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Why US Mileage Ratings Are So Inaccurate

timothy posted about a year ago | from the if-you're-wrong-enough-ways-at-once dept.

Transportation 374

Why does a car rated for 47mpg fall so far short? The Houston Chronicle features an article on just why EPA gas estimates can be so different from real-world drivers' experience at the pump (or in looking at the dashboard display), in particular for hybrid cars. From the article: "A geometric average of the FTP-75 and HFET results (with city driving weighted at 55 percent and highway driving weighted at 45 percent) produces a vehicle's CAFE fuel economy, which is then incorporated into a manufacturer's corporate average. CAFE is measured using these tests to the present day. In fact, this methodology will be 50 years old when it's used to gauge compliance with the forthcoming 54.5-mpg CAFE requirements in 2025. That kind of continuity is admirable in baseball, but not in transportation. These tests are irrelevant to contemporary real-world driving. For example, the maximum acceleration on either test is 3.3 mph per second. At that rate, it takes more than 18 seconds to hit 60 mph. Even in the horsepower-deprived 1970s, most people were driving harder than that. And the 60-mph maximum speed on the highway test does not accord with the 75-mph truth of today's interstate traffic."

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First Post (0)

Anonymous Coward | about a year ago | (#43633491)

So my mileage must be great right?

Choice of average (0)

Anonymous Coward | about a year ago | (#43633499)

Geometric average? Why would that be relevant?

Re:Choice of average (4, Informative)

swalve (1980968) | about a year ago | (#43633589)

When you are calculating the average of ratios (miles per gallon) and the denominator is the thing that changes, you have to use the geometric mean. If they used liters per 100km, then they would use the regular average.

Simple explanation (2, Informative)

johnw (3725) | about a year ago | (#43633505)

Well obviously - it's because your gallons are smaller than proper gallons.

Re:Simple explanation (1)

AmiMoJo (196126) | about a year ago | (#43633569)

Actually the European tests do tend to be a little bit more realistic, but are still gamed by manufacturers tuning their cars to perform well in them instead of in real life.

I'm not sure what TFA is saying either... Is 60 the speed limit on American motorways (er... freeways) or is it 75? If it's 60 then I don't see a problem with testing at the legal speed limit, and if you break it then naturally you can't expect to get the same mileage.

Re:Simple explanation (4, Informative)

Anonymous Coward | about a year ago | (#43633583)

American highway speed limits vary depending on the state and location. It's usually 65 but inside a large city it is often 55. In the Texas desert it can be 85.

In any case... (5, Funny)

BrokenHalo (565198) | about a year ago | (#43633847)

I was under the impression that the standard unit for fuel consumption in the US is furlongs per hogshead.

Re:In any case... (4, Funny)

JustOK (667959) | about a year ago | (#43633867)

It was updated, now it's LoC / firearm

Re:Simple explanation (4, Informative)

houghi (78078) | about a year ago | (#43633613)

http://en.wikipedia.org/wiki/Speed_limits_in_the_United_States [wikipedia.org]
The highest speed limits are generally 75 mph (121 km/h) in western states and 70 mph (113 km/h) in eastern states. A few states, mainly in the Northeast Megalopolis, have 65 mph (105 km/h) limits, and Hawaii only has 60 mph (97 km/h) maximum limits. A small portion of the Texas and Utah road networks have higher limits.

So if you live in a 60MPH state, it is accurate. If you live in a 75MPH then it isn't.

So they should have different information for different states. And obviously for city driving as well.

Re:Simple explanation (2)

Kjella (173770) | about a year ago | (#43633725)

So they should have different information for different states. And obviously for city driving as well.

And it still wouldn't really match all real world conditions. I think most cars engines now have very accurate electronic control on the amount of fuel spent at any time, so just make a standard set of "unit figures" for cruising, acceleration etc. given a certain speed, resistance (passengers, luggage, uphill, downhill etc.) and see if you get accurate figures for a full drive profile. That way you can change what is considered a "representative" drive without the need for retesting, or even people could check custom profiles more suited to their actual needs.

The Testing Process is Flawed (1)

nefus (952656) | about a year ago | (#43634017)

In the whole article it never mentions physically how the vehicles are tested. According to Consumer Reports, they are put on a frictionless "treadmill." There is no way in the world you can get realistic numbers from a frictionless testing device designed to falsify the numbers.

Re:The Testing Process is Flawed (4, Informative)

Ironhandx (1762146) | about a year ago | (#43634051)

Consumer reports tends to be a bit sensational. They do get put on a treadmill but the EPA numbers are also based on a circuit of real road driving. 3 tests are done and the average of those tests are then used as the EPA rating.

Additionally theres no such thing as a frictionless treadmill, and the treadmill they use is actually able to adjust its load to simulate real world resistances.

There are plenty of real reasons to bash the EPA ratings, there was no need for consumer reports to exaggerate and make shit up.

Re:Simple explanation (4, Interesting)

kwark (512736) | about a year ago | (#43633703)

The European tests are also flawed, they might be more realistic but the "mileage" is still not applicable to real world situations. The tests are highly optimized, there is almost no way to get these results as an ordinary driver.

There as a consumer program on TV a couple of weeks ago, people were complaining they were only getting 16km/l instead of the advertised 25 km/l for a certain car. This was after driving instructions/coaching from the importer. The conclusion was something like:
Every car is tested in the same way, highly optimized. You will not get these results in real life, but you can use the results to compare cars, a 25 km/l car will be more efficient than a 20 km/l car of the same fuel type for the same driver.

BTW I am able to almost reach the manufactures mileage in my car, but it means I have to drive really slow, stay of the throttle (0-100 km/h in 20s), look ahead/anticipate to avoid breaking/acceleration, drive under the max speed limit, don't drive in the city, don't drive during rush hours, make sure the car is empty (not carrying unnecessary weight). But realistically this will almost never happens.

