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My car is a Citroen Xsara coupe 2000.

I am little tight financially at this point and I try to save money from everywhere I can...

I was wondering what is the ideal speed for my car to achieve the best MPG during my way to work which is 21km... My first assumption is to go in 5th (highest) gear at give or take 1500 RPM...

But I've read online that cars achieve the best MPG at speeds around 55mph... But I can't think of a reason why my car would achieve better MPG running at higher RPM on the same gear, in order to reach 55mph.

What is the recommended approach?

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    $\begingroup$ Can you do 55mph all the way to work? $\endgroup$
    – Solar Mike
    Aug 1, 2021 at 12:07
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    $\begingroup$ key to best mpg tends to be to brake as little as possible rather than to reach the best aerodynamic speed - it doesn't do you any good to accelerate to 55 before having to brake all that away before a stop sign. $\endgroup$
    – Abel
    Aug 1, 2021 at 15:22
  • $\begingroup$ If you are really interested in this search on "hypermiling". $\endgroup$
    – Eric S
    Aug 1, 2021 at 17:38
  • $\begingroup$ Don't race to stop at a red light. Try to drive without stopping. Waiting for lights to change is burning fuel while you're stationary. Look ahead & notice what the traffic & any traffic lights are doing, try to anticipate what the lights will do by the time you get there & if possible adjust you speed, particularly slowing down, to get there while they are green. Adjust your speed by taking your foot off the accelerator & not putting it on the brake. $\endgroup$
    – Fred
    Aug 2, 2021 at 4:43
  • $\begingroup$ If you leave five or ten minutes earlier, do you get significantly less traffic? That would help with driving in a more relaxed style, with less braking needed. $\endgroup$ Aug 2, 2021 at 17:23

3 Answers 3

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When you hear the engine roaring, it is guzzling a lot of gas. don't do that. When you brake to correct your excessive speed you are wasting all the gas burned to give you that speed.

In traffic don't drive like New York taxi drivers, constantly putting your foot on gas then brake pedal.

Try to create some space between you and the car in front of you( not as big as encouraging fellow drivers to claim it) to avoid having to be jerked forward and back to stay in a formation with them.

Have your engine tuned and tires inflated with correct pressure.

All of the above are common sense, only require discipline.

Not only do you save gas, but you also add years to the life of your car.

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If you really want to get into details, such as optimal RPM and aerodynamics, it might get complicated. Every engine has an optimal "operation" RPM, where it runs most efficently, this means that the engine will produce the most amount of torque at the minimum cost of fuel. You can probably find this information online which is sometimes provided by the manufacturer or measured by car enthusiasts. I found it for my Audi A4 2011, 2.0 TDI which was about 2200 RPM in 6th gear.

Aerodynamics are somewhat more difficult to account for, since weather might change during your trip or on different days of the year. But in general a good estimation of the fuel consumption can be measured on most cars by their own on-board-computer. If you take all the other answers into account and start measuring your fuel consumption, you can get a good estimate of what RPM and drive-style gives you the most MPG.

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The biggest circumstance is CONTROL YOUR SPEED. Air resistance (drag) increases with the square of speed, and therefore the power needed to push an object through air increases with the cube of the velocity. So....a vehicle needs 8 times the engine power to reach twice the speed. In principle, this means that fuel consumption will increase fourfold. if you lower the speed, fuel consumption is decreased by the full 75%. How fast are you going? If you're on a major highway, AVOID going above 90 km/h.

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