Where's the True Fuel Economy?

The U.S. practice of measuring automotive gasoline use in terms of miles per gallon (mpg) is flawed, according to the U.S. National Research Council (NRC). By relying on this figure, consumers undervalue small increases of 1-4 mpg in fuel economy for vehicles in the 15-30 mpg range.

So let me get this straight:

According to the U.S. National Research Council (NRC) ... consumers undervalue small increases in fuel economy... so measuring gasoline use in (mpg) is flawed.

The NRC suspects that the numbers might be mis-perceived therefore the calculation mechanism is flawed???

It sounds to me like the NRC isn't happy with the outcome, so they want to change the rules.

True. You save much more fuel going from 10 to 20 mpg than from 40 to 50 mpg. In the first case from 5 gal per 100 miles, in the second 1/2 gal per 100 miles.

The normal way of expressing fuel economy in most metricated countries is litres/100 km. This is similar to what they are proposing (except they are using funny numbers not used anywhere else)

I run propane on my 99 Ford F250 super duty pickup so I figure it a cost per mile ratio. It gives a far more realistic cost per mile rating that way.

Plus being that propane around here is about half the cost of gasoline, some times cheaper too, I can say that my 10 MPG on propane costs the same as having gotten a 20 - 25 MPG cost per mile equivalent on gas which is nice for a big pickup!

In the CA Bay area propane runs from about 85% of the cost of gasoline if you've got a 500 gallon tank and a contract to as much as 130% if you're filling one or two 5 gallon barbeque tanks. You farm folks in ND are pretty lucky if you can get propane for half the cost of gasoline. However, I realize that ND is pretty far from the refineries so that figures into the cost of fuel.

But really the cost per payload-ton-mile is the best measure. Given the electronics in today's cars the cost per mile ought to be right there on the dashboard. An RFID system in the pump and some sensors to tell the vehicle payload is all that would be needed. No reason why the car shouldn't be able to read the cost/gallon of the last fillup and tell the driver how he's doing; but for the sad fact that both the automakers and the energy companies don't want you to know that info.

The railroads have caught on to the ton-mile per gallon idea and are loudly promoting it. I'm not sure it has sunk in to most of the thick-headed American public yet.

Ed Weldon (still wishing I could buy a 108" wb 2800 pound pickup with a 150hp turbo diesel and a 25 gallon fuel tank in it)

Wow that's a great price. Around here in Maryland, you will pay about 3.75 per gallon or more at a retailer. It costs me about fifty something bucks to fill up my two 30-lb tanks for my caravan (travel trailer). I don't know what it costs if you have a large tank with a contract.

Its a dumb idea. I grew up with MPG and now we are metricated I think in km/litre (as well as MPG), but cannot understand the logic of the (German?) system of litres/100km. It is a daft measure, it requires extra calculation to get it for no gain. Simply divide the distance travelled by the fuel used and you get MPG or km/litre.

If your car gets 10km/litre it is 10 litres/100km so there is no increase in accuracy, MPG is slightly different, but when the Americans finally give up their hanging on to the last vestiges of mother England and join up with the metric system, then that won't matter.

I'm struggling to see how volume per distance is any better or worse than distance per volume.

If you can't do the math on mpg then how would you be able to do any calculations on gallons per 100 miles? Anyone that actually wants to know their mpg will test with the odometer and gas receipt. Run till nearly dry then fill up. How far did we get and how many gallons did it take? Or you could even test over shorter distances.

This sounds to me like a government organization trying to justify their existence. The fact that taxpayer dollars are paying for this is ridiculous.

To answer your questions: Yes I trust mpg stats because it gives me a baseline of what to expect from various cars I may purchase. If it's rated for 20-26 mpg then I expect that I may get 18 or may get lucky and get 28 because there are many variables that go into mpg. If I get 12 mpg then I'm contacting the vendor and manufacturer.

And no I do not agree with the NRC recommendation because I think it is a waste of time. I think my text above covers my thoughts.

Personally I prefer the volume per distance figures.

I feel it is far easier to calculate what you need on a trip. Say you want to drive 350 km and the vehicle needs 10l/100 km I know immediately I will use 35 liters. Granted, if the car needs 8.5 L/100 km it is 8.5 * 3.5 or roughly 30 liters which is a bit harder to calculate in your head. But you don't have to be too precise and you need a cushion anyway.

The same goes with cost. From above I multiply with the cost per liter or per gallon and voila, I know the trip cost. All simple multiplications.

Using distance per volume always requires division of numbers which I find much harder to do then multiplying.

But that is just me.

Essentially that is the difference between the two systems. In Europe or Metric you just multiply, in the US you must divide to get your results.

I just use calculus to solve these. Much simpler that way.

