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

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

#321

Post by takeda »

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 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).

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

#322

Post by TylerE »

Theodores wrote: post #319
TylerE wrote: post #307

Earlier quoted context omitted.

> 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?

Wing = drag.

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

#323

Post by frankzinger »

enraged_camel wrote: post #193
ticktocktick wrote: post #103

Earlier quoted context omitted.

Just stay off the brakes as much as possible. No big secret really.

Unless your car has regenerative breaks, in which case you should randomly and unpredictably break to generate free energy. edit: downvoters are once again proving that HN doesn't get jokes.

I thought it was a decent enough joke. Tough room.

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

#324

Post by marze »

eveningcoffee wrote: post #264
marze wrote: post #209

Earlier quoted context omitted.

Uh, it is the same. Fixed amount of carbon in a gallon of fuel, all will be emitted.

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 w…

Uh, so you think an appreciable amount of carbon is going out another way? Like carbon monoxide? Or unburned hydrocarbons?

Neither compares to CO2, as a fraction. You are simply wrong. CO2 emission is proportional fuel consumed.

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

#325

Post by joe_the_user »

rnovak wrote: post #316
joe_the_user wrote: post #306

Earlier quoted context omitted.

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 f…

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 fur…

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]

[1] http://blog.caranddriver.com/how-volkswagen-got-busted-for-g...

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

#326

Post by yoz-y »

mikeash wrote: post #205
yoz-y wrote: post #200

Earlier quoted context omitted.

It is kind of weird that this is surfacing just now. There are magnitudes more VW owners than Tesla. Why have not the consumer studies revealed this a long time ago?

You have to put in a fair amount of effort to monitor the fuel efficiency of a gas (or diesel) car. It's not hard , but you have to keep manual records and do some math. If an electric car is much less efficient than claimed, you'll notice as soon as you try to drive to the limit of your car's range, because it won't get there.

Hm, I see. However I imagine entreprises with large car parks should have quite a lot of information (taxi services, car rentals, ...)

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

#327

Post by [deleted] »

[deleted] wrote: post #34
mpweiher wrote: post #22

Earlier quoted context omitted.

I actually drove my Golf TDI at around the level of 5l/100km in Berlin for many years. Carefully. My girlfriend's Polo is significantly below that. Of course, these cars aren't ton and a half, but more around a ton.

[deleted]

[deleted]

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

#328

Post by epsylon »

emp_zealoth wrote: post #8
yc1010 wrote: post #2

"On average, two-thirds of the claimed gains in CO2 emissions and fuel consumption since 2008 have been delivered through manipulating tests" How deep does this rabbit hole go :( Here in Ireland the motortax for cars newer than 2008 is based on CO2 emissions, if motorists find their tax rising due to cheating by car manufacturers thats an unexpected and direct cost to their wallets.

Or maybe we abolish nonsensical, contrary requirements? Whoever actaully believed the fuel consumption figures is a fool. You cant have a 1,5t of a car and expect it to use only 5l/100km. That's a good rate for a goddamn motorbike (450ccm,one piston, dont exceed 90 km/h and you might reach 4,5l/100km) Its one fifth of the mass...

Your numbers are also false for motorcycles (which all run on gas and not diesel which is the subject of the conversation here). My BMW's 800cc rotax paralell twin does exactly that (4.5L cruising on the highway). Even the 1200cc boxer does that AFAIK.

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

#329

Post by [deleted] »

kbenson wrote: post #207
mattlutze wrote: post #58

Earlier quoted context omitted.

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.

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'…

[deleted]

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

#330

Post by mattlutze »

snuxoll wrote: post #262
number_six wrote: post #225

Earlier quoted context omitted.

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…

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).

https://www.fueleconomy.gov/feg/tech_transmission.shtml

http://www.nrel.gov/docs/fy11osti/47806.pdf

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