Driving faster decreases mileage?

[Diabolus Ex Deus]

Originally Posted by jimmy101_again

Simple perhaps, but wrong. The more you have the gas pedal depressed the faster the car is moving (at least while cruising)

I agree with what you're saying but I don't think my comment is completely irrelevant. If you're going faster, you're likely depressing the gas pedal further regardless. Simple mechanics. Gearing, etc comes into play for sure but I still say my comment is relevant.

[UrbanLegends101]

Originally Posted by Diabolus Ex Deus

I Simple mechanics. Gearing, etc comes into play for sure but I still say my comment is relevant.

Perhaps, but all the variables come into play only if comparing different vehicles. Two identical vehicles should have roughly the same MPG characteristics, but that isn't necessarily the point. Well, perhaps it is, when the claim that all vehicles get poorer fuel economy numbers above 55 MPH.

Perhaps looking at the original claim, and asking a somewhat different question. Are there any automobiles which get better fuel economy numbers at steady state speeds above 55 MPH? If 55 MPH is the fastest speed for the MPG peak, then there could be a claim that all vehicles get poorer fuel economy numbers at speeds above 55 MPH.

I think it would be nice to know if there really are vehicles which get better fuel consumption numbers at, say 70 MPH compared to 55 MPH. I realize that we will probably never return to the 55 MPH, and the typical 65-70 MPH limits are a concession to the somewhat higher fuel consumption numbers with the slightly shorter trip times.

I would suspect a detailed true speed to MPG graph would not be a smooth bell curve, but perhaps a series of mini-bell curves, as the engine speed goes from the lowest speed in each gear, an increase in the MPG vs speed for the gear to the maximum MPG and then back down as the engine RPM exceeds the RPM for that gear and can operate in the higher gear. Finally, in the top gear, there would also be a peak in MPG and then on the downside, as drag and internal friction losses increase to the maximum speed of the test.

[jimmy101_again]

Originally Posted by Diabolus Ex Deus

I agree with what you're saying but I don't think my comment is completely irrelevant. If you're going faster, you're likely depressing the gas pedal further regardless. Simple mechanics. Gearing, etc comes into play for sure but I still say my comment is relevant.

You are missing my point. If you are going faster that says nothing (or at least fairly little) about fuel efficiency. If you are using 2 gallons/hour going 60 MPH then that is still more efficient than using 1.5 gallons/hour going 30 MPH. In the first case you are getting (60MPH)(hour/2gallons)= 30 MPG, in the second case you are getting (30MPH)(hour/1.5gallons)= 20 MPG. In the first case you have the gas pedal depressed more than in the second case, but you are getting better MPG. Just because you are consuming fuel more slowly does not necessarily mean you are getting better mileage.

[David102]

Consider an SUV that gets 5MPG at 55MPH. Generating 60MPH you reduce 5MPG: that would provide you with 0MPG - the motor would eat all petrol you provided it as quick as you could add it in, and not go anywhere. Go another 5MPH quicker and you reduce another 5MPG, and the scenario turns around. If you could go 65, you now get adverse 5 MPG. For every 5 kilometers you generate, a quart of gas amazingly seems to be in your reservoir. 70MPH gives you 2 gallons of gas for every 5 kilometers you generate. . . . . . . .

We should all generate large gas unguzzling SUVs at insane rates of rate far above the lawful posted rate restrict and fix the power problems. . . . . . . . .

[hambubba]

In my '88 Ford Ranger, the 55 MPH speed limit was in force when it was manufactured. It definitely behaved worse at higher speeds. Now, I believe fuel economy is set for overall performance at all speeds. My Jeep gets no better than 19, and that is using a computer that adjusts EVERYTHING in the engine for performance, including timing. But, that's a brick on wheels!

I miss that truck... 24 mpg.