The way you do it might be a little easier, but for those of us that would actually calculate using either method, we can probably do most of the math in our head right? I'm just saying that I think the arguement is pointless to begin with. Maybe the taxpayers should see the labor costs involved in doing this study.

And anyone that pays attention to fuel consumption (I'm referring to mpg since that's what I use) knows that you get much better gas mileage driving 60 mph with the cruise set on the highway than in town with stop-and-go traffic. So it's not uncommon to go outside the rated range from the manufacturer.

There are far too many variables that affect fuel consumption to say that there are obvious benefits for one system over the other.

It doesn't make any difference what you call it. 99% of the buying public couldn't care less how much fuel their favorite vehicle gobbles, as long as they are the first one away from that damn stoplight that made them stop in the first place.

How many soccer moms out there care about fuel consumption when they're already late for the game because their make-up didn't cooperate.

It's only people like "us" who even know how to calculate fuel consumption anyway.

My comments are directed mainly at drivers here in the USA.

I've never understood why anybody would waste time burning LPG when they can get diesel with far more energy capacity per unit volume.

These fuel efficiency numbers are all geared to the sales. In Japan, and Europe efficiency is mandated. Diesel engines rule in the world, why not here? A diesel engine in Japan is turned in every 80,000 miles or so for a complete refurbishing. and in Europe, well , diesels have always ruled. A diesel engine, running on biofuel will last for many, many hundreds of thousand miles because there is no spark plug to make carbon, and destroy the engine. Granted, cold starting of a diesel is hard, but there are ways to lessen it's affects.

There should be more companies installing 4 cylinder turbo diesels in our older cars. I think that there is one in California, anybody know about these emerging companies? Also Toyota diesel pick ups not allowed in this country, Why?

Spark plugs create carbon? How does that work? Anyone who has seen black smoke belching out of an older diesel engine might envision that carbon is precipitated out of those exhausts as well.

you are right about older diesel engines,and for that matter all diesels on a "cold start up". They do not have to start so cold. The explosion of the fuel in a spark plug engine slowly destroys it. The "compression" ignition in the diesel engine is much less damaging, AND you can run various bio fuels in it, your choice. The rest of the world know the advantages of diesel engines ( 4 cylinder turbo's especially) but we are stuck in the muscle car mentality. We want our power and we want it now.

craig -- re: "companies installing 4 cylinder turbo diesels in our older cars. I think that there is one in California, anybody know about these emerging companies? Also Toyota diesel pick ups not allowed in this country, Why?"

This is almost heartbreaking. The perfect vehicle for me would be a Toyota like the description in my siggie. With a 5th wheel right over the rear axle it could easily pull my race car on a 14 foot aluminum gooseneck trailer over these high western summits. And I could still use it for everyday driving; thereby going from two trucks down to one. Anybody have leads into your rumored CA diesel conversion source?

Ed Weldon (still wishing I could buy a 108" wb 2800 pound pickup with a 150hp turbo diesel and a 25 gallon fuel tank in it)

Thank you for responding .

The company in question as I remember, was wanting to do away with the gasoline engine. When you drove your gas guzzler (let's say a 55' Chevy nomad) into their shop, they pulled the engine and put it in a compactor for scrap, right before your eyes. Then two weeks later, you came back and picked up your new ride, with a hypo 4 cylinder turbo diesel, and any other restorations you wanted. I think they would also restore cars to the showroom spec's. Wish my old brain could remember the name of this company. ( 5 or so years ago ). But maybe if we can peak peoples interest, more of these cool factories could be built and put some people to work. I really do believe that people love their older cars and trucks, and would gladly crush the Detroit engine. Although I have to admit, the sound of a v-8 muscle car is pretty awesome. (I'll get over it).

Didn't the original dodge ram have a diesel in it? (none for sale, they know what they got)

Thanks again, hope more people respond (especially far thinkers who would like to come to my area and build such a plant and put me to work)

Hello Ed, found some pretty interesting stuff about the Mitsubishi Mitty Max sold by Chrysler in 1982. They were available with a turbo diesel 1983 to 85 , then all of a sudden, they were no longer available. (go figure, maybe the Mitsubishi name was still too fresh in my dads mind), They came in various wheel bases, but probably were under powered for our "truck mentality". ( I was in Europe in 2008 for 3 weeks and did not see 1 pick-up, and all other trucks were diesel of course, AND They "DRIVE RIGHT".)

It depends on how one thinks about their vehicle use.

Right now I have a 10 gallon tank with a 35 [mpg] highway rating, so I can go 10*35=350 miles per fill-up. Was that difficult for anyone?

Per NRC recommendation, I have a 10 gallon tank with 2.857 [gallon/100 mile] highway rating. So now I can go 10*100/2.857=350 miles per fill-up. Same result, but was that really an easier calculation?



