If you read the full report, the automaker with by far the largest gap between its claimed improvements in fuel economy and its actual on-the-road performance is General Motors. Much worse than VW and Mercedes (who also did very poorly), by this measure.
The source of the data is actually www.spritmonitor.de, which is a self-reporting mileage tracking site (like www.fuelly.com). With ~501k vehicles tracked and 8.885B kilometers tracked, the site represents ~17k kilometers per car of user-reported mileage information.
Is this the best, or a reliable source, of information to start the reckoning/witch hunt to come? I'm not sure.
I thought the same. In my anecdotal experience, drivers tend to get much lower than the manufacturer mileage because they optimize for things other than fuel economy (e.g., speed).
My dad taught me lots of tips on conserving fuel and thankfully I've exceeded the sticker numbers on every car I've owned.
But that's actually irrelevant for the cited report. What the referenced graph says is that from 2008 to 2014, auto manufacturers declared a certain increase in emissions/economy, real world people reported a different amount, and those amounted to, unique to GM in this report, a negative percentage in how well they achieved their claims. That is, on average, GM car fuel economy got worse over this period, or people's driving habits changed for GM cars. (I can't discount the possibility of something else is going on, such as an influx of a different type of car for GM over that period, I haven't read yet how they normalized the study and accounted for things like that).
Manufacturers report fuel consumption during a controlled environment, with specific driving habits, etc.
Real world people drive insane (at least in the US), and most wouldn't even re-pass their drivers-license test, so most assuredly do not have the best driving habits.
So drawing the conclusion that manufacturers are "lying" from the discrepancies between those two data sets is ridiculous.
It's irrelevant because unless both a) people changed their driving habits on average over that time frame to cause more emissions and b) that change was primarily limited to drivers of GM vehicles, then driver habits do nothing to explain the data.
> So drawing the conclusion that manufacturers are "lying" from the discrepancies between those two data sets is ridiculous.
Perhaps you should pay attention to actually what I said, not what you think I said. I didn't say GM was lying, I implied their numbers deserve extra scrutiny.
The whole controversy is over manufacturers reporting false numbers, i.e. lying.
Saying a manufacturer deserves extra scrutiny can absolutely be inferred to be an accusation of them reporting false numbers, i.e. lying.
My reading comprehension isn't at fault here.
Secondly, it's still irrelevant.
You would have to prove that an improvement at throttle position 0.10 over 5 years equates directly to an improvement at throttle position 0.40.
How an engine performs in condition A has no inherent relation to its performance in condition B.
So yes, I stand by what I said. Maybe before accusing people of "not paying attention", you should look at your own language and see if it's ambiguous?
> Saying a manufacturer deserves extra scrutiny can absolutely be inferred to be an accusation of them reporting false numbers, i.e. lying.
> My reading comprehension isn't at fault here
Except that I very clearly said "I can't discount the possibility of something else is going on, such as an influx of a different type of car for GM over that period, I haven't read yet how they normalized the study and accounted for things like that."
> Maybe before accusing people of "not paying attention", you should look at your own language and see if it's ambiguous?
You ignored clear text from me saying that it didn't necessarily indicate GM was at fault. What am I supposed to infer from that?
As to the matter at hand, you still seem to be under the impression that driver habits can account for a change in the numbers we are talking about, when that would mean that GM drivers specifically drive very differently than all other car drivers in the report. We are talking about number across the industry, categorized by manufacturer. Everything listed on the graph in question shows automakers overreporting gains, which could be driver habits. GM specifically shows vastly different numbers from event every other manufacturer, not just the reported numbers. I fail to see how driver habit accounts for a specific manufacturer being so out of bounds with it's own reported numbers (keep in mind engines are often shared across multiple manufacturers).
> You ignored clear text from me saying that it didn't necessarily indicate GM was at fault. What am I supposed to infer from that?
I didn't ignore anything.
I said the source of data is not irrelevant. That's my entire argument.
And I was specifically refuting your thesis that the source of data is irrelevant.
and, "as to the matter at hand", yes, driver habits can account entirely for the discrepancy in numbers. Flawed data can account for it. Poor sampling can as well.
The report seems to have come from a self reporting site in the EU. Are you asserting that a US car manufacturer has sold a uniform distribution of make/model/engine cars across the globe?
