A New View of Fuel Efficiency

By Charles Krome

In addition to my writing here at Autosavant, yours truly also has a number of other auto-related gigs, including a semi-regular spot on a weekly web-based “talk show” called Open Line (check it out on Mondays at http://bit.ly/OpenLine). And in this past episode, we chatted briefly about a new approach to fuel efficiency that I’m eager to try out on my fellow Savants.

Here’s my thinking: It’s always struck me as odd when vehicles in two different segments somehow ended up with very similar EPA numbers. For example, both the Ford Fiesta and the new Ford Focus are going to post marks of 40 mpg highway. Now, one way of looking at this is “wow, Ford was able to build a compact car that gets the same great fuel economy as its subcompact.” But I can’t help approaching this from the other side, wondering how, if the Blue Oval can get that kind of performance from the Focus, it can’t do better with the smaller, lighter Fiesta.

Clearly, the Focus is a more efficient package, since it’s delivering the same fuel economy even though it’s bigger and heavier than the Fiesta, right? And, by that kind of standard, a porky full-size sedan with even lower EPA numbers might actually be more efficient than either.

Thus was born what I humbly call the Krome Score.

What you do is calculate how much gas it takes to move a given car a mile, than divide that number by the car’s curb weight. What you’re left with is a measure of how much fuel it takes to move one pound of that vehicle one mile. (Of course, you have to do some adjusting of decimal points to make the numbers “look good.”)

For the Fords, the Fiesta SFE with the automaker’s PowerShift automatic weighs in at 2,575 lbs. as a hatchback and gets the aforementioned 40 mpg highway. Preliminary specs on the five-door Focus with the same transmission and EPA number show a 2,927-lb. curb weight. The outcome here is a Krome Score of .971 for the Fiesta and .854 for the Focus, with the lower number, reflecting the lower amount of gas needed to move one pound of vehicle, being better. Now, when you run the Fusion through this math, it gets even more interesting, because the number for Ford’s mid-sizer comes to .907, which means it too is more efficient than the Fiesta.

The two-ton 2011 Ford Edge? Again, more efficient than a Fiesta, thanks to the Blue Oval’s ability to wring 27 mpg highway out of a vehicle that tips the scales at 4,082 lbs.—the crossover also notched a .907 Krome Score.

Who’d have thunk it?

Author: Charles Krome

Charles Krome is a long-time automotive journalist who spent more than 10 years on the inside at General Motors and Ford, and also has corporate communications experience with Audi, Porsche and BASF Automotive Refinish. As a big motorsports fan growing up in the Detroit area, Krome was lucky enough to be able to attend numerous NASCAR, Indy car, F1 and SCCA events while still in his formative years. This, combined with a childhood that included significant (passenger) seat time in cars from Lotus and Jensen Healey, made him a car guy at an earlier age. Today, he lives in metro Detroit with his car wife, raising car kids.

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16 Comments

  1. The answer is simple: technology. The Fiesta doesn’t have GDI, the Focus does. It comes down to price, Americans still buy cars by the pound, so a smaller car must be cheaper – even though the cost to produce a small car isn’t much less than to produce a larger car. So you have to go lower tech to get the price down.

    2011 will be very interesting for shoppers. You have 3 new compact sedans taking 3 different approaches to 40mpg. You have the Focus with a 2.0L GDI motor and a dual clutch transmission, the new Elantra with a 1.8L non-GDI motor and a traditional 6 speed automatic, and the Cruze with a 1.4L turbo and a 6 speed.

  2. Well, that doesn’t really work.

    Fuel consumption is not proportional to a vehicle’s curb weight, and it would have to be for your numbers to be useful. If you double the weight of a car, you double it’s rolling resistance and its inertia, but aerodynamic drag would be unaffected, so the overall increase in fuel consumption would be less than 100%.

    The way you’re calculating it, heavier vehicles will always score better than light ones, not because they’re more efficient but because the math is wrong.

    In fact you could improve the Krome score of a Fiesta by loading it with 2500 lb of bricks. Twice the curb weight, but you wouldn’t be cutting the highway mileage in half (because the aerodynamic drag remains the same).

  3. The thing I dont understand is next time you go to a Ford Dealership, get the EPA numbers for the New Taurus and the Fusion with the same V6 3.5 litre engine!

    The Taurus is a heavier and larger car with the same engine as the lighter Fusion, the Taurus is rated almost the same city and highway fuel mileage as the Fusion!

  4. Highway mpg is, in my experience, totally overrated. Manufacturers love it because they’re allowed to advertise it in bold letters without even mentioning the city mpg, but in day-to-day driving people will typically see much closer to the city mpg rating as that is where most modern driving is done. Plus, mpg is inherently deceptive. For example, a car rated 25mpg city/40mpg highway is not 32.5mpg combined, it’s 30.8mpg combined. It is gallons per mile that will give you a clear indication of your car’s fuel consumption.

