Where are the most important MPG increases, at the upper or lower end?
by Sam Abuelsamid on Jul 23rd 2009 at 11:37AM 
Imagine, if you will, taking a sheet of paper and cutting it in half. Now take one of those halves and cut it in half again. Now keep repeating the process. As you keep cutting, the difference in the size of the subsequent pieces gets progressively smaller. This simple example is a demonstration of why continuing to increase the fuel mileage of a vehicle has less and less impact once you get beyond about 35-40 mpg.Time for a bit of a math lesson. The amount of fuel consumed by vehicle is determined by dividing the number of miles driven by the miles per gallon. With the mileage being in the denominator, as it grows at a linear pace, the overall result gets progressively smaller. This is what's known as a geometric series. One last example: imagine you have a pie that represents the amount of fuel you use to drive a certain distance at a given mileage. Continue reading after the jump to find out what happens to the pie.
Slice the pie in half. Half of the pie represents the fuel used if you double the mileage. At first, each cut is a big deal. You can go from one pie to half a pie by doubling the mpg. But now cut the pie again and again. As you keep going, the difference in the size of the slices gets smaller and smaller. It also gets progressively more difficult to slice the pie. Similarly, improving the efficiency of a car gets more and more difficult. The cost of increasing efficiency rapidly outweighs the savings – both financially and in terms of its effect on the environment – particularly if you are looking for a larger vehicle.
In the United States, where larger vehicles have long been the rule, the benefits of hypermiling a Prius to get from 50 to 60 mpg may be personally satisfying to the individual driver, but in the grand scheme of things, it will have almost no measurable impact. On the other hand, smaller improvements to vehicles that get mileage in the teens and even twenties has a much bigger impact. Another way to understand this phenomenon is to think in terms of gallons per mile (GPM) instead of miles per gallon.
An improvement from 12 to 15 mpg yields a fuel consumption reduction of 200 gallons per year over 12,000 miles. Even going from 21 to 24 mpg saves 71.4 gallons annually. By comparison that 10 mpg increase from 50 to 60 mpg only saves about 35 gallons. That's why, when General Motors introduced its two mode hybrid system, it went for the big bang for buck by applying it to full-size SUVs and pickups. In retrospect, as big truck sales collapsed in 2007-8, the demand for the hybrid versions was too limited. Still, similar reasoning explains why Ford is introducing it's EcoBoost direct injected turbocharged engines starting with the new 3.5-liter V6.
Gallery: Lincoln MKS with EcoBoost
The same phenomena is part of the reasoning behind cash for clunkers. Taking older, lower mileage cars off the and replacing them with vehicles that only get 8-10 mpg more can have a much bigger impact than replacing a 35 mpg car with one that gets 45 mpg. Of course, there are other issues with the specific implementation of cash for clunkers in the U.S., but that's another story. The really important thing in the near term is to make improvements to high volume, high consumption vehicles.
If two million vehicles that currently get 15 mpg were improved to 24 mpg, that would save 267 million gallons of gasoline annually. The American Petroleum Institute estimates that each 42 gallon barrel of crude yielded 19.4 gallons of refined gasoline. That would amount to savings of 13.7 million barrels a year. A similar 9 mpg improvement from 33 to 42 mpg would only save 4.9 million barrels a year. With an additional 2 million new vehicles displacing older vehicles every year, the savings would be compounded. It's certainly important to improve as many vehicles as possible, but with limited resources, the poorest vehicles deserve the biggest efforts. Now, who's got a bit of pie for me?