Are you also asserting that this site is getting a proper randomized sample of the car-buying population, such that they don't all have a similar complaint? In my experience, the people who report such things are one of two cases 1) Extremely Satisfied, or the much more common 2) Extremely Dissatisfied.
Are you then also asserting that if GM optimizes for test conditions, which they believe to be similar to normal driving habits, that their engines would be optimized to perform well under conditions that people actually drive in? That's just sloppy. That's like comparing data from your Dev environment to that from Production, I believe there have been a few academic articles to refute that as well.
But, ultimately, are you asserting that we should just accept the source of data as a source of truth, and never question whether or not that it's valid? Should I just go buy a bunch of tabloids and take that as my "new news", since.....the source is irrelevant, right?
> And I was specifically refuting your thesis that the source of data is irrelevant.
Please stop trying to tell me what my thesis is, as you've misunderstood my statements. The portion of the comment I was responding to is "In my anecdotal experience, drivers tend to get much lower than the manufacturer mileage because they optimize for things other than fuel economy (e.g., speed)." That, by itself, is irrelevant to the question as to why one manufacturer has vastly different numbers than another. As to testing methodologies, yes, this could entirely be testing error. I've never stated my opposition to that possibility. I have repeatedly stated my only intention was to say these numbers need more investigation.
I'm done trying to discuss this with someone who ignores what I actually state in favor of what they decide I must be implying.
The whole controversy is over manufacturers reporting false numbers, i.e. lying.
No, actually it isn't. The controversy is over manufacturers tuning their vehicles' engine behavior to give economy for the tests and for the tests only. By your criteria, that's not a problem but VW has already been bitten really hard by the revelation that they did this.
...You would have to prove that an improvement at throttle position 0.10 over 5 years equates directly to an improvement at throttle position 0.40....
The EPA has essentially said that if this isn't a least somewhat true, the manufacturers are breaking the law.
I'm not sure what your definition of alter is, but for me to alter means to lie.
They weren't simply optimizing for test conditions, they were outright lying during test conditions.
that's what the EPA is saying is against the law.
Here's the thing, and this is my main point:
If the EPAs test conditions reflected normal driving habits, there would be zero difference between Manufacturer reported numbers and real world reported numbers.
If the EPAs test is completely different from normal driving, then it stands to reason that there is no inherent correlation between manufacturer numbers and reported numbers.
IDK if you've ever been through an emissions test (like the ones GM actually goes through), but they're a complete joke as to simulating real world behavior.
So I threw together a histogram [1] of car CO2 emissions as reported by manufacturers for 1200+ model/engine combos. It's not exactly uniformly distributed, to say the least, there is a strong peak at 99 g/km etc. Now that's maybe not conclusive evidence that they are lying, but it's certainly suspicious.
I'm not sure what that proves, at least relative to what I'm saying?
IFF the EPA's regulatory test procedure accurately described/expressed normal driving habits, then the only way that numbers would differ between the real world and the reported numbers would be fraud/lying/alteration, like what Volkswagen Group engaged in (let there be no mistake, it WAS fraud/lying, not a case of poor optimization).
BUT the EPA's regulatory test DOES NOT accurately depict normal driving conditions.
In the current case, a manufacturer has to:
- Realize and Formally accept that the test procedure is inaccurate
- Optimize for:
- Simulated driving conditions, aka the Test Procedure
- Real life driving
To me, it looks like GM just didn't do any of that, and only optimized for the simulated conditions and not real world road conditions.
Depending how far out of wack the test procedure really is could explain the entire data-set.
So the point is that these official numbers should be taken with a generous pinch of salt.
Now, when you talk about GM, remember this is data from Germany, so GM essentially means Opel. Now I believe that before the quite successfull Insignia which launched in 2008, Opel were mainly known for cheap and efficient and small cars like the Corsa and Astra, while now they have a more premium lineup, and "Turbo" versions of several models.
Yes exactly, with a pinch of salt. Exactly what I was trying to say.
And yeah, I've driven a Chevy Spark, and that thing was so slow I could get out and walk faster. I could totally see people driving with their foot to the floor in it.
IDK if you've ever been through an emissions test (like the ones GM actually goes through), but they're a complete joke as to simulating real world behavior.
