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Why US Mileage Ratings Are So Inaccurate
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."
So my mileage must be great right?
Geometric average? Why would that be relevant?
Well obviously - it's because your gallons are smaller than proper gallons.
Its all just a game so they can boost there average and still sell the trucks that have terrible MPG that people want.
Memory is deceptive because it is colored by today's events. - Albert Einstein
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.
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.
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 savings are reportedly 5-10%.
Please correct me if I got my facts wrong.
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.
It's really quite a simple choice: Life, Death, or Los Angeles.
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!
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.
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.
Please correct me if I got my facts wrong.
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.)
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.
No sig. Move along - nothing to see here.
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
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 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.
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.
Correct Horse Battery Staple: 72 bits of entropy. Enter "Correct H" into google. When it generates the phrase, that's
Could someone explain this with a car analogy?
rewriting history since 2109
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.
Chewbacon
The Bible is like Wikipedia: written by a bunch of people and verifiable by questionable sources.
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.
Peter predicted that you would "deliberately forget" creation 2000 years ago...
I was under the impression that the standard unit for fuel consumption in the US is furlongs per hogshead.
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.
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?
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.
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.
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.
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.
There is no "-1 offended" or "-1 you don't agree with me" mod options for a reason.
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 (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.
The Digital Sorceress
So I wonder, do you thing more accidents are caused by those going below sit speed limits or those going above. it? Think this over, one day you too will live to be one of the geezers that you right now despise. What traffic laws would you propose that protect both the brash young and the conservative elderly that would protect the rights of the most people belonging to such groups?
Time is what keeps everything from happening all at once.
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
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
"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.
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
25 mpg driving 70 mph
In addition, the six speed transmission has *barely* enough power to maintain cruising speeds in its highest gear. Any time you accelerate, experience a headwind, go up any hill, drive with a cold car, or have a lot of weight in your vehicle, it doesn't use the highest gear and instead pushes back one or two gears for additional power, dropping your fuel efficiency further.
So, there are considerable variables there that will cause wide variation with highway driving. Grandma and grandpa will be very pleased that they get 32 mpg driving on the highway, while joe leadfoot will probably return the vehicle complaining it only gets 25 mpg (or less) on the highway.
In addition, I only get 12.5 mpg driving in the city. I live in a "city" of 5,000 people. My trek two-and-from work is 2 miles each way. I have six four-way stop signs between here and work. The fastest street I can drive on has a limit of 30 mph. My car is parked outside overnight, and I don't let my car warm up for more than one minute before driving it. Any other city driving is very similar. And that's all why I don't get the EPA-rated 21 mpg in the city.
i'm a young person and I actually do that as i never drive over limit +5:)
I never really considered this but when I think about it, it's true, my Prius doesn't really get the same km/L it should. Shouldn't the car company's be held to the same standard for data as everyone else aka is they lie it's fraud?
They are wrong. There are 2 different tests that are used. The cafe test is the 50 year old test and is not what automakers are using to report their mileage to consumers. They developed another test that they have been using since 2007 for this.
http://en.wikipedia.org/wiki/Fuel_economy_in_automobiles
The existing disrupting the flow of traffic laws that are nearly never enforced. Geezer doing 55 in the passing lane or kid weaving in and out gets tickets.
No sir I dont like it.
I think your calculation is off. I pulled up one of my favorite utilites, GNU units, to figure out what performance level that is. (This program takes a lot of the guesswork out of dealing with measurements when you live in a country full of Luddites.)
You have: 3.3 mph/s
You want: m/s^2
* 1.475232 <-- this is the actual number
You have: 3.3 mph/s
You want: gravity
* 0.1504318 <-- That's about 1/6 G
You have: 60/3.3
You want:
Definition: 18.181818 <-- Zero to 60
You have: sqrt(.25 mi / ( 0.5 * 3.3mph/s))
You want: s
* 23.354968 <-- Quarter mile
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.
An effective "democracy" creates the illusion the people have a say in their government.
I'd be very surprised if any of the mileage ratings are accurate. They're all done in laboratory settings simulating very specific things.
Just because your car is rated at xx highway, doesn't mean that's what you'll be getting. It's more of an aid for comparison than accurate ratings.