| Mileage (MPG) | Amount of fuel used per year (gallons), 12,000 miles | Savings per year (gallons), 12,000 miles | |
| 3 | 4,000.00 | 4,000.00 | |
| 6 | 2,000.00 | 2,000.00 | |
| 9 | 1,333.33 | 666.67 | |
| 12 | 1,000.00 | 333.33 | |
| 15 | 800.00 | 200.00 | |
| 18 | 666.67 | 133.33 | |
| 21 | 571.43 | 95.24 | |
| 24 | 500.00 | 71.43 | |
| 27 | 444.44 | 55.56 | |
| 30 | 400.00 | 44.44 | |
| 33 | 363.64 | 36.36 | |
| 36 | 333.33 | 30.30 | |
| 39 | 307.69 | 25.64 | |
| 42 | 285.71 | 21.98 | |
| 45 | 266.67 | 19.05 | |
| 48 | 250.00 | 16.67 | |
| 51 | 235.29 | 14.71 | |
| 54 | 222.22 | 13.07 | |
| 57 | 210.53 | 11.70 | |
| 60 | 200.00 | 10.53 | |
| 63 | 190.48 | 9.52 | |
| 66 | 181.82 | 8.66 | |
| 69 | 173.91 | 7.91 | |
| 72 | 166.67 | 7.25 | |
| 75 | 160.00 | 6.67 | |
| 78 | 153.85 | 6.15 | |
| 81 | 148.15 | 5.70 | |
| 84 | 142.86 | 5.29 | |
| 87 | 137.93 | 4.93 | |
| 90 | 133.33 | 4.60 | |
| 93 | 129.03 | 4.30 | |
| 96 | 125.00 | 4.03 | |
| 99 | 121.21 | 3.79 | |
| 102 | 117.65 | 3.57 | |
| 105 | 114.29 | 3.36 | |
| 108 | 111.11 | 3.17 | |
| 111 | 108.11 | 3.00 | |
| 114 | 105.26 | 2.84 | |
| 117 | 102.56 | 2.70 | |
| 120 | 100.00 | 2.56 | |
Reader Comments (Page 1 of 3)
ronEbear 11:45AM (7/23/2009)
Let`s flip it around and state how much fuel is wasted by NOT improving mpg.
Reply
Lorena Palin 12:25PM (7/23/2009)
The article isn't saying that improving MPG is bad- it's saying that improving it to the biggest gas guzzlers has a much bigger impact than improving it to the millage kings.
Which is dead on. The fact is that a family of 4 can't fit in a smart car (at least if they have any friends), you can't deliver mail in a prius, and you can't haul construction equipment on a vespa. So more efficient versions of these larger vehicles are better than driving a 50mpg prius over a 35-40 mpg civic.
locoyocal 1:24PM (7/23/2009)
Lorena, its not about improving big vehicles, it is about getting them off the road.
The popular Dodge Sprinter with diesel gets 30mpg.
http://www.caranddriver.com/reviews/car/03q4/dodge_sprinter_2500-road_test
Phil L. 1:31PM (7/23/2009)
locoyocal -
I'd love to have a Sprinter for family-hauling duties. But they're still awfully pricey - and just *try* to test drive a passenger-equipped Sprinter at a dealer. They're pretty hard to find.
I believe a Sprinter derivative sized closer Econoline/Express models has real potential for families that find normal minivans a tight sqeeze - but it appears far more money is to be made in the cargo/delivery van market, so family-friendly Sprinters will remain a rare sighting.
mike 2:40PM (7/23/2009)
locoyocal - "its not about improving big vehicles, it is about getting them off the road." you are wrong.
There are an incredible amount of trucks sold every year that are used for heavy hauling/towing, contruction, and oilfield uses. 99.9% of which could not be replaced by a van aka sprinter. I have driven a sprinter in greece and they are great for delivery vehicles and light hauling but thats about it. They would never cut it out in the muddy rough conditions up in alberta and british columbia. And what about semi trucks, boats, planes yadda yeadda yadda
It IS about improving BIG vehicles! I bet every 0.1% reduction in fuel for pickups and heavy duty trucks saves more fuel than every prius in the world uses total
polo 7:18PM (7/23/2009)
"Let`s flip it around and state how much fuel is wasted by NOT improving mpg. "
True. This whole "don't improve upper-mileage range" argument is pure propaganda to confuse consumers. The fact is having cars that get 50,60,70 miles per gallon has a significant psychological effect on consumers, even if those figures mean a more marginal savings compared to earlier models. The oil heads would much rather see us worried about going from 12 to 15mpg on SUVs than getting car fleets to average 60+ miles per gallon.
Sam Abuelsamid 10:13PM (7/23/2009)
Polo, having a psychological effect on consumers may make them feel better about what they are doing, but it doesn't do much to actually reduce emissions or fuel consumption.
why not the LS2LS7? 11:59AM (7/23/2009)
Stop trying to say the most-fuel using version of a vehicle (Flex EcoBoost, Taurus SHO) is somehow a fuel saver.
You literally cannot get a version of these cars that uses MORE fuel.
Reply
John 9:00AM (7/24/2009)
Geez LS2LS7, can you not get over your blind and tedious love for all things GM.
The author did not imply Ford was saving fuel with the Ecoboost vs the standard V6 in the Taurus. The implication is that Ford can save more fuel by using a V6 rather than a V8 in larger vehicles (or a V4 instead of a V6) instead of just tweaking the mileage of an already efficient V6 or V4.
why not the LS2LS7? 10:05PM (7/25/2009)
Don't be a bonehead. The article is directly comparing the Ecoboost 3.5L to hybrids. The difference is hybrids are the most efficient versions of the cars in question while the Ecoboost 3.5L is the performance version (and most guzzling in 2 of 3 cases).
