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Transportation Government Stats

Why US Mileage Ratings Are So Inaccurate 374

Posted by timothy
from the if-you're-wrong-enough-ways-at-once dept.
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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Why US Mileage Ratings Are So Inaccurate

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  • Simple explanation (Score:2, Informative)

    by johnw (3725)

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

    • by AmiMoJo (196126) *

      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.

      • by Anonymous Coward on Sunday May 05, 2013 @05:42AM (#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.

      • by houghi (78078) on Sunday May 05, 2013 @05:52AM (#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.

        • by Kjella (173770)

          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 c

        • 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.
          • by Ironhandx (1762146) on Sunday May 05, 2013 @08:13AM (#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.

            • by cffrost (885375)

              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.

              Perhaps nefus was referring to dynamometers, [wikipedia.org] which would provide over-optimistic measurements of fuel efficiency and/or vehicle performance, since they don't account for the effects of aerodynamics on those figures. (I'm not claiming that any organization presents figures obtained this way, merely that that's what nefus may be referring to).

        • I don't think having different information for different states but a list of MPG per average rate of speed:
          xMPG@60MPH
          xMPG@65MPH
          xMPG@70MPH
          and so on because even though the limit might be xMPH doesn't mean that's what the average driver follows.
      • by kwark (512736) on Sunday May 05, 2013 @06:21AM (#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.

        • 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!
      • by MightyYar (622222)

        The summary is quite misleading, conflating the CAFE standards test and the window sticker EPA mileage. The window sticker standards have changed many times, most recently in 2008. They will change again as reality changes.

        The European tests are a joke in comparison. The exact same car will have fantastic mileage in Europe for some mysterious reason :) Carmakers over-inflate tires, put tape over body panel seams, and remove rear-view mirrors. There is less of that kind of thing in the US because the governm

    • by rossdee (243626)

      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.

    • Ratings are based on Gasoline, not gasoline diluted 10% or more with Ethanol.

  • Game (Score:3, Informative)

    by DKlineburg (1074921) on Sunday May 05, 2013 @05:05AM (#43633527)
    Its all just a game so they can boost there average and still sell the trucks that have terrible MPG that people want.
  • by mondovoja (2914901) on Sunday May 05, 2013 @05:11AM (#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.
    • by swalve (1980968) on Sunday May 05, 2013 @05:49AM (#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.
      • by realityimpaired (1668397) on Sunday May 05, 2013 @06:24AM (#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.

        • Re: (Score:3, Informative)

          by Trepidity (597)

          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.

        • by GrumpySteen (1250194) on Sunday May 05, 2013 @10:55AM (#43634879)

          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

          Let's take a closer look at your point:

          2L/100km is obviously twice as efficient as 4L/100km since 4 is twice as large as 2. Easy enough to do in your head.

          50km/L is obviously twice as efficient as 25km/L since 50 is twice as large as 25. Just as easy since it's the exact same math.

          The problem with your idea is that you read that a 10 mpg increase in fuel efficiency doesn't represent the same percentage of increase when it's applied to different starting mpg figures (i.e. from 30mpg it's a 33% increase, but it's a 50% increase if you start with 20mpg). And that's true, but you're assuming it affects all calculations using mpg figures. The L/km measure behaves in exactly the same non-linear fashion. A 1L/100km increase in efficiency from from 3L/100km is a 33% increase but it's a 50% increase from 2L/100km. Once again, the math is exactly the same.

          tl;dr L/km isn't particularly better than mpg. You just suck at doing math that you haven't practiced, so you think it's harder.

      • 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

        • by PRMan (959735)
          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.
          • by drinkypoo (153816)

            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.

            • 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.
              • by drinkypoo (153816)

                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.

              • Headwind drag increasing greatly above 65 is a myth that needs to fucking die. Unless you are driving INTO the wind, wind drag on most modern cars isnt a large concern until at least 80 and for some car designs not even up to 100mph. It is true that wind resistance gets very very bad very very fast after a certain point, but that point is not 65mph. The only vehicles for which its anything close to 60-65mph are transport trucks.

                By large concern I mean a gearing change can't take care of the wind resistance

                • by Sique (173459)
                  Actually, the headwind drag is a function of speed. It's proportional to the square of velocity. Thus there is no single point where the headwind drag suddenly increases. If you drive 40 mph, your headwind drag is four times the headwind drag of driving at 20 mph, but only a fourth of the headwind drag while driving at 80 mph.
                  • Thus there is no single point where the headwind drag suddenly increases.

