Miles per Gallon versus Liters per 100 Kilometers | Hacker News Reader

Miles per Gallon versus Liters per 100 Kilometers

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112 pointstokenadult87 comments

A poorly written post on a subject that is surprisingly intriguing when better elucidated. A study published in Science [0] several years ago makes for good discussion. That study found a systematic misinterpretation of the miles-per-gallon metric in the sense that participants consistently overvalued vehicles with high MPG ratings. They assigned values linear in MPG rather than linear in its inverse.

The study's authors told participants to "assume you drive 10,000 miles per year for work, and this total amount cannot be changed." The participants were then asked to come up with values for vehicles of varying fuel-efficiencies. That is indeed the sort of optimization problem people face when choosing which car to buy, and clearly a fuel-efficiency metric that puts the amount of fuel in the numerator makes the problem easier to solve [1] because expenditure is proportional to amount of fuel if distance driven is taken as given.

But in reading the article, I was struck by the lack of attention paid to the "miles" part of the equation. I don't fault the authors, but taking distance driven as fixed is surely an enormous detriment to the goal of reducing carbon emissions in America. Yes, reordering your daily life to drive fewer miles is more disruptive than simply buying a more car that goes farther on a gallon of gas. And, granted, once you've chosen your lifestyle, minimizing the amount of gas you burn as you go about your daily routine is the thing to do. All the same, it's ludicrous to ignore the basic inefficiency of the suburban style of life that dominates in this country while we wait for automotive engineers to come up with clever solutions to pricey gas and carbon emissions that are twice as high per capita as in many similarly wealthy countries. Surely living closer to where you work, using mass transit, biking, and walking more must be part of the solution as well.

Maybe houses and apartments should come with a "miles per day" multiplier denoting how far you'd typically travel getting to and from shops, restaurants, entertainment venues, and your place of work each day you live there. ...

0. http://nsm.uh.edu/~dgraur/niv/theMPGIllusion.pdf [PDF]

1. Apparently taking reciprocals is beyond the capabilities of most people. Or at least of the Duke undergrads who participated in the study.

All the same, it's ludicrous to ignore the basic inefficiency of the suburban style of life

The trouble is an individual often has little power to do anything about it.

How on earth do you figure that? Sure, as an individual you don't have the power to single-handedly repeal the zoning laws, but there is plenty you can do to eliminate or at least reduce the number of miles you drive.

It's not a matter of whether individuals have the power to do something about the inefficiency of suburban living - after all, you can choose to live/work/commute in any manner you wish. The problem is that the balance of incentives and subsidies strongly encourages people to choose suburban living instead of something more sustainable, healthy and fulfilling.

The solution to global warming and pollution does not lie with persuading people to change, but making technological breakthroughs which allow us to carry on enjoying our lifestyles for a much lower cost to our enviroment.

More than that, the key point of contention is the fact that several countries with a total population of billions of people (China, India, Indonesia, Pakistan, Brazil, and others) are going to transition into developed "first world" economies in the 21st century. Currently there is no known technology that would allow them to avoid heavy reliance on carbon based energy sources while that transformation occurs. It's easy to sit on our 1st world thrones and imagine that if only we drove our cars a bit less everything will be fine, in reality the issue is about holding back people who are living in poverty, who don't have access to modern medicine, who don't all have access to clean water, etc. It puts into perspective the putative hazards of global warming to weigh against the cost of holding half the population of Earth in poverty.

You make a very good point. Taking Brazil in perspective, middle class is growing rapidly and with better credit the automobile industry is heavily targeting these potential car owners. Makes good sense economically and the state has been granting tax isemptions periodically which boosts sales significantly.

However, car models are still pretty much inneficient fuel consumption wise. That I know of, there exists only one hybrid model avaiable and it's very expensive. Ethanol's price also turned it into a non-option for flex fuel models.