That being said, it would be nice if the rating had an error bar attached to it. Something like 5.5 l/100 km +/- 0.5 would be helpful
So one level of complaint is that "I get nowhere near the EPA mileage because who drives like that" apart from hyper-miling geeks, old persons, and dudes with a passive-aggressive anti-social attitude. I can see the point, however. Suppose I drive (legally) at 70 MPH and the car is optimized for 50 MPH, how do I read the EPA sticker to find a car that gets OK mileage for the way I drive?
The next level of complaint is that "I am a hypermiling geek, and even I don't get the EPA mileage."
So the question is, is the EPA test even accurate on its own terms?
My limited experience with a Taurus and with a Camry and using a Scan Gauge, if you drive about 10 miles on a 70-deg day without the AC at an average speed of 20 MPH in traffic, you will get better than the derated window sticker and will be within 5% of the "raw EPA numbers." If you drive a constant 55 MPH on a calm wind day, you will get the raw EPA Highway numbers.
The Taurus started to not get the EPA numbers. It turned out to have dragging brakes from rusted caliper pins.
I don't doubt there is cheating, however. I look over the EPA "Test Car List Data" and have seen some fishy drag or coast-down time numbers.
But are people experiencing that if you drive like Granny, some cars get the EPA and o/thers don't? Are there variations between cars of the same model and year, that some engines are manufactured "tight" with much friction and other cars have a natural aptitude for MPG?
My god! You must be a twenty-something. Or, lived in the country that made the Renault.
Let me introduce you, young sir, to the 1972 Chevy Malibu!
"Flyin' in just a sweet place,
Never been known to fail..."
FTFS:
Where I live the posted limits are 75 mph. Very few people here drive that slow unless the radar detector is going off or there is a cop actually in view.
The reason I know this is because I *do* drive the posted limit, and I am *constantly* being passed.
And the very *idea* of your typical driver taking 18 seconds to hit 60 mph, or accelerating at such a rate, is hilarious. Near as I can tell, any typical mom-n-pop vehicle, the pedal goes to the floor until the desired speed is hit.
I've fallen off your lawn, and I can't get up.
The estimates published by Consumer Reports are pretty good. They very closely match my observed results with a 2007 Honda Accord and 2007 Honda Civic.
I've always gotten better average mileage than the advertised EPA estimates on every car I've owned for the 28 years I've been a licensed driver. (Though on my current car, the discrepancy between actual and EPA is narrower than it was on my older cars.) I suspect that for every person like me, there's a person whose average is lower than the EPA estimate. I'm not sure it's fair to call the EPA estimates "inaccurate." It's more likely that there is a wide margin of error, depending on how well the EPA test matches actual conditions and driving styles. Without knowing the margin of error, it's impossible to determine if the estimates are accurate or inaccurate.
Gas quality is a factor. Your mileage will vary depending on the gas you put in your car. Octane will make a difference if you buy cheap gas from a cheap station that has a low octane vs buying gas from a station that sells higher quality gas that is refined more and has a higher octane your mileage will be greater.
Tire pressure. Slightly over inflated tires will get slightly better mileage than tires that are under inflated because there is less friction in the overly inflated tires because there is less tire in contact with the road.
Properly changing your oil. If you use good quality oil in your car and change it as needed the engine works much more efficiently. The harder the engine works the more gas it has to burn to run.
Road conditions. Smoothness, how straight, blacktop vs concrenete, cobblestone and so on all factor into it.
Weather conditions. Rain, hot pavement, snow, ice, wind resistance and so on matter.
Where you drive. Constant stopping and starting, slowing and accelerating. or being able to cruise along on an open highway make a difference.
Sure all of those things apart make a very small difference that is almost unnoticeable but put together they make a larger and very noticeable difference. If you took a car from say one part of the country and took it someplace else in the country your gas mileage would be different.
Then you have the money factor. Mileage is a huge thing for consumers so obviously car manufacturers will skew their mileage every single inch they can in order to get the best mileage they can on the window sticker to entice buyers. They test their cars on closed tracks under very specific conditions with a car tuned as well as possible using fuel additives and so on.
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.
I recently bought a 2013 Impreza with a CV transmission. This car actually exceeds the manufacturer's MPG rating if you let the cruise control do the driving for you. I've hit 49mpg on long stretches of road.