                    Depending on the aerodynamics of the vehicle there's a point somewhere between Mach 0.85 and Mach 1 where this is true.

          • 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 ca

      • by Cassini2 (956052)

        Cars from the mid-70's to mid-80's will easily outperform cars from today in terms of real-life fuel economy, when cars with similar EPA ratings are compared. Real-life fuel economy has been declining for a long time now.

        The reason for this is that modern emission controls have made it possible to put large engines inside vehicles and still meet the CAFE fuel economy ratings. People *like* large engines. They like the acceleration. They like massive vehicles like the Ford Excursion. The statistics hav

  • by Anonymous Coward on Sunday May 05, 2013 @05:34AM (#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.

  • 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 savin

    • by EzInKy (115248)

      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

  • 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 t

    • Re: (Score:2, Insightful)

      by Totenglocke (1291680)
      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.
      • ...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...

    • by J'raxis (248192)

      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.

      • by Lumpy (12016)

        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.

    • by PRMan (959735)
      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.
      • by FlatEric521 (1164027) on Sunday May 05, 2013 @08:23AM (#43634097)

        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.

        I would recommend you consider double checking your car's trip computer calculation against the tripometer and gas pump readout method of manually calculating miles per gallon. I bought a Hyundai with a trip computer that includes Avg. MPG as one of its readouts. Prior to owning that car I had gotten into the habit of resetting the tripometer on my car at every fuel up after writing down the miles from the tripometer and gallons from the pump readout (then just divide the miles travelled vs gallons to refuel the tank). I kept up that habit after getting the Hyundai and found that the manual calculation method consistently reports 2-4 MPG lower than the trip computer. If your trip computer is anything as optimistic as mine, then you may actually be getting less than you think.

    • by EzInKy (115248)

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

  • by dtjohnson (102237) on Sunday May 05, 2013 @05:51AM (#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.

    • 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.

    • by AmiMoJo (196126) * <[ten.3dlrow] [ta] [ojom]> on Sunday May 05, 2013 @06:32AM (#43633727) Homepage

      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.

    • by c (8461)

      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.

    • by PRMan (959735)

      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.

    • 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

  • 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 wors

    • by Controlio (78666)

      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

  • 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.

  • 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 th

    • Those unmitigated muscle cars were rated for power on engine dynos with race pipes, no alternator, no drivetrain, etc. There will little standards to horsepower ratings in the 70s. Now, it is still engine power (as opposed to actual power at the wheels), but they are required to be measured with all accessories and emissions equipment.

      Plus, brake specific fuel consumption has skyrocketed since then. A 1970s 5.7L engine gets a whopping 200-250 hp, where today's get 400-500.

      When I worked at a dyno shop, we we

  • OK (Score:5, Funny)

    by JustOK (667959) on Sunday May 05, 2013 @06:39AM (#43633747) Journal

    Could someone explain this with a car analogy?

    • I can explain it with some data regarding my car, a 2011 Kia Sportage. Some would call it a crossover, other would call it a supersized hatchback.

      2.4L 176hp four-banger w/ 6-speed transmission. EPA rated it at 21/28. It has an onboard mpg-meter that I've found to be pretty accurate. When cruising on the highway in optimal conditions (no wind, flat terrain, warm weather, inflated tires, etc.), I get:

      34 mpg driving 45 mph
      32 mpg driving 50 mph
      31 mpg driving 55 mph
      28 mpg driving 60 mph
      27 mpg driving 65 mph
      2

  • 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.
  • 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 (Score:4, Interesting)

    by OneOver137 (674481) on Sunday May 05, 2013 @07:52AM (#43633963) Journal

    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.

    • by mstrjon32 (542309)
      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 aggres
  • Because it benefits car companies to have a higher MPG rating.