  5. highway mileage is only loosely connected to a car’s weight; it depends more on overall efficiency and aerodynamics

    the krome score is bunk IMO. You might as well calculate the ratio of the square root of wheelbase to upholstery threadcount and call it a meaningful metric!

  6. Try it with the city numbers and you’ll get a different result, I’d wager. Long cruising gears help highway mileage in big and heavy vehicles.

  7. Thanks for your input, everyone. But I’m just not sure we’re all on the same page here. This just measures how much gasoline it takes to move one pound of a given vehicle one mile. If it takes more gas to move a pound of Fiesta one mile than it takes to move a pound of Focus a mile–for whatever reason–the Focus is being moved more efficiently, whether it’s by reason of aerodynamics or technology or whatever.

    Of course, that doesn’t mean highway mpg is a good starting point or that numbers wouldn’t be different if I started with city mpg or a combined. Certainly, vehicles also operate at different efficiency levels in different parts of the EPA cycle.

    Also, as far as the adding bricks business, heavier vehicles aren’t always more efficient: Consider the Nissan Titan. When you run the numbers on a 5,231-lb. 4X4 that gets 17 mpg highway, the score comes out to 1.124, making it much less efficient than any of the lighter vehicles mentioned in the story.

  8. No one gets the highway mpg numbers in real-world driving because very, very few people get on a highway every day and cruise at a sustained 60 mph for an hour or two.

    They might drive at 60 mph for a couple of bursts on their way to 70 mph or on their way down to 45 mph, but it’s for brief moments in commuter traffic.

    Of course their mileage is going to be closer to the city rating…

  9. Charles, trust us, let it go. You’re digging yourself a hole and losing credibility defending this silly thing you made up.

    Look at it this way: you may feel like you invented hot water, but it was really so simple and insightful, don’t you think someone else might have come up with it before? There are 10,000+ automotive engineers that work on various efficiency subjects every day.

    How intellectually arrogant is your pursuit? Sorry if it sounds like a personal attack, it’s not. Just trying to help you save face before you dig deeper!

    Call it an off-season April’s Fool and move on. We still love AS!

  10. What you have there is a crock. Both in technique and (probably) the initial EPA ratings.

    In other markets, those two cars have very different urban/highway/combined fuel efficiency ratings for example.

    I would humbly suggest that all you’ve provided in this article is two examples of ‘you’re doing it wrong’.

  11. Hmmm. There seem to be some issues out there in Savantland.

    This is just comparing how much gasoline it takes two different vehicles to do the same amount of work. The one that uses less gas is more efficient.

    In all seriousness, I’m wide open to input on what’s specifically wrong with that conclusion.

  12. Correction:-

    0.564 for the Volkswagen
    0.179 for the Kenworth

    My point still stands.

  13. But why isn’t it possible that the Kenworth is operating more efficiently than the VW? From my point of view, your example just shows that getting 7 mpg with an 80,000-lb. vehicle is a more impressive achievement than getting much better mpg numbers with a much lighter vehicle. I don’t find that hard to believe.

  14. You are in a sense correct, the Kenworth is a wonderfully efficient machine, and it explains why goods are not shipped around the country in fleets of VW Polos. You miss the point however when you fail to realise that the Kenworth is wonderfully efficient at shipping bulk goods, yet patently horribly inefficient at shipping me down to the supermarket to buy a loaf of bread. In this case the most efficient vehicle is a small, light vehicle with a high MPG. Something like the VW or even better a small motor scooter is best, even though the KromeScore is higher. There is no utility in me lugging 80,000lbs of metal and whatnot down to the supermarket and back. 7mpg tells me this. Sure, I moved 80,000lbs very efficiently, but to what end? Your definition of efficiency is all wrong. Efficiency is not necessarily moving mass from point A to point B for as low a price per lb as possible. It may well be if what I’m interested in is shipping bulk product between cities, but it certainly isn’t if what I’m interested in is getting my groceries home at the lowest cost possible.

    You are ignoring the utility of the vehicle entirely and if you can’t see that, then there seems little point in continuing the discussion.

  15. The miles per gallon (MPG) of fuel a vehicle uses can be deceiving without entering the vehicles gross weight! For an example, a 5,000 lb. pickup truck gets 20 MPG, and a loaded semi-truck weighing 80,000 lbs., gets 7 MPG. Which one is the most efficient?

    The pickup truck delivered 100,000 lbs. in 20 miles, using 1 gallon of fuel. This can be referred to as 100,000 lb./miles. (20 x 5,000 = 100,000)

    The semi truck delivered 560,000 lbs. in 7 miles, using 1 gallon of fuel, and its rating is 560,000 lb./miles. (7 x 80,000 = 560,000)

    With this rating, the pickup truck has to get 112 MPG in order to compete with the semi truck in delivering the same amount of weight per gallon of fuel.
    [(560,000 / 100,000) x 20 = 112 MPG]

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