Yes, I've been meaning to add that link at the bottom of the page with a short piece of text for context - I'll do that soon.
Thanks.
Edit: Done that now. Not sure why this comment got a downvote, though.
Extra Edit: Hmm, now been re-upvoted. Bizarre, but thanks for the votes! I know that they're not actually worth anything, but they do indicate that what I've done is appreciated, and considered to be of value.
With or without illustration, really enjoyed the write up.
Also fun to think about what would happen if you plot the value that is represented by the "mm^2" over time, and do an integration of the plotted graph. You somehow end up with a volume, or total fuel consumption over the period you integrate over.
I wonder if posts that have no genuine reason to be downvoted (like yours) get more votes if they add a comment to the effect "Not sure why this comment got a downvote" since multiple people will try and correct the erroneous downvote with no idea whether anyone else already has.
It is odd. When there's a strange downvote people might then make more upvotes because they can see it was downvoted, but can't see when it's been corrected, because the scores are no longer visible. But voting is weird anyway. I don't take it personally, and I don't want to complain, but I genuinely get confused when there are downvotes I don't understand, and I want explanations purely so I can decide either that I was right and to hell with it, or I was wrong and I need to reconsider things.
With just a downvote I don't get the chance to learn.
Conversely, if people could just upvote outright but to downvote would need to provide a minimum 10 character reason that was made public, would this break of improve the system?
Sometimes the ten characters minimum I would enter would be "You're a fucking moron." Since that's probably either unproductive due to incorrectness or unproductive because the person is not in a position to do anything about it or counter-productive because nothing good can from such a comment, the downvote is much better. I can allow the button to proxy for voicing the opinion "You're a fucking moron" and move on.
By extension the downvote as proxy covers lots of other cases which would add little of benefit to HN.
If the comment in question constituted destructive behaviour, go ahead, vote it down.
Let's assume now it was not destructive.
Error on the side of doubt that maybe you are wrong. If you can convince yourself with reasons that what is said is wrong, state your reasons. If you can't, don't down-vote.
That you are thinking "You're a fucking moron." is a big problem it itself. You are not alone with this problem, and it haunts HN.
On what basis have you come to believe that you are well positioned to offer reasoned advice in regard to how I, or anyone else should vote and comment on HN?
It already is suitable for those things. Downvoting in lieu of wrestling pigs in mud puddles is, in my experience is one reason why. [1] Complaining about karma and its mechanisms is a dead end from both a metaphysical and literary point of view.
Downvotes avoid turning disagreements into excuses to accuse other people of character flaws, as in your comments toward me.
[1] Though here apparently I cannot avoid the invitation.
Downvoting in lieu of wrestling pigs in mud puddles is, in my experience
is one reason why.
Downvoting is often used on controversial comments. That blocks controversial discussion.
I think we should not block a controversial discussion if it's serious, rational and constructive.
Complaining about karma and its mechanisms is a dead end from
both a metaphysical and literary point of view.
Here you are overstating. It depends on the participants.
You can avoid that from happening by being constructive, respectful and serious, and stoping the discussion if the other is not.
Downvotes avoid turning disagreements into excuses to accuse
other people of character flaws, as in your comments toward me.
I see more options than either
(1) to downvote to disagree or
(2) to accuse other people of character flaws.
The attitude of thinking of other people one disagrees with as "fucking morons" is problematic independently on whether one downvotes for disagreement or not. It's not accusing a character flaw, it's simply criticizing one specific attitude.
I think you should be told. So, if nobody else would have said it, I would have done it anyway.
At +5, It is the best moderation system ever published. Immune to brigades, and reader-tunable to their individual preference level for jokes and flames.
A way to give feedback to the poster on inconsequential details such as language/spelling/typos/grammar/etc that isn't displayed to anyone else would be useful.