There is a war going on for your mind.
This endangers traffic around them. How is that safe?
I have a relative working in the auto insurance industry - she says that seniors do have the experience to drive safely. But they also drive less. Per kilometre/mile driven, seniors have generally the same amount of accidents as new drivers. Their insurance should reflect this, but it doesn't. Nice that young drivers get penalized, but seniors don't.
You cannot, by definition, drive safely and slow in the left lane on a road with multiple lanes in one direction. Assuming that slow means driving below the speed limit or conditions.
In your example, the person needs to speed up and merge. If they are incapable, then perhaps they should reconsider driving, change when they drive, or get more practice. A person who has their turn signal on for extended periods is pretty much classified into the "poor, unsafe, or clueless driver" category.
Acceleration is distance per time per time. The time units don't have to be the same. In this case, it's miles per hour per second -- unusual, but correct.
Dear Slashdot: next time you want to mess with the site, add a rich-text editor for comments.
no offense, but the USA still uses miles and gallons? lol haven't heard about MPG since I was in the USA. I use kilometres per litre (km/L) :p Kilometres per hour is so much easier with maths. sorry, didn't mean to start an argument.
The test should be redesigned, but you all are missing the consequences. You only have so much power in your gas tank, and F = ma means that you really only have a couple good options for improving MPG. There's a limit to how much you can reduce the mass, so manufacturers will start limiting the rate that you can accelerate at. If you have driven a Prius, you know what I am talking about.
Personally, I'm not in a hurry, and I figure time spent accelerating is probably going to be a small component of total travel time. The rest of you should be aware of what you're asking for.
Those who advocate genocide deserve every protection afforded by law, and none afforded by common human decency.
My experience:
I live just outside of Boston.
In trucks I have owned, I get 3-5 mpg less than EPA estimate for both highway and city.
For cars, I get significantly more. In my SAAB 9-3, I average 32mpg combined. On long highway drives I achieve anywhere from 38mpg to 43mpg (depending on whether I open the windows, or the weather; rain decreases it quite a bit)- which is way over EPA estimate. In my ZR-1 Corvette, I achieve 27mpg combined with the stock program, or with the tuner's program (a very aggressive tune) I achieve 22-23mpg. In the city with the stock program, I get 19 - 23 mpg unless traffic is particularly bad, in which case I get 19mpg, and on the highway I get 32mpg (with either program), or over 33mpg at 92mph (I do not drive that fast any more - I like having a clean driving record, but I have been at speeds which see 8mpg in the distant past). I get better highway economy than some friends who drive hybrids, but their city economy slaughters mine.
Years ago I had an MR2 - no matter how I drove it (I was young and arrogant so I drove like a bat out of Hell), I would achieve 37 to 38 mpg combined, regardless of how hard or conservatively I drove that car. Again, well over EPA estimate. I attribute that to shift points and the ultra low mass of the car, and flawed EPA tests of the time, with their fixed RPM shift speeds which do not reflect real-world driving scenarios.
I have a scangauge installed in my SAAB (it won't work in my ZR-1 since it is OBD1, not OBD2 but in that car I use instant MPG to monitor my driving), and I find that accelerating quickly rather than like a snail and choosing shift points carefully makes a huge improvement in economy; I have tried hypermiling techniques in both but I find that trying to shift early and accelerate more slowly significantly increases fuel consumption, so I accelerate somewhat (but not brutally) briskly and shifting a little later results in fantastic economy. In the SAAB it comes down to keeping boost down, and in the ZR-1 it comes down to not opening up the secondary intake manifold and not activating the second bank of fuel injectors (it has 16 fuel injectors, two per cylinder). The hypermiling techniques I use is not braking around turns if I have a clear view, and coasting down hills when the slope is sufficient to overcome drag and friction.