Re:Simple explanation (2)

the_cosmocat (1009803) | about a year ago | (#43633829)

One of the big problem of these false numbers given by the manufacturers for fuel consumption is that these numbers are directly linked to CO2 emissions. And lots of governments give ecological aids when a car emit few CO2. So, with low (false) numbers manufacturers obtain ecological aids for expensive cars that emit in fact a lot of CO2! A these aids are paid with everybody taxes. So the poor pays taxes for rich people buying big polluting cars where aids should encourage to buy smaller ecological cars!

Re:Simple explanation (-1)

Anonymous Coward | about a year ago | (#43633607)

and your fat people are fatter than average.

Re:Simple explanation (1)

rossdee (243626) | about a year ago | (#43633983)

The reason US cars get fewer miles to the gallon is because they have bigger cars and smaller gallons

And the cars run on gas instead of petrol.> An uncle of mine converted his car to run on gas instead of petrol, and it did get fewer miles to the gallon but was still cheaper because gas was cheaper than petrol.

Game (2, Informative)

DKlineburg (1074921) | about a year ago | (#43633527)

Its all just a game so they can boost there average and still sell the trucks that have terrible MPG that people want.

Re:Game (0)

Joce640k (829181) | about a year ago | (#43633733)

The simple answer is to mandate a huge, prominently placed MPG display in all new cars. That way people can see their current MPG see how their driving affects it, compare with their neighbor's car, etc.

Re:Game (1)

PRMan (959735) | about a year ago | (#43633799)

My Acura TSX tried that and the got sued because it wasn't accurate enough (within .5 mpg). In the next version of the GPS software, they removed this screen.

consistency more important (5, Insightful)

mondovoja (2914901) | about a year ago | (#43633537)

Whether those numbers represent a real world mix of driving accurately really doesn't matter all that much, since fuel economy for other driving styles strongly correlates with fuel economy for the conditions that are actually measured. Long term consistency, on the other hand, matters a great deal for car buyers and for evaluating progress on reducing emissions and consumption.

Re:consistency more important (4, Insightful)

swalve (1980968) | about a year ago | (#43633597)

Yes, exactly. The CAFE ratings aren't meant to tell you what your personal MPG is going to be, they are meant to tell you how cars of a specific model year compare to each other. If you do 10% better in one car, you'll probably also do 10% better in the other one.

Re:consistency more important (0)

Anonymous Coward | about a year ago | (#43633629)

The CAFE ratings aren't meant to tell you what your personal MPG is going to be, they are meant to tell you how cars of a specific model year compare to each other.

Ok, but why are they using miles-per-gallon if these numbers aren't actually miles?

If these are not supposed to be miles driven per gallon, couldn't they use a different unit (like EPA or fuel efficiency rating)?

Re:consistency more important (5, Interesting)

realityimpaired (1668397) | about a year ago | (#43633709)

Yes, exactly. The CAFE ratings aren't meant to tell you what your personal MPG is going to be, they are meant to tell you how cars of a specific model year compare to each other. If you do 10% better in one car, you'll probably also do 10% better in the other one.

That may be so, but miles per gallon is a misleading measurement on which to base the "10% better" calculation. 30MPG to 33MPG is *not* 10% better efficiency. In fact, the two are so close that it's within the margin of error for most of us, and can easily be outweighed by simply getting a bad dice roll with the traffic lights.

If they switched to a burn rate measurement, like L/100km (that the rest of the world uses), or even Gal./100mi, then you actually could do the math in your head for how much more or less efficient the vehicle is. MPG isn't a linear scale, but L/100km is. As a result, the higher the MPG, the less actual benefit you get: 50MPG to 75MPG isn't even close to a 50% improvement in fuel efficiency (it's actually only about 25%), and the disparity between reality and perception only gets worse as you get higher.

30 mpg vs 33 mpg (1)

Anonymous Coward | about a year ago | (#43633851)

MPG (miles per gallon) or distance over usage, is not a good way of measuring gas usage. It should be usage over distance.

9900 miles at 33mpfg takes 300 gallons and the same distance at 30mpg takes 330 gallons, note that the difference in usages from high to low is 10%, the lower mpg (30) cars uses 10% more gas than the higher mpg, but it is not correct to say that the 33mpg car uses 10% less gas (more like 9.1% less gas).

Another way is to look at the 75mpg vs 50mpg cars, 7500 miles at 75 mpg takes 100 gallons compared to 150 gallons at 50 mpg.
One way of expressing this difference is to say that the 50 mpg car uses 50% more gas than the 75 mpg car,
another was of expressing this difference is to say that the 75mpg cars uses 33.3% less gas than the 50mpg car.

Re:consistency more important (1)

Zawahiri (963352) | about a year ago | (#43633907)

What if perceived personal utility of the benefit to the person is also not linear?

Re:consistency more important (1)

kdawgud (915237) | about a year ago | (#43633935)

MPG may not be the most intuitive way to measure fuel efficiency, but it is certainly still linear. 50 MPG actually is 50% less efficient than 75 MPG.

Re:consistency more important (0, Informative)

Anonymous Coward | about a year ago | (#43633975)

I don't know where you went to school, but that's not linear.

Re:consistency more important (2, Informative)

Trepidity (597) | about a year ago | (#43633999)

If they switched to a burn rate measurement, like L/100km (that the rest of the world uses)

The rest of the world? Here in Denmark we use km/L, a distance-per-fuel-unit measurement like the U.S. does. Afaik that's fairly common internationally.

Re:consistency more important (2)

Ironhandx (1762146) | about a year ago | (#43633711)

Thats not even slightly true. The Highway speed limit here is 65mph but normal highway speed is actually 75-80mph. At 80 mph in a 2010 Honda Civic I get WORSE gas mileage than in a 2003 Mustang thats had mods done to it that reduces its gas mileage. Its entirely due to the fact that the last gear on the automatic trans in the civic is designed for optimal gas mileage for the EPA rating @ 60MPH and there is no shorter gear. My old 2000 Chev Cavalier wasn't as bad because there seemed to be some sort of extra half overdrive gear at around 75-78.

