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Although automobiles are rated in miles/gallon, such ratings are not generally arithmetically significant. For example, going from 10mpg to 12.5mpg will save much more gasoline than going from 50mpg to 100mpg even though the former only represents a 25% improvement while the latter represents a 100%
improvement).
Translating published fuel economy figures into gallon-per-hundred-mile fuel consumption figures would provide a much more direct and immediate basis for comparison. The afforementioned vehicles would have g/100m ratings of 10.0, 8.0, 2.0, and 1.0 respectively. Reducing fuel consumption from 10.0 to 8.0 will save two gallons of gasoline for every hundred miles driven. By contrast, reducing fuel consumption from 2.0 to 1.0 will only save one gallon.
Publishing fuel consumption in terms of fuel-per-distance will translate much more accurately into most people's lives than distance-per-fuel. If someone drives 1,000mi/month and gas costs $1.75/gallon, then every g/100mi of fuel consumption will cost them $17.50/month. Having fuel-consumption figures that scale directly to dollars would make it much easier for people to judge the differences between vehicles. Going from 40mph to 1,000,000mph may seem like a big difference, but it's not as big as the difference going from 12mph to 18mph. But express those numbers as 2.5 and 0.0001, 8.3 and 5.5, and the relationships will become much clearer.
Baked
http://www.fueleconomy.gov/feg/label/
A mere 7 years later [goldbb, Aug 31 2011]
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Trip meter, fuel gauge .... why have both? |
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In the UK, litres per 100km are quoted for all models. On my trip meter it is also shown in this way.
Unfortunately, I immediately convert it into mpg, to make it familiar.
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I hadn't realized that Europe already posted fuel consumption per distance rather than distance per fuel consumption. Perhaps that makes the idea already m-f-d baked. Oh well. |
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It just seemed like measuring fuel consumption per distance would allow people to more accurately judge whether particular vehicles were really what they wanted (at both ends of the economy spectrum--e.g. in deciding whether to get a 25mph vehicle for primary use and occasionally rent a larger vehicle, or getting a 16mph vehicle that can meet all one's needs; or in deciding whether to spend an extra $3,000 to get a vehicle which gets 50mpg instead of 34). |
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In the former case, one might decide that the extra 2 gallons every hundred miles would add up to much more than occasion rental costs (or, if one didn't do too much driving, one might not). In the latter case, one might figure that the more expensive car would save one gallon every hundred miles, or about 1,000 gallons over 100,000 miles. Unless the car was expected to last over 150,000 miles or gasoline went and stayed over $2.00/gallon, there would be no way the more expensive car could recoup the extra investment. |
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[supercat], be careful of the mpg/mph typo's. Yes, you are right about investment vs. savings. $2.00 per U.S.gallon! You're being robbed. |
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Hm. I don't think your approach is more meaningful, I think it just tells you something different. MPG tells me how far a vehicle should travel on a gallon of gas. |
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Your figure tells me how many gallons would be used if I drove a hundred miles. I can extrapolate that quite easily if I wanted to know it. Haven't wanted to, yet. |
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For me a much more useful number would be "days between fuelings." |
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Kawasaki ZXR1100, $10 = 110 miles
Mazda 6 $35 = 300 miles
Astro Van $50 = 300 miles
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Thats the information in a user friendly format. |
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waugs: If people were given a certain ration of fuel, then knowing how far they could drive with that fuel would be the most useful measure. As it is, most people have a certain amount of driving and vary their fuel purchases to match. |
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Do ya think? I imagine most people just fill up their tank when the gauge is low. |
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[ato_de] you may be on to something -
how about when you fill up the £/$ you
spend per litre is sensed by the car and
a cash register counts up how much
you are spending (in addition to how
many miles you have left). This would
have to be a rolling average for partial
fills. |
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This way we can also tell the difference
between costlier/cleaner fuel and the
drum-slop some stations sell at a
fractional discount. |
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but, [waugsqueke] is right - most
people fill up when getting low and fill
up before a long journey. |
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[waugsqueke], isn't filling up when your tank is low the same as varying your fuel purchases to match how much driving you are doing? If you drive more, your tank will get low more often and you'll buy more fuel. I think [supercat]'s point was that if economy goes down people buy more fuel rather than drive less, so the amount of driving we do is fairly constant week to week and a mpg measure would make it easier to quickly calculate how much fuel you'll be buying for your relatively fixed driving distance. |
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In Australia, all new cars have their litres / 100 kilometres rating displayed on the windscreen. Except 4-wheel-drives (SUVs) that is, which I think is an absolute rort because they probably have the worst economy and the one of the biggest ranges between the least and most economical. |
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"rort?" Another for the glossary. |
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A rort is a scam or dishonest scheme to gain benefit from systems that either allow it on a technicality or have no way of stopping it. For example; if I were to claim unemployment benefits under two different names at the same time I would be rorting the welfare system. |
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In this case, I think the technicality is that SUVs are classified as commercial vehicles, not passenger vehicles. |
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Baked to a turn: It's common practice in Europe to describe a vehicle's consumption in terms of litres per 100km. I was unimpressed to hear about VW's "STUNNING NEW 3-LITRE" until I found out those litres were fuel, not engine displacement.