Also, collective transportation is decades lagging pretty much everywhere that it's needed. This leads anyone that can afford it to purchase either a car or motorcicle in order to have decent mobility. It also makes it a class distinction thing, as in public transportation is a lower class problem.

On the long run, IMO things look bleak for Brazil in terms of urban mobility and greenhouse emissions.

Let's do both!

Walkscore.com

I don't understand the hate for this post. If you're shopping for a car, you're trying to balance factors like comfort, carrying capacity, impressing coworkers, purchase cost, resale value, maintenance costs, and of course, fuel costs.

Using a MPG measure would lead one to think that 20 mpg and 30 mpg are equidistant from 25 mpg, when in fact, going from 20 mpg to 25 mpg saves you $4,000 over 100,000 miles at $4/gal, while going from 25 mpg to 30 mpg only saves you an additional $3,667.

This has political implications as well, since CAFE standards are based on this non-linear value, a car company with a barbell of an extremely inefficient car and an extremely efficient car can have a better average than a company with a moderately efficient car even though the barbell uses more gas and pollutes more. (We'll ignore the irrational averaging by models rather than by sales -- that's another issue.)

I recently started looking at whether it would be worth it to replace my current gas guzzler and this was part of the calculation. You can see my numbers here: https://docs.google.com/spreadsheet/ccc?key=0AkSgUqAZJOp-dEJ...

The hate comes from OP's description of MPGs as clearly inferior to L/100km when in reality he's just engaging in a Holy War between two things that are nearly equivalent.

The non-linearity argument is not as strong and you and OP think, because many people naturally think in ratios. In fact, in some anthropological studies hunter gatherers that don't know arithmetic mostly said that the value halfway between one and nine is three.

Fascinating on the anthropological perspective - would you happen to have a source?

http://www.freakonomics.com/2011/11/29/addition-is-useless-m...

http://www.unicog.org/biblio/Year/2008.complete.html#Dehaene...

Abstract from the original paper:

The mapping of numbers onto space is fundamental to measurement and to mathematics. Is this mapping a cultural invention or a universal intuition shared by all humans regardless of culture and education? We probed number-space mappings in the Mundurucu, an Amazonian indigene group with a reduced numerical lexicon and little or no formal education. At all ages, the Mundurucu mapped symbolic and nonsymbolic numbers onto a logarithmic scale, whereas Western adults used linear mapping with small or symbolic numbers and logarithmic mapping when numbers were presented nonsymbolically under conditions that discouraged counting. This indicates that the mapping of numbers onto space is a universal intuition and that this initial intuition of number is logarithmic. The concept of a linear number line appears to be a cultural invention that fails to develop in the absence of formal education

In fact, in some anthropological studies hunter gatherers that don't know arithmetic mostly said that the value halfway between one and nine is three.

Which still doesn't produce the right answer; you save three times as much gas going from 10MPG to 30 compared to going from 30 to 90. (More generally, going from k to kn MPG saves n times as much as going from kn to k*n^2).

I don't think the emphasis on saving is correct. You're picking an arbitrary origin which is not zero.

If you go from 10 MPG to 30 MPG you are now using 1/3 as much gas. If you go from 30 MPG to 90 MPG you are once again using 1/3 as much gas.

In computing CAFE numbers, the inverse of mpg is used in the average. They are also weighted by sales, so both your points are specious.

Correct. Indeed, they are taking the average of the mpg directly, just the harmonic average (http://en.wikipedia.org/wiki/Harmonic_mean) rather than the arithmetic one we are more familiar with.

They should be weighting by miles, not sales, though that is harder to measure.

Thank you for the correction. I suspect I must have read a simplified explanation once and missed that it was simplified.

I don't understand the hate for this post.

It's because it's much writing and reasoning about comparing two ways to describe exactly the same thing, and comes to the conclusion that there is somehow a meaningful difference between them.

No matter how you slice it, you have to do some third grade math to figure out the economic impact of fuel economy. This is not a big deal.