2. You said what you thought you said but didn't say it in a way that everyone understood.
:or
3. You said what you thought you said and someone didn't think it was worth saying.
:or
4. You didn't say what you thought you said and some didn't think what you said was worth saying.
:or
5. Karmic forces were at work.
It's worth assuming that the ones over which you have control are the reasons for a downvote, since those are the only ones from which you can learn. And given that everything else evens out statistically over time, it's not as if downvotes will ever stray too far from constructive criticism.
It's very easy to downvote comments by mistake when trying to upvote them on mobile. Shortly after posting just one mistake can make people feel they've done something wrong but it usually sorts itself out over time.
Thanks for that! Not being a native English speaker I couldn't really grasp what the author was trying to describe when he started talking about a "trough with a cross-sectional area of 0.1 mm2" and the following paragraph. This image made everything clear!
I will never understand why Americans keep using miles per gallon instead of liters per 100 km. Miles per gallon is only good if you want to advertise your car ("look, with this car you can travel 50 miles with one gallon whereas with that one you can only travel 40 miles").
But you never do that in real life, you never fill your car with say, two gallons and say "now I'll travel 80 miles".
Instead you always know the distance between two points and you want to know how much will that travel cost you. So you think like this: "distance from point A to point B is 250km, my car uses 6 liters per 100 km so I'll use 15 liters, 1 liter price is 2€ so it'll cost me 30€". Easy as pie and you can't do that with miles per gallon.
The USA is BIG. Foreigners who come here often have little idea what an unfathomably huge place the USA is. And unlike say, Russia or Canada which are even bigger geographically, virtually all of that territory is navigable by car throughout much of the year.
In the USA, therefore, it was historically pretty likely that grandma and grandpa lived far away, say, back at the farm while mom and dad moved into the big city or the suburbs to get jobs and raise a family. So in America there was a much bigger market for grand tourers -- cars designed to go long distances and be fun to drive. Early consumer automobiles were promoted as such -- "See the USA in your Chevrolet" and the like. Now you know why American cars are reputedly so big and ugly: in Europe GTs are rich boy toys whereas in America they had to appeal to middle-class sensibilities which meant things like big engines and rocket fins on the rear and such.
So in this environment, it made much more sense to market a fuel-economical car not with statements like "you can use less fuel and save money over your trips to the market and to work" -- oil was cheap at least until the 1970s -- but with statements like "you can go this much further on a single tank of gas". Hence the metric of miles per gallon, rather than litres per 100km or gallons per 100 miles -- which is still in use today.
I've never been to Europe, and I'm actually curious if the Eurozone has changed driving behavior much. Would it be unusual for someone in Berlin to drive to Rome or Athens on vacation? For similar distances in the USA my experience is that it would be common, partly because Americans like to have their car when they arrive. Even when gas prices were quite a bit higher Americans still drove. Who gets in a car and only burns one gallon of gas? An F150 only gets about 20mpg, and I know people who go farther than that for groceries.
The thing about mpg that is problematic is that it obfuscates the savings in going from a 10-20 mpg vehicle to a 20-30 mpg vehicle (and exaggerates the benefits of a 50 mpg vehicle).
15 mpg -> 25 mpg is a much bigger step than 25 mpg -> 35 mpg (a savings of 2.6 gallons per 100 miles vs a savings of 1.15 gallons per 100 miles). The jump from 35 mpg to 50 mpg only saves 0.85 gallons per 100 miles.
For everything else it just introduces some trivial difference in the arithmetic.
To me, this is the best argument for l/100km (or gal/100mi). I don't know of anyone who really thinks about how far they can go before they have to refuel. They just check the gas gauge and fill up when it's low. There's very few places, even in the US, without a nearby gas station so it's not really much of an issue. The arguments about multiplication vs. division also seem silly, especially since your math teacher lied about not always having a calculator.
That said, as an American I grew up with MPG so that's what's intuitive to me and I'm happy with it. Something like l/100km seems like it would be mostly useful when shopping for a car than actually getting around.
> The thing about mpg that is problematic is that it obfuscates the savings in going from a 10-20 mpg vehicle to a 20-30 mpg vehicle (and exaggerates the benefits of a 50 mpg vehicle).