With a manual it comes down to learning the right shift points, and on the highway the best cruise speeds. In my SAAB the best cruise speeds are around 48mph, and around 68 mph, either of which will not get me pulled over in a 45mph or 65mph zone. In my ZR-1, the best cruise speed is 92mph, so I settle for a best of 32mpg on the highway. In both cases I am happy because it significantly decreases the number of fuel stops on road trips, saving a significant amount of time. My favorite vacation spot is in western PA, and in both cars I can drive nonstop there without stopping to fuel up; the only stops are for Starbucks or lunch and nature calls. :-)
I think the reason my trucks were so bad was that both had the entry-level engine which were underpowered six cylinders, so on steep grades the engine would be consuming a lot of fuel to overcome gravity and drag, and coasting down hills wasn't practical unless the grade was significant, so I would never be able to overcome the average incurred going uphill in the first place. Friends with the same model pickups (one of mine was an F-150, the other one was a C1500) with the V8s would actually get better economy than I did, because they did not have to get into the throttle as much, plus I had caps on the trucks all the time because I would often be hauling servers and other electronic equipment, and the caps were a PITA to remove.
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My Gen III Prius is rated for 50 MPG highway. I regularly take extended trips where I get 52-54 MPG. Even my daily highway driving is in that same range, depending on traffic (heavy traffic = less MPG.). Typically the worse I do is 47-48 for combined City/Highway. Of course I can drive like a maniac and get mileage in the low 40's.
http://www.hawknest.com/
Notice how all the commercials now are very careful to say "Em Pee Gee" instead of "miles per gallon". There is a reason for it. "MPG" can mean anything a lawyer can weasel his way into explaining. "Miles per gallon" is a specific measurement that customers could hold car manufactures to.
How quickly you accelerate is almost certainly going to be the biggest factor in fuel efficiency. There are optimizations beyond that, though, as you point out. I adjusted the way I drive after reading this article about hypermilers.
If you drive carefully, you can get mileage that exceeds EPA estimates. If you don't drive carefully, you're probably not saving a lot of travel time, and your mileage is pretty much going to be terrible. You don't need to be Speed Racer every time you sit behind a wheel. Eventually market forces will limit that ability to the privileged class anyway, but until then you're pretty much a douche for speeding.
Those who advocate genocide deserve every protection afforded by law, and none afforded by common human decency.
My two vehicles have been spot on for mileage. Actually, my Pontiac G6 exceeds what was rated and it is 5 years old.
So I wonder, do you thing more accidents are caused by those going below sit speed limits or those going above it?
Neither is a problem by themselves. It's the difference in speeds that cause problems.
You have: 60/3.3 You want: Definition: 18.181818 <-- Zero to 60
That's why the tests are insanely unrealistic. Even the most underpowered car can manage 0-60 in far less than 18 seconds, and the vast majority of standard sedans will accomplish the task in less than half the time.
The idea of Hybrid cars for a long term solution to this problem is generally retarded. Generally speaking, you can get pretty acceptable mileage in large vehicles today (28mpgh advertised in a Ford Explorer - I'll buy that rating, and we'll get to that in a second) and regardless of what people say, they really do want a large car.
I own a 2005 Ford Freestyle, it has a CVT and 200hp v6 engine, but performs acceptably for driving maneuvers. It is roughly the size of a Ford Explorer, but it has large sedan mileage, the CVT is usually pointed at as the direct cause to how this car gets such good mileage compared to it's era competition, hell, the new Explorers are built on the same platform as the Freestyle and they're just now starting to beat the mileage of this 2005 car. The difference is, my 80 dollar tank (19 gallons@4.20USD/Gallon) has a near 600 mile range if you drive conservatively. Slow acceleration, slow stops, drive the speed limit, keep RPM in the power band. Here's the thing: The original EPA rating for this car is 27mpgh (Front Wheel Drive), and is now 25mpgh. I can divide however, and know that when I operate my car on a highway trip, I can get 32mpg out of the car. Easily. It's not hard to not drive like an asshole. What is that, a 22% difference? Isn't that what this article bitches about? Except in my case it's the other way around. Driving like you want to save money instead of wanting to save time (Which in my experience, doesn't actually save you any time) has more to do with the amount of time you spend at the pump than any amount of technology. I'll bet I could (on a closed course) get a Toyota Prius to get worse mileage than my Freestyle, it would just be dumb to drive that way.