Does not matter. Your argument is something like, that by dumb luck auto manufacturers produced good emissions results and terrible results in the field.
As understand it, the EPA is saying that if a manufacture is engaged in your two stage approach, "Optimize for:- Simulated driving conditions, aka the Test Procedure [and achieve high fuel economy] - Real life driving [and achieve high power, low fuel economy]" then they are engaging in systematic fraud and are going to get hit big time.
You seem to think it's just a matter of technicalities in the test condition. I'd like references for that.
No. That's not my argument. It has absolutely nothing to do with dumb luck.
The EPA has a set of standards, and manufacturers optimize for those. That's it.
Cheating != optimization. Cheating is like a kid copying someone else's answers. Optimization is studying before the test. Completely different things. And optimization isn't illegal.
If you still don't get it, I don't know what to say, I can't explain it any further.
OK, I get that you saying "Cheating != optimization". That may be your opinion. It may be true in a moral sense.
However, I have good evident that VW's optimization was considered criminal in this instance. And Indeed, since many manufacturers do this, things are pretty dicey.
"“Developing an engine software to optimize certain aspects of an operation cycle that you know the parameters of is a challenge, but it is very possible,” says Thiruvengadam. “Knowing when to switch to the EPA-favorable cycle is the trick; it could be set up to detect the absence of steering-wheel movement, or, and this is known, we often turn off the traction control for testing purposes.” Either way, the result is the same: it turns the emissions controls on for EPA testing and off for real-world driving. Somewhat ironically, the presumed benefits of turning off the controls for normal driving include improved fuel economy and engine power." [1]
It's the old saw about the drunk looking under the light post for his keys, when he probably lost them in the alley; the light's better over here.
If you make laws that can't be verified then you can't enforce them. So you test for things you think you can actually test and hope everything works out.
Wiring up an exhaust sensor to everybody's car every time they need to renew their tabs and having them drive around the city is so infeasible as to be laughable. So they put your car on a dyno or even have you put it in neutral with the parking brake on and have you rev the engine a little bit and see if the tailpipe is a mess.
Nevermind that a lot of cars belch smoke only under load.
No matter how careful I am, it's hard for me to get lower than 130% of the fuel consumption reported by the manufacturer. Perhaps I can do 120% of the reported consumption at 90 km/h, but I can hardly get lower than 140% on the highway (130 km/h) and in city traffic.
Actually, it depends. Modern cars do better in rolling hills than on perfectly flat land, since they can cut fuel entirely on the downhill, and the climbs don't require that much extra fuel over just maintaining speed.
> Modern cars do better in rolling hills than on perfectly flat land, since they can cut fuel entirely on the downhill
This is physically impossible. Even if the car was perfectly efficient at overcoming the force of gravity on the uphill portions (which it is not), you cannot do better than flat terrain (unless by hilly you mean 'net downhill').
The StackExchange post that he linked lists several cases where it's possible. I was skeptical too - I was a physics major in college, I know all about potential vs. kinetic energy and rolling resistance. But engines are not perfectly efficient: you're going to lose some energy to internal friction within the engine, and to combustion efficiency, and to transmission losses, and to a number of other effects which vary based on speed, RPM, and torque. Add in an engine computer that's trying to minimize these effects based on inputs, and actual fuel efficiency will vary significantly from the simple "chemical energy in = kinetic energy out" model.
I've also observed the effect that the OP mentioned: in my Honda Fit, I get a fairly consistent ~45 MPG on 101 (completely flat highway terrain), ~40 MPG on 280 (rolling hills, highway), and ~43 MPG on 84 (across the Santa Cruz Mountains; ascends 3000 ft. in a series of tight switchbacks and then descends 3000 ft. in a wavy line). My working hypothesis is that the descent on 84 is consistent enough that the engine computer can idle the engine for all of it, burning no fuel - this is consistent with the car being nearly silent on the downhill, and of the instantaneous mileage display being stuck at its max of 80 MPG. Probably also helps that speeds are much lower, so there's less air resistance.
Anyway, the point is that cars are complex enough that the simple models you learn in Physics 101 don't really hold.
Engines are most efficient at WOT. Hilly ascents at WOT will burn the fuel more efficiently (even though you're using more). Add a descent in which the computer stops providing fuel and it's possible that you could get a better mileage.