I think the EPA's estimated-fuel-cost-per-year (based on standardized assumption), which I believe is part of the standard rating disclosure for new vehicles just like MPG is, addresses for most consumers that better than MPG or gal/100mi, and for the subset of consumers for whom it isn't better -- i.e., the ones that have good numbers on their own usage patterns that they are going to calculate out from to get a personalized estimate -- MPG and gal/100mi are exactly equal in utility.
I haven't shopped for a new car so didn't realize that they had changed the labeling. The motivation for the cost estimates is clear enough from their literature:
(If you have a tiny screen, make sure to scroll down to the "MPG Illusion" plot.)
Edit: You conclude: " i.e., the ones that have good numbers on their own usage patterns that they are going to calculate out from to get a personalized estimate -- MPG and gal/100mi are exactly equal in utility.".
What else did you take "For everything else it just introduces some trivial difference in the arithmetic." to mean?
This is a great point, but except for policy makers, where this information matters, to say, incentivize mfgs, or consumers with rebates, this context is not practical in day to day dealings of most drivers.
> So you think like this: "distance from point A to point B is 250 miles, my car gets 25 miles to the gallon, so I'll use 10 gallons, 1 gallon price is $3.00 so it'll cost me $30.00". Easy as pie.
That's why. It's exactly the same thing you're talking about.
MPG is useful when you are thinking in terms of vehicle range. This isn't most people's default, but it does have its usefulness.
As for why US doesn't use l/100km. the simplest answer is all our vehicle odometers are calibrated in miles, and we buy gasoline in gallons, so l/100km is a number with no grounding. To get most people in the US looking at it it would have to be gal/100miles or similar.
Which is either larger or smaller than your gas tank, so I think fuel volume over distance traveled is still easy enough to use for the range calculation, and better for almost everything else.
"I have 40 miles roundtrip of errands to run today, and 3 gallons of gas left, do I have to fill up before I leave and maybe be late to my first appointment or am I good for the day?"
Well at 20mpg the answer is really easy. 3*20-->60, I'm good.
Our odometers are in miles though - so it's not completely mindbogglingly stupid.
In the end realistically almost no one uses these numbers for range, what they do is compare car A to car B and know that higher is better. The figures from the manufacturer are meaningless and anything with an on board computer telling you your mpg can just as easily tell you range on remaining fuel.
I'm Canadian and buy litres of gas, but I still check the mileage in mpg. It's just because I have an instinctive idea of how many mpg I should get, whereas I have no instinct for l/100km. I know 35mpg is decent and 50mpg is exceptional, and 10mpg is unacceptable. What does 10L per 100km mean? I have no idea.
> I will never understand why Americans keep using miles per gallon instead of liters per 100 km.
Because:
(1) neither liters nor km or meaningful measures to Americans in general; were Americans going to use a measure of fuel:distance, it might be gallons per 100 miles, but not liters per 100 km, and
(2) Even then, I think there's a pretty strong preference for more-is-better measures rather than less-is-better.
> Miles per gallon is only good if you want to advertise your car
That's pretty much the only thing MPG ratings are used for, manufacturers selling cars. So, its not really surprising that that is what is used.
> But you never do that in real life, you never fill your car with say, two gallons and say "now I'll travel 80 miles".
No one I know ever do the reverse, either; you don't decide "I'm going to go eighty miles, and this car consumes 2 gallons per 100 miles, so I need to make sure the taken has at least 2×80/100 = 1.6 gallons".
> Instead you always know the distance between two points and you want to know how much will that travel cost you.
For people who care about that, there is a reason that auto magazines doing reviews often publish things like total per-mile fuel + maintenance costs for reviewed vehicles. If you just care about fuel costs, it takes about as much work (same number of multiplications and divisions, just changes which figures are being multiplied and which divided) to calculate that from MPG and gas price as it does from gal/mi (or gal/100mi) and gas price, so there's no real advantage to using one over the other for that purpose.
