I can get equal to or better than the official combined figure in my car without even trying.
Oh dear, have I said that before? Am I reiterating iterating?
;-)
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Does one reiterate if one has previously iterated?
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Check out www.fuelly.com for real world figures
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I'm really pleased to see the article didn't include the oft quoted myth:
"As the tests are done on a rolling road, in a lab, they don't include the effects of drag"
The article does correctly point out that manufacturers design and calibrate their cars to perform well on the official tests.
There is a difficult problem here - the tests absolutely must be standard to be fair and meaningful, but, in being standard, they will not fit with many people's definition of normal driving, and they will be susceptible to manufacturer optimisation.
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>> the oft quoted myth:
>> "As the tests are done on a rolling road, in a lab,
Is it a myth N_C? How can they standardize the tests absolutely, outside in the wind and the rain and the variable pressure and humidity?
This sort of thing reminds me a bit of the Mobil Economy Run. Winners used to record some astonishingly low consumptions in those carburetted cars, but only by using tuning methods and driving techniques that, er, can't have done the engines a lot of good, super-lean tuning, pedal to the metal in top gear from 10 or 12 mph to 35, stop engine and coast back to 10 or 12 mph, repeat exercise ad infinitum. Must have taken the patience not of a saint but a car-hating fiend.
The first manufacturer to use a set of real-world good-driver tests giving figures the ordinary mimser might hope to match under normal conditions will be doing itself a favour in the market. Perhaps in parallel with all the Euro emissions carp which is probably compulsory, bad cess to it.
Last edited by: Armel Coussine on Fri 27 Apr 12 at 15:23
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>>How can they standardize the tests absolutely
By being rigorous at every stage.
The drag of representative vehicles is measured using a method defined in a standard. The ambient conditions are included in this test, and the results then normalised to standard conditions.
With the drag as a function of road speed now known, the rolling road can be calibrated to add this drag function onto the loading of the rollers, thus incorporating road load drag in a standard and repeatable manner.
When the rolling road part of the testing, the ambient conditions are again measured, and again, the results are adjusted back to standard conditions.
While on the rolling road, a robot is typically used to "drive" the car - again, optimised to just comply with the lower limits of the test cycle definition.
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Thank you N_C, admirably concise. Of course it had occurred to me that drag could be factored in electronically on a rolling road. I imagine drag doesn't vary much with shape of vehicle up to about 50mph, and testing doesn't use much higher speeds than that?
I suppose it's more annoying than an actual problem that the resulting figures are so remote from what a driver can get in practice. In the days of carburettors and contact breakers not only the car's (usually defective) tune but the way it was driven could make a palpable difference to fuel consumption. I have the impression that these modern electronic engines, all Teutonic efficiency, are always in proper tune unless damaged or with knackered plugs, and are far less sensitive to a jittery, restless right foot - no carburettor pump - although it must make some difference. So the manufacturers could still utter some consumption figures people might actually match or approach, if they wanted.
Perhaps that would make the mandatory Euro-compliant across-the-range figures look false though. Something like that. Legislation, don'tcha just love it?
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>>This sort of thing reminds me a bit of the Mobil Economy Run. Winners used to record some astonishingly low consumptions
I used to compete in club events back in the '70s when economy runs were popular. I quickly learnt to adopt the tactics of the best:
1. Charge the battery the night before
2. Run with the windows closed and no heating/cooling fans.
3. Accelerate to 35 then cut ignition, coast to 25 and bump start
Result, ninety-odd MPG from a 1750 Maxi on a fifty mile run that required an average of above 30MPH, beaten only by a 2CV that managed a couple MPG more.
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>> The article does correctly point out that manufacturers design and calibrate their cars to perform well on the official tests.
And, if I understand correctly, they have good reason for doing so, since performing well in fuel consumption tests is directly related to performing well in emissions tests, which is related to the VED band the car falls into, which has a major impact on sales figures.
So, if we assume that What Car? is correct, and that the official figures are much closer to real life figures for some cars than others - then what are the factors which cause the figures to be more accurate for some cars than for others?
(For example, I've always assumed, for example, that if a car has tall gearing, then the official figures are likely to be highly optimistic, whereas if a car's gearing is short, then the figures are more likely to be realistic.)
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>>I imagine drag doesn't vary much with shape of vehicle up to about 50mph, and testing doesn't use much higher speeds than that?
As the drag tests are done on a representative type of car, the drag values are specific to that car type - there are some rules about what changes from the drag tested car are allowed without needing to re-test - allowable changes in mass for example. So, the drag is added onto the rollers as a polynomial function of vehicle speed.
>>I suppose it's more annoying than an actual problem that the resulting figures are so remote from what a driver can get in practice.
>>- then what are the factors which cause the figures to be more accurate for some cars than for others?
It does vary, but, I'm not sure what the causes are that mean some cars get close while others rarely do. As we are about to get our dyno up and running again at the polyversity, and I'll have some students asking for masters projects soon, perhaps I'll ask one of them to have a look, and see what they find.
