Comparing mileage: Not all mpg's are created equal

When thinking about saving gas, it's useful to remember that not all mpg's are created equal.

Among very fuel-efficient cars, the incremental savings for every extra mpg is small. However, among very inefficient cars, even a 1 mpg savings can be significant.

Researchers at Duke University Fuqua School of Business recently released a study showing that consumers often make poor decisions when it comes to fuel savings.

For example, consider a family that owns a Chevrolet Tahoe as a family vehicle and a Toyota Camry as a commuter car. The Tahoe gets 14 mpg and the Camry four-cylinder gets 24 mpg, according to Consumer Reports testing. (Mileage figures used to illustrate the mpg mathematics are based on late-model cars.) Assume each vehicle is driven the national average of 12,000 miles per year. In an effort to save fuel, the family might be tempted to buy a high-mileage hybrid. To maintain the convenience of the Tahoe, they consider trading in the Camry for a Honda Civic Hybrid that gets 37 mpg—a 13 mpg improvement. This transaction would save them 176 gallons of fuel a year. At $4 a gallon, that would be a savings of about $700 in gas alone.

MPG	Gallons per 100 miles	Fuel cost for 12,000 miles	Cost savings from 5 mpg gain
10	10	$4,800	—
15	6.67	$3,200	$1,600
20	5.00	$2,400	$800
25	4.00	$1,920	$480
30	3.33	$1,600	$320
35	2.86	$1,371	$229
40	2.50	$1,200	$171
45	2.22	$1,067	$133
50	2.00	$960	$107

But the savings could be even greater if they considered replacing the Tahoe with a Toyota Highlander that still seats seven and gets 18 mpg. While that’s only a 4 mpg improvement, the total savings in replacing the gas-guzzling Tahoe would be 190 gallons a year, or $762 in fuel.

While the Civic Hybrid might yield better bragging rights, differences of a few miles per gallon are amplified with cars that get poor fuel economy, while cars that get good fuel economy face diminishing returns for each additional mile per gallon. Of course, when considering downsizing, it is important to look at the complete owner cost situation, as trading in too soon (say, mid-way through a loan term) may not be the best deal in the long run. (Read “When to downsize your car.”)

To help consumers make better comparisons, the Duke researchers propose comparing fuel consumption—gallons per mile—rather than fuel economy in miles per gallon. This would help consumers make more direct comparisons between fuel costs, emissions, and a car’s contribution to global warming or global oil consumption.

In addition to our fuel economy measurements, Consumer Reports also translates that into annual fuel consumption and costs in our model pages, available through pulldown menus on the major Cars pages and through the New Car Selector.

The chart embedded in this post illustrates the numbers, based on rounding the current national gasoline price average of $4.06. To look at this in a different way, try the university's "The mpg illusion" interactive quiz.

This Duke study shows the importance of knowing how numbers translate into real dollars and supports the notion that it is key to factor the total owner costs when considering buying a new vehicle, especially if pain at the pump is the prime motivator. Ultimately, every gallon saved helps not only your wallet, but also aids national conservation and benefits the environment. Just make sure you understand the full picture before you buy that next car.

—Eric Evarts

For more information on saving fuel see our reports on how to get the best gas mileage and where to find the cheapest gas.

Comments

[Gareth]

So you should have two fairly high MPG cars as opposed to a Hybird and a Hummer. I guess it's all to do with a graph - if you have two cars and plot the costs, you wanna get those two cars to be consistent and not too far away from each other.

[Gerald Wilson]

You presume in your article that a Highlander is a direct replacement for a Tahoe, and this simply isn't accurate. These two vehicles are, excuse the cliche, "apples and oranges". I seriously doubt many people that require the capabilities of a Tahoe-like vehicle are going to cross-shop with a Highlander, or consider a Highlander-sized vehicle an equal replacement. One needs only to compare the vehicles respective load capacities and towing capabilites to understand this.

Conversely, the Honda Civic Hybrid as referenced is a much closer replacement for the Camry, hence the reason most families would make a decision to replace the Camry, not the Tahoe, in your scenario. The monetary benefit to replace the Tahoe is only $62.00 ($762 - $700) annually, not at all worth the loss in functionality that if offers for most families that require such a vehicle.

[Sid]

Europeans have long used liters per 100 kilometers to measure fuel economy. The lower the number, the better.

[Paul Rivers]

To the person commenting about the Tahoe vs. the Highlander above, the "capabilities" of the Tahoe to the Highlander are different, but not different enough to support your "apples to oranges" claim. We're talking about 2 suv's here, not an SUV and a convertible.