It's known that you can get better fuel economy by oscillating speed on flat ground - using WOT to gain speed, coasting back down, opening up WOT again. This is because the engine is most efficient under load and the average consumption works out better. Adding in the hills would average this effect.
Generally not wide open throttle - see the efficiency maps I linked to in another reply. Generally peak is at somewhere around 1/2 to 2/3rds maximum output.
Wide open throttle and percentage of maximum output are two different concepts. An engine operating at partial throttle has higher pumping losses (pulling air past the partially closed throttle plates).
An engine operating at WOT but still producing a fraction of its maximum output is certainly possible (and generally more efficient than an engine producing the same output at a partial throttle setting). A diesel engine is almost always in this configuration (metering fuel but generally not restricting air with a throttle plate) and a gas engine at low RPM but WOT is also in this state.
If tuned for efficiency in that config, it can be very efficient and is how many piston airplane engines are regularly operated where fuel consumption is an important part of range (and operating economics).
I think you should reconsider "physically impossible". Sure, in some idealized situations, the statement you're responding to would be wrong, grievously wrong.
But the actual situation has two novel features: (1) the engine uses up power just by being on; (2) you must maintain a minimum speed in order not to block traffic.
If you put these constraints in, you can see that it's possible for a pulsed-acceleration strategy to win. You put in a pulse of acceleration to get up the hill, turn the engine off, and coast down, maintaining enough speed to keep up with traffic.
Now sure, without the minimum-speed constraint, you'd probably be better off flat, and possibly using a pulsed-acceleration strategy.
I haven't done the math, but I think it would be reckless to say it's "physically impossible" for all values of static energy use and slopes.
Take a look at the stack exchange answer the commenter above linked to.
I read years ago that pulsing was the most efficient strategy. Engines have very different efficiencies at different rpms and power settings. The idea with pulsing is to try to operate it at its most efficient rpm and throttle setting, which of course rarely corresponds to the speed over flat ground you'd like to be travelling at. Hence pulsing.
Yep, and this is why moderate hills are better. It's essentially constant speed pulse-and-glide. Just building and releasing potential energy rather than kinetic.
Not at all, in many vehicles. 6th gear in my car is quite long (Turns 1950RPM at 75MPH) and I have no problem maintaining speed on highway grades.
Even if you do downshift that doesn't necessarily mean you're being less efficient either. Being a bit higher up the rev range may actually put you in a better spot on the efficiency curve for a given power output.
ICUs are more efficient if you open the throttle more (up to a point...). So it could be possible that the extra potential energy you store going uphill at better efficiency makes a difference.
I recently purchased prius which has much better mileage than my previous car so I'm monitoring each of my trip.
I actually observed this and it is true in my case; I do get better mileage when choosing a route through a canyon than when using regular freeway.
I suspect though that the real reason is that it basically affects how I'm driving. When I ride in a canyon I can't accelerate much because there are constant turns, while on straight freeway I most likely will accelerate.
This also would explain why most of the time I get better mileage in traffic (the EV is used most of the time).
I cannot imagine a cyclist imagining this to be true!
Obviously aerodynamics play a part, however the cyclist's 'engine is cut' on the downhill and on big cross country roads no brakes need be used on the descents. When the 'engine' is on it goes at a certain not-quite-racing amount whether up hill or on the flat. But place a hill in the way of A to B and vastly more 'fuel' is used than A to B 'going the flat way'.
Consider a different visualization: what if instead of a hill, you were crossing a valley? Starting at the top of the hill, you coast down and make it most of the way up the other side. Are you certain this will take more energy than pedaling the whole way across the flat?
What if you can start by coasting 90% of the distance with zero expenditure of energy? What if it was 95%? Now assume that your chain is extremely rusty (low efficiency drivetrain). Would it be possible that the energy to go the short distance up the remaining hill (after coasting downhill and halfway up the other side) might be less than overcoming the friction of pedaling the whole way?
I'm not certain that they occur on a bicycle in the real world (perhaps you need a custom crafted rusty chain that has essentially constant high losses regardless of pedaling speed), but I think there are cases where the variable losses due to friction might make the hilly case more efficient than the flat.
(Yes, I realize that chain friction is not the dominant factor in the real world. It's a stylized example.)