My Auto 2011 F-150 and the 2009 Silverado I had before it both had the same problems. They were most efficient sitting right at 60mph... which isn't even the speed limit. 5 over wasn't so bad, but once you hit 10+ over....

With expressways and everything else becoming so prevalent, the 25 minute trip that my wife used to take to get to work is now 15-18 minutes but 10 minutes of that is now at 75+ so she's getting there faster and over a shorter distance but where there should be some gas savings there are none at all.

Re:consistency more important (1)

PRMan (959735) | about a year ago | (#43633811)

My TSX is most efficient at around 65-68 MPH. This accurately reflects real-world conditions for most people. Even at 78 (my typical cruising speed in Southern California), it gets very good gas mileage, better than at 55. So not all cars (or even all Hondas) are like that.

Re:consistency more important (1)

drinkypoo (153816) | about a year ago | (#43633917)

My 1989 240SX got the best mileage at 80, so does my 1992 300SD. That assumes you slow up hills and so on, keeping your burn rate low.

Re:consistency more important (1)

beltsbear (2489652) | about a year ago | (#43633949)

That is because you never drove it slower. You might get better mpg at 60 then at 55 in a few cars due to odd gearing but you are not going to get your best mpg at 80 due to headwind as drag increases greatly above 65.

Re:consistency more important (1)

drinkypoo (153816) | about a year ago | (#43634035)

That is because you never drove it slower. You might get better mpg at 60 then at 55 in a few cars due to odd gearing but you are not going to get your best mpg at 80 due to headwind as drag increases greatly above 65.

I've driven it slower many a time, the mileage can actually get worse. At higher speeds, I'm in a better gear going up hills, and I live in Northern California, which is all hills. But the same is true on long trips, drive at 65 get mediocre mileage, go 80 all the way, get good mileage.

Re:consistency more important (1)

Ironhandx (1762146) | about a year ago | (#43634023)

It does greatly depend on the car, as I mentioned my old Cavalier was better on fuel at the higher speeds. Now the civic is better than anything else I've ever had just driving around town at ~35mph but it fails badly at highway speeds. Not bashing on Honda, Honda does make some decent reliable vehicles, I did buy one after all. Besides that though the TSX is basically a civic but slightly better in all ways, I wouldn't be surprised if the tranny had an extra half-overdrive gear similar to the one my old cavalier, or at least a shorter final gear. Its entirely possible and even likely that your TSX is better on fuel at those speeds than the civic I'm talking about.

Also I'm not sure how it is where you are but a speed limit of 65 is fairly common everywhere I've driven, and your cruising speed of 78 is extremely common here for any highway/expressway driving when the listed limit is 65. I don't even know why the hell you've listed 65-68 as real world conditions for most people and then straight away admitted your own comfortable cruising speed is at least 10mph higher.

Speed limits and police attitudes are starting to catch up to car technology and ability and the EPA needs to play catch up. They should introduce a new tier of MPG at 75 MPH so that the consumer can buy a vehicle more suited to their own driving conditions and style. When a 350 RWHP 10 year old Mustang is getting better mpg at any sort of highway speed than a new what I consider an "economy" car its fucking frightening.

Re:consistency more important (0)

nzac (1822298) | about a year ago | (#43633631)

That's just stupid. It makes sense only if there is a (commonly known) conversion factor (or more generally a function of CAFE) that gives a reasonably accurate of what you can actually expect (knowing that tests expect you to drive somewhat conservatively).
It looks even worse when the CAFE value is so inaccurate for real world driving that it can not be used to compare different cars fuel efficiency.

When you have such a poor estimate of fuel efficiency that consumers should not be using to make decisions with, consumers can no longer chose cars based on their fuel efficiency and it improves at a slower rate.

Re:consistency more important (1)

mondovoja (2914901) | about a year ago | (#43633801)

Your analysis is just stupid because you wrongly assume that this can be measured "accurately". There are too many ways in which people drive, and any choice of a standard is arbitrary. The current standard actually matches driving around here quite well.

Depends on the car (0)

Anonymous Coward | about a year ago | (#43633539)

My BMW gets over 10% better gas mileage at 75 than 60.

I don't know about acceleration but I get 5% or so better mileage if I try to limit how often I come to a complete stop. Even rolling very very slowly is much better than stopping completely.

Re:Depends on the car (1)

mendax (114116) | about a year ago | (#43633601)

If your car has an automatic transmission then I would guess that this is due to the way your car's transmission works. I bet you're in a lower gear when you're going 60 than when you're going 75. After all, this is a German car. People driving BMWs, designed to scream on the autobahn. It makes sense that they would gear it to run more efficiently at 75 than at 60.

Re:Depends on the car (1)

drsmithy (35869) | about a year ago | (#43633887)

I bet you're in a lower gear when you're going 60 than when you're going 75.
I doubt it. Every remotely modern (under ten years old) auto car I've ever driven has reached top gear by 60km/h or so (=40ish mph). Unless you put it into "sport" mode, or whatever the equivalent in your vehicle is.

Re:Depends on the car (0)

drinkypoo (153816) | about a year ago | (#43633937)

Every remotely modern (under ten years old) auto car I've ever driven has reached top gear by 60km/h or so (=40ish mph).

Reaching overdrive is not the same thing as being designed to run at high speeds there. I can reach overdrive at 40 mph in my 300SD, but it gets its best mileage around 70 or 80 MPH. Not as I drive it, because I have the turbo at 11.5 psi (stock is supposed to be 11 but is usually around 9) and I maintain that speed up hills and accelerate hard to get around idiots and so on.