It's the same faulty logic behind the supposed superiority of the metric system. Big whoop. You can multiply by 10. It's literally two sides of the same ruler.

> "It's the same faulty logic behind the supposed superiority of the metric system."

In grad school (applied math) it was always good for a laugh when we heard someone make a big deal out of metric. We always scaled out as much as possible to get nice dimensionless equations with the minimum number of parameters.

That said, sometimes one choice of units or basic quantities is more convenient than another for a particular application. Not right or superior in a general sense, just better suited to some specific context.

This is great point. For metalworking, inches are great for length because the tolerance limits of a typical machine are around .001". You can use cm, but it's awkward.

I've also found that with complex calculations, the metric system's ease can be frustrating - it hides "off by a power of 10" unit errors.

> It's because it's much writing and reasoning about comparing two ways to describe exactly the same thing, and comes to the conclusion that there is somehow a meaningful difference between them.

This difference has been empirically demonstrated: people have a much harder time comparing comparisons in MPG than in L/100: they over-estimate efficiency changes in high-MPG and underestimate efficiency changes in low-MPG (e.g. 10 to 11 MPG and 30 to 45 MPG are roughly the same efficiency improvement of 1 gal per 100 miles but most people will eyeball the second case as being a significantly better improvement than the first)

> No matter how you slice it, you have to do some third grade math to figure out the economic impact of fuel economy.

No, L/100 (or gal/MI) is linearly related to fuel economy, there's no math to perform (you can do it if you want precise figures, but it's optional).

> Big whoop. You can multiply by 10.

Yeah, who cares if bytes are 4, 6, 8 or 9 bits after all?

What an incredibly poorly reasoned post. First of all, the complaint has nothing whatsoever to do with the metric vs non-metric issue---we could as easily report gallons per hundred miles if it mattered that much.

More importantly, though, this business about the scale being "linear" is at best a red herring: linear with respect to what? And who cares if you save "one gallon" on a hundred mile trip? It's much more relevant how much you save relative to your overall gas budget, and saving one gallon out of three is much better than saving one gallon out of every seven.

And, surprise surprise, either system will tell us that just fine. Going from 14 mpg to 17 mpg may save about a gallon on a 100 mile trip (slightly more, actually), but it cuts your gas budget to 14/17 of its former amount, a savings of about 18%. And going from 33 mpg to 50 mpg may save a gallon on a 100 mile trip, but it cuts your gas budget to 33/50 of its former amount, a savings of about 33%. So, just as our intuitions would indicate, that's a much better improvement!

Linear with respect to your budget. The post is correct, that putting consumption on top gives a better "feel" for how much money you'll save.

Correct? When did comparisons of interpersonal utility schedules become a factual matter?

I agree that the article is poorly reasoned. I think part of it is the writing style. The first two sentences make no sense to me. I still cannot figure out what the "related measures" are related to and I have never understood why people type the contraction "we're." It makes me wish I could place a thousand upvotes on the recent "please learn to communicate" article.

When psychologists were invented. People understand linear measures better than inverse measures.

But linear vs inverse depends entirely on what questions you are asking.

If I want to know how much discretionary driving I can afford, MPG is a better measure. If I want to know how much the car will cost to operate over fixed driving requirements (commuting, etc) GP100M is a better measurement. Maybe we can just have both ;-)

…and most people aren't asking that question. Gasoline is an incredibly inelastic commodity.

Don't tell the economists...

First of all, the complaint has nothing whatsoever to do with the metric vs non-metric issue---we could as easily report gallons per hundred miles if it mattered that much.

Exactly.

The measurement of gallons per 100 miles shows a much clearer picture of gas usage:

  MPG = gallons per 100 miles (100/MPG)
  14 = 7.1
  17 = 5.9
  33 = 3.0
  50 = 2.0

  MPG = Cost of gasoline to drive 15,000 miles at $4/gal (15000/MPG*$4)
  14 = $4285.71
  17 = $3529.41
  33 = $1818.18
  50 = $1200.00

Yeah, most of the time when someone talks to me about gas mileage, they're interested in better mileage in order to save money or conserve gas, not to go further between fill-ups. So phrasing it as a 33% vs 18% savings hides that you actually save more gas, and so more money, going from 14 to 17 than 33 to 50.