"How much faith do you put in mpg stats? "

Driver habits and environmental/regional conditions can significantly affect ratings so ANY rating system should only be used as an approximate guideline for vehicle comparison.

"Do you agree with the NRC's recommendation?"

To me, this just seems like another pointless attempt at bureaucratic self-justification (or self-gratification). Are we really that numerically and computationally challenged? What if the manufacturers just translated fuel-economy into the colors of the rainbow so no one even has to "think" about multiplying or dividing 2 numbers ever again? "I'll take the car with the 'violet' fuel rating please."

Both ratings in any unit system provide the SAME data. As long as one standardized format is provided for consumers, comparison between vehicles is easy.

As an engineer I always prefer to work in SI units, but our maps, road signs, and fuel sales are still predominately in miles and gallons. Having both unit systems on any vehicle is fine, but the metric units will just be ignored by most people here. Only when every other infrastructure is switched to metric will the masses BEGIN to recognize vehicle fuel ratings in units other than [mpg].

"What if the manufacturers just translated fuel-economy into the colors of the rainbow so no one even has to "think" about multiplying or dividing 2 numbers ever again?"

You don't want to leave the option on the table for someone to pick bad fuel economy because their favorite color is red.

I say we dumb it down even more to one of two categories..."Good" or "Bad." Let's give the NRC a couple months to organize a committee to decide what cars fall into each category.

Was this research done in a Dilbert cartoon?

Hi i have been in USA for a few weeks. Living with some colleagues, and i am really choked about the use of gas, (all kinds of energy), that i saw, all your car use about double the gas ore diesel, that we use in Europe, but you pay only half, if you want to do something about your fuel consumption, use TAX and TAX. Even when we pay double of you i think it is still to little. in Denmark for the last year people seem to buy cars with less mpg. so a price equal to 2.1 us$ per gall is not enough. Furthermore we all have to think about what society can do of good things schools, health care etc. with that money.

When we made calculations on electricity from a biogas installation our numbers was 6 cents per kWh. in Denmark 0.78dk.kr about 14 cents, and we complaint that we have to low price compared to Germany.

Wow thanks for reminding me that I was subscribed to this post.

So in Europe, how far do you normally drive? I mean on a daily basis or on your way to work.

The European high energy prices are nothing but taxes to support the social systems the countries have.

If one wants the nanny state and it's tax burden OK. Most in the US don't want anything to do with that system.

The only high mileage vehicles in Europe are the common rail diesels or the ultra mini cars.

The brevity of this article is somewhat mis-leading to all of us.

This issue has been haunting the vehicle industry for many years and the figures produced have to be reassessed again bit I am not sure what is the implication of the questioning.

Miles per gallon is such an antiquated issue as to be wrong particularly when you talk of a US gallon and in other parts of the world they refer to an Imperial Gallon and yet in others they refer to kilometres per litre.

Moving on therefore we also have the other issue of the Urban Cycle and the Combined Urban-Motorway Cycle for fuel economy of cars and to me that is equally as confusing as the other measures.

Perhaps one issue that needs clarifying in all of these is the reference to a common standard that is not managed by the Manufacturers of Vehicles or The Vehicle Manufacturers' Reference Agency but to have a really neutral/impartial one set up to reflect the fact that it is truly imparial and not a fudge.

People who give a $#*! about gas mileage will buy cars that get high gas mileage. The rest of the people don't give a $#*! about it so they will not pay any attention to the fuel economy no matter how it is expressed.

A person who buys an SUV or pickup truck does not care what mileage it gets so there is no use in even calculating it for them.

MPG is the correct way to express fuel efficiency in the USA. As previously stated, the move to change it is just so the goobermint bureaucracy can attempt to justify their existence. It may also be being pushed by auto makers to disguise the crappy mileage of their vehicles. Everyone can see with no question that if a car gets only 25 mpg on the highway that it's a gas guzzler, and that embarasses the car manufacturers and the people who buy those vehicles, and they don't like that and would love to be able to hide the truth.

Diesel will never go over in the US because there are too many cars and all diesels stink. If a significant fraction were diesels, you would not be able to breathe in traffic. Diesel lovers will say the new ones don't stink. Get behind one and you'll know the truth.

Thanks for telling the truth. I'll predict in advance that many will squeal like sows giving birth to a litter of broken bottles when they read it.

Just a reminder, in Europe there is a 'significant fraction' of Diesels on the road and people breath very easily in traffic. No sign of "not being able to breath in traffic".

I think diesel have a hard time in the US because of the attitude expressed in your reply. Nothing personal of course, I know you are not alone, but I think the problem with diesels in the US is one of attitude, and of course of technology as the European Diesel are of very high standard hardly reproduced by the big three.