(And, IME in practice, fuel costs are usually a concern with trips where the consumption consideration isn't "how many gallons will I get based on the cars stated ratings" but "how many tanks will it take based on my driving experience", in which case the people using it often are using something like the miles per unit of fuel ratings, but the rating is determined by experience with the vehicle, and the unit is whole fuel tanks.)
If people start thinking of individual car trips as spending money (rather than the generalized cost of having a car), I wouldn't be surprised if people drastically reduced their travel and, correspondingly, consumption (by not leaving their houses). People seem to highly resistant to impulse purchases for dollar amounts smaller than they are willing to spend on road travel without thinking. This would be a Very Bad Thing for the American economy, so I'm not surprised that we are encouraged to reason about gas milage in language that makes this more difficult.
Who is doing this encouraging "to reason about gas milage in language that makes this more difficult"? MPG as a fuel efficiency metric goes back many decades.
I don't actually disagree that that if there were a big ticking dollar gauge that tallied up the cost of each trip in a car, some people might drive less. But it's not the reason we use the MPG metric.
> I don't actually disagree that that if there were a big ticking dollar gauge that tallied up the cost of each trip in a car, some people might drive less.
Some cars already have those (well, not necessarily big and ticking, but, some have a fuel-cost-of-trip measure that is displayed, either on one of the information screens or when you end a trip, or both.)
Only on HN would a stupid "herp derp you guys are using the wrong metrics" post be voted this highly. I get it, snotty Eurpeans get snotty upvotes from each other with their snotty, "We dont like your imperial units" whining on the internet. Umm, congrats? The rest of your argument is bunk as its trivial to find out what your gas capacity is and know your max range is. Most people don't worry about how much it will cost to drive to grandma's cost.
Also, gas is cheap and Americans are wealthy. We don't buy one or two gallons and walk away hoping to get through the weekend. We typically fill our tanks and off we go. Long drives are the norm here as you may have friends/relatives in the suburbs or out of state.
On top of it, our geography is HUGE and unlike "big" countries like Russia or China or Canada its almost all drivable/livable/usable. Knowing your range is more important to most people than knowing how much it costs to get to grandma's house. Its in your countries where gas is super-expensive that you have to worry about those things. Not here, at least for most people.
MPG is a perfectly rational way to talk about car efficiency, even in everyday use. Considering the typical IT automation in cars nowadays, this argument is academic as you can trivially bring up up all sorts of info on the console.
Sorry, but the usual "the Euro way is the only and the best way" whining is wrong again. Turns out there are lots of good ways to do things and "good" is relative to the needs and expectations of the user.
Can you even get a 10-20mpg car without resorting to niche items like heavy trucks and such, where the buy would be fairly sophisticated in fuel usage considering its pretty much a work truck? This probably isn't too big of a concern from a practical standpoint. Avg fuel economy in the USA in 2014 is 24.1. Changes from there are small increments, ignoring hybrids and ultra-efficient vehicles.
I'm British and prefer mpg. Why? Because for starters kilometres are alien to me, but also because it's just familiar and relatable. But with that said, the numbers manufacturers give are never even vaguely useful IMHO (my car is technically 40mpg but I get low 20s) so it's more for comparison of efficiency between journeys than anything else.
It's just as simple doing the same conversion for mpg. If I'm going 250 miles and get 25mph I instantly know that's 10 gallons multiplied by whatever the cost of fuel is
Sorry, this is a non-argument because you are trying to solve a non-existing problem.
The calculation used to determine range or cost when you have miles-per-gallon or km-per-liter is trivial and just as familiar as the liters-per-distance calculation when viewed in context.
My point is that if you actually LIVE in an environment where miles-per-gallon is the norm you develop familiarity with the numbers. You develop a sense of proportion. The calculations are not difficult because they are normal to you. To anyone transitioning back and forth between the two systems, well, there will have to be an adaptation period during which things will be uncomfortable until they are not.
Besides, people very rarely have to make these calculations today. My car tells me how many miles I have left in the tank based on the average historical fuel consumption since I've owned it. No math required. When I fill up, it updates that number.