That's one question ,but another one is:

How far can I drive per $100?

When looking at the car in part for discretionary uses, that's a valid question.....

The difficulty with this is the widely varied price of gasoline. If we assume $4/gal, $100 would buy us 25 gallons of fuel, so we can just multiply those 25 gallons by the MPG:

  MPG = Miles per $100 (MPG*25/$_per_gallon)
  14 = 350
  17 = 425
  33 = 825
  50 = 1250

> That's one question ,but another one is:

That is a question I've never seen anybody ask in my whole life. There are precious few people who drive for the sake of driving, for the vast majority driving is utility to go from point A to point B.

Therefore, why optimize for the significantly less common (almost irrelevant, even) case of "I've got money burning my pocket, how far can I drive?"

"how far can I drive for this amount of $" is a question I've only heard a few times. But I do often hear "how far can I drive on a tank" or "how far can I drive on my remaining amount of fuel".

Perhaps the disconnect we see in this comment thread is between people who do almost entirely city driving and people who drive long distances. If you only ever drive a few miles at a time, you don't really care what sort of distance you can manage on a tank, you just care how much it's going to cost you to go to work every day (you'll probably convert the fuel/distance ratio into a money/time ratio.) If you spend a lot of time driving across central Kansas, how often you have to stop for gas becomes a more significant consideration (you'll probably convert distance/fuel into stops/time.)

> Perhaps the disconnect we see in this comment thread is between people who do almost entirely city driving and people who drive long distances.

That's an interesting thought, and it probably has more than a grain of truth.

Maybe. I tend to live in rural areas so maybe that's a factor.

But I was more thinking of this:

"We have a vacation budget of X for a weekend trip. We don't want to spend more than Y for gas. What options do we have?"

How often you stop for gas is surely better covered by a "range" measurement for the car? Maybe it's different in the states, but all the cars I've ever been in show your remaining fuel as a fraction of a tank. In that case, volume of fuel is completely irrelevant, so MPG vs liters/100km has not place. e.g. My tank takes me 400 miles => I have half a tank left => I can go another 200 miles ...is exactly equivalent to... My tank takes me 600 km => I have half a tank left => I can go another 300 km

(For the purposes of this post, 1 mile = 1500m. If the size of a gallon changes with locale, why not a mile? :-p )

In practical terms it's not that clear cut. Let's say I have an old car that gets 14 mpg and I'm considering two new cars, one that gets 33 and one that gets 50 mpg.

If I drive 500 miles a week, either vehicle is going to save me at least 20 gallons a week in fuel. But going from the 33 to the 50 is only going to save me 5 more gallons. However to get 50 mpg I probably need to buy an expensive new hybrid, whereas it's not too hard to find a good used car that will get 33 for a fraction of the new hybrid's purchase price. Then you have to consider cost of financing and insurance (both more for the new car). If I go for the 50 MPG car I'll probably never make up the difference in fuel savings unless I drive a LOT of miles.

You do not need a hybrid to get 50 mpg. Many diesel cars easily do more than 50 mpg

MPG comparisons are pretty intuitive, but where MPG comparisons fall apart is when you're comparing comparisons.

Let's say you have a 10-MPG truck and a 50-MPG hybrid, and you drive both equally far each year, and you've got a $40k budget to replace one or the other.

Should you spend your money on a new truck that gets 11 mpg or a whiz-bang new EREV that gets 100 mpg (equivalent)?

Most people would think that improving the miles-per-gallon by 200% saves much more fuel than improving it by about 10%, but in this case both replacements save the same amount of fuel per mile driven.

