Better highway gas mileage at high speed

[JESSE69]

I get better mpg at 65 mph than 60 on my 99 Grand Caravan Sport. My 99 HX M/T seems to get the same mpg at 65 and 70 mph too.

[mini-e]

the odd thing is the only way i can go faster is to depress the gas pedal further, which would seen to indicate more use of gas, and a corresponding decrease in gas millage. i think airplanes get better millage just on the other side of the speed of sound, mayby it has something do do with that? huh.

[theholycow]

Originally Posted by mini-e

the only way i can go faster is to depress the gas pedal further, which would seen to indicate more use of gas, and a corresponding decrease in gas millage

You forgot to figure in the increase in speed. Sure, if you depress the gas pedal further and don't go any faster, then the more gas means less mileage; but if you're getting more speed for the extra gas, then it may or may not be better.

Taken to an extreme, you could idle along at 5 or 10 mph, using the least fuel your engine can use while still running, but you'll probably get better mileage at 30mph.

[mini-e]

Originally Posted by theholycow

You forgot to figure in the increase in speed. Sure, if you depress the gas pedal further and don't go any faster, then the more gas means less mileage; but if you're getting more speed for the extra gas, then it may or may not be better.

Taken to an extreme, you could idle along at 5 or 10 mph, using the least fuel your engine can use while still running, but you'll probably get better mileage at 30mph.

Oh, so there is a speed (or time) component to miles per gallon. I did not know that.

[thisisntjared]

1st 15mph headwind is considerable
2nd averages do not represent the same route with speed as the only variable.

test is inconclusive.

[dosco]

Originally Posted by mini-e

Oh, so there is a speed (or time) component to miles per gallon. I did not know that.

Yes. If you do some "dimensional analysis" you can conclude...

speed (mi/h)/volumetric fuel flow rate (gal/h)= mi/gal

If you think about it a little bit, it makes sense. Lets say for the sake of argument that your car burns .5 gal/h at 2200 rpm. If you compare lower speed (i.e. 2200 rpm in low gear) with high speed (2200 rpm in high gear) you will see that the mileage is impacted pretty significantly.

Which also makes it easy to see if you can maximize the time your engine is idling (using little fuel) while simulatenously maximizing distance travelled, P&G is a great way to improve mileage.

[mini-e]

Originally Posted by dosco

Yes. If you do some "dimensional analysis" you can conclude...

speed (mi/h)/volumetric fuel flow rate (gal/h)= mi/gal

If you think about it a little bit, it makes sense. Lets say for the sake of argument that your car burns .5 gal/h at 2200 rpm. If you compare lower speed (i.e. 2200 rpm in low gear) with high speed (2200 rpm in high gear) you will see that the mileage is impacted pretty significantly.

Which also makes it easy to see if you can maximize the time your engine is idling (using little fuel) while simulatenously maximizing distance travelled, P&G is a great way to improve mileage.

Silly me! All this time i thought mpg (miles per gallon) had to do with how many miles my car went on a gallon of gas! So under some circumstances, I can go more miles per gallon if i go faster?

[dosco]

Originally Posted by mini-e

Silly me!

Sorry dude. Wasn't trying to be a prick or anything.

So under some circumstances, I can go more miles per gallon if i go faster?

Well, you seem to have answered your own question. Not sure I have much more to add.

[SolidLiquidSnake]

Originally Posted by mini-e

Silly me! All this time i thought mpg (miles per gallon) had to do with how many miles my car went on a gallon of gas! So under some circumstances, I can go more miles per gallon if i go faster?

Haha, it doesn't have to be too hard for anybody to understand these things. I just like to know the basics and use a little common sense as well. My gallons per mile and miles per gallon and gallons per hour are all so interesting...

[mini-e]

Originally Posted by dosco

Yes. If you do some "dimensional analysis" you can conclude...

speed (mi/h)/volumetric fuel flow rate (gal/h)= mi/gal

If you think about it a little bit, it makes sense. Lets say for the sake of argument that your car burns .5 gal/h at 2200 rpm. If you compare lower speed (i.e. 2200 rpm in low gear) with high speed (2200 rpm in high gear) you will see that the mileage is impacted pretty significantly.

Which also makes it easy to see if you can maximize the time your engine is idling (using little fuel) while simulatenously maximizing distance travelled, P&G is a great way to improve mileage.

I think I am starting to understand. miler per gallon is not simply gallon/miles = mpg.

it is really:

speed (mi/h)/volumetric fuel flow rate (gal/h)= mi/gal