Right now, the Ecoboost has not been used in any eco situation, and ABG trying to imply it has by comparing it to hybrids.
There is zero eco about a 355HP family sedan.
merlot066 11:25PM (7/26/2009)
LS2, you and so many other people are obsessed with the "Eco" part of EcoBoost, you forget the "Boost" part. Like they say, "V6 like economy with V8 like performance". If anybody is comparing eco-boost to a hybrid, they're crazy, but if you look at it as it is intended, then it is a complete success so far. Just one example is the Lincoln MKS, I can do this with all the other models if I have to, but I don't really see it necessary.
Lincoln MKS 3.7L V6 274hp 270 ft lbs torque 17/24 MPG FWD 16/23 MPG AWD
Lincoln MKS 3.5L V6 355hp 350 ft lbs torque 17/25 MPG AWD
1 more highway mpg vs. the FWD version and 1 city and 2 highway mpg vs. the AWD would be the "Eco" part, as well as the other things like reduced emissions especially on cold starts. The 80 hp and ft lbs of torque would be the "Boost" part.
It's exactly as they say, V6 like economy (better in this case), V8 like performance.
Ross 12:11PM (7/23/2009)
This is why the European unit of L / 100km is a much better way to measure fuel consumption. Linear.
Reply
PopSmith 12:56PM (7/23/2009)
I also like the European spec of L \ 100 km. It is much more accurate, as are most things done using the metric system. (Although that's another problem, for another time).
why not the LS2LS7? 5:49PM (7/23/2009)
The Metric system doesn't hold any accuracy advantage over any other system. Jeez, what a ridiculous statement. Either system can measure anything you want to as many decimal places as you'd like.
ND07 10:45AM (7/24/2009)
@LS2LS7
I don't think Ross was trying to say that the metric system is more accurate, but rather that measuring "fuel consumption" rather than "fuel economy" might be a better idea. He referenced L/100km, meaning liters per hundred kilometers (note the reversal from a miles-per-gallon standpoint). This has nothing to do with metrics versus imperial units but with how you consider fuel use. Do we want to know how much fuel any given car uses going a fixed distance, or do we want to know how far any given car can go on one gallon of fuel?
Matt 9:43AM (7/26/2009)
We use L / 100kms in Australia too. This article shows it makes more sense than MPG.
12 -> 15mpg converts to 19.57 -> 15.66L/100km
50 -> 60mpg converts to 4.69 > 3.91L/100km
A lot easier to see what saves more fuel
jpm100 12:31PM (7/23/2009)
I think the American mindset got influenced by an orientation of caring more about the time between fill-ups than actual efficiency.
Part of this is from when fuel is cheap, the fill-up nuissance factor is part of the issue. But I believe back in the 70's during our first 'energy crisis' where gas shortages were real people would have to wait in long lines to get their share of gas. So the longer it lasted the better. And in that respect, mileage is the more immediate story teller.
Size of the fuel tank matters too. If makers realized that it was time between fill-ups and not actual efficiency that drove customers when gas was cheap, we'd all have bigger gas tanks. Case in point, the H2. It got complaints about fuel efficiency. Anyone buying an H2 knows what they're getting into in terms of efficiency. What they don't realize is that some genius gave it a tinie winie gas tank. And the only way people have to complain about the frequency of needing to fill up is to ping them in the checkbox labelled fuel economy.
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Rain 12:41PM (7/23/2009)
It's been a long time since third grade,thanks for the refresher,ABG.
If You could somehow come up with a solution for my grammar block,now,that would be useful.
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GoodCheer 12:44PM (7/23/2009)
"That's why, when General Motors introduced its two mode hybrid system, it went for the big bang for buck by applying it to full-size SUVs and pickups."
Really? You think GM did that to reduce total American fuel consumption? What on earth would the benefit to GM be of lower total US fuel use?
I think they put it in big vehicles because the high (initial) cost of a complex system would be a comparatively small increase in total vehicle cost.
Reply
Brian 1:31PM (7/23/2009)
Actually, GM applied the two-mode to large vehicles because it was adapted from a hybrid bus system that GM acquired when GM Powertrain alligned with Allison Transmission in 2003. At the time it was easier to fit it into a larger vehicle than try to cram it into a compact.