U.S. drivers should think in gallons per mile

http://news.yahoo.com/s/nm/20080619/sc_nm/fuel_efficiency_dc

CHICAGO (Reuters) - If soaring gasoline prices have prompted you to look for a more fuel-efficient ride, using miles per gallon as a guide could lead you astray, U.S. researchers said on Thursday.
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Instead, they propose a new standard based on gallons per mile, which gives people a far better idea of how much gasoline they might save by switching trading in that gas-guzzling minivan.

"There is a math illusion here," said Richard Larrick, a management professor at Duke University, whose research appears in the journal Science.

Larrick said most people think improvements in miles per gallon are all the same, where a 5 gallon per mile improvement would yield the same gas savings in a car that gets 10 miles per gallon or 20 miles per gallon. (One mile equals 1.61 kilometers, and one U.S. gallon equals 3.79 liters.)

"The reality that few people appreciate is that improving fuel efficiency from 10 to 20 miles per gallon is actually a more significant savings than improving from 25 to 50 miles per gallon for the same distance of driving," Larrick said.

He tested this out in a number of different experiments on U.S. college students.

When presented with a series of car choices in which fuel efficiency was defined in miles per gallon, the students could not easily identify the choice that would result in the greatest gains in fuel efficiency, he said.

People had a much easier time when fuel efficiency was expressed in gallons per 100 miles. In that case, a car that gets 18 miles per gallon uses 5.5 gallons of gas per 100 miles, and a car that gets 28 miles per gallon uses just 3.6 gallons per 100 miles. With gasoline prices over $4 a gallon, that's a difference of about $8 per 100 miles.

"If we just turn everything around, you can see where are the large savings in gallons of gas," Larrick said in a telephone interview. The idea is not new. Many other countries, especially in Europe, already use a standard that compares gas used per trip.

To translate miles per gallon into gallons per 10,000, Larrick said people can simply divide 10,000 by miles per gallon. Cars with the highest miles per gallon are always the most fuel efficient, he said. It is when people are trying to replace a car that they may be misled.

That's how he became interested in this problem.

"We were trying to decide whether to get rid of a minivan and go for a station wagon versus getting rid of a sedan and going for a really high-mileage hybrid car," Larrick said.

"We realized in the end we were better off trading in the minivan and only gaining 10 miles per gallon then we would be trying to swap out the sedan for a highly efficient car."

To help make these choices easier, Larrick and colleagues recommend consumer publications and car makers start listing fuel efficiency in terms of gallons per 10,000 miles driven, which he said is roughly the distance people in the United States drive in a year.

Larrick's team has developed a conversion table that can be found at http://www.fuqua.duke.edu/news/mpg/table.pdfgallon.

um. Im smart enough to figure it out myself thanks.

Wow, it took "research" to figure this out? Its really sad how people in America have stopped thinking for themselves and figuring things out and trust so much on the media to tell them what they should do when it comes to cars. I guess its easier to have someone else do the research for you than to do it yourself and know your getting the right info. Though, I prefer the cost per mile method since there you will find out real quick which vehicle is cheaper to drive. This is why I have been using 30% E85 with 70% 87 octane in my Mustang. I get about a 2mpg hit from it, but the cost per mile is half a cent cheaper than running straight 91 octane.

He tested this out in a number of different experiments on U.S. college students

These must be the same ipod jamming geniuses that I almost run over every day because they think the proper way to cross the street is to just step out there and trust that the traffic will stop.

Ok, so what? I really don't think a lot of people are going to keep a 10MPG car and trade in the 25MPG car right now, even for a 50MPG car. They'd trade in the 10MPG car for the 50MPG car. OMG even better savings!?

The reality that few people appreciate is that improving fuel efficiency from 10 to 20 miles per gallon is actually a more significant savings than improving from 25 to 50 miles per gallon for the same distance of driving

In either case you're cutting your cutting yoru current gas bill by 50%...sure the dollar amounts are higher going from 10mpg to 20mpg so the delat is higher. This article is stupid :lol:

Our mileage (kilometreage?) ratings up here are in litres per hundred kilometres, but it still doesn't make as much sense to me. Perhaps because I grew up with miles per gallon so that's how my brain is hardwired. But I like knowing that if I have 2 gallons of fuel left in my tank, that I can go 60 miles before I'm empty. If I had to think in gallons per mile, or litres per hundred kilometres, it's not nearly as straighforward.

