faster=better mpg
Joined: Sep 2006
Posts: 417
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From: S2KAtlanta
One major assumption that seems to be continuously quoted by the naysayers in this thread seems to be that if a person is quoting his anecdotal evidence that he got better mileage at Y miles per hour as opposed to X miles per hour, that the improvement is somehow expected to be linear and continue as you increase speed. I think that assumption is the most ludicrous of those put forth so far.
While I'd far rather test the mileage in real-world conditions at various speeds, it's still quite possible for the car to have a 'sweet spot' at a higher-than-average speed where the fuel-air mixture approaches the ideal and aerodynamic drag and rolling friction haven't yet completely negated the benefits of the leaner mixture.
This may very well result in better gas mileage as you approach, say, 80ish miles per hour, but then starts to rapidly take a nosedive as aerodynamic friction rapidly increases.
To satisfy my own curiousity, I'm going to hunt for gadgets that can measure fuel economy in a more accurate manner than reading the odometer at each fill-up...
Oh, another possible explanation that doesn't seem to have reared its head in the thread is the obvious: At slower speeds, you're more likely to drive with the top down, and at higher speeds, put it up.
I'd certainly imagine that to have an effect on gas mileage
While I'd far rather test the mileage in real-world conditions at various speeds, it's still quite possible for the car to have a 'sweet spot' at a higher-than-average speed where the fuel-air mixture approaches the ideal and aerodynamic drag and rolling friction haven't yet completely negated the benefits of the leaner mixture.
This may very well result in better gas mileage as you approach, say, 80ish miles per hour, but then starts to rapidly take a nosedive as aerodynamic friction rapidly increases.
To satisfy my own curiousity, I'm going to hunt for gadgets that can measure fuel economy in a more accurate manner than reading the odometer at each fill-up...
Oh, another possible explanation that doesn't seem to have reared its head in the thread is the obvious: At slower speeds, you're more likely to drive with the top down, and at higher speeds, put it up.
I'd certainly imagine that to have an effect on gas mileage 
Joined: Nov 2002
Posts: 2,063
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From: Durango, Colorado
Krenath:
Of course you are correct. I say I get better mpg out of my AP1 at 90 than I do at 60, which I do (with the top up). But in no way am I meaning to imply that I would get STILL better mpg at 140. To the contrary, I'm fairly confident that if I pushed her to 140, the mpgs would drop to Hummer levels! I say that I get better in-town mpg shifting at about 5K rpm or a little more, when compared with shifting at a lower rpm. But this does not mean that the mileage would improve even further if I shifted at 9K each time. I have little doubt that this would hurt gas mileage.
Your concept about a "sweet spot" is correct, IMO. And mpg will suffer both below and above it.
Of course you are correct. I say I get better mpg out of my AP1 at 90 than I do at 60, which I do (with the top up). But in no way am I meaning to imply that I would get STILL better mpg at 140. To the contrary, I'm fairly confident that if I pushed her to 140, the mpgs would drop to Hummer levels! I say that I get better in-town mpg shifting at about 5K rpm or a little more, when compared with shifting at a lower rpm. But this does not mean that the mileage would improve even further if I shifted at 9K each time. I have little doubt that this would hurt gas mileage.
Your concept about a "sweet spot" is correct, IMO. And mpg will suffer both below and above it.
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Joined: May 2005
Posts: 208
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From: San Antonio Texas
So what if we got 4.77 gears in a ap1?
It would be the same rpm as if you were cruising at 75-80mph but you would be going 65mph... so you can get the best of both situations; less drag and hit the rpm band a little higher (leaner engine)...
Or how about this? Or mabey 4.44 gears and go about 70mph instead of 65mph...
btw i really want 4.77 gears but I dont know if this statement would be true- i hope it is (i dont want to be wasting to much gas on the freeway, but by the wat that i am thinking right now i think i could actually save fuel )
It would be the same rpm as if you were cruising at 75-80mph but you would be going 65mph... so you can get the best of both situations; less drag and hit the rpm band a little higher (leaner engine)...
Or how about this? Or mabey 4.44 gears and go about 70mph instead of 65mph...
btw i really want 4.77 gears but I dont know if this statement would be true- i hope it is (i dont want to be wasting to much gas on the freeway, but by the wat that i am thinking right now i think i could actually save fuel
)
On a lucky day.