If you invert both numbers it's immediately clear that this is the case (10 versus 9 gal/100mi, 2 versus 1 gal/100mi).

Don't forget miles driven per vehicle either.

I disagree.

I think that most people think about gas in the following way (I know that I do). I commute distance x a day to work, how much am I going to pay in gas?

The 100kms/liter figure makes this straightforward. I can figure out how many km I'll drive in a typical year, multiply by that figure, and I have how many liters. Multiply by the cost of gas, and I have how much I have out of pocket.

With mpg I have to do a division step in there instead of multiplication. Division is a more complex operation. Laugh if you will, but people are more likely to screw it up.

It has been found empirically that people are worse at reasoning about MPG than L/100km. That's the argument this post should have made. Source: http://wheels.blogs.nytimes.com/2008/06/20/the-illusion-of-m...

That's the argument it tantalizingly came close to making at the end, but it stopped dead in its tracks before reaching it.

When we talk about a car’s fuel economy, what we want to know is how much fuel does it use, not how far does it go

I've never understood this phenomenon. I realize he's talking about car economy here, but for me a car is a vehicle to take me from point A to point B, which means my most important metric is how far it goes, not how much fuel it consumes. Once I'm home and can (or want to) run calculations on my costs, then I'd like to know how much fuel it consumes.

It's a misnomer, sometimes you want one, and sometimes you want the other, so knowing a ratio, any ratio, and 8th grade algebra, you'll be fine. This is a silly post.

Right. Sometimes, you want to know how much beer you can get for a fixed amount of money, and sometimes you want to know how much money you have to pay for a fixed amount of beer.

I think that's his point. Usually you know how far you want to go and the question is, how much gas will it take. For example, I know my car gets 8 L/100km. If I want to go 400kms, I can quickly figure out that's 32L, or about 2/3s of my 48L tank. Doing this calculation with mpg requires division.

I don't see the big deal.

If I know my car gets 40 miles per gallons and I need to go 120 miles, I can quickly figure out that I'll need 3 gallons of fuel.

I can't imagine either measurement being hard to use for anybody who's made it to high school.

They're two ways of measuring the exact same thing and neither one has an advantage over the other. Although it would be nice if we used kilometers per liters instead.

Equivalent unit systems absolutely can have advantages over one another for particular contexts. I don't know which of these systems is most convenient (and most immediately useful) for most people, but I find it reasonable that there would be an objective winner by that measure.

I wager you don't know many people who have only made it to high school then.

Uh, how exactly are you saved from division (and multiplication) on 8L / 100km = xL / 400km? As opposed to just division on 25mi / 1gal = 250mi / xgal...

The division in the first will always be x / 100km while in the second the division will be x divided by your mpg ratio. The first division is way easier as your mpg ratio is more likely to be something random.

I don't understand what people are moaning about - it's well written and has valid points. To me MPG is like Kg/£ price labels - not that intuative at all.

Measuring fuel economy in miles per gallon is like setting up a budget in months per thousand dollars.

Big improvements to inconsequential expenses would result in huge mpkd improvements, but they wouldn't save you a lot of money.

> "setting up a budget in months per thousand dollars"

A lot of people actually do that: given the amount of money they have saved up, they figure out how many months they could get by without a paycheck.

Big improvements to inconsequential expenses aren't going to help you save a lot more money if you're gainfully employed, but they can help you last a lot longer if you're unemployed. Huge mpkd improvements matter in that situation.

Similarly, with the MPG or GP100M question, use the measurement that's most convenient for answering the question at hand. If you want to know how much fuel/money it'll take to go to Chicago, use GP100M. If you want to know what destinations are within reach for a certain amount of fuel/money, use MPG.

Right, and the first is way more common.

> "the first is way more common."

Is it?

Figuring out total fuel costs is the sort of calculation I run once in a while. When I buy a new vehicle, or when I'm planning a long trip, I figure out how much I can expect to spend in fuel. I'm almost always at a computer when I make this sort of plan, though.