The best terrain I've ever ridden a bike on was a well-paved path of little resistance over forrested dunes. You start on top of a dune, pedal a little on the way down (not a lot of effort) and arrive on the top of the next dune with nearly zero speed. Perfect coasting and a cool breeze most of the time.
Even a rusty chain is ridiculously efficient - in the high 90%'s. An ICE and drive chain is pitiful in comparison, so let's substitute the chain for a missing rear axle nut so that, when pedalling, the wheel pulls to one side and creates tangible frictional losses.
I grew up in a very hilly area plus I have done a few continental rides where hills can be graded nicely and go on for 10 - 20 miles with little change of gradient. The hope to coast up the other side of the valley never really works out as well as one might hope, with a road that goes down a big hill you are invariably pedalling on the lower reaches of the down hill part, even if you were doing a good 30+ mph at the top. This can be due to the valley heating during the day giving a prevailing headwind due to air expanding.
Meanwhile, in the steep hills I grew up in, you can get a measured 40+ mph, conservative guessing (I would be boasting if I mentioned top measured speeds as they can be quite incredible but 40 mph is the town limits speed and it is cool to exceed it on a bike). Clearly this speed scrubs off with aerodynamics not being favourable. So you really do not blissfully roll up the other side, roller-coaster style.
On a daily basis I go over an arched bridge that does have a hill leading in to it. So you can coast down the hill, up over the arch and on down the other side. The fun is to not pedal over the bridge, to be in 'roller-coaster' mode. This feels good, and easy, but there is a psychological factor going on here. One's brain is distracted by the 'roller coaster' (or traffic) and not really noticing how much of a slog things are.
Essentially the only way things could work out anywhere near how you imagine is if there is no atmosphere. The cost of speed is aero and you just do not get the free ride up the other side of the valley, period.
If it was quicker/more efficient to go up and down hills we wouldn't have land speed records be they by bicycle or rocket car set on dead-flat courses, would we?
With the sibling reply regarding undulating paths, that is part 'mind trick' as it is mentally stimulating going up and down like that. It is just an illusion...
However, I can in part rescue your line of thinking on this - muscle groups... I actually like hills and you can use your arms, legs and plenty of muscles in between to 'conquer' a hill. On the flat you are more likely to just spin (unless sprinting). Maybe if you factor in the baseline power your body needs for pumping blood around, maybe that could make things 'possible'.
But the more I think about it - no... Look at motorways and trucks. Trucks are more efficient than cars even if they have lots of wheels and no obvious aerodynamic considerations. Lorry drivers do not choose the undulating 'A road next to the motorway when one is available. They stay on the motorway doing their most efficient speed (as that is how to make a profit). Hills that any car or lorry could go up are cut through with motorways, to make things as flat as possible.
> If it was quicker/more efficient to go up and down hills we wouldn't have land speed records be they by bicycle or rocket car set on dead-flat courses, would we?
That's a total non-sequitur. Land speed record attempts happen in flat places to keep them from turning into AIR speed record attempts.
Nope. If your vehicle goes over a hump back bridge then maybe, but not if you go down one side of a valley and up the other side, obviously with an inverted wing shaped profile to the vehicle?
Did you read the linked stackoverflow discussion? I thought it made a convincing case that greater efficiency was possible across a valley given a sufficiently-aerodynamic low-rolling-resistance vehicle with an engine of non-constant efficiency. Would your intuition also say that analysis is wrong? Is it?
I suggest you enroll in a physics course, this is physically impossible for the average case of net-zero displacement at a near-constant speed (i.e. roundtrips).
There are scenarios where it's true, but there are a lot of factors involved (drag, power/efficiency curves of the engine, etc..., net-negative displacement, etc...)
My Subaru Outback has been a nice surprise in this area.
The combined highway/city mileage on the sticker was 24 mpg, and I've been getting 27 or 28 mpg for the entire 2 years I've owned it. For a while I was commuting between Denver and Boulder (about 45 miles each way) five days a week and taking it up to the mountains for hiking or skiing every weekend, so it's been over a wide variety of terrain.
I'm using the numbers on the in-car, computer, though, so maybe I should double check...
