Argument over speed vs consumption

skeptic_SA

skeptic_SA

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So the argument is that if you drive faster - you spend less time on the road as you get to your destination quicker (ergo fuel use is less per duration).

Sound principle?
 
How much time do you have and what's more important to you? Most of the time it's traffic blocking me...
 
skeptic_SA said:
So the argument is that if you drive faster - you spend less time on the road as you get to your destination quicker (ergo fuel use is less per duration).

Sound principle?
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Energy lost to drag increases as the square of speed. So as you travel faster, your fuel consumption per unit distance travelled increases exponentially.
 
Time is not a measure of fuel economy.

Otherwise it would be litres/minute instead of litres/km.

If your time is more valuable than what you spend to operate a car then you use an aeroplane.
 
Lupus said:
Kind of both you'll use more fuel sitting in 40 minutes of traffic to do two kilometres than you'll use sitting in 10 minutes of traffic to do 6km.
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You could spend an hour at the coffee shop while waiting for traffic to settle and then take ten minutes to do the two kilometres.

You’d have “wasted” 30 minutes but had a much better and more economical time for it.

Unfortunately the real world mostly doesn’t work like that and hence time isn’t a measure.

It should be though.
 
Driving ur vehicle on the highest gear with the lowest possible rpm gives u the maximum fuel economy.
 
joker08 said:
Driving ur vehicle on the highest gear with the lowest possible rpm gives u the maximum fuel economy.
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Not always.

There is a particular gearing/torque and aerodynamic drive ratio that is ideal but different for each car.

Gearbox and engine isn’t all a car is made of and even then some engines are more efficient at higher revs.
 
SauRoNZA said:
Not always.

There is a particular gearing/torque and aerodynamic drive ratio that is ideal but different for each car.

Gearbox and engine isn’t all a car is made of and even then some engines are more efficient at higher revs.
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I know, dint want to write a lengthy post so replied with the shortest answer
 
SauRoNZA said:
You missed the word consumption next to fuel.
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No I did not. More engine power = higher consumption regardless of distance traveled. If you drive in 4th gear you use more fuel vs 5th or 6th. Higher RPM consumes more fuel due to stationary combustion rate vs increased mean speed of piston. Ignition advance reduces the difference slightly but is not perfect.
 
Magnum said:
No I did not. More engine power = higher consumption regardless of distance traveled. If you drive in 4th gear you use more fuel vs 5th or 6th. Higher RPM consumes more fuel due to stationary combustion rate vs increased mean speed of piston. Ignition advance reduces the difference slightly but is not perfect.
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You forgot weight from your equation and the torque required to override it.

In a heavier load case a lower gear at higher revs can be more efficient than a higher gear at lower rpm due to the torque required to carry the load.

More power does use more fuel, more torque doesn’t necessarily mean the same. Which is why every car/engine will have a different ideal speed where it is more efficient as it’s likely where it makes the most torque.

Aerodynamics also come into play.
 
SauRoNZA said:
You forgot weight from your equation and the torque required to override it.

In a heavier load case a lower gear at higher revs can be more efficient than a higher gear at lower rpm due to the torque required to carry the load.

More power does use more fuel, more torque doesn’t necessarily mean the same. Which is why every car/engine will have a different ideal speed where it is more efficient as it’s likely where it makes the most torque.

Aerodynamics also come into play.
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I'm removing all those you mentioned from the equiation by keeping the speed the same. required power and torque remains the same, rolling resistance and wind resistance the same. Aero-dynamic effect only enter the equation from 100 - 120 Km/h depending on vehicle. Stay below that and the difference is negligible.
 
Faster. Yes. No. It depends what stops you in between point A and B. If there were no toll gates, stop streets, speed bumps, traffic lights, single lanes, trucks..... Yes. You will get there faster. Now you just get faster to what ever will hold you back so that which is behind you catch up.

Fuel use. There is an average. Too fast. More fuel. Little time difference. Too slow. More fuel. Big time difference. Average. Good.

That brings me to the final conclusion.


What matters is not how fast you get to your destination , but the journey in between. :D
 
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