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Study: Some car models consuming around 50% more fuel than official results

transportenvironment.org

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Re: Study: Some car models consuming around 50% more fuel than official results

#241

Post by MagnumOpus »

eveningcoffee wrote: post #185
vonmoltke wrote: post #158

Earlier quoted context omitted.

> You cant have a 1,5t of a car and expect it to use only 5l/100km So you are telling me that my actual, measured fuel consumption numbers of 4.25l/100km on flat highways in the US South are impossible? I have a diesel Passat (yes, one of the NOx Boxes :P) and can get from Dallas, TX to Pensacola, FL (650 mi) without refueling and with a decent reserve (~2 gallons) still in the tank.

The thing is that this report does actually not provide any data about fuel consumption - only about CO2 emissions. What they do is wild speculation and possibly a smear campaign because people care more about the fuel economy (their own money) than CO2 emissions. It is interesting that this (some) data is provided but how it is presented does not make it look very credible.

What are you on about? For any given type of fuel, fuel consumption is related exactly 1:1 proportionately to CO2 emission (as carbon particulate and CO emissions are microscopically small these days). That is basic chemistry - where else would the fuel go?

Therefore any claim about CO2 emissions equates to a claim about fuel consumption.

Re: Study: Some car models consuming around 50% more fuel than official results

#242

Post by jo909 »

JonFish85 wrote: post #173
JustSomeNobody wrote: post #162

Earlier quoted context omitted.

Assuming wrongdoing: GM will get another pass because it is "too big to fail." This has to stop. Execs need to start going to prison.

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…

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.

Re: Study: Some car models consuming around 50% more fuel than official results

#244

Post by bayesianhorse »

mattlutze wrote: post #58
Bud wrote: post #29

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. A reckoning is coming. source: see page 13, here http://www.transportenvironment.org/sites/te/files/publicati...

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.

German highways often don't have a speed limit... And when you go over a certain speed, the fuel consumption doesn't have a limit either.

Re: Study: Some car models consuming around 50% more fuel than official results

#245

Post by Drdrdrq »

mattlutze wrote: post #58
Bud wrote: post #29

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. A reckoning is coming. source: see page 13, here http://www.transportenvironment.org/sites/te/files/publicati...

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.

If anything, I would expect users of such pages to be more careful about fuel consumption than general population.

Re: Study: Some car models consuming around 50% more fuel than official results

#246

Post by bayesianhorse »

protonfish wrote: post #194
lucaspiller wrote: post #172

Earlier quoted context omitted.

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. - 135 km/h 7.8l/100km (30 mpg) - 125 km/h 6.5l/100km (36 mpg) - 115 km/h 5.4l/100km (43 mpg) I never realised speed made such a difference! (Mpg is US gallons)

That's - 84.0 mph - 77.5 mph - 71.5 mph For us in the states.

No, for you in the states it's 70mph ;-)

Re: Study: Some car models consuming around 50% more fuel than official results

#247

Post by rnovak »

kbenson wrote: post #235
rnovak wrote: post #229

Earlier quoted context omitted.

It's not irrelevant at all. 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 ridiculo…

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…

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?

Re: Study: Some car models consuming around 50% more fuel than official results

#248

Post by randyrand »

The conclusions in the article are bullshit. There are a number of possible explanations.

1. offical does not reflect real world. 2. defeat devices.

If every car manufacturer is using defeat devices it really shows how poorly EPA requirements have worked. Blame car manufacturers, sure, but they're supposed to be selfish. That's how economics works.

Re: Study: Some car models consuming around 50% more fuel than official results

#249

Post by mturmon »

aianus wrote: post #210
TylerE wrote: post #191

Earlier quoted context omitted.

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. Now, mountains are another story, of course. Some good stuff in this SE question: http://physics.stackexchange.com/questions/6220/can-a-car-ge...

> 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').

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.

Re: Study: Some car models consuming around 50% more fuel than official results

#250

Post by nostrademons »

aianus wrote: post #210
TylerE wrote: post #191

Earlier quoted context omitted.

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. Now, mountains are another story, of course. Some good stuff in this SE question: http://physics.stackexchange.com/questions/6220/can-a-car-ge...

> 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.

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