Re:Depends on the car (1)

drsmithy (35869) | about a year ago | (#43634005)

The statement made was "I bet you're in a lower gear when you're going 60 than when you're going 75".
The point is that most (probably all) modern autos will be in top gear well before 60mph - ie: same gear regardless of cruising speed.
Whether they're designed to be optimal at that speed is an entirely separate issue.

Re:Depends on the car (1)

flyingfsck (986395) | about a year ago | (#43633701)

My Dodge Durango hemi also consistently gets better fuel consumption at higher speed. At 120kmh it runs at only 2000 rpm. I'll probably have to exceed 200kmh before the mileage will get worse.

Re:Depends on the car (0)

BrokenHalo (565198) | about a year ago | (#43633857)

Yes, but maybe nobody has told you that DODGE stands for "Doing Overhauls Daily Gets Expensive".

Not only the milage ratings are false (5, Interesting)

Anonymous Coward | about a year ago | (#43633567)

The biggest reason that real-world fuel economy is so different is that the testing is done with a specific "standard" fuel that does not contain any ethanol or other "oxygenator for cleaner burning fuel". The stochiometric ratio required for proper catalitic converter operation on modern cars is maintained by the oxygen sensor adjusting the amount of fuel injected into the engine - too much oxygen in the exhaust gas, add fuel to decrease; too little oxygen, decrease the amount of fuel. This is a closed-loop system that does not take into account fuels that have additional "oxygenators" added - it only cares about the oxygen in the exhaust gas. Add oxygen from fuel additives, reduce oxygen in the exhaust gas by adding more fuel, reduce mileage. "Clean burning fuels" with additional oxygenators is one of the biggest government-mandated ripoffs ever devised. The "testing" done to prove the "value" of oxygenated fuels is done with a single-cylinder carbureted engine in a test lab, with no emission control systems. In the "bench" testing, a specific amount of fuel is burned with the oxygen in the air, and the resulting exhaust gases analyzed for hydrocarbon emissions. Add an "oxygenated" fuel, burn the same specific amount metered at the same air-fuel ratio, and TADA, look, it burns cleaner! Of course it does - there is now additional oxygen in the exhaust gas! But in the real world, the emission systems on a modern car sees the extra oxygen and adds more fuel to the engine to "correct" the air-fuel ratio and reduce the oxygen level in the output gas. They don't tell that part to congress or the consumer, so the use of "oxygenated" fuel is mandated by the law at both federal and state levels - and so 4.) Profit!

And the milage you get on the road does not match the testing...

note: I designed and manufactured fuel control computers for a while, so I know a littile about how things work.

Error goes the other direction, too (1)

inglorion_on_the_net (1965514) | about a year ago | (#43633575)

There's plenty to gripe about with the EPA mileage estimates. My personal pet peeve is not accounting for some fuel saving techniques. When I drive in city traffic, especially on my way to work, I spend a substantial amount of time stopped in front of traffic lights. Some cars actually turn off the engine in that scenario. It seems to me that this is a fairly simple optimization to make. Yet many cars don't have this feature. I've been told it doesn't affect the EPA rating, even though real-world fuel savings are reportedly 5-10%.

Re:Error goes the other direction, too (1)

EzInKy (115248) | about a year ago | (#43634019)

Wouldn't better be to figure out the timing of the lights? In my area this seems to be usually about 5mph below the set speed limit. Normally I only get hit by one light out of the 9 between me and my destination if I adhere to this rule. I've come to regard the one abhorrency causing me to stop on those who exceed the speed limit, jaywalkers, and everything else that prohibits me from maintaing a steady speed without interruption.

Of course we all know there are other things in the variables such as lights that respond to emergency vehicles and such, but in the end once you realize that slowing you down is ultimate goal of most of these systems your life will be so much better when you slow down.

Seriously, I will never understand those who jackrabbit from on light to the next. Why in the world would you do that when slow and steady nearly always wins the race?

Drive conservatively! (2)

mendax (114116) | about a year ago | (#43633587)

When I accelerate slowly (yes, I'm the guy in front of you you regularly curse), drive a pickup with a stick shift and a 2.3 liter four-banger, keep my highway speed to about 60 mph (that's about 90 kph for you metric folks), and use my magic powers to keep the headwinds and crosswinds to a reasonable level my little pickup will get what the EPA said it gets: 29 miles per gallon. I think a lot of it really has to do with how a person drives. Now, in practice I drive a lot faster than that but it's nice to know that the EPA actually got it right.

Re:Drive conservatively! (1, Insightful)

Totenglocke (1291680) | about a year ago | (#43633635)

Hey, as long as you stay in the right lane when driving like a granny, I'm totally fine with it. It's when people pull that crap in the middle or left lane that makes me want to Hulk out.

had this explained to me by a driver ed instructor (0)

MickLinux (579158) | about a year ago | (#43633695)

First, the AARP cares most about old folks keeping their freedom, so they keep their licenses past the time that they can safely drive fast. But they do drive safe. It's just slow, in the left hand lane.

A mile ahead of where he has to turn left, Geezer puts on his signal. Car after car burns by them. He gets frustrated; says to his wife, âoeGeeza, they won't let me in." Twenty miles later, he finally turns left, gets his vehicle turned around, and gets back home.

But next time, he says "this isn't going to happen again. I know what I need to do; I need to get into my lane ten miles ahead of time, and stay in my lane."

So the impatience of those who are more able then comes back to bite them.

So go ahead and hulk out. Or maybe, instead just leave yourself enough time to get to work on time, and don't be blaming everyone else for why you are late. Then you'll be freeto be patient.

Re:had this explained to me by a driver ed instruc (1)

PRMan (959735) | about a year ago | (#43633839)

I think he was talking about the geezers who still think the speed limit is 55 and are sitting in the left hand lane on the freeway. You know, the lane where everyone else is going 80. There are very few left exits, so get your hunk of ancient junk over to the right lane where it belongs.