Still, you very quickly learn that you get X number of miles with a full tank of gas. You just know that. You also learn you need to refill your tank N number of times in the course of a month on average due to your normal driving patterns. None of this requires much thought. And, if you are going on a long trip you generally know how far you can go on a single tank of gas and hopefully you've verified that there are gas stations along the route to top-off as you go (which in the US is generally the case).
As far as calculating the cost of a trip, again, if you live in miles-per-gallon land it is easy. Nobody goes into a crying frenzy screaming "Why, oh why don't we use liters per 100 km. This is so hard!". No, instead people have an estimate of their average miles-per-gallon or an accurate historical average from their car's information display system. They get the distance to their destination and divide. And, no, there's no need to divide 483.5 miles by 21.3 miles-per-gallon. That's insane. Nobody does that. Your goal is to get a sense of proportion of how much fuel you'll need. So, you divide 500 by 20 and you'll get a decent number. It won't be twice that many gallons nor half. There are plenty of gas stations along the route. No worries. And, if you need an accurate number for reimbursement purposes, well, keep the receipts.
So, again, I think you are trying to solve a non-existing problem.
Now, on the question of metric vs. imperial. Well, I detest the imperial system of units. I hate it. I use metric for engineering purposes. The world is metric. It is ridiculous that we haven't made the switch.
That said, I fully understand why. Unless you've traveled through the US it is hard to get a sense of proportion. This place is huge. The infrastructure is of unimaginable proportions. Going metric could very well take 100 years due to the sheer amount of work and cost involved. So, yeah, I get it.
There are other seemingly minor examples of this. We sell internationally so I am very aware of cultural and systemic differences. For example, most of the world would write one thousand dollars like this: $1.000,00. In the US it is written like this: $1,000.00. In the US 1/2/2015 means January 2nd, 2015. In the rest of the world it means February 1st, 2015. In the US we use AM and PM. In a good deal of the world it is a 24 hour clock (which makes far more sense).
There are a lot more examples of this. If we can't fix something as simple as what the comma and period mean when speaking about money or the order of the day and month on a date we are doomed to fail in shifting the US to the metric system.
Sorry, but I never never said it was metric vs imperial. The emphasis was on mpg vs gallons per 100miles if you prefer it this way. The first one is good for advertisers the other one for truly understanding how much your travel costs you. (Yes, you can do a division instead of multiplication as pointed out but ask an average Joe how much a trip costs him)
>I'll never understand why different [organizational unit] does things differently than me. My way is superior because I've formed a mental model of it.
As a car nut, this actually seems pretty reasonable; if you take that diameter and divide it by (fuel injector duty cycle at cruise rpm, times number of injectors), the resulting diameter should be pretty close to the car's injector outlet effective diameter!
The one issue with the blog post that nobody seems to realize or point out. Is that fuel consumption is measured, and calculated internally as kilograms per kilometer. The change to volumetric units is done for the benefit of the population.
This comes into play because namely, thermal expansion. Normally even in return less engines fuel is used to cool injector heads, as well as some body block parts (depending on engine design), as hotter fuel more readily reacts, and is already being routed to the warmed parts of the engine.
That seems like a coincidence, that the relative velocity between the car and the fuel shooting through its injector should be approximately the same as the relative velocity between the car and the road.
One could conceivably build a car with half-size injector nozzles that squirt in the same volume of fuel per unit time.
> Note also that there are approximately 3.785 liters in a gallon, not 4.5461 as stated in the original article.
"gallon" is a unit of volume in several systems of measures, most notably the US Customary system and the Imperial system (these systems are often incorrectly conflated because many of the units are the same, and where the units are different many of the names are still the same.) The size of the gallon is not the same in those systems:
If you start with mass per distance (kg/km), and you divide by fuel density (mass per volume, kg/L or g/mL), you get area (ca or m^2).
If you start with distance per volume (km/L) and cancel the matching units, you get inverse area (ca^-1 or m^-2).