Towing Capacity
Tahoe: 6,700
Highlander: 5,000

Size
Tahoe: 202 inches
Highlander: 188 inches

Cargo Area:
Tahoe: 50.5
Highlander: 37.5

3rd row seat comfort rating:
Tahoe: 1/5
Highlander: 1/5

[Elan]

I don't know why Consumer Reports continues to propagate the myth that a Civic Hybrid gets only 37 MPG. I've owned a Civic Hybrid for more than three years and have kept complete mileage records. I get 45 MPG, even though I live at the top of a hill that reduces my mileage by 1-2 MPG.

The database at greenhybrid.com also shows hundreds of Civic Hybrid owners averaging 45 MPG.

[Jeff Bartlett - Consumer Reports]

Gerald - The assumption here, and with other blogs written on downsizing, is that this consumer is looking to reduce operating costs. To do so, some compromises have to be made.

Elan - The figures published by Consumer Reports reflect our scientific, repeatable testing providing a reliable basis for comparing models. Without question, results may vary based on real-world driving situations and individual driving style. (These elements are carefully controlled by our test methodology.) We provide more detailed fuel information on our model pages. On the highway, we rate the Civic Hybrid at 40.

[Francois L]

Why is it that everytime you talk about economy, you automatically want to have it replaced with a Toyota or Honda?

Acadia awd: 18 mpg
Yukon Hybrid: 20 mpg

Why ,in your article didn't you talk about:

Sequoia: 14MPG
Acadia FWD: 19MPG

Or:

Nissan Armada: 14 MPG
Ford Edge: 19MPG

By the way, the big player now is Toyota. You can stop the beatification process. It is not necessary anymore.

[Jeff Bartlett - Consumer Reports]

Francois - The reason Toyota and Honda models have been used so frequently in our fuel economy pieces as downsizing examples is that they excel at fuel economy in their given categories and meet our criteria to be recommended. All fuel economy figures we quote are based on our own testing. You cite the Acadia at 18 mpg. We got 16 mpg overall in our testing. Likewise, we got 16 mpg with the Edge. Neither then is an appealing down-sized alternative if fuel economy is a major concern. True, we could have used other comparisons, starting with the Nissan Armada or Toyota Sequoia, but we try to focus on popular scenarios. The Tahoe simply outsells them both.

You can sort our SUV ratings by mpg to explore other scenarios (available to online subscribers).
http://www.consumerreports.org/cro/cars/types/suvs/ratings-comparison.htm

[Dave Renken]

While the Highlander and Tahoe have differences, the point is- savings on a low mpg vehicle is way better than savings on a high mgp vehicle. The chart shows an amazing difference.

[Alan Dooley]

Early in this thread there was a reference to "people who require the capabilities of a tahoe-like vehicle." There certainly aren't many of them. "Want?" Maybe. But certainly not need. And that's America's problem -- it's not a shortage of fuel but an over supply of people who just "want."

[Mark]

I think the subject of the article is worthwhile, but the way it is written is convoluted. The whole focus is on whether to keep a three year old model vehicle. It would have been nice to have a table that shows the economics of trading in at 3, 4, 5 and 6 years. This wouldn't have to be for every model, but it would give an idea of the progression. The charts are confusing also, because at first glance, you can't see where depreciation figures in. You have to read the text of the article and trust that it is there.

Having said this, I got the point of the article. Thank you.

[Dude]

Um... 1700 pounds difference and 13 cubic feet of space. Yeah that's apples and oranges. Don't believe me; put your 3 kids and luggage in the Highlander then hook up to your 6000 pound boat. I'm pretty sure you're gonna see a difference.

[Jeff Bartlett - Consumer Reports]

Mark - The intent here was to explore this alternative way of looking at mpg figures. We have recently published a comprehensive report on the economic realities of downsizing, including specific examples.

Check out the main story at:
http://www.consumerreports.org/cro/cars/pricing/car-downsizing-fuel-economy/overview/car-downsizing-fuel-economy.htm
There are links to related blogs that drilled into other issues and examples scenarios.

Dude - To make a marked improvement in fuel economy, and ownership costs, it is necessary to choose a different fruit. Otherwise, the option would be to spend more than $50k on a Tahoe Hybrid.

Alan - Great point. The economy is pushing consumers to better balance their "wants" and "needs." Our recent gas prices survey shows that is exactly what is happening:
http://www.consumerreports.org/cro/cars/new-cars/resource-center/gas-prices-survey/overview/gas-prices-survey.htm

[Colin Fisher]

I am a subscriber to Consumer Reports. You list Overall mpg for cars evaluated. Can this figure be related to the EPA City mpg and Highway mpg?

[Jeff Bartlett - Consumer Reports]

Colin - On our model pages online, we present city/hwy for both our test numbers and the EPA. It can be found on the "Ratings/Specs" page for any vehicle. Generally, we feel the revised EPA numbers are much improved and although they are often a touch optimistic.