Car computers are notoriously inaccurate. I have observed errors up to 12% in vehicles from multiple manufacturers. Car computers can be helpful in a relative sense to tell you whether one style of driving is more or less efficient than another but they're basically worthless for absolute calculations. The only reliable way to accurately calculate fuel economy (in mpg units) is to divide the number of miles since you last refueled by the number of gallons to fill the tank.
One of the things I like most about my Jetta TDLie is that the DSG will downshift if you keep the brakes on for more than about 5 seconds. On long downhills I can take my foot off the brake for about half the trip down and the gearbox does the rest until the speed slowly creeps back up.
Except some models are significantly more off the mark than others. Maybe some owner populations have worse driving habits than others, but it's worth investigating.
This is by no means an exhaustive list, nor an authoritative one. Would love to hear other's thoughts on these:
- When accelerating, try not to over-extend the throttle. If the engine is at 2k rpm, you get just as much acceleration from 30% throttle as 100%, at half the fuel cost.
- Release the throttle well before you reach a traffic light/stop sign. Deceleration by engine will cause a smoother stop and gives the traffic light more time to turn green. You spend less fuel trying to reach the stop line, and spend less fuel accelerating again. Bonus points for shifting down while decelerating.
- Keep tires well-inflated and oil levels up. Less friction means less wasted energy on both.
- Choose the highest gear when cruising. Most cars since 1990 can do 50kmh (30mph) even in fifth gear, as long as you don't need to accelerate.
- Drive slower. Most car engines are most efficient around 3500 rpm, which maps to somewhere between 90-110 kmh (60-70mph). Most highways allow for a higher speed. Diesel engines have their optimum at 2000 rpm, or so I've been told.
Of course most of this works best with a stick shift. I've never driven an automatic.
You can do this for automatics too - you just have to learn where the shift points are and drive at the right speed. Lift up on the accelerator quickly to upshift, press it down quickly to downshift. One thing that I notice easily when riding is when the driver is constantly staying at only a few km/h slower than the shift point, causing the engine to spin faster and consume more fuel than necessary. It often means the car is louder and vibrates more too, so not a good thing overall.
This is harder to do for newer models with quieter engines and smoother shifts but older automatics have very noticeable shifts and engine noise to judge whether you're near the bottom or top of each gear. It's very noticeable in larger trucks and buses.
Edit: another point I'll add to the list is traffic light phasing - look far ahead and observe the timing of the lights, and adjust your speed so that you're not going too fast (you'll arrive at a light before it turns green) or too slow (it'll turn red very shortly before you arrive). Obviously, you should do this only if traffic permits, but it's a great "trick" (not so much a weird one) when you can get from your origin to your destination at a constant speed with nearly no stops.
You can usually get the shift points for a model from its technical manual. Depending on the car, those shift points can be modified as well (using the appropriate software and cable).
ICE and Diesel engines are most efficient at full throttle. There have been some tests that show, in certain conditions, that using full throttle to get to speed and then maintaining speed is a more efficient way to drive than gradual acceleration.
> - When accelerating, try not to over-extend the throttle. If the engine is at 2k rpm, you get just as much acceleration from 30% throttle as 100%, at half the fuel cost.
I have a CVT transmission and while I'm sure it is very smart I still feel like I could do better with a manual. I don;t like my car vey much, but it is too practical and cheap to change.
> I have a CVT transmission and while I'm sure it is very smart I still feel like I could do better with a manual. I don;t like my car vey much, but it is too practical and cheap to change.
Is it a actual Continuously Variable Transmission (CVT) or an automatic transmission? There's nothing 'smart' in a CVT since there's gears to shift between, and it's highly unlikely you're going to do 'better' under normal driving since the point of a CVT is to allow the engine to run at ideal RPM's no matter the speed.
A CVT has a pair of pulleys with variable ratios, and a big belt between them, to allow the belt to shift between ratios and find the best ratio.
CVT has some inefficiencies that can be improved by putting the gear selection process from an automatic onto a manual (with an automated sequential manual gearbox or a "double-clutch" transmission).
I did some tests on a long drive last week, for the Smart Forfour I had this was the fuel consumption. It was all along flat, straight parts of the highway. Reports were based upon the cars own fuel efficiency monitor.