This doesn't make sense until you realize it is the conversion factor between volumetric flow rate and volumetric flux, and is the number you need to associate volumetric fuel consumption rate (volume per time) with speed (distance per time), which is exactly what you're doing when you think of the fuel supply as a continuous trough.
This is a simplification. Different vehicle speeds will be more or less efficient. Volumetric flow rate is an integral of the volumetric flux over an area. So the area is the average aperture size. If your vehicle had a mass-ignoring, initially-empty reserve tank of infinite size, scooping up fuel from an infinitely long trough with the specified cross sectional area, it could go an infinite distance. You need the tank because different speeds may require more or less fuel flux. You need to travel at a more efficient speed before you can go to a less efficient speed.
You could do even better if the tube were carrying electricity instead of gas. Maybe it would have enough power to carry a whole bunch of people at once? Hey, I think I'm on to something!
(0.1 mm^2 is half the cross-section of AWG 24, getting close to hair thin.)
I don't think you're correct here. For round numbers, let's take a 100 kW engine (134 hp), and suppose we feed 100 V. At full power, we'd be running 1000 Amps down that wire. Even at 1 kV it would take 100 A.
Better get a superconductor. Or a much thicker power cable.
He was using the wire AWG as a way to visualize the size for those of us that are familiar with human hair, but unfamiliar with visualizing things that are fractions of a mm thick.
He was not saying anything about replacing the amazing energy density of gasoline with electricity over a copper wire.
Agreed, the south shore chicago trains have feelers to harvest electricity as they go. Maybe a Tesla with a whisker on top could go indefinitely on long stretches of highway.
1 kg of fuel reacts with 3.51 kg of oxygen to produce 3.09 kg of carbon dioxide and 1.42 kg of water
Scaling that to the standard density of 0.755kg/L, that means 2.65kg of oxygen for 1L of gasoline. Assuming the typical 20% oxygen content of air at standard temperature and pressure, that is over 9000L of air.
So the air consumption of a car with fuel consumption of 0.1mm^2 is 0.0009m^2 or 900mm^2.
If one needs 9000L of air to burn 1L of fuel, that would be 9000(0.1mm^2) not (90000.1mm)^2. 900mm^2 is much saner don't you think. I doubt the car would be able to scoop 900000mm^2 as it is 0,9m2. Can you imagine that amount of air fed into engine? Me neither.
It's not a strange assumption to make, given how the prefix system works for true SI units. The litre/liter is defined as a decimeter cubed, or 0,1 m^3. It is a metric unit, but not SI. Still, it is allowed within the SI system...
Of course, you'd probably do a little better than that, because at no point would your car be carrying all of that gas. But the trough would have to get wider when you went uphill or had to get going at a light.
Instead of scooping up the fuel, you could think of it as laying out the fuel in a line behind the car. All the fuel starts off in the fuel tank, and slowly drains out of the car. Fuel efficiency is how large the hole is that the fuel drains out of. In reality, it gets turned into a gas and blows away, but the effect is much the same.
Not really, fuel consumption as an input takes carrying or not carrying fuel into account...same as wind resistance of the pickup or the friction of it moving through a trough of liquid or the force of the liquid moving into the void behind the pickup, etc.
For comparison, what would be the radius of a continuous cylindrical battery that powers the Tesla Model S? Assume, perhaps, that the battery has the same energy density as a typical AA battery.
Using liters/100 km, it's a tad easier, we just have to get the orders of magnitude right
- liter = (100 mm)^3 = 1e6 mm^3
- 100 km = 1e8 mm
So, 10L/100 km is 0.1 mm^2.
(Note that we want low values, and this is on the high side for European cars - the usual advertised numbers for sedans are half of that, with reality somewhere in between.)
I suppose it depends on your definition of "car", but they've been doing this for many years in the World Solar Challenge. GM's Sunraycer drove across Australia in 1987 on solar power alone: http://en.wikipedia.org/wiki/Sunraycer.
[0]: http://what-if.xkcd.com/11/