While the EPA ratings aren't the end all be all to the mileage you actually get, I've never been in a car that I couldn't get to tell me I was beating the EPAs estimates on both Highway and City driving. The problem isn't mostly the EPA, or mostly the car companies, its mostly the fact that today by and large, people drive like shitheads. Now, if we had a society of well adjusted drivers who don't feel the need to race to red lights, or accelerate to 50mph in the space of 10 feet, or drive 30 miles an hour over the speed limit, there's a pretty good chance that we wouldn't need this article, because companies wouldn't have the space to lie and the EPAs estimates would probably seem low in comparison to the real world, but we don't. So Instead we get sensationalist articles about how "badly" these cars perform when in reality, they're just like any other machine. Garbage in, garbage out.
I find the tracking my kms on fuelly has led to much more knowledge about how many L/100km I am actually getting, rather than relying on "ideal" conditions. When doing research before buying new cars, it is also nice to have a "real world" database. I used to track using just the trip counter but it turns out that was wildly inaccurate. http://www.fuelly.com/
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Of course they're inaccurate. Do you imagine that anybody in the government or the auto industry believes otherwise?
Politicians want to set minimum MPG so they can win the environmental vote. But actually raising real world MPG is very expensive and puts an artificial constraint on the automotive market: they have to sell cars with more money allocated to MPG and less allocated to whatever it is that the market would otherwise induce them to do. To a certain point most people are comfortable with the government nudging industries in this fashion, as they also do with safety - but the resulting 'standards' are just Emperor's clothes so that all involved can go around patting themselves on the back.
It's a machine that has to be constantly fed, as well. It doesn't matter how many strides the automotive industry made four years ago; every fresh batch of politician needs to bring home fresh victories against Big Corporate America and this is one of them. Of course it's a desirable goal anyway, but by ceding the responsibility for this kind of thing to our elected officials we are telling them that they'll be rewarded for having a dog and pony show about their intentions to one day solve a problem (by which time they will be long gone) and so if we don't care for the resulting disconnect between reality and the pronouncements coming out of where executives are lying in bed with politicians, we have only ourselves to blame.
It's the same thing with health care and online sales taxes. The really big corporations - the ones with large lobbying budgets who can eat added costs - actually want regulatory compliance to be expensive. They've already made huge investments in people whose job it is to satisfy Washington. Small businesses can't do that, so they either go out of business or get bought by bigger business, and the result is that every industry in which the government has a large stake (which is most industries, these days) gets a big barrier to entry and you don't see as many people starting new ventures. That's why start-ups are synonymous with software. Before the ear of 1,000 page regulations passed by a congress that hasn't read it, you had automotive and aviation and energy startups, too. Now these things only happen with lots of money or as second or third ventures for people who have already got that money.
My boss recently bought a 2012 Versa, rated 28/34 if I remember, he is actually getting 22 in the city and around 25 in the freeway and they are slow drivers. He can only get 210-220 miles on a tank, kind of sucks for a small car. On the other hand, I had a 98 subaru wagon, its only rated 18/24 on the new numbers, but I use to get around 30 and 31 a few times with mostly freeway driving, usually around 400 miles on a tank.
Original article: http://www.caranddriver.com/features/why-is-the-epa-so-bad-at-estimating-hybrid-fuel-economy-feature
Mmm, Freetos.
*Still* negative function...
I'm a "hypermiler" and it was natural when I switched from bicycle to car. Perhaps if more people drove in their 20s instead of their teens they would be better drivers.
Driving style has a lot to do with it. I get 10mpg over other people in the same car if I try hard.... and since driving is so dull I may as well keep myself occupied with the road by driving smarter.
Highway limits should be 55mph. maybe 60mph now that cars are more aerodynamic. Above 55mph the majority of your gas is going into PUSHING AIR not propelling you to your destination. Back when 55 was chosen it was the best rate for fuel economy and safety and today it might be 60 or 65 but for safety it's still better at 55.
More people die from cars than bombs or terrorists... but we just won't give up our 5 minutes of time commuting to work... that 5 minutes of savings is just soooo valuable .... except when it is tv commercials... we've let them extend TV advertizing to nearly 8 min out of 30 min... 1/3 and we don't seem to mind losing THAT TIME... (this applies to the 90s before TV was on the internet.)
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Google agrees
3.3 (mph per second) = 1.475232 m / (s^2)
... the argument against yourself, yourself:
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.