Our mileage (kilometreage?) ratings up here are in litres per hundred kilometres, but it still doesn't make as much sense to me. Perhaps because I grew up with miles per gallon so that's how my brain is hardwired. But I like knowing that if I have 2 gallons of fuel left in my tank, that I can go 60 miles before I'm empty. If I had to think in gallons per mile, or litres per hundred kilometres, it's not nearly as straighforward.

I've NEVER understood the liters per hundred kilometer use. It has to be one of the dumbest ways to measure fuel usage. I could really care less how much fuel it takes to drive 100 kilometers (or miles, or whatever unit of length you want to use). It's only important if you are going to drive exactly that distance all the time. It's FAR easier to use how far I can go on a single gallon of gas, then divide the distance by that, and that's how much fuel you use.

I don't get it. The proportional differences in the different figures for different cars are identical whether you divide miles by gallons or gallons by miles.

Example:

Car #1 gets 30 miles per gallon.
Car #2 gets 20 miles per gallon.

30 divided by 20 is 1.5. (150%) Car #1 clearly goes one and a half times as far on each gallon. Going the other way, 20 divided by 30 is 0.667, or 66.7%. Car #1 uses 66.7% as much fuel as Car #2.

Converting to their "new" method:

Car #1 requires 3.33 gallons to go 100 miles.
Car #2 requires 5 gallons to go 100 miles.

5 / 3.33 = 150%
3.33 / 5 = 66.7%

Same figures as before, same meanings, same significance.

This is ridiculous.

Fuel usage isn't about percentages - it's about actual volume (cost) consumed. Therefore, it's much more useful to improve mileage from 12.5 MPG to 25 MPG than it is to go from 25 MPG to 50 MPG. In the both cases, the percentage improvement is the same, but the absolute improvement in the first case is substantially higher than the second for the same distance driven.

Fuel usage isn't about percentages - it's about actual volume (cost) consumed. Therefore, it's much more useful to improve mileage from 12.5 MPG to 25 MPG than it is to go from 25 MPG to 50 MPG. In the both cases, the percentage improvement is the same, but the absolute improvement in the first case is substantially higher than the second for the same distance driven.

Yep.

I sit and ponder that folks get far more worked up about the costs involved in driving a vehicle than they do about their home and the costs it generates.

So little concern seems to cross the divide, as it were. Specifically, how many cost concerned or environmentally sensitive folks harp on house size?

How many who are rushing away from an SUV in the driveway have a similar crusade to get out of their non fuel efficient domicile and move to a smaller residence?

Even Al Gore clings to his huge house...

I'll grant that the housing market has taken a hit, but it wasn't over air conditioning bills.:eek:

In regards to the article from the original poster...

Diminishing returns. What a concept.

I sit and ponder that folks get far more worked up about the costs involved in driving a vehicle than they do about their home and the costs it generates.

So little concern seems to cross the divide, as it were. Specifically, how many cost concerned or environmentally sensitive folks harp on house size?


In defense of the McMansion crowd (my wife and I with our little 1100 sq. ft. home probably don't qualify for inclusion), home efficiency has made such huge improvements since the 70s that its far outstripped the improvements in automotive fuel economy. As bad as cars may have been in the 70s, apparently homes were far worse!

That's not to say that smaller homes wouldn't be far better, however, and I certainly find humorous that people buy a 3000+ sq. ft. home for 3-4 family members, and then install a few CFLs and park a Lexus RX400h hybrid SUV in the driveway in an attempt to be "green".

Cars with the highest miles per gallon are always the most fuel efficient, he said.

:lol: Brilliant!