It's actually neither square nor cubed, but you can use those approximations with varying success for different car shapes and Reynolds numbers. There are several different physical effects that together create drag: you have form drag, skin drag, interference drag, and even lift-induced drag (the last one essentially only on sports cars).
Aerodynamic drag i.e. force opposite the direction of travel is proportional to the square of your velocity. Power consumption for steady cruising is equal to drag multiplied by speed. Thus power consumption is proportional to the cube of speed.
Right. And if you're measuring miles per gallon, you're interested in energy consumed per mile traveled, not energy consumed per second. And aerodynamic drag tells you energy consumed per mile traveled thanks to the relationship that energy is force times distance.
A dramatic demonstration of this is the Bugatti Veyron. Between the original version (1,001 hp) and the SuperSport version (1,184 hp) - the top speed only increased from 408 kmh to 431 kmh. So a 183 hp increase in power yields only a 23 kmh increase in top speed - bearing in mind that 183 hp is more than most passenger vehicles have in total.
It gets exponentially harder to push air out of the way the higher the speed gets.
Whether it's the most reliable or not, to me the indicated graph at least shows something massively different going on with some GM cars. Every other manufacturer ranges from achieving ~20% to 80% of their claimed fuel emissions improvements from 2008 to 2014, and then there's GM, all by itself with negative 40%.
That is, for GM cars alone, people are reporting not just a lack of increased fuel economy, but that it's gotten significantly worse. Whether it is accurate or not, it indicates something very wrong, either in the testing or in those cars, and that deserves some serious attention IMO.
Edit: s/fuel economy/fuel emissions/ Graph says economy, subtitle say emissions, text says emissions.
For starters, the average person probably drives a great deal more aggressively than the fuel-economy ideal. At least, the automotive industry is convinced enough of this to install behavior-modification techniques like "eco scores" into dashboards.
The official .gov propaganda is a 3% penalty, but self reports vary from 5% to 15%. E10 is a thirsty fuel and people buy a lot of groundwater at gasoline prices, which likely accounts for some variation.
Bizarrely the NEDC procedure allows carmakers to actually declare (use) a value 4% lower than the
one measured. The provision is designed to minimize the testing burden but is being abused by
carmakers to declare lower test results systematically."
I wonder if there is a person that didn't expect this to happen.
This is going to sound backwards, but consider this: People buy cars based in part on MpG, however MpG is within itself an abstract thing (i.e. you don't actually get X miles per gallon, never did, never will too many other factors to include).
So if everyone removes 4% from an abstract number, the entire market has shifted down, but the relative difference between two models remains identical (e.g. if one car has 21 MpG and another has 25 MpG, even with 4% removed from both they retain their relative position).
If some were removing 4% while others weren't, that would legitimately be a problem. If they're all removing 4% then we're essentially where we would be at the start just with lower abstract numbers.
>you don't actually get X miles per gallon, never did, never will too many other factors to include
This wouldn't be hard to fix.
Loan cars to a random selection of non-professional beta drivers.
Graph the results, showing the median and sd.
It would be cheaper to do this than to get hit by a class action for misleading buyers.
Of course reality-based non-expert mpg would look very bad compared to the dishonest figures you get now. But that's because of manufacturing and design decision, and not really the fault of the drivers.
In the US the EPA confirms the MPG ratings for 10%-15% of vehicles and has prescribed (edit: prescribed vs proscribed) testing regimes for each of the estimates. The issue isn't with manufacturers lying so much as the test schedule laid out by the EPA just doesn't reflect how people drive.
It does because emission regulations are not there for comparison purposes alone. We need to reduce emissions to a certain level, and the environment won't be fooled. This is similar to the way unemployment is now calculated based on active job seekers rather than people who are, well, unemployed.
Wow. I thought about shorting GM, after the VW thing broke. I figured they would have the highest incentive to cheat and everyone is about to get caught.
You're also assuming that execs necessarily knew about everything. There's a reasonable chance that the execs set the targets and feed it to the middle managers who pass it along to teams.
Somewhere along the line I imagine there are those who are terrified of missing those targets and perhaps losing their jobs and resort to bending the rules a bit to hit their goals. And there's a very good chance that these people aren't at the top.
The same was most likely true in the subprime mortgages--I imagine that some of the worst actors in that weren't necessarily the people at the top, it was the guy who is decidedly mid-level who is looking to make a nice bonus to put in a swimming pool for his kids.
