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I think warm up cycles per mile impacts mpg more than speed. This proves out in just about all of my rides.
Slow Down a Little, Save a Lot of Gas
- Thread starter Cory
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Originally Posted By: mechtech2
Going from 35 to 30 MPG is about a 16% difference.
16% of 3.25/gallon is only about $0.38, not $0.54.
The increase in fuel consumption is not directly proportional to the increase in speed. There's an equation involving exponents at work here.
Of course, their numbers could be off. I don't know how scientific their testing is. I'd like to see the EPA publish fuel economy values at various speeds for each vehicle during steady-state driving. They already have all the data they need to do it.
Going from 35 to 30 MPG is about a 16% difference.
16% of 3.25/gallon is only about $0.38, not $0.54.
The increase in fuel consumption is not directly proportional to the increase in speed. There's an equation involving exponents at work here.
Of course, their numbers could be off. I don't know how scientific their testing is. I'd like to see the EPA publish fuel economy values at various speeds for each vehicle during steady-state driving. They already have all the data they need to do it.
My general thoughts are that going 75 instead of 65 would be a 1/2-2 MPG difference, not 5.
I think it would depend on the amount of drag a car has, the "cd" that's quoted in many car magazines.
Something shaped like a brick will have a greater percentage of it's fuel consumption just moving the air out of the way if all other variables are equal for a car. While something more streamlined will have a smaller loss to drag.
So while that loss does increase in the same exponential fashion, if you start with a smaller number, it doesn't increase as much.
So I suspect the 14% figure tossed out is either a worst case figure, or some sort of average.
Just a hunch.
Something shaped like a brick will have a greater percentage of it's fuel consumption just moving the air out of the way if all other variables are equal for a car. While something more streamlined will have a smaller loss to drag.
So while that loss does increase in the same exponential fashion, if you start with a smaller number, it doesn't increase as much.
So I suspect the 14% figure tossed out is either a worst case figure, or some sort of average.
Just a hunch.
Originally Posted By: javacontour
I think it would depend on the amount of drag a car has, the "cd" that's quoted in many car magazines.
Something shaped like a brick will have a greater percentage of it's fuel consumption just moving the air out of the way if all other variables are equal for a car. While something more streamlined will have a smaller loss to drag.
So while that loss does increase in the same exponential fashion, if you start with a smaller number, it doesn't increase as much.
So I suspect the 14% figure tossed out is either a worst case figure, or some sort of average.
Just a hunch.
Lets put some limits on the problem. Assume the only drag is aero drag. Work to cover a given distance would be (75/65)^2=1.33 or a 33% increase. We know the drag isn't all aero drag, but if it were 1/2 aero drag, the number would be 16.5%, assuming mechanical resistance is directly proportional to speed. It would actually be a little less than that because the engine is working harder at 75 mph so should be operating at a bit higher efficiency.
14% is very believable.
Anecdotal economy numbers are often clouded by the fast that people tend to report the nominal cruising speed they drove on a trip and not count all the time they had to go slower because of traffic etc. If your nominal cruising speed is lower, you spend less time below nominal.
I think it would depend on the amount of drag a car has, the "cd" that's quoted in many car magazines.
Something shaped like a brick will have a greater percentage of it's fuel consumption just moving the air out of the way if all other variables are equal for a car. While something more streamlined will have a smaller loss to drag.
So while that loss does increase in the same exponential fashion, if you start with a smaller number, it doesn't increase as much.
So I suspect the 14% figure tossed out is either a worst case figure, or some sort of average.
Just a hunch.
Lets put some limits on the problem. Assume the only drag is aero drag. Work to cover a given distance would be (75/65)^2=1.33 or a 33% increase. We know the drag isn't all aero drag, but if it were 1/2 aero drag, the number would be 16.5%, assuming mechanical resistance is directly proportional to speed. It would actually be a little less than that because the engine is working harder at 75 mph so should be operating at a bit higher efficiency.
14% is very believable.
Anecdotal economy numbers are often clouded by the fast that people tend to report the nominal cruising speed they drove on a trip and not count all the time they had to go slower because of traffic etc. If your nominal cruising speed is lower, you spend less time below nominal.
Originally Posted By: mechtech2
My general thoughts are that going 75 instead of 65 would be a 1/2-2 MPG difference, not 5.
As noted previously, my wife and I both drive 100 mile round trips every day to work. I could easily see a MPG difference of 5mpg driving 65mph over 75mph. (We both drive mid-sized Chrysler 300M sedans) There is not doubt in my mind, probably because I've been keeping track of mpg for over 2 years. As steady as the gas prices have risen, I've done all I've could to counter it and stretch fuel economy.
FYI....Though the 300M is pretty streamlined, it's not light.
My general thoughts are that going 75 instead of 65 would be a 1/2-2 MPG difference, not 5.
As noted previously, my wife and I both drive 100 mile round trips every day to work. I could easily see a MPG difference of 5mpg driving 65mph over 75mph. (We both drive mid-sized Chrysler 300M sedans) There is not doubt in my mind, probably because I've been keeping track of mpg for over 2 years. As steady as the gas prices have risen, I've done all I've could to counter it and stretch fuel economy.