This video gives a basic overview:
http://video.consumerreports.org/services/link/bcpid1329233564/bclid1631259885/bctid1281309774

Article gives more complete explanation:
http://www.consumerreports.org/cro/cars/new-cars/resource-center/fuel-economy/epa-mileage-figures/overview/0709_mpg_ov.htm

Random example, the Ford Fusion 4-cyl:
CR 15 city / 32 hwy, 23 overall
EPA 24 city / 32 hwy

[Francois L]

Jeff,

I used the info from Fueleconomy.gov, which is a federal agency. Now, combined ratings is very very misleading because it is based on a % of city/highway driving.

The numbers I gave to you are accurate, as far as US gov is concerned.

Reliability is another topic. Highlander has been redesigned, so how can you tell it is going to be reliable? Keep in mind the Camry.

The subject of your article is fuel economy.

How did you test the fuel economy of those vehicles and why is it your results differ from those of the US dept of energy? It seems to me that US agency must have reliable methods, I think.

How about this one:

FJ Cruiser : 17
Pontiac Torrent AWD: 19

My point is this: average fuel economy is no longer an accepted norm to evaluate a vehicle. The US agency is a norm which is easy to verify. Fuel consumption is a very evasive norm to evaluate and can vary a lot dependind on who's the tester.

http://www.energy.gov/yourcar.htm

[Corbey]

Interesting perspective. Any chance CR might develop an interactive calculator that would help people decide whether it's financially advisable to trade in a vehicle? With so many factors to consider these days, like MPG, depreciation, declining trade-ins, finance charges, insurance, etc., it's a difficult decision to make. Thanks.

[Alex]

I congratulate the author for bringing the problematic MPG scale to the public attention.

The key message in this article is to show problems with the currently use of the MPG-scale. The scale can be misleading since 5 MPG difference between 10 and 15 MPG is not the same compared to 30 and 35 MPG difference, even if someone could argue that 5 miles remains the same distance.
Let me give another example. The way people measure their income is usually by $/time unit (i.e.) 20$/hour or $50,000 per year. Translated into the fuel economy world that would mean hour income is measured by hours to work to make $100.
I guess everyone would agree that the difference between 10 and 15 hours of work is not the same compared to 30 and 35 hours to make $100.

[Ed]

Do people really pat themselves on the back when they down size from a Tahoe (that they probably do not use) to a highlander (also useless)? I mean to go from 14 mpg to a wopping 18! GIVE ME A BREAK! No one NEEDS an SUV everyone on the planet earth go along just fine up until about 15 years ago when SUV were not popular, and now it seems that only people in the USA NEED them.... Grow up. You say that downsizing from a gas hog to a gas hog that get slightly better millage will improve your saving most significantly. However, did you take into account how many THOUSANDS and THOUSANDS of SUV owners will never take them off road, never pull ANYTHING, and sometime fill the back up with groceries from costco to help justify their stupid purchase? How about downsizing from the tahoe to a civic hybrid and see what the savings are! "Ed I cant downsize to a small puny car, I have a 2 kid, a hamster, and dog named muffin!" Get over it. If you have a boat, consider renting a truck for the 1-2 days a year you actually use it. Yo use it more than that? Pay a few bucks to store it closer to the dock/lake. These are really not that hard of problems to solve guys. No one should be commuting in a 6,000 pound piece of metal. Period. Sell the status symbol and stop whining about gas prices/environment/war/economy.

[jen]

Nice article, Eric. Very helpful -- Thanks.

[Angie]

I think Ed is forgetting one point. I can buy and drive whatever vehicle I so choose, be it a "gas hog" or a "hybrid". When I was younger, I drove Nissan & Honda. As I got older and had children, I chose a havier, sturdier, safer SUV. I started out with Chevy Blazer, then Tahoe, then Yukon and now the Chrysler Aspen. I do not mind paying more for fuel than someone who drives a Civic Hybrid. So long as our new President does not decide to shut down gasoline sales (for everyone except for his big non-hybrid Tahoe and Chrysler 300), I will be just fine.

Vehicles are a personal choice Ed. You are free to make your choice and others are free to make their choice. Though, I must say, those of us in the South who actually "DO" use their Big SUV's for off road purposes, laugh at you city folk who own them as a status symbol. A Chevy Tahoe and Ford Expedition are a necessity in the South. A Lincoln Navigator is a joke. Hmm. Maybe someone should pass the word on to all the "green" celebrities, Al Gore, Barack Obama and Nancy Pelosi - that they should all dump their big fat gas hogs and buy a Civic Hybrid... I bet they won't. They like their luxiry suv gas hogs as much as I like mine.

It's a free country Ed (for now) - stop trying to indoctrinate or bully.