Experts find key to saving fuel: say gallons per mile | Hacker News Reader

Experts find key to saving fuel: say gallons per mile

guardian.co.uk

41 pointsczik29 comments

If you cross the pond often, it's useful to remember the following: x mpg * y l/100km = 240 (or more exactly 235 and change, but 240 has more divisors and is easier to manipulate).

Illustrated:

10 mpg = 24 l/100km

20 mpg = 12 l/100km

24 mpg = 10 l/100km

30 mpg = 8 l/100km

40 mpg = 6 l/100km

60 mph = 4 l/100km

Small cars in EU are i the 4-6 l/100km range, or between 40-60 mpg. Sedans are typically between 8-12 l/100km, or 20-30 mpg.

HTH

My brain's frazzled. Are you using US gallons or Imperial gallons in those calculations?

I'd suggest they go a step further though. The first thing I do when looking for a new car is convert the mpg figures into pence per mile.

I used US gallons.

If they did that then the figures would change daily and be different for each market in which the car were sold.

if it could be done in a way you could see something updated a week, would be interesting - maybe would make people think twice before a longer trip (would work with me).

This is the kind of rephrasing of concepts that's just so ingenious and makes you wonder why no one thought of it before. Props to the people behind the (so obvious, so effective) idea!

Uhmm, it's been used in the rest of the world (I can vouch for Europe) since forever? In the form of liters/100km.

OK, then props to whoever is bringing this idea to the USA :)

That's like pointing out the Arabs invented algebra before the Europeans started using it, so the European mathematicians don't deserve any credit at all.

Props to these guys and the entire denizens of Europe, if that makes you feel more politically correct :)

Canada requires fuel economy figures in liters per 100km.

So does China

And the rest of the civilized world.

(Sorry, I just like the SI system of units.)

It can be confusing in the UK where economy is usually quoted in mpg whilst petrol is sold in litres.

Actually I think the Imperial system is better in this case. I find it easier to remember a number which is an integer in the 20-40 range than a real between 5 and 10.

I find that in my mind, most of the relevant numbers tend to get rounded up to "a bit less than ten" anyway.

Only for you - and only for the current state of efficencies.

I still can't wrap my head around celsius. Is 20 celsius hot? Is 25 hot? I'm not sure. I'd have to convert it to fahrenheit in order to get a feel.

Same thing. I know that 20 mpg is somewhat bad, 30 mpg is somewhat good. How about... 0.05 gallons per mile? I'd have to divide it first. This is the reason why grocery stores sometimes advertise prices at 4 dollars per 9 units, and similar. They know people can't work out that math instantly...

But like everything, if you use it for a little while you get an intuitive sense for the numbers.

I used to struggle with celsius as well, but then I lived in Spain for a while. Once I stopped converting to Fahrenheit all the time and just tried to associate the numbers with days that I remember, I got where I know that 20 is fresh, 25 is warm, 30 is getting toasty, and 42 is a smokin' hot summer day in Sevilla.

This is a solution looking for a problem. This just solves the 'I save exactly x gallons' while most people just want to drive to work slightly cheaper.

The problem is that "miles per gallon" gives you a false impression of your costs and the fuel savings you get by switching to a more or less fuel-efficient car.

This is likely not a problem that many U.S. citizens are aware that they have, though.

They're a lot more aware of it than they were a year ago.

I think it's pretty clear that the problem is car pollution. Like the article says, effectively communicating a cars "greeness" is the point. However, I do admit that changing completely to this number might be a bit weird. I'm not very good at math, but wouldn't the GPM number be a decimal usually? Like .025 GPM? That might be a bit of a mental leap for the general population to take.

I suppose a compromise could be reached if these numbers where used in tandem i.e. 15mpg/.0XXgpm

edit: Scratch that. It's not really about car pollution as it is about conservation of fuel/saving money which are different things.

In Germany you usually talk about how many liters it takes to drive 100 km. And you get numbers of around 5 to 10 (or higher).

Even the article says: "When the tests were repeated using gallons per 100 miles, the volunteers correctly picked the greenest option from those available."

Yeah, as the Verizon reps made stunningly obvious[1], the average person struggles with small decimals, but making it a figure like gallons per hundred miles (or liters per 100 km like I have seen in Europe) would make it easier.

I heard a similar story to this on NPR the other day. It pointed out that the EPA already gives it's efficiency ratings in gallons per mile, which are then converted back to miles per gallon for the (not so) benefit of the consumer.

I actually really liked the idea of gallons per 10k miles. This gives a nice beefy number to think about. For instance, my 2004 Chevy Aveo uses 294 gallons per 10k miles. My dad's truck uses 625.

I think they could take it even further and just put a dollar figure on the car. Say the entire industry agrees that 15k miles a year is normal. Pick a gas price for that year and put the total cost of gas on the vehicle. At $3.50 a gallon, my car would have $1544 on the window, whereas my dad's truck would have $3281. That is a difference that is immediately obvious to everyone. They do something similar with appliances, where they list the estimated annual operating cost, which makes picking the most efficient fridge quite easy.

[1] http://imgs.xkcd.com/verizon_billing.mp3

Actually, the window stickers on new cars (at least in this state) do have a "total estimated annual fuel cost", don't they?

That reference clip is amazingly sad.

I couldn't find one listing of a gallons per mile in the article.

http://www.google.com/search?q=20+mpg+in+gallons+per+mile

Is that correct for what they are looking for? My car gets .05 gallons per mile! Wait the structure on that sentence is wrong isn't it?

They corrected for this in the tests:

> the tests were repeated using gallons per 100 miles

You could also say "aught-5 gallons per mile," where the decimal is placed by convention. Though then you run into trouble with the .009 gpm cars...

My car shows me this on its onboard computer. It gives me instantaneous and averaged litres per 100 kilometres.

Yes, but will the car manufacturers actually do this? Sounds to me that it could cost them some sales...

Only if gas guzzlers are more profitable than efficient cars, which, granted, has been the case up until now. However, with so many companies trying to differentiate based on green credentials now, it seems likely that their high margin business will be in efficiency in the future.

So short answer: maybe.

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