FYI....Though the 300M is pretty streamlined, it's not light.
Originally Posted By: oilyriser
. . . Driving slow also is kinder on your suspension components, electrical connectors, steering, and you're less likely to get black bagged after an accident.
And less likely to be caught by a cop or a red light/speeding camera, too.
. . . Driving slow also is kinder on your suspension components, electrical connectors, steering, and you're less likely to get black bagged after an accident.
And less likely to be caught by a cop or a red light/speeding camera, too.
speeding really takes its toll on my fuel tank.. never really noticed that until gas prices surged. now on the highway instead of 75-85 mph its 70-75 mph tops.. i save on gas! no kidding i bet i save a gallon or two a week just by going the speed limit.. its not so bad. i just set the cruise control, turn the radio up, and keep my middle finger against the driver window 
really i save about 5-10$ of gas week by slowing down just 5mph or more..
really i save about 5-10$ of gas week by slowing down just 5mph or more..
Originally Posted By: Cory
Originally Posted By: mechtech2
My general thoughts are that going 75 instead of 65 would be a 1/2-2 MPG difference, not 5.
As noted previously, my wife and I both drive 100 mile round trips every day to work. I could easily see a MPG difference of 5mpg driving 65mph over 75mph. (We both drive mid-sized Chrysler 300M sedans) There is not doubt in my mind, probably because I've been keeping track of mpg for over 2 years. As steady as the gas prices have risen, I've done all I've could to counter it and stretch fuel economy.
FYI....Though the 300M is pretty streamlined, it's not light.
This seems funny to me... you've done all you could to counter high gas prices and stretch fuel economy? How about buying a more efficient vehicle than a 300m? Especially considering you have two 100 mile round trips made every day.
Originally Posted By: mechtech2
My general thoughts are that going 75 instead of 65 would be a 1/2-2 MPG difference, not 5.
As noted previously, my wife and I both drive 100 mile round trips every day to work. I could easily see a MPG difference of 5mpg driving 65mph over 75mph. (We both drive mid-sized Chrysler 300M sedans) There is not doubt in my mind, probably because I've been keeping track of mpg for over 2 years. As steady as the gas prices have risen, I've done all I've could to counter it and stretch fuel economy.
FYI....Though the 300M is pretty streamlined, it's not light.
This seems funny to me... you've done all you could to counter high gas prices and stretch fuel economy? How about buying a more efficient vehicle than a 300m? Especially considering you have two 100 mile round trips made every day.
Well, if Cory's two Chryslers are paid for and running well, would it make sense to dump them and incur a new car payment just to save some more gas money? Maybe he meant he'd done everything *reasonable* to save on gas.
Moving closer to work, or working closer to home, would make more sense, but it might be impossible.
Moving closer to work, or working closer to home, would make more sense, but it might be impossible.
Yup, if you already have a ...well, somewhat _less_ fuel efficient vehicle, it likely won't make sense to buy a new (or even good used) more fuel efficient car to replace it. Not until gas gets well up past $5, anyway. Wait until it dies.
It is due to the car I drive, but in general, the intensity of my happy face is inversely proportional to the distance between the gas pedal and the floor. It's quite an enjoyable freedom, as the car is just fuel efficient enough that the extra money spent is worth it.
It is due to the car I drive, but in general, the intensity of my happy face is inversely proportional to the distance between the gas pedal and the floor. It's quite an enjoyable freedom, as the car is just fuel efficient enough that the extra money spent is worth it.
Originally Posted By: Saturn_Fan
Seems like there is a little doubt here about my 45.04 mpg in my 00' Saturn. It really happened, that is all I can say guys.
I don't doubt it. 45mpg at 60mph is very reasonable. I get 42MPG when I do 65-70mph in my 2.2L Ecotec (04 Sunfire). In Iowa doing 55mph-60mph on straight flat roads I averaged close to 50MPG on some trips.
Seems like there is a little doubt here about my 45.04 mpg in my 00' Saturn. It really happened, that is all I can say guys.
I don't doubt it. 45mpg at 60mph is very reasonable. I get 42MPG when I do 65-70mph in my 2.2L Ecotec (04 Sunfire). In Iowa doing 55mph-60mph on straight flat roads I averaged close to 50MPG on some trips.
Originally Posted By: rangerdood
This seems funny to me... you've done all you could to counter high gas prices and stretch fuel economy? How about buying a more efficient vehicle than a 300m? Especially considering you have two 100 mile round trips made every day.
If you're buying, I'm all for it!
It would take a very long time to pay for the new vehicle in just the difference in the gas it saves. Especially spring to fall when my 300M can achieve 30+mpg driving slower. 65mph to work which is slightly downhill and 60mph on the uphill return. Not as much traffic @ 9pm and 98% of it is freeway. Besides, the family's already asleep by the time I get home, nothing to rush home for.
This seems funny to me... you've done all you could to counter high gas prices and stretch fuel economy? How about buying a more efficient vehicle than a 300m? Especially considering you have two 100 mile round trips made every day.
If you're buying, I'm all for it!