Re:Drive conservatively! (-1)

Lumpy (12016) | about a year ago | (#43633835)

Middle lane is for slower traffic as well you fool, go back to driving school. Left is for passing and fast, middle is for through traffic, Right is for slow and merging traffic. Note how the Semi trucks are allowed to use the middle and right lanes.

Re:Drive conservatively! (1)

Sponge Bath (413667) | about a year ago | (#43633947)

...me want to Hulk out.

Another habit of mature people that makes the impatient want to "hulk out" is counting out exact change. I like to combine the two. Wait, don't honk, I'll have to start the count over again...

Re:Drive conservatively! (1)

kwark (512736) | about a year ago | (#43633739)

Hear, hear. I get the same results in my 9-11 km/l rated 2004 4x4. But most of the time I get a 7-8 km/l. That is the same relative difference the article measured:
"We were impressed when Ford announced that the 2013 Fusion hybrid earned an EPA rating of 47 mpg for both city and highway driving. Here was a generously sized and relatively conventional-looking sedan rivaling the efficiency of the Toyota Prius.

Then we racked up a mere 32 mpg in our road test"

This problem has always existed, but with better mileage, the relative error results in more easy to spot absolute differences.

Re:Drive conservatively! (1)

J'raxis (248192) | about a year ago | (#43633745)

The article basically says, when people drive in a completely unnatural manner---accelerating slowly and five miles under the speed limit---they get x miles per gallon. You stated that when you do the same thing, you get the same x miles per gallon. Wow, really?

No one is claiming the EPA is publishing false results. They're claiming the EPA sets unrealistic test criteria to produce their results, and all you did was confirm this.

Re:Drive conservatively! (1)

Lumpy (12016) | about a year ago | (#43633823)

Many states the speed limit is 55mph. what they need to do is test at 70mph. OR test on a track with a moron in a SUV riding their bumper and semi trucks in the right lane doing 55.

Re:Drive conservatively! (2)

PRMan (959735) | about a year ago | (#43633831)

I agree. On my car with a built-in MPG screen, if I drive well, I get about 26.5 to 27 MPG on a car that's rated 23/31. Driving through town poorly, my wife gets about 23. Driving straight through to Vegas (from SoCal), I've gotten 32. And this was on the old "inaccurate" EPA scale. Seems pretty accurate to me.

Re:Drive conservatively! (1)

EzInKy (115248) | about a year ago | (#43634027)

You are an excellent driver. Let those racing to the next red light get ahead of you. Slow and steady wins the race.

Units wrong (-1)

jamesl (106902) | about a year ago | (#43633595)

For example, the maximum acceleration on either test is 3.3 mph per second.

It's hard to take a paper seriously when it gets the units of measure wrong.

Re:Units wrong (5, Informative)

xaxa (988988) | about a year ago | (#43633633)

For example, the maximum acceleration on either test is 3.3 mph per second.

It's hard to take a paper seriously when it gets the units of measure wrong.

What's the problem? That *is* an acceleration.

(The SI measure is ms^-2, metres per second squared, or metres per second per second. 3.3 (miles/hour)/second = 0.44704 m s^-2.)

75mph??? (0)

jamesh (87723) | about a year ago | (#43633609)

And the 60-mph maximum speed on the highway test does not accord with the 75-mph truth of today's interstate traffic.

Well there's your problem. If you are doing 75mph on the highway you are burning around 20% more fuel to cover the same distance as you would at 60mph, with the resulting increase in wear and tear as your engine works harder to push you through the air. Make sure you tailgate a big truck to lessen your fuel usage - they love it when you do that!

Re:75mph??? (1)

Totenglocke (1291680) | about a year ago | (#43633647)

That all depends on your transmission. Air resistance, gear ratios, etc are all factors that determine the rpm - and that's all that really matters is the rpm. I can do 80 mph and beat the EPA highway ratings on my car by about 3 mpg, as long as it's a fairly steady mph.

Re:75mph??? (0)

Anonymous Coward | about a year ago | (#43633759)

"Air resistance, gear ratios, etc are all factors that determine the rpm"

Only gearing ratios determine rpm for a certain speed. All other influences determine how much fuel is needed to keep the motor at said rpm.

Re:75mph??? (1)

PRMan (959735) | about a year ago | (#43633849)

You realize that makes almost no sense, right? It typically takes nearly EXACTLY the same fuel to maintain the same RPMs. After having a car with an MPG screen for 10 years, I can assure you that keeping your RPMs low IS efficient driving. They are exactly correlated.

Re:75mph??? (0)

Anonymous Coward | about a year ago | (#43633925)

At the same speed a different gears will result in different fuel consumption, that is true. Which gear to take depends on lots of things, but mph and rpm are directly correlated by gearing. Take a manual gear and it all becomes clear: for a certain mph (rpm from the wheels) there is per gear a known ratio for the rpms of the motor itself. The gearbox and all parts between motor and wheel are a rigid fixed system (if not there is somethins terribly wrong with your car). Going downhill at a certain speed in a certain gear will make the motor do x rpms. The same is true for going uphill in the same gear with the same speed, but one of them uses less fuel. Go figure.

Re:75mph??? (0)

Anonymous Coward | about a year ago | (#43633977)

http://en.wikipedia.org/wiki/Gear_ratio#Example_2 [wikipedia.org]
supports the point that motor rpm to speed through gearing has a fixed ratio.

Re:75mph??? (1)

PolygamousRanchKid (1290638) | about a year ago | (#43633681)

If you are doing 75mph on the highway you are burning around 20% more fuel to cover the same distance as you would at 60mph

I used to have a car like that.

Now I drive a German one. It idles in sixth gear at that speed.