I agree that a lot of the driving habits that go into good hybrid mileage are the same as that go into non-hybrid mileage. But the regenerative braking thing is actually important, and not limited to braking (hills are another example).
My 1984 300TD begs to differ. I'm happy if I make 0-30 in 20 seconds.
I don't suffer from insanity, I enjoy every minute of it! --Longbottle
You're kidding, right?
I wish I could go that fast. Aside from a few trips on open roads, I'm lucky to average about 40 MPH on a freeway commute. And that's the difference between about 14 mpg (at 40 MPH) and 18 mpg (at 80 MPH) for my car.
Have gnu, will travel.
Anybody who drives a 1999-2003 VW Golf or Jetta diesel knows that the then-current EPA tests were EASY to beat for those models, and the now-current EPA tests are absurdly pessimistic. There weren't many competitors to these light models then, and still aren't, but a few are on the way. I suspect today's common rail diesels won't beat the EPA nearly as soundly as the old rotary pump VW TDI diesels did, though.
When dealing with ratios, you should compare them via decibels. Pick any vehicle as your standard, and determine dB relative to that. I suggest using the worst vehicle that can reach the required speeds and acceleration, with anything more efficient getting a positive number.
Whoops, my figure was for 1 mph/second, not 3.3.
I was lazy and used Google. I have GNU units installed, but I forget to use it. It's much better than trying to coax Google into giving the correct conversion.
I'm curious about what the equivalent term for "mileage" is.
This is Slashdot. We are geeks. We embrace the scientific method, which includes experimental control.
One knock on the EPA is that they "do a lab test that is never reproduced out on the highway."
What I am saying or suggesting is that driving 55 MPH on a calm wind day without the A/C is a good proxy for the EPA Highway test. I am not saying you have to drive 55 or should drive 55, it is just that there are some stretches of road with a 55 MPH limit that would be a good place to test a car.
So Question 1, what gas mileage do you get driving at 55 MPH on the highway under calm wind conditions, and how does it compare with the EPA test. It's called "experimental control." That is, you first try to see if a car gets anywhere near the EPA gas mileage when driven under as close to EPA conditions as is reasonable for someone without a chassis dyno and an exhaust gas analyser like they have in Ann Arbor, MI at the EPA testing station. If the C-Max and Fusion Hybrid are not getting their EPA numbers, and I am talking the raw numbers and not the "adjusted" numbers on the window sticker, then there is a case to be made that Ford is cheating.
Then Question 2, what gas mileage do you get, say, driving 65 MPH as in the Consumer Reports test? If the C-Max and Fusion do OK at 55 MPH but are not so thrifty at 65 MPH, maybe Ford isn't cheating, but they have optimized those cars for 55 MPH when most people drive 65 MPH (or faster) on the highway. This is an important distinction to us geeks grounded in Experimental Control and the Scientific Method.
So them my Question 3, why doesn't Consumer Reports conduct a road test that best replicates EPA conditions before they start knocking cars for not "living up to the EPA numbers." I don't care about the song, "Pull my license, and all that jive, I . . . can't . . . drive . . . 55!" For cryin' out loud, doesn't Consumer Reports believe in Experimental Control? Report a highway number at a constant 55 and then report a highway number at a constant 65.
Question 4, so why did Consumer Reports change their "highway" road test mid stream? I think they sped up their highway road test to be more consistent with the way their readers drive. Fine. But then you have an apples and oranges comparison between a car built now and maybe a car you owned 30 years ago. Suppose I want to know how a Prius stacks up against the low-tech non-hybrid 1.6 litre 5-speed manual-shift Nova/Corolla I had purchased back in 1986? Can't compare by going through old stacks of Consumer Reports.
As far as it is known, every model of every car maker has to go to Ann Arbor for the original "EPA" drive cycle -- this is for smog control certification, and you extract the EPA City numbers from that, and I think the old "Highway" test is included, both tests used for CAFE regs.
EPA has a new or extended cycle including the high speed highway driving used for the current window sticker. For most cars, they get the "new" sticker numbers be a formula applied to CAFE, but for selected cars, they or the car makers run a full test on them.