BTW, 3 litres/100km = about 3.25 qts / 62 miles. Stingy. |
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I really don't like the European system of L/100kms. |
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Why 100kms? Why not 10, 1, 1000, even 50? |
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A straight division of distance by consumption seems more logical. Can anyone explain the thought process behind the L/100kms decision? |
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//Why 100kms? Why not 10, 1, 1000, even 50?
... Can anyone explain the thought process behind the L/100kms decision? // |
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Probably because it gives numbers in a memorable range. From a online conversion site:
20 miles/gallon(UK) ~= 14 liters/100 km
I rounded it to the nearest int. |
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10km would be 1.4 l. Rounding this would be unwise as too much precision would be lost |
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1km would be 0.14 l. This adds an unnecessary extra psychological layer of difficulty. |
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1000km would be 140 l (OK, 141 l). Again this is psychologically difficult, the numbers are too large. |
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These considerations explain why earthquakes are measured on the Richter scale, douvets in togs and so on. |
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//I was unimpressed to hear about VW's "STUNNING NEW 3-LITRE"// I was hugely impressed at first, considering the car was a Polo... |
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//These considerations explain why earthquakes are measured on the Richter scale, douvets in togs and so on.// |
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A number of scientific measurements, including the Richter scale for earthquakes, are performed using logarithmic "units". This is most commonly done for things whose variation can be many orders of magnitude. Measuring sounds in dB, for example, makes it possible to use "nice numbers" on the same scale to measure a jet engine at 140dB and a fan at 60dB, even though the former has a power level 10,000,000 times greater than the latter. |
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Canada must use the fuel per fixed distance method too. The ol' 87 Deville I use as my lake car switches from MPG to L/100KM when you hit the little metric button. I just like hitting it at highway speeds to suddenly jump the speedo into the 3 digits. The truly half-baked idea is that any Cadillac ever intentionally brought attention to mileage. |
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Gallons per mile is volume
divided by distance, which
yields area. |
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I think you should do the
math, and rate fuel efficiency
in square millimeters. |
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so a 30 mpg car would
be rated as
0.0784 sq.mm. |
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Heh, I love it, except that it is 1/d for mpg. |
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L/100kms is the right way round: 10L/100kms would work out as 0.01m3/100,000m = 0.1sq.mm. |
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Having a conversion like that would help you better manage how much fuel you actually use and need to buy. I am sure that the oil companies know this thus, they would rather the auto makers and the EPA report it as miles per gallon. |
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If I know that its a 20 mile trip to work every day I can buy enough gas to last me until payday in lieu of filling my tank completely because I dont know how much gas I will use. And rather than budgeting my money I will begin to budget my milage. |
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I like [Goedin]'s idea best here. Except it should be measured in square microns. So 30 MPG would be about 78,404 square microns. 15 MPG is 156,809 sq microns, while 60 MPG is 39,202 sq microns. |
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Anything under 100,000 could be considered decent, and anything under 40,000 would be enough to brag about over cocktails. |
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The number doubles as you cut the gas mileage in half, giving the perspective you desire. |
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The European system is metric (liters per hundred kilometers), to be consistent with the "English" measurement system, the US version should be quarts (or gallons) per hundred miles. |
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That rating might be useful when making a purchase decision, but in day-to day driving I find the miles-per-gallon numbers more meaningful. |
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Better yet is a vacuum guage or a fuel-flow meter (IMHO, both should be mandatory equipment on all automobiles); these give an immediate real-time indication of fuel consumption. |
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The cost for supplying this information would be trivial and I'd like to see it. When gas prices rose quickly enough that people started dumping bigger cars and trucks, a few articles suggested looking at how much you drive before doing so in order to compare your "savings" against the expense of the new car. |
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engines: where are the "fuel consumption per hp/torque at revs" graphs ? and powertrains "loss @ rev", that would actually be useful in determining a driving style. |
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Anyways l/100km might be easier if you want to know how much gas it takes on a specific trip if your odometer works but your gas gauge doesn't, but mi/gal or km/l is better as a comparison metric. "bigger is better" is sortof ingrained into the human psyche... go with it. |
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