It would take a very long time to pay for the new vehicle in just the difference in the gas it saves. Especially spring to fall when my 300M can achieve 30+mpg driving slower. 65mph to work which is slightly downhill and 60mph on the uphill return. Not as much traffic @ 9pm and 98% of it is freeway. Besides, the family's already asleep by the time I get home, nothing to rush home for.
Originally Posted By: Benzadmiral
Well, if Cory's two Chryslers are paid for and running well, would it make sense to dump them and incur a new car payment just to save some more gas money? Maybe he meant he'd done everything *reasonable* to save on gas.
Moving closer to work, or working closer to home, would make more sense, but it might be impossible.
Thank you. Yes, everything *reasonable* to save on gas.
Better driving habits to include the anticipation of future events, regularly checking tire pressure to include (nitrogen in the wife's car with TPMS), switching to synthetic motor oil & transmission fluid (also the benefit of extended OCIs), reducing any excess weight in the car (I could shed a few more pounds too
), and regular preventative maintenance to name a few.
Well, if Cory's two Chryslers are paid for and running well, would it make sense to dump them and incur a new car payment just to save some more gas money? Maybe he meant he'd done everything *reasonable* to save on gas.
Moving closer to work, or working closer to home, would make more sense, but it might be impossible.
Thank you. Yes, everything *reasonable* to save on gas.
Better driving habits to include the anticipation of future events, regularly checking tire pressure to include (nitrogen in the wife's car with TPMS), switching to synthetic motor oil & transmission fluid (also the benefit of extended OCIs), reducing any excess weight in the car (I could shed a few more pounds too
http://www.fueleconomy.gov/feg/driveHabits.shtml
EPA's MPH/MPG graph basicly is flat 35-60 mph and obviously does drop off after that. More aero cars do better at higher speeds, that was my premise with my RSX and Accord Coupe, because I do drive fast.
For now, I just employ the most appropriate mpg stragety and dont' cheat myself out of enjoying a normal pace. I don't hammer it unless I can maintain the momentum a while. I recall info that otto engines (or similar) are most efficient at a wide throttle plate opening. The trick seems to be anticipate any and everything and coast a lot. My new EPG is 21/31, I get 28-29 regularly and have got 32 iirc. Old EPA was 24/34
EPA's MPH/MPG graph basicly is flat 35-60 mph and obviously does drop off after that. More aero cars do better at higher speeds, that was my premise with my RSX and Accord Coupe, because I do drive fast.
For now, I just employ the most appropriate mpg stragety and dont' cheat myself out of enjoying a normal pace. I don't hammer it unless I can maintain the momentum a while. I recall info that otto engines (or similar) are most efficient at a wide throttle plate opening. The trick seems to be anticipate any and everything and coast a lot. My new EPG is 21/31, I get 28-29 regularly and have got 32 iirc. Old EPA was 24/34
The EPA numbers are just a guide. When it came out, I think, my big grey monster was rated at 19/27, and I better that by 2 MPG most of the time.
For those of you that don't believe this is possible; that driving 65mph vs. 75mph saves 15% in fuel economy (wind resistance being the main contributing factor). Then tell me how a light rain (another resistant factor) netted me only 27mpg going to work yesterday (64mpg) vs. the 32mpg obtained today at the same speed? A 15%+ loss on the rainy day as compared to today.
Cory - Like you stated, there is substantial resistance with the heavy water droplets in the air.
Also, a tire may slip a little [hydroplane] and thereby incur a loss.
How about wind? That is a contributing factor.
Your MAF sensor may be influenced by water vapor to read a bit differently, and maybe use more fuel.
Your exhaust pipe is much cooler, and will condense the exhaust gas and make it harder to push out - resulting in a net loss of engine efficiency.
There is additional cooling in the engine compartment, and if a cylinder head is cooler, it uses more of the available power from the fuel to heat the head [trying to reach homostasis] - this results in a loss of fuel efficiency.
If because of drag you have to give a slight bit more throttle, maybe your computer ignition timing and fuel map goes richer and allows less ignition advance, which would result in another loss of MPG.
Cooler tires may have more rolling resistance, as well.
There will be a bit of extra drag on the engine because of headlights and wipers being on.
Now, we have to figure out answers if someone's MPGs go UP in the rain!
Also, a tire may slip a little [hydroplane] and thereby incur a loss.
How about wind? That is a contributing factor.
Your MAF sensor may be influenced by water vapor to read a bit differently, and maybe use more fuel.
Your exhaust pipe is much cooler, and will condense the exhaust gas and make it harder to push out - resulting in a net loss of engine efficiency.
There is additional cooling in the engine compartment, and if a cylinder head is cooler, it uses more of the available power from the fuel to heat the head [trying to reach homostasis] - this results in a loss of fuel efficiency.
If because of drag you have to give a slight bit more throttle, maybe your computer ignition timing and fuel map goes richer and allows less ignition advance, which would result in another loss of MPG.
Cooler tires may have more rolling resistance, as well.
There will be a bit of extra drag on the engine because of headlights and wipers being on.
Now, we have to figure out answers if someone's MPGs go UP in the rain!
Also, tires are pumping water away and out of the sipes, which takes energy.
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