade ago

    In a boat it is the cruise speed . in a car it varies but it may be available from the manufacturer. the important factor is engine rpm

  • 1 decade ago

    Depends on the car. Probably near 55mph.

  • 1 decade ago

    it's different for different cars depending on engine power/transmission ratio, etc.... but it's usually between 35 to 45 mph in top gear.

  • JAMES
    Lv 4
    1 decade ago

    Low speed costantly.

  • Anonymous
    1 decade ago

    55 mph

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