And to figure it all out is going to take years and years of investigations to assign blame (whether in this case or in the subprime case). By the time it's sorted out, it could be a decade after the fact, and even then people have moved on to other jobs, records are difficult to dig up, and at the end of the day, what has been accomplished?
Of course if there is blatant wrong-doing, execs should absolutely be punished (the peanut company CEO comes to mind [1]). But it's extremely difficult to pin down blame on any one person, exec or not.
You can't just lock up the execs without evidence, that's unjust.
You can't just investigate, the nature of large power structures is that some underling will take the fall.
Breaking the rules for economic advantage should be met with new rules to force economic disadvantage. Put a 2% tax on total revenue for the next X years, possibly with the addition of a fee based on perceived past benefit. Honest players in the market will reap the lower cost of doing business, and better business practices will prevail.
The evidence is that X underling, which Y exec is directly responsible for the business conduct of, demonstrably broke the law in Z way. Vicarious liability I beleive is the term I'm looking for.
Again - with taking the credit comes taking the responsibility. I'd like to see the law amended as such.
Put fear of prison into the people at the top and they'll find a way to prevent this, or subprimes, or—hell—Enron from ever happening again. The buck has to stop somewhere[1]
Well, if the trickle-down theory says that execs and management get the most shares of profit trickling down, maybe the punishments should flow the same way...?
I would compare it to involuntary manslaughter vs first-degree murder. Inaction, negligence, lack of oversight etc that allows bad things to happen, when you were in the position to prevent it, should be punishable.
US regulatory bodies have no teeth and we've already propped up GM once. The only reckoning that's coming is going to be another round of market jiggling, or maybe an unrecoverable failure.
If you assume perfect burning then all carbon burned will turn into CO2. Therefore more CO2 may actually mean more efficient burning and smaller fuel usage (for the same amount of power i.e. less CO, less other particulate matter).
This could happen for example when the engine could not take enough air to burn efficiently (for example because it is stationary).
Unless we have also fuel consumption we could not know which case we are dealing with when we only see CO2 emissions.
For example when the test only measures (and prioritises) CO2 emissions, injection software may decide to use more fuel in inefficient manner to reduce the CO2 emission and then use exhaust filter to capture the extra particulate matter. Well, it is only a wild speculation, but it could be.
The problem is that the report authors do not explain their methodology and interchange freely fuel consumption and CO2 emissions without clear explanation (did they measure CO2 emissions directly? did they calculate it from fuel consumption?).
This is not proper reporting in my mind.
Beside they base their reporting on self reported (i.e. not automatically measured) data from http://www.spritmonitor.de/ that does not provide any objective information about the driving cycle.
See for example these two entries for BMW 3er 320d touring efficient dynamic
Well, maybe the first driver drove very carefully. Maybe the other car is broken or the driver likes to accelerate a lot or is driving on the hilly terrain.
It is also not known how many kilometers were driven on the city roads or highway as they are hard to separate in the data.
We also do not know which driving mode (eco, normal, sport etc) was used as it is not reported.
Car makers report different fuel consumption or CO2 profiles. Against which was comparison completed?
I think that this is sensationalist reporting with an agenda that is not well executed.
>Mercedes cars have the biggest average gap between test and real-world performance, with real-world
fuel consumption exceeding test results by nearly half.
Yes, your facts are valid too, but that's a different comparison than the one I am citing. Read my comment word-for-word and you will see the difference.
It's not my comment. It's data presented in the report. My comment is taken directly from the chart I cited. So if you want to quarrel with it, you need to quarrel with those who compiled the data, I suppose.
You first misread my comment, and now you're misreading the chart, apparently, so let me explain: the chart I cited shows the percentage of claimed improvement in fuel economy which was actually delivered in real-world driving.
This is precisely what my comment said.
Edit: I think your confusion might lie in the math that you think is being done, perhaps? The chart is showing the DIFFERENCE between two numbers. It's not based on just the claimed improvement. It's the actual improvement divided by the claim.
GM made a claim of improvement and their performance actually went down, so their number is around -38%. Daimler was the next-worst at around 16%.
A reckoning is coming.
source: see page 13, here
http://www.transportenvironment.org/sites/te/files/publicati...