Re:75mph??? (2)

Lumpy (12016) | about a year ago | (#43633809)

German cars now violate physics? Was that a dealer option?

the air resistance is nearly doubled at 75 from 60. Pushing air around actually takes up about 40% of a car's energy at highway speeds. Traveling faster makes the job even harder...The increase is actually exponential, meaning wind resistance rises much more steeply between 70 and 80 mph than it does between 50 and 60.

Re:75mph??? (1)

drinkypoo (153816) | about a year ago | (#43633927)

I'm on my second car which gets its best mileage around 80 mph. It's a 300SD, which does happen to be German. But the prior one was a 240SX. Note that both cars were specifically designed primarily for aerodynamics...

Re:75mph??? (1)

jamesh (87723) | about a year ago | (#43633843)

If you are doing 75mph on the highway you are burning around 20% more fuel to cover the same distance as you would at 60mph

I used to have a car like that.

Now I drive a German one. It idles in sixth gear at that speed.

And has some magic device to negate the effects of wind resistance?

Your mileage may vary... (5, Insightful)

dtjohnson (102237) | about a year ago | (#43633611)

No one cares what the testing procedure is as long as everyone does the same test and it's repeatable. The purpose of the test is to provide a method for consumers to compare different models with respect to their fuel economy, not to provide a precise prediction of exactly what the buyer's fuel economy will be. Everyone drives differently. People warm their car up in the driveway, fill it up with heavy weight, carry lots of passengers, do a lot of long-distance driving, tow trailers, drive up and down hills, ride their brakes, accelerate briskly to beat their neighbor, drive at high altitudes, drive in cold weather, or whatever. Even more significantly, the energy content of 'gasoline' varies widely depending on how much ethanol it has (more is less) and what its boiling point range is. Just do the same test and do it in a way that someone else could repeat the test the same way and get the same result. That's all we need rather it's a 50 year old test or not.

Re:Your mileage may vary... (0)

Anonymous Coward | about a year ago | (#43633719)

Mod this up to +100 and mod down slashdot article-baiting...

Re:Your mileage may vary... (1)

realityimpaired (1668397) | about a year ago | (#43633721)

Fine, but could you please switch to a unit of measure that scales linearly? 50MPG to 75MPG does *NOT* represent a 50% increase in fuel efficiency. Not even close to it.

Re:Your mileage may vary... (0)

Anonymous Coward | about a year ago | (#43633865)

Another way is to look at the 75mpg vs 50mpg cars, 7500 miles at 75 mpg takes 100 gallons compared to 150 gallons at 50 mpg.
One way of expressing this difference is to say that the 50 mpg car uses 50% more gas than the 75 mpg car,
another was of expressing this difference is to say that the 75mpg cars uses 33.3% less gas than the 50mpg car.

Instead of using distance over usage (MPG), it would make more sense to use usage over distance.

The 75mpg car becomes 13.33 (gallons per 1000 mile) verses 20.00 (gallons per 1000 mile) for the 50mpg car.

Re:Your mileage may vary... (1)

djmurdoch (306849) | about a year ago | (#43633899)

Instead of using distance over usage (MPG), it would make more sense to use usage over distance.

Most countries do that. For example, in Canada it's L/100km.

And while you're at it, you should drop those "gallons" and "miles".

Re:Your mileage may vary... (4, Insightful)

AmiMoJo (196126) | about a year ago | (#43633727)

The problem is that manufacturers tune their cars to do well in these tests at the expense of efficiency in more realistic conditions. Nobody accelerates at 3mph/s but cars are optimized for that because that's the test that is administered. If they made the test more realistic everyone would benefit.

Re:Your mileage may vary... (0)

Anonymous Coward | about a year ago | (#43633729)

While it's true a lot of people don't care, they should. Cars can and are tuned to be more efficient at certain speeds and scenarios (low vs high acceleration, stop and go vs cruising, etc). If the 50 year old test is not measuring how people actually drive their cars, then what do you think car companies are going to do to meet the 54.5 mpg standard. Are they going to tune the car to be most efficient at the speeds I'm going to drive at, increasing the value of the car for me? Or are they going to teach the car to the test... sorry, TUNE the car to the test so they can meet the fleet standard easier?

Re:Your mileage may vary... (2)

c (8461) | about a year ago | (#43633793)

No one cares what the testing procedure is as long as everyone does the same test and it's repeatable.

Wrong.

It's like standardized CPU or GPU benchmarks; manufacturers cannot be trusted not to cheat on the tests and blow off "real world" scenarios just to make the numbers look good for marketing.

If a car spends 80% of its lifetime on the Interstate at 70MPH, you'll probably care if it's getting 45MPG or 35MPG, irrespective of the 47MPG it claims to get at 60MPH in testing.

Re:Your mileage may vary... (1)

PRMan (959735) | about a year ago | (#43633863)

Even more significantly, the energy content of 'gasoline' varies widely depending on how much ethanol it has (more is less) and what its boiling point range is.

I wouldn't have thought so before getting my current car (with an MPG screen), but this is correct. My results:

Chevron/Exxon/Mobil: 27 MPG

Shell/Valero: 26.5 MPG

76/Texaco (gone now): 26 MPG

Arco: Who knows? I don't put that dirty garbage in my car

This is absolutely consistent over 10 years to take these sorts of penalties based on the brand of gas. I used to be a Shell die-hard, but now I look for Chevron or Mobil.

Re:Your mileage may vary... (1)

Anonymous Coward | about a year ago | (#43634037)

This has been thoroughly tested, there is no difference in fuel from different vendors, there is no difference between premium fuels and standard from the same vendor. In the Netherlands almost all fuel for the different vendors comes from the same storage facility in Rotterdam. In the lab the results were the same, variance in actual users may be because during testing themselves they may be actually trying (subconsciously) to drive more efficient.