>> In the days of carburettors and contact breakers not only the car's (usually defective) tune...
Yes!
In the introduction to his useful book "Motor Vehicle Fuel Economy", Richard Stone describes the results of a survey reported by Atkinson & Postle (1977) where 72 vehicles were checked for compliance with their maufacturer's specifications;
83.4% incorrect mixture at idle
75.0% incorrect static ignition timing
40.6% incorrect dwell angle
29.2% incorrect valve clearances
23.6% required spark plug replacement
20.8% required contact breaker replacement
18.1% incorrect mixture strength at 2000 rpm
16.7% had excessive cylinder leakage
5.6% required air filter replacement
While many get hot under the collar about electronic engine controls, it's clear that ECU engine control, by removing many items from that list is making a significant saving overall. I admit that's a difficult point to see if you are unlucky enough to need to replace an ECU.
>>So the manufacturers could still utter some consumption figures people might actually match or approach, if they wanted.
I don't see how. Once the test is standardized; as it must be, then, manufacturers will design, tune, and tweak to make their cars perform well.
>>(For example, I've always assumed, for example, that if a car has tall gearing, then the official figures are likely to be highly optimistic, whereas if a car's gearing is short, then the figures are more likely to be realistic.)
I'm not sure. I know there are some tricks manufacturers use to get the best results, so, a lot does depend upon how artful and cunning the manufacturer's engineers have been.
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>> Does one reiterate if one has previously iterated?
Definitely, categorically, absolutely, indubitably, unquestionably, ............!
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www.fuelly.com seems to be for the American market even though the figures are reported in UK MPG, you may not actually be looking at the same car that you'd get in the UK
Dare I say it but HJ website does have a realistic fuel economy section
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Depends on the car - the section I use are all European based
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www.youtube.com/watch?v=gDW_Hj2K0wo
Bill Hicks on marketing the ral world.>:) Some swearing.
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Problem is real for company car drivers as these figures are used for the official mileage reimbursement rates from HMRC meaning that many company car drivers are significantly out of pocket.
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>> Problem is real for company car drivers as these figures are used for the official
>> mileage reimbursement rates from HMRC meaning that many company car drivers are significantly out of
>> pocket.
>>
But they pay less BIK as the cars quoted MPG means lower CO2 and therefore lower tax bands......
Swings and roundabouts.
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What Car's new tool is meant to give a more real life mpg figure.
www.whatcar.com/truempg/
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The Other Site also has real world figures, submitted by users.
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>> The Other Site also has real world figures, submitted by users.
>>
And You believe them? Some must drive everywhere at 40 mph. :-)
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Sad to see a diesel Golf in the offenders list. These were once one of the few cars that did achieve their claimed figures, albeit with the old PD lump under the bonnet.
Our old mk4 is easily capable of its 52.3 mpg combined figure. Only deliberate hard driving or sustained city use knocks it below 50 mpg.
It's surprising to see the mk6 1.6 TDI Bluemotion is actually no more economical in the real world than our ancient mk4 for all the newer car's common rail trickery, stop/start technology, and 25 bhp power deficit.
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>> It's surprising to see the mk6 1.6 TDI Bluemotion is actually no more economical in
>> the real world than our ancient mk4 for all the newer car's common rail trickery,
>> stop/start technology, and 25 bhp power deficit.
>>
Probably to do with weight, most newer versions of cars have middle-aged spread to some extent.
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>>Swings and roundabouts.
It would be if they didn't move the goalposts. A car with a 15% BIK rate two years ago will be 19% soon.
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My car is supposed to do 48mpg I think. It actually does 45 or so. Not too bad really for a biggish auto. My wife's is listed at 42mpg and again it falls short by a couple of mpg. Not very disappointed. I can live with both.
It's all a dear do anyway nowadays isn't it?
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>>It's all a dear do anyway nowadays isn't it?
New, smaller, more economical MB coming to the market in a year or so...
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Lounge lizards queue here...
:-)
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Slip-on shoe wearer's car that.
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It'll be selling like hot cakes - you wait n' see.
Last edited by: Clk Sec on Sat 28 Apr 12 at 17:08
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Not the most reliable of newspapers may I say? I think they have a history of not letting the truth get in the way of a good story.
I have noticed that in user car reviews, whenever the reviewer says that performance is not good, they then go on to say that mpg is poor. I think the truth is that driving style is very important, as well of course as the nature of the journey. So a short journey means the engine never warms up and runs rich. But even on a longer journey, an 'enthusiastic' driver will regularly accelerate and break, destroying fuel economy. My old Micro gave me about 45mpg, which was the official figure. My Ka gave 40 mpg in winter, and 45mpg in summer, with an official figure of 42mpg. My VW Up gave 54mpg on the first fill, the official figure being 63mpg, and I was regularly doing 75 mph on the motorway. The engine is still running in, and I believe mpg will get better. The second fill gave 57mpg. Pretty damned amazing in my view.