Fuel usage isn't about percentages - it's about actual volume (cost) consumed. Therefore, it's much more useful to improve mileage from 12.5 MPG to 25 MPG than it is to go from 25 MPG to 50 MPG. In the both cases, the percentage improvement is the same, but the absolute improvement in the first case is substantially higher than the second for the same distance driven.

Okay, but how does representing those figures in gallons per 100 miles change the perception of the figures?

The only difference I see is that lower is better, rather than higher is better. I think people tend to understand "higher is better" more intuitively than the alternative. Plus, once you get really low, the numbers become a big pain. Today's most efficient cars are using <2 gallons per 100 miles (on the highway). The Volt will get <1 gallon per 100 miles.

So will we, in fifty years, need to adjust our unit of measure again (to gallons per 500 or 1000 miles)?

Miles per gallon suffers no such inconvenience.

Our mileage (kilometreage?) ratings up here are in litres per hundred kilometres, but it still doesn't make as much sense to me. Perhaps because I grew up with miles per gallon so that's how my brain is hardwired. But I like knowing that if I have 2 gallons of fuel left in my tank, that I can go 60 miles before I'm empty. If I had to think in gallons per mile, or litres per hundred kilometres, it's not nearly as straighforward.

Well, the article is telling people to think in terms of gallons per mile. The metric system of fuel consumption is the same thing, except it's litres per kilometre. And so that you don't work with strange fractions, it's multiplied by 100, so what you get is litres per 100 km.

For example, 10 L/100 km is equivalent to 23.5 mpg. The metric system is easier to follow when doing $$$ calculation, although you can get into fractions, such as 6.8 L / 100 km, and so on.

Anyone who was raised on the metric system finds it very easy to work with fractions - multiply by 10 or 100 in your head to get rid of fractions. You can use percentages as well, you can treat 8.4L / 100 km as 84%, and if you need to drive 400 kms, you just do 84% of 400, which is 84 x 4 = 376, and this tells you you'll need 37.6 litres to drive 400 kms if your car consumes 8.4L/100 km.

It's a rather simple system that makes sense across everything, since it's all base-10. It is rather difficult to work with measurements that are not consistent, such as 12 inches in 1 foot, 3 feet in one yard, 1760 yards or 5280 feet. Then you get absolutely retarded US vs Imperial, and so on.

A litre is a litre in Burma as well as Chile.

Edit: the metric system was developed to get rid of chaos otherwise common in measurements. It was scientific progress. The question is, why are there people still resisting progress and insisting on sticking to old ways of doing things? Mars satellite that slammed into the red planet did so precisely because someone decided to do things in the English system of measurement rather than metric.

I do admit, since (nearly) all car magazines sold here are American, the miles per gallon is something I have gotten used to, though I still prefer the metric system.

Okay, but how does representing those figures in gallons per 100 miles change the perception of the figures?


Because making a 10% improvement in mileage on a 15 MPG vehicle is much more meaningful than making a 10% improvement in mileage on a 45 MPG vehicle - but it's not all that easy to see this if we look at the window sticker. The 15 MPG vehicle goes to 16.5MPG, while the 45 MPG vehicle goes to 49.5 MPG - the latter looks better to many buyers, but someone who drives 15,000 miles/year will save 91 gallons/year with the first vehicle but only will save 30 gallons/year for the second.

To be honest, though, I thought that new-car window stickers already had some indication of average fuel consumption (either gallons per year or dollars per year at an assumed per-gallon cost - I cant remember which).

Today's most efficient cars are using <2 gallons per 100 miles (on the highway). The Volt will get <1 gallon per 100 miles.

So will we, in fifty years, need to adjust our unit of measure again (to gallons per 500 or 1000 miles)?

Miles per gallon suffers no such inconvenience.

Hence the beauty of the metric system. Let's say a car gets 50 mpg. That's 4.70 L/100 km. If the car that VW developed gets 1 L /100 km, that's 235 mpg. You can see that litres per 100 km works over a large range of mpg, and the gallons per mile is a rather strange way of computing at this point.