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Joined: Jul 2005
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From: Gie
Originally Posted by Krenath,Jan 29 2007, 02:01 PM
One major assumption that seems to be continuously quoted by the naysayers in this thread seems to be that if a person is quoting his anecdotal evidence that he got better mileage at Y miles per hour as opposed to X miles per hour, that the improvement is somehow expected to be linear and continue as you increase speed. I think that assumption is the most ludicrous of those put forth so far.
While I'd far rather test the mileage in real-world conditions at various speeds, it's still quite possible for the car to have a 'sweet spot' at a higher-than-average speed where the fuel-air mixture approaches the ideal and aerodynamic drag and rolling friction haven't yet completely negated the benefits of the leaner mixture.
This may very well result in better gas mileage as you approach, say, 80ish miles per hour, but then starts to rapidly take a nosedive as aerodynamic friction rapidly increases.
To satisfy my own curiousity, I'm going to hunt for gadgets that can measure fuel economy in a more accurate manner than reading the odometer at each fill-up...
Oh, another possible explanation that doesn't seem to have reared its head in the thread is the obvious: At slower speeds, you're more likely to drive with the top down, and at higher speeds, put it up. I'd certainly imagine that to have an effect on gas mileage
While I'd far rather test the mileage in real-world conditions at various speeds, it's still quite possible for the car to have a 'sweet spot' at a higher-than-average speed where the fuel-air mixture approaches the ideal and aerodynamic drag and rolling friction haven't yet completely negated the benefits of the leaner mixture.
This may very well result in better gas mileage as you approach, say, 80ish miles per hour, but then starts to rapidly take a nosedive as aerodynamic friction rapidly increases.
To satisfy my own curiousity, I'm going to hunt for gadgets that can measure fuel economy in a more accurate manner than reading the odometer at each fill-up...
Oh, another possible explanation that doesn't seem to have reared its head in the thread is the obvious: At slower speeds, you're more likely to drive with the top down, and at higher speeds, put it up.
I'd certainly imagine that to have an effect on gas mileage I'm making an effort to shift around 4500 RPM on this particular tank of gas. I rarely break 65 in my daily commute and I think staying out of 6th gear altogether will actually help to improve my fuel mileage. I'm sure everyone else has noticed it, but the engine "feels" about 1000x better at 4500 RPM than at 3500 RPM.
A fairly accurate flow meter could be placed in the fuel line to take real-time readings at various highway speeds in various gears. Should provide enough evidence to clear up this issue.
"not it" on performing the test.
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Joined: Mar 2005
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I say I get better mpg out of my AP1 at 90 than I do at 60, which I do (with the top up).
So what if we got 4.77 gears in a ap1?
It would be the same rpm as if you were cruising at 75-80mph but you would be going 65mph... so you can get the best of both situations; less drag and hit the rpm band a little higher (leaner engine)...
Or how about this? Or mabey 4.44 gears and go about 70mph instead of 65mph...
It would be the same rpm as if you were cruising at 75-80mph but you would be going 65mph... so you can get the best of both situations; less drag and hit the rpm band a little higher (leaner engine)...
Or how about this? Or mabey 4.44 gears and go about 70mph instead of 65mph...
-b
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From: Gie
I still think that one of the main reasons that people think that better mileage is to be obtained at some higher speed than 50ish miles per hour (other than the fact that its probably true ) is that there is SO much more data supporting the case for high speed mileage. Who drives sustained speeds of 50-55 MPH? No one. Almost all travel at sustained speeds on highways is in the 65-85 range. I'm not really familiar with an area of the country that has long straight roads with 50-55 mph traffic. Sustained highway speeds are where you will experience best mileage so its no suprise that more data is around to support the high speed case.
) is that there is SO much more data supporting the case for high speed mileage. Who drives sustained speeds of 50-55 MPH? No one. Almost all travel at sustained speeds on highways is in the 65-85 range. I'm not really familiar with an area of the country that has long straight roads with 50-55 mph traffic. Sustained highway speeds are where you will experience best mileage so its no suprise that more data is around to support the high speed case.
Joined: Nov 2002
Posts: 2,063
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From: Durango, Colorado
Instead of going 90 in 6th, if I drive at a slower wpeed in 5th, my mpg will actually suffer. Fuel consumption per hour will remain about the same, but miles traveled will be less. So when I calculate mpg, it will be less.
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Joined: Mar 2005
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Instead of going 90 in 6th, if I drive at a slower wpeed in 5th, my mpg will actually suffer. Fuel consumption per hour will remain about the same, but miles traveled will be less. So when I calculate mpg, it will be less.
-b