But when I'm actually driving and having to do calculations in my head, the range calculation is far more useful. Am I going to have to stop for gas between here and there? Should I fill up today or can I wait until tomorrow? Can I make it to Colby or should I fill up in Goodland? This subject comes up every time I take a medium length trip, and several times on a long trip, as compared to the other calculation which comes up only rarely.

This probably doesn't impact that many people, but on a motorcycle with no fuel gauge, you use the odometer as your fuel gauge. You need to know how many miles to reserve, and how many miles to empty. So I regularly monitor how many miles to go from a full tank to reserve. While quantity per distance may be an easier metric at purchase time, that only happens once every few years. Distance per quantity is a calculation I do in my head several times a week to ensure that my vehicle maintains a good state of tune.

If you're using the odometer as a fuel gauge, surely volume becomes irrelevant for judging your range (excluding the tuning purposes)? e.g. My tank lasts 200 miles => I've gone 100 miles => I can go another 100 (top) before refilling.

Marginally related at best, but I only recently realized that a Quart is a quart-er of a Gallon. And a Liter is also a quarter of a Gallon (approximately). So basically a Liter is a Quart.

In the US, the dealer stickers are standardized by the EPA and DOT and contain annual fuel costs (either electricity or gas) based on 15,000 miles/year so you can make an easier comparison.

It also contains gallons per 100 mile ratings for gas cars and KwH per 100 miles for electric. I know it is shocking it can be done in imperial units, but somehow we managed.

That's only at the dealership though, not in most marketing and conversations.

The biggest problem with miles per gallon as advertised is that it is inaccurate. Having every vehicle be required to provide that information without having to buy a separate device should be required by law.

And every vehicle should keep track of the cost required for the gas added to it, and then both provide stats on gas usage in volume/day, mpg (or similar), and show an average of how much it is costing you per day to use it, perhaps pointing out things you are doing that waste gas, like you ran the air conditioner with the windows down, your tires are underinflated, you need a tune-up, etc.

The U.S. says it wants to curb unnecessary energy usage, but instead of making laws that would actually help its citizens in this regard, it wastes money refunding money spent on ridiculously overpriced cars and bails out auto companies that were destined to fail. There are good reasons why it does this, but it's crappy nonetheless.

Usually I care about how far I can go in my car before I need to refuel. This is exactly what MPG tells me.

The only time the inverse is useful is when buying cars on the basis of fuel efficiency. That's a much rare occasion since I drive every day but only buy cars every ~5 years.

But that is mostly a function of the size of your gas tank and not so much about fuel efficiency.

"When we talk about a car’s fuel economy, what we want to know is how much fuel does it use, not how far does it go."

Not sure about that. For Internet speed would you prefer to know how many seconds it takes to download 100MB as opposed to Mbps?

Depends if you have a fixed MB demand or a fixed time budget, doesn't it? Which is better when you are downloading a 4.6G ISO?

When we talk about a car’s fuel economy, what we want to know is how much fuel does it use, not how far does it go.

Now I grew up with the metric system and I would not generally agree with that statement. The function of a car is to transport me, so its output is distance. Measuring the output I get, rather than how much a standard unit of output would cost, makes sense to me.

Do you drive as far as you can on a hundred euro note, or do drive to your destinations and then refill your spent petrol? Unless you enjoy cruising in your car with no time limits, it's the latter.

One more thing: there are multiple definitions of "gallon". A lot of Canadians live near the USA border, and many cross the border to buy low-tax gasoline. The volume of a "gallon" differs by nearly 20% between the two countries.

for the Americans who might wonder : 100km -> 1h of driving on the highway (limit is 120km/h or 130km/h, remove urban part on start and finish and you're at 100km/h average).

>> 100km -> 1h of driving on the highway (limit is 120km/h or 130km/h, remove urban part on start and finish and you're at 100km/h average).