I've NEVER understood the liters per hundred kilometer use. It has to be one of the dumbest ways to measure fuel usage. I could really care less how much fuel it takes to drive 100 kilometers (or miles, or whatever unit of length you want to use). It's only important if you are going to drive exactly that distance all the time. It's FAR easier to use how far I can go on a single gallon of gas, then divide the distance by that, and that's how much fuel you use.

The metric system is a very versatile system, and I am a firm believer in it. Litres per 100 km measurement is to indicate a car's consumption of fuel. However, it can be converted into how many litres will be required for the trip rather easily by those who grew up on it or those who can do math in their head, since it's base 10. The difficulty is the initial change.

Because making a 10% improvement in mileage on a 15 MPG vehicle is much more meaningful than making a 10% improvement in mileage on a 45 MPG vehicle - but it's not all that easy to see this if we look at the window sticker. The 15 MPG vehicle goes to 16.5MPG, while the 45 MPG vehicle goes to 49.5 MPG - the latter looks better to many buyers, but someone who drives 15,000 miles/year will save 91 gallons/year with the first vehicle but only will save 30 gallons/year for the second.

To be honest, though, I thought that new-car window stickers already had some indication of average fuel consumption (either gallons per year or dollars per year at an assumed per-gallon cost - I cant remember which).

Interestingly, if you use the gallons per mile system or the metric system, percentage improvement is easier to spot and identify accurately. Since 10% of a lesser number is smaller than that of a bigger number, it eliminates confusion as to which is the bigger accomplishment (and thus money saver).

Because making a 10% improvement in mileage on a 15 MPG vehicle is much more meaningful than making a 10% improvement in mileage on a 45 MPG vehicle - but it's not all that easy to see this if we look at the window sticker. The 15 MPG vehicle goes to 16.5MPG, while the 45 MPG vehicle goes to 49.5 MPG - the latter looks better to many buyers, but someone who drives 15,000 miles/year will save 91 gallons/year with the first vehicle but only will save 30 gallons/year for the second.

Eric, you've latched on to the fact that I used percentages in my first post. It's beside the point and is not what I'm asking about. :)

I still don't see how using the gallons / 100 miles (or liters / 100km for that matter) makes the gravity of the change more apparent.

In defense of the McMansion crowd (my wife and I with our little 1100 sq. ft. home probably don't qualify for inclusion), home efficiency has made such huge improvements since the 70s that its far outstripped the improvements in automotive fuel economy. As bad as cars may have been in the 70s, apparently homes were far worse!

That's not to say that smaller homes wouldn't be far better, however, and I certainly find humorous that people buy a 3000+ sq. ft. home for 3-4 family members, and then install a few CFLs and park a Lexus RX400h hybrid SUV in the driveway in an attempt to be "green".

Thanks for catching my drift, as it were...

Sometimes I feel as if some of my commentary is akin to a dog howling at the moon, and little more.;)

...

I have no problem with the metric system; my post was complaining about measuring fuel consumption by volume/distance instead of distance/volume regardless of the system. But it's probably a personal preference thing.

I was brought up as Canada was switching systems so I was taught a bit of both. But since my family was obviously imperial-minded, I had a natural tendency to learn that, especially being on a farm. And of course we'll never completely get rid of imperial measurement since some of them define standards that cannot be easily changed, e.g. 4x8' sheet of plywood, 16" wheels, etc.

The metric system is a very versatile system, and I am a firm believer in it. Litres per 100 km measurement is to indicate a car's consumption of fuel. However, it can be converted into how many litres will be required for the trip rather easily by those who grew up on it or those who can do math in their head, since it's base 10. The difficulty is the initial change.

It has nothing to do with the metric system. I love the metric system (went to school for engineering, most everything you do is in metric rather than imperial). My problem is with the idiotic L per 100 km. Put it into km/L and be done with it.

I can figure out how much fuel my car is going to consume in my head with km/L (or mpg, I can use both systems with no problem) information in about 1 second. All you need to do is take the distance you are going to drive and divide it by the km/L (mpg). If all I have is a L per 100km, then I have to take the time to convert it km/L, then divide. It's an even more complicated equation if you want to take L per 100km into mpg.