With respect to cheating rather than optimizing for or "teaching to the test", EPA relies on the car makers to conduct coast-down or other tests to come up with the drag coefficients to put into the chassis dyno in Ann Arbor. Folks should look up the Test Car List Data (Google for it) for the raw EPA results along with the drag coefficients for the different car models. I am thinking that if we "crowd source" that task, there may be "interesting" findings.
Doomed from the start. First we have people expecting that they can do more together than apart, usually untrue. Totally untrue if it involves voting...that is, the idea that a community can make a decision and compel its members to go along. Legitimate when arguably the survival of community and members is at stake but not otherwise. Neither fuel economy nor automobile exhaust is a problem at all, in that sense.
Then we have the idea of standards and objectivity, another set of false concepts, more trouble than they are worth.
I doubt it is possible to regularly operate an automobile without obtaining a pretty good idea of its fuel economy. Enough said.
The whole thing just taxes people with better things to spend their money on for something that really does not matter, except maybe to people who believe in such fantasies as nations controlling their fate, governments having wisdom, or that people are too stupid to conserve if they find something to be scarce or expensive and being used wastefully. If it’s cheap and abundant it CAN’T be wasted.
Just a note - my grandfather willingly gave up his license when he was 94, but even in his late 80's he'd complain about slow people on the road.
"The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants." ~Thomas Jefferson
More accidents are caused by those going at or below the speed limit by more than 2:1.
Statistics consistently show that "speeding" is an element in 30% of collisions. Although many people try to spin that as "30% of accidents are CAUSED BY speeding", the actual fact of the matter is simply that a little shy of 1/3 of collisions involve a vehicle that was traveling above the speed limit, not that the excess speed actually caused the collision.
If you consider the 85% rule followed by road engineers in many places, where under normal conditions, the roadway is meant to carry 15% of drivers at a higher speed than posted for normal flow (yes, that's right--the speed limit is designed to put about 1 out of every 6 drivers on the wrong side of the law, which is why speed limits were never meant to be literally enforced except for blatant violations), then you're actually only dealing with about 10-15% of collisions more than you'd expect from a perfectly representative sample.
Elevated risk? Yes, but less elevated than distracted driving, mechanical problems, or weather conditions.
This is pretty simple really. The accuracy isn't important as every person on the road drives differently and of different roads. The important thing for a mileage rating is that they can be compared from car to car. As long as all the cars follow the same procedure in determining their rating, then you can compare between them. Changing the test will require all the cars to change at the same time. And if you did that you would no longer be able to compare current cars with past cars which some people might like to do when looking at improvement over the years. And even if you did that it would not be accurate anyway as the driving conditions for most people will not match the testing conditions.
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I have a picture of my crossover SUV doing 36 MPG. Why? Because I reset the trip odometer and coasted down a hill for a mile. I also have a picture of the same car doing 16 MPG. Why? Because I reset the trip odometer and drove up a mountain. These are extremes. In reality, it gets about 24 city and 29 highway. It's rated for 21/27, too.
(2012 Subaru Forester, 5-speed manual if anyone cares to try to replicate the results.)
I propose that the Daytona International Speedway set aside four weeks each year for fuel economy testing.
First, each tested vehicle should be driven 40 laps (100 miles) around the circuit at a constant 70 mph, using a very carefully measured quantity of fuel. That will produce the highway mileage rating.
Then, a course laid out in the infield, with sectors of different speeds, stop signs and stop lights, simulated passing zones, etc, would produce an urban cycle fuel economy rating.
The grandstands could be opened to the public, though the testing itself would probably be pretty boring. But at least it would be a transparent procedure and superior to the current problematic methodology.
Ganted people drive and accelerate fast, however, it is not solely the car or driver's fault, some blame can be put on the traffic control systems. I have seen the lights cycle and bring 40-50 cars to a dead stop to let just 2-3 out out on to the parkway.
For cubic inches. None.
The job market is good too! Endemic psychopathic lying.
Drove a 2012 prius from ATL to LA and back thru saltlake, denver, Nashville, etc ... Averaged 47 MPG most of it at 65-85 MPH. Close enough to advertised.
Read the fine print.
Americans don't know how to drive.
I get 30 MPG in my 2005 Focus automatic. But my 5 speed Neon got 40.