  • 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

  • by guidryp (702488) on Sunday May 05, 2013 @08:22AM (#43634093)

    First the current 5 cycle EPA test isn't limited to 60mph, it goes up to 80 MPH:
    http://www.fueleconomy.gov/feg/fe_test_schedules.shtml [fueleconomy.gov]

    That isn't the real problem. The real problem is that 85% of "EPA Testing" is actually done by the manufacturer themselves. In effect this is a Take home test.
    http://www.caranddriver.com/features/the-truth-about-epa-city-highway-mpg-estimates [caranddriver.com]
    "While the public mistakenly presumes that this federal agency is hard at work conducting complicated tests on every new model of truck, van, car, and SUV, in reality, just 18 of the EPA’s 17,000 employees work in the automobile-testing department in Ann Arbor, Michigan, examining 200 to 250 vehicles a year, or roughly 15 percent of new models. As to that other 85 percent, the EPA takes automakers at their word—without any testing—accepting submitted results as accurate. "

    Since EPA MPG plays a big part in overall advertising campaigns, and potential EPA penalties, there is strong temptation for manufacturers to cheat.

    Two years ago Hyundai had an ad campaign featuring how all models of many of it's cars got 40MPG highway without needed special models. Hyundai scored big increase in sales. But later testing a Consumer Reports showed a few of Hyundais models got less than 40 MPG in CR testing. This is ODD because CR testing is more straight forward and the vast majority of cars beat their EPA Highway rating when CR tests them on it's own test. So the CR testing is something of a Sanity check for catching cheaters. Eventually Hyundai was found to have a systemic "mistake" in their testing (AKA cheating). They had to roll back mileage claims across the board and give payouts to customers.

    The discrepancy between CR and EPA for Hyundai models before they were caught cheating was 1-3 MPG.

    Fords new Hybrids are now falling short by 6-9 MPG and Ford has a new (successful) Ad campaign targeting Toyota, claiming better fuel economy. These new Ford hybrids are the first to make significant sales inroads against Toyota. If anything MPG advertising has even more effect on Hybrid sales.

    It isn't hard to see how Fords interests are benefited by high test scores, on a test they administer to themselves, even more than they were for Hyundai before they were caught cheating. It certainly smells like something rotten in Dearborn Mi.

  • by emaname (1014225) on Sunday May 05, 2013 @09:33AM (#43634373)

    I worked for just over 2 years in a wind tunnel for a company that manufactured cooling equipment (eg, radiators, oil coolers, A/C condensers and evaporators). We tested products for a variety of manufacturers which meant a wide variety of equipment; ie, compressors, farm tractors, semi tractors, passenger cars, and on one occasion a small city bus to be used in Miami, Florida.

    We had a reputation for maintaining a very stable, controlled environment (air flow, heat load, dynamometer load, and positioning of thermocouples for sampling temperatures) and consequently consistent test results.

    Now in the interest of full disclosure, this was in the early 70's. But at that time, that's also where the manufacturer's typically got their mileage estimates.

    I think this might also be the era from where we get the expression "Your Mileage May Vary" (aka YMMV). I think they included this disclaimer in car ads in an attempt to comply with the "truth in advertising" laws (remember those?).

    Clearly nobody can drive a vehicle in a manner as controlled as that.

    So if the manufacturers are still getting their mileage results from a wind tunnel test, forget it. You'll never match those results especially if you live in a large metropolitan area (where it's not uncommon to sit idling in traffic) or you live in a mountainous area or where you have really cold weather.

    There are several really good comments here with additional insight as to why mileage can vary drastically from the manufacturer's estimate; type of fuel mix, for one.

    So remember, when you're buying a car and read those mileage estimates, YMMV.

  • by CodeBuster (516420) on Sunday May 05, 2013 @10:19AM (#43634631)

    Why aren't "official" MPG ratings accurate you ask? Because almost everyone, except stupid consumers, benefits from this system. The politicians can point to rising average fuel economy, real or exaggerated, that burnishes their green credentials. The environmentalists and their pressure groups don't have to admit that fuel economy isn't going up as much as advertised or even worse "declined" from previous inaccurate measurements. The auto companies are also happy with this fiction because it allows them to continue business as usual which is more profitable for them. In short almost nobody cares about accurate "official" MPG numbers because accurate don't serve the interests of anyone with skin in the game. Consumers who care about the real MPG can find this information with a few Google searches or a visit to one of the consumer review sites where they can pay for detailed reports with the real numbers (often worthwhile when researching a major durable goods purchase). What do you expect out of government? Accurate numbers? The truth? Don't be naive.

We don't know who it was that discovered water, but we're pretty sure that it wasn't a fish. -- Marshall McLuhan

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