The only way L per 100 km makes sense is if I'm going to drive 100 km, or an easily divided number of 100 km, such as 50 km, 200 km, 400 km, etc. Not quite so easy to calculate how much fuel you are using when you just drove 137 km. Not to mention the difference between city driving and highway driving. L per 100 km is just a very poor way of representing fuel usage, no if, ands, or buts about it.

It has nothing to do with the metric system. I love the metric system (went to school for engineering, most everything you do is in metric rather than imperial). My problem is with the idiotic L per 100 km. Put it into km/L and be done with it.

I hope I am not coming across like i'm jumping on your case :) :cool:

This whole L/100 km is metric, it's what the metric world uses, and the liquid volume and distance measurements are both metric.

I can figure out how much fuel my car is going to consume in my head with km/L (or mpg, I can use both systems with no problem) information in about 1 second. All you need to do is take the distance you are going to drive and divide it by the km/L (mpg). If all I have is a L per 100km, then I have to take the time to convert it km/L, then divide. It's an even more complicated equation if you want to take L per 100km into mpg.

The only way L per 100 km makes sense is if I'm going to drive 100 km, or an easily divided number of 100 km, such as 50 km, 200 km, 400 km, etc. Not quite so easy to calculate how much fuel you are using when you just drove 137 km. Not to mention the difference between city driving and highway driving. L per 100 km is just a very poor way of representing fuel usage, no if, ands, or buts about it.



If the only way the metric L/100 km makes sense to you is in 100 km intervals, you're probably confused about the L/100 and the interaction of that number with distances. As I said in my other post, it's not complicated. Example. You need to drive 664 kms (413 miles)? You car consumes 7.8 L per 100 km (or gets 31 mpg)? Multiply 7.6 by 6.64. Don't have the calculator? Approximate 8 x 6.5. Just as you'd use a calculator when dividing 413 miles by 31 mpg (or approximate 400 / 30). Either way (mpg to gallons or l/100km to litres) is rather simple math.

As for the need to convert L/100 km into mpg or the other way around, it's not necessary unless measurements are given in one system and you're used to the other system.

The only way L per 100 km makes sense is if I'm going to drive 100 km, or an easily divided number of 100 km, such as 50 km, 200 km, 400 km, etc. Not quite so easy to calculate how much fuel you are using when you just drove 137 km. Not to mention the difference between city driving and highway driving. L per 100 km is just a very poor way of representing fuel usage, no if, ands, or buts about it.

Wait, so you can easily divide arbitrary numbers by your MPG, but you can't divide 100 by anything but its common multiples?

Eric, you've latched on to the fact that I used percentages in my first post. It's beside the point and is not what I'm asking about. :)

I still don't see how using the gallons / 100 miles (or liters / 100km for that matter) makes the gravity of the change more apparent.

OK, let's ignore percentages for a moment. Which saves more gas per year - improving from 15 MPG to 20 MPG (+5 MPG), or going from 40 MPG to 100 MPG (+60 MPG)? OK, you're going to dig out your calculator and figure it out. The average mouth-breather won't, though.

OK, let's ignore percentages for a moment. Which saves more gas per year - improving from 15 MPG to 20 MPG (+5 MPG), or going from 40 MPG to 100 MPG (+60 MPG)? OK, you're going to dig out your calculator and figure it out. The average mouth-breather won't, though.

It can't really be figured out since someone who gets worse MPG might not be inclinded to drive as many miles as someone who gets really good MPG ;).

Wait, so you can easily divide arbitrary numbers by your MPG, but you can't divide 100 by anything but its common multiples?

No, but which is easier, having to do 1 calculation to get your solution, or having to do 3-5? I don't frequently carry a calculator around with me, unless you count my cell phone, which I hate using to calculate anything.

And L/100 km might be metric, but so is km per L. The type of measure determines if it is metric or not, not the manner in which you express it. If a car gets 10 km per Liter of fuel, thats a far better way of expressing it than in the equivalent L/100 km (don't know what it is off the top of my head, and I'm not goint to spend the time to figure it out). Sorry, there is no reason to use L/100 km when km per L (just like mpg) is a better way of expressing fuel economy.