Re:Your mileage may vary... (1)

Jah-Wren Ryel (80510) | about a year ago | (#43634009)

The purpose of the test is to provide a method for consumers to compare different models with respect to their fuel economy, not to provide a precise prediction of exactly what the buyer's fuel economy will be.

That is the intenet of the test. But the result is that manufacturers "teach to the test" - i.e. they optimize for the test and not for more real-world scenarios.

I think we are nearly at the point were crowd-sourcing could significantly fix this problem. If we could just get a bluetooth profile for wireless access to all the major vehicle metrics included in the next ODB standard (or whatever they are calling it), then everybody with a smart phone could record and publish their own MPG results.

It sill won't capture ALL of the variables, but we can break out things like jack-rabbit starts and performance with excessive passenger weights. Crowd-source that over hundreds of thousands of vehicles and we can get some really useful info. Of course the early adopters won't get all the benefits, but they still could get useful info like how to modify their driving habits to get better MPG specific to their particular make and model.

Works for me (1)

inglorion_on_the_net (1965514) | about a year ago | (#43633619)

I've only driven 2 cars since the 2008 revision to EPA estimates, but they have been close for me. I drove a Honda Civic Hybrid and got about 47 mpg (EPA estimate 45 mpg). Then, credit shenanigans made most cars unaffordable to me, but I ended up getting a good deal on a 2012 Nissan Altima. With my city driving, I get a little over 20 mpg (EPA rating 23). On long highway trips, I get about 30 mpg (EPA rating 32).

So, with one car, I got a few mpg better than the estimate. With the other, I get a few mpg worse than the estimate. Both of them are close. I do note that both frequent stops and high speed tend to destroy fuel economy. I blame the ridiculous number of stop signs for the former, and drivers' choice to exceed the speed limit for the latter.

Re:Works for me (1)

Controlio (78666) | about a year ago | (#43633861)

Agreed. I own a 2008 car, which was re-stickered with the new EPA estimates before it was sold to me. The EPA estimate was 35mpg. In a combination of 60/40 freeway to city, I get a dashboard estimated 35mpg, and an actual number damn close to 35mpg (34.5 the last time I bothered to do the math). I've measured that freeway driving alone (65-75mph) gets me around 36.5mpg.

But realize the number changes significantly if you have your heat or A/C on. Usually colder temps and cranking the heat averages about 31.5mpg, and if I use my remote start on cold mornings all of that fast idling gets me closer to 29mpg at the end of a tank.

So most likely the problem is that people aren't comparing apples to apples. Montana in the winter or Texas in the summer will get you worse mpg than Tennessee in the spring. And that's BEFORE you take driving habits, acceleration patterns, and fuel type (ethanol blends lessen your MPG) into account.

Depends on the driver... (1)

Antony T Curtis (89990) | about a year ago | (#43633641)

For all the vehicles that I have owned in America, including my current vehicle, I have usually exceeded the EPA estimates except during weeks of especially poor traffic. I consider myself a fairly aggressive driver, especially when compared to the majority of the drivers I see every day.

I think that the EPA estimates are a reasonable "middle ground" but people who drive poorly or inefficiently should not expect to achieve them.

Re:Depends on the driver... (0)

Anonymous Coward | about a year ago | (#43633819)

If you're aggressive, try a hybrid. Quick takeoff doesn't come with a penalty of extra fuel burn.

the driver & it's car & driving profile (1)

burni2 (1643061) | about a year ago | (#43633653)

Why do the numbers not match ?
- huge capacity cylinder (lower consumption ONLY for constant speed driving bad for city profile)
- high horsepower car (requesting power is paid in more fuel burned because this is the power source and the more horse power one can request it will request)
- burnout type

---------
You can drive your 2006 "Nissan Micra 5 gear manual shifting" (http://en.wikipedia.org/wiki/Nissan_Micra) with mileages

from
5.5 L/100km (51.4 miles/galon)
up to
10 L/100km (28.3 miles/galon)

Changing the profile from far commuter to close range commuter with driving inside a city this changes to 6.5 L/100km (44.1 Miles/Galon)

THE PROFILE:
commuter 80km over all 20km countryside / 60km AUTOBAHN (no speed limit)

THE DRIVER:
for operating it with 5.5L/100km you may not exceed (110 km/h) 68 mph
for operating it with 10 L/100km you must go full throttle (ca. 175km/h ) 109 mph

ps.
converting constants
1,609km equals 1iM
4.546L equals 1iG

remark:
it's interesting that EU measures fuel consumption in volume per distance and the "american way" is the invert
- US - higher is better
- EU - lower is better

Re:the driver & it's car & driving profile (1)

Anonymous Coward | about a year ago | (#43633693)

That's because Europeans want to know how much it costs to get somewhere and Americans just want to know how far they can go.

Re:the driver & it's car & driving profile (1)

citizenr (871508) | about a year ago | (#43633827)

No, Americans just want another way of saying their dick is bigger.

Re:the driver & it's car & driving profile (0)

Anonymous Coward | about a year ago | (#43633897)

4.546 litres in a gallon? There's 454 grams in a pound. That neat coincidence makes it easy to remember :)

Muscle cars (1)

michaelmalak (91262) | about a year ago | (#43633671)

horsepower-deprived 1970s

Um, no. Cars were unmitigated leaded-fuel-guzzling muscle cars (or land yachts, depending on your preference) until the 1973 Yom Kippur War. It would take 20 years [sightline.org] of technology before horsepower was restored while keeping MPG high. And as you can see from that linked graph, the 1973's war effects on horsepower were not realized until model year 1977. And since not everyone rushed out to buy new cars at the same time in 1977, that means the vast majority of cars on the road throughout the entire decade of the 1970's were "high" (1990's level) horsepower.

It's those early 1980's cars that were underpowered -- follow-on effects of gas rationing and Nixon price controls.

