8

As the question title says.

I am a new driver and I understand that driving at higher RPMs can burn more gas faster. However getting to a destination longer would mean you were spending gas at a longer period of time.

Are there any scientific explanations? Do I save more getting to the destination faster?

My Car is Honda Mobilio (1.5 Gasoline Engine)

  • This is bordering on a driving question which brings the close hammer down. Are there some edits you can make to the question to get the information you desire? – DucatiKiller Feb 10 '16 at 0:31
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    @DucatiKiller what details would you like to know? – Jomar Sevillejo Feb 10 '16 at 0:35
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    Your question is a driving technique question, I'm suggesting you modify it to take out driving technique and modify it so it does not get closed. – DucatiKiller Feb 10 '16 at 0:37
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    I see. Thanks Ducat, basically, what I need to know is if getting to the destination quicker would save more gas compared to driving slow at lower RPMs. – Jomar Sevillejo Feb 10 '16 at 0:40
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    That version should fly. :-). – DucatiKiller Feb 10 '16 at 0:48
7

In a perfect world from a physics textbook, you might be able to ask the question you have, and expect to compare time vs. engine speed, but there are many more factors in the real world.

The speed-agnostic measure is Miles Per Gallon (or l/km). Speed doesn't appear in the name, because it doesn't matter. At higher speeds, things like wind resistance and your tire's rolling resistance have a noticeable effect on fuel consumption. If a car gets 21 MPG @ 80mph and 28 MPG at 50mph, the implication is clear - higher speed decrease fuel economy.

The US television show Mythbusters did some hypermiling (trying to get the best MPG at all costs) tests as outlined in this article and found that 45mph is generally the best speed for decreasing fuel consumption.

  • I have heard 45-50 from other sources as well. This is the speed where aerodynamics starts to play a large role. Before this point, wind resistance is basically negligible. Most vehicles have gearing to be efficient at about 50mph. – rpmerf Feb 10 '16 at 19:58
  • Mythbusters.. Those guys just clear out a lot of things. link was very useful. Just one question though, is there anyway to apply hyper miling even on parts you have to climb a hill? Do I save gas If I target 45 - 50 before going up hill and trying to maintain that? I travel to meet clients and am wondering how I can cut down gas cost. – Jomar Sevillejo Feb 10 '16 at 23:43
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    @JomarSevillejo, on a hill your constanly pushing the car against gravity, and it's going to be your highest fuel consumption scenario. One tip that I didn't see the Mythbusters mention (maybe they did) that will help on hills and every where else is to use the cruise control as much as possible. The car's fine adjustments to the throttle will be much more precise than your foot pressure. You can easily and almost unintentionally speed up and slow down (wasting fuel) while the cruise control will only use as little throttle as it can to maintain speed. – JPhi1618 Feb 11 '16 at 13:54
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A lot of that depends on the type of vehicle, and your definition of 'fast'.

Take this with a grain of salt, but a while back BBC's Top Gear did a test involving a V8 powered BMW M3 and a Toyota Prius. The Prius was driven as fast as it could go around their test track, while all the M3 had to do was keep up. After a few laps, the Prius had done ~18 mpg, while the M3 achieved ~20.

There are several factors that could have caused this:

Obviously, the M3 is much faster than the Prius in a straight line, so while the Prius was buzzing it's little 4-banger engine to redline, the M3 could trundle along at half throttle, short-shifting, and never having to use more than a small fraction of its power.

When the Prius approached a corner, it slammed on the brakes, scrubbing all the speed it worked so hard to achieve, so it could round the corner on its tiny, low grip eco-tires. The M3, on the other had, could coast into the corners, and retain much more speed due to its large, grippy, performance oriented rubber. The suspension setup also provided the M3 with better cornering performance, while the soft suspension on the Prius was more comfort oriented. Same goes for weight distribution/center of gravity, aerodynamics etc.

Using the brakes has a direct, negative effect on MPGs, as you are essentially turning the gas you just used to speed up into heat energy in the brakes. In everyday driving, this generally lends benefit to slower drivers. When that light you were speeding toward turns yellow, you have to slam the middle pedal and waste all that gas you used getting to 50 mph, while grandma back there had only accelerated to 15 before coasting to a stop right next to you.

  • Of course the other advantage that the M3 had in this test is that they had it following closely behind the Prius so the Prius had to punch its way through free air and the M3 effectively has a Prius creating a "tunnel" through the atmosphere for it. – Steve Matthews Jul 23 '18 at 15:16

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