I find that to be a bit of a pointless observation. The speed limit that's on the sign on the highway is already a pretty decent indicator of how far you'll get in an hour, whether you're using metric or imperial.

Cool, but I don't read HN on the highway.

Actually, in Brazil at least, everyone thinks about fuel usage in km/liter (normally with two measures for city and roads).

First, gas in the U.S. has been ridiculously cheap for decades. Housing, healthcare, and education costs are utterly teabagged, but gas is cheap, even now at $4. People who whine about gas prices are either (a) typical Boomer Republicans throwing their sense of entitlement around-- you know, the assholes who thought it was okay to go to war over "price gouging" in oil but clapped their fat hands together when their house prices octupled in one generation and young families got robbed (by them)-- or (b) people who live too ungodly far from where they work and are paying far more in lost time than in gas. Commuting (although less so by subway and not at all by bike) is corrosive and it has nothing to do with fuel costs.

Because gas is so cheap, people don't usually think in terms of, "how much gas will I use to get there?" Instead, it's "How far can I drive until I have to fill up?" That's a question that's easier to answer with a miles-per-gallon number.

Still, I agree that it would be better to see the inverse posted. Maybe people would think twice about driving those enormities. Probably not, but one can hope.

It's true that gas is cheap, but it's not true that people who whine about gas prices belong to any political or demographic group. It's basically a national past time here. It's like talking about the weather. It's part of our culture and it's something we'd all do at $0.50 / gallon or $5.00 / gallon.

Aside from the ad hominem attacks, I think you're factually wrong. The reason people get upset about jumps in gas prices is because it directly affects the bottom line for a majority of Americans, whether they're Republicans or Democrats.

The median family income at the end of 2011 was about $50k. Take home would probably be around $3k/month. If you have a single earner driving 15K miles annually, in a car getting 25mpg, that's going to require 50 gallons of gas a month. So when gas jumps from $3 to $4, that's $50/month of take home pay that vanishes. For a two earner family, $100. Boom, there goes over 3% of take home pay.

For people with incomes below this, the percentage only rises. And they're not likely to have the latest Prius to minimize the impact.

In short, not everyone upset about higher fuel prices is a warmongering, fat-handed asshole who made out like a bandit during the housing bubble.

yes, the relationships are inverted, but it doesn't make the relationship any less linear. also, the graph in the article is useless

Perhaps there's something here I'm missing, but this doesn't make sense to me at all: "Going from a 14 mpg car to a 17 saves exactly as much fuel (and carbon) as going from a 33 to a 50."

As the driver of a car, I want to go more miles on less gas.

If the car uses 1 gallon of gas to go 50 miles, and another uses 1 gallon to go 30, then it seems obvious that the first car is much more gas efficient. More miles on less fuel.

If car A gets 17 miles to the gallon, then it will take ~2.94 gallons to make 50 miles.

If car B gets 50 miles to the gallon, then it takes 1 gallon of gas to drive the same distance.

So comparing 13mpg to 17mpg and saying that its the same as the difference between 33mpg and 50mpg just doesn't make any sense at all.

Try doing the rest of the math.

33mpg -> ~1.52 gallons 50mpg -> 1 gallon for a 50 mile trip

So going from 33mpg to 50mpg saves half a gallon.

13mpg -> 3.84 gallons for a 50 mile trip 17mpg -> 2.94 gallons for a 50 mile trip

.9 gallons saved. So in your scenario, going from 13mpg to 17 saves more gas than switching from 33 to 50.

If you're just comparing percentages, then yes 0.9 > 0.5.

However, overall the comparison doesn't stand up. 1 gallon for 50 miles vs 2.94 gallons, the 50 mpg is what is saving more gas, therefore it wins.

MPG is actually much better for humans to use, as the end result is "bigger is better", which is how humans naturally think. It is unnatural to think "the smaller numbers are better". If you want it metric, it should be kilometers per liter.

Golf? Race times? Cost?

The people at the grocery store must love you! Bigger price? Sounds like Better price!

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