OK (5, Funny)

JustOK (667959) | about a year ago | (#43633747)

Could someone explain this with a car analogy?

Variables (1)

Chewbacon (797801) | about a year ago | (#43633773)

Don't forget, these cars are rated not just for ideal driving habits, but ideal driving conditions. MPG drops drastically once you get over the 60mph mark. My truck gets closest to the EPA rating when I'm doing 60 on highways, but 70-75 on the interstate puts me further from the rating.

Driving habits. (-1, Troll)

Anonymous Coward | about a year ago | (#43633789)

I see Prius's on the highway going 85-90 every morning. The biggest problem to gas mileage is that most people do not know how to drive. Mashing the gas pedal when the light turns green is not correct, driving 20mph over the speed limit is not correct. The problem is that the Population is full of morons that cant figure out that they are not important so they dont need to drive like idiots. and they cant figure out they are driving like idiots.

12MPG SUV (1)

EmagGeek (574360) | about a year ago | (#43633895)

My SUV had a sticker mileage of 15/18, but I get more like 10/14, mostly because of the way I drive. I'm almost always towing something (my boat, my camper, or my utility trailer), or driving 70+ on the highway with a bunch of road bikes and my cargo box on the roof. Worst case is I get about 12 on the highway towing my boat AND having everything on the roof.

Whatever the government thinks my SUV gets for mileage doesn't really concern me, though. The vast minority of people drive their cars the way government thinks they do.

Besides, are any of us really that surprised that government can't get it right?

US mileage ratings are so inacurrate because (1)

mark_reh (2015546) | about a year ago | (#43633957)

that's how the auto industry wants them. The classes/descriptions of vehicles don't make any sense either (SUV's are classed as trucks, not cars) except that it allows the manufacturers to continue to produce gas-hog, mega-polluting vehicles without investing in technology to improve either fuel economy or emissions.

Fusion Hybrid Owner (3, Interesting)

OneOver137 (674481) | about a year ago | (#43633963)

I'm own the much maligned 2013 Fusion Hybrid, and my current tank is averaging about 44 mpg. My work route currently averages between 43 and 50 mpg.

My driving conditions are a mix of heavy suburban traffic and stretch of 25-55 mph interstate, with speeds averaging 15-20 mph during rush our. The terrain is rolling hills, with a delta of about 200 feet.

On a warm (T >70 degree), dry day with no wind and little traffic, the car will easily get the 47 mpg.

Temperature has a large impact on the mpg. The same example above in 25 degree weather will net about 36-38 mpg, consistent with the reporting done over the winter. Obviously, cold starts and running the defroster has a big effect, and the electric traction motor eats away at the battery much quicker at lower temps.

Rain will cut the mpg on my work route to about 43 mpg, and the extra drag is very noticeable. A headwind has the same effect. Tailwinds are fun though, and it kinda feels like sailing when the ICE is off.

Cruising at 55-60 mph on the highway, in no traffic on a warm, dry, and windless day, I can get the 47 mpg.

A quick temperature and mpg plot (assuming dry, windless conditions) looks like:

(T deg F, mpg): (25, 36), (30, 38), (40, 40), (50, 43), (60, 45+), (70, 47+), (80, 45).

There is some roll-off at the higher temps because you have the A/C running.

Driver style has a huge impact on observed mileage, and this cannot be stated enough. My wife is your typical, jackrabbit starting, bumper riding, race-to-red driver. Her mpg is far worse than mine. I doubt she's ever seen 40 mpg. A trip that I can do at 45 mpg, she'll get 36 mpg. I've tried to coach her on the basics of hybrid driving, but she just doesn't get it. I imagine a lot of people are the same way. You either "get" how to drive a hybrid, or you don't.

Re:Fusion Hybrid Owner (1)

EmagGeek (574360) | about a year ago | (#43634053)

My wife also has the 13 Fusion Hybrid, and like your wife, the accelerator pedal may as well be a toggle switch on the dashboard.

She gets around 30mpg in hers.

I have a 2012 Fusion SE with the normal 2.5L in it, and I get better mileage in that than she does in the hybrid. Heh.

It's all about driving habits and utility. My SUV gets horrible mileage, but then I'm always using the hell out of it as anything but a passenger car.

Re:Fusion Hybrid Owner (2)

mstrjon32 (542309) | about a year ago | (#43634057)

There is nothing to "get" regarding a hybrid versus any other car. If I drive my turbo roadster with my foot hard down all the time, I might get 18 mpg or worse on a trip. If I drive it gently, accelerate slowly (keeping it off the turbo), brake early, keep to the speed limit or a reasonable speed--I can quite easily exceed 35 mpg for the entire trip. Purely on the highway it's possible to exceed 40 mpg. The same variations are true for hybrid cars, with the only real difference being that really aggressive braking will throw away some of the energy that might have been recovered by regenerative braking.

In other words... (1)

DaveV1.0 (203135) | about a year ago | (#43634025)

The tests are based on how people should drive as opposed to how almost all people actually drive, that is to say like rude, arrogant, impatient assholes.

Why? (1)

PrimeNumber (136578) | about a year ago | (#43634031)

Because it benefits car companies to have a higher MPG rating.

How much doe Ethanol contribute to this? (1)

DigitalSorceress (156609) | about a year ago | (#43634059)

Most gasoline I can find contains 10% ethanol.

Since ethanol has about 70% of the energy density of gasoline, I would expect to see a 3% loss of fuel efficiency just to start with.

I know I don't get my car's rated MPG just because ... well, I own a car that's fun to drive, so I tend to accelerate a bit faster than I'd bet they test with, and I tend to drive a bit higher than the speed they are likely to test at.

Last time I was in Virginia, I found a gas station that made a big deal about having 100% gasoline (no Ethanol) and I wanted to try filling up with it and seeing if I do indeed get my 3% increase... unfortunately, my tank was already full when I saw it.

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