There are ways to get better mpg: keep a distance from the car in front to minimise braking, avoid coasting with the clutch depressed (coasting in gear uses almost no fuel), keep revs low, don't accelerate rapidly and then brake and so on. All pretty obvious really isn't it!
I do think that mpg figures are getting better, not just because manufacturers are better at fiddling the figures,but because engines are getting more efficient.
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>> There are ways to get better mpg: keep a distance from the car in front to minimise braking...
Tailgating reduces drag massively.
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>> >> There are ways to get better mpg: keep a distance from the car in
>> front to minimise braking...
>>
>> Tailgating reduces drag massively.
Yes, and life expectancy.
I think to reduce drag you'd have to be about 1m behind the vehicle in front. So any gain through lower drag would be lost via regular braking and accelerating, and add on the cost of vehicle repairs, and increased insurance and it's not a good idea. But ... add on an automatic tracking device, and it would be worthwhile if, and only if, the drive in front drove smoothly (unlikely) or you had regenerative braking.
Anyway, I was referring to keeping a decent distance behind, rather than the usual a bit close but not tail gating that is commonplace. It also gives you better forward visibility esp. with a 4x4/bus/lorry in front. I've seen more than a few people unwilling to overtake a wide vehicle, but sitting on their tail, thus making it impossible for anyone else to overtake, but that's a rant for another day. ;)
But as I said, I usually get the combined figure or close to it.
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Do they test cars in a wind tunnel? Doing that would help.
The article makes no mention of which figure they're looking at as being wrong. Combined, urban or extra urban?
Personally I'd ignore all but the urban and assume the urban figure is what you'll get. Then you'll be less disappointed or pleasantly surprised.
They also fail to mention that run in engines can be more economical than brand new ones and diesels in particular are prone to this.
If they want some real world mpg then I'm happy to sacrifice my time for a modest remuneration and test a different car each week :)
I also suspect that underpowered cars will do worse as they'll need hammering just to do basic tasks like joining a motorway or going up hills. Hills also drop economy noticeably. While I borrowed a bmw with an instant economy read out it was amazing to see how much difference a slight incline made or a major incline. Are all the dispossessed living in hilly areas?
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>> I also suspect that underpowered cars will do worse as they'll need hammering just to
>> do basic tasks like joining a motorway or going up hills.
I think that is exactly why some people fail to get the combined figure when driving a smaller car than usual. They expect big car performance, and hammer the gears and engine to get it. And bang goes the fuel economy.
The term 'underpowered' is subjective. I'm always amazed when a journalist says that a given car does not really have the power for motorway driving. Errr, yes it does, but you can't do the 'expert driver' swooping in and out among other powerful cars. And you do have to drop a gear or two for some overtakes to be safe.
>> Hills also drop economy
>> noticeably. While I borrowed a bmw with an instant economy read out it was amazing
>> to see how much difference a slight incline made or a major incline. Are all
>> the dispossessed living in hilly areas?
It is surprising isn't it? But I could point out the compensation for this, where you can get almost zero fuel consumption, but I'll let you figure that one out. :)
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Today's Sunday Times has an article on this as per the Daily Wail. Apparently What Car magazine also has an article with some tables. I wonder if the official tests have changed much in the last 15 years?
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i bet you would never find out.
what we could do with is some government tester coming online and state what they actually do for the test and if the cars are picked from the production line.
not supplied from the car maker with some custom programmed ecu.
i did read somehere on the web that since only the driven wheels are put on a rolling road, the ecu could go into low emissions mode when driven with the handbrake on.
possibly true as all cars have a display when the handbrake is on, so the ecu could look for this.
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>> i did read somehere on the web that since only the driven wheels are put on a rolling road, the ecu could go into low emissions mode when driven with the handbrake on. possibly true as all cars have a display when the handbrake is on, so the ecu could look for this.
That wouldn't work on cars where the parking brake works on the driven wheels.......
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>>what we could do with is some government tester coming online and state what they actually do for the test
All of the test procedures are available online, there's nothing hidden - look for UN/ECE
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What Car magazine have a true mpg calculator:
www.whatcar.com/truempg/
The only car I have owned that they list is my brand new VW Up and I get significantly more mpg than the calculator would suggest, and the car is not broken in yet, so it should improve.
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>> The only car I have owned that they list is my brand new VW Up and I get significantly more mpg than the calculator would suggest, and the car is not broken in yet, so it should improve.
>>
As an aside, I did hear that VW were due to launch a new factory option range... special colours, trims etc, bu have now cancelled the idea.
The cars would have been badged;
Golf Yours, Passat Yours, Polo Yours, Up Yo........ ;-)
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>> As an aside, I did hear that VW were due to launch a new factory
>> option range... special colours, trims etc, bu have now cancelled the idea.
>> The cars would have been badged;
>>
>> Golf Yours, Passat Yours, Polo Yours, Up Yo........ ;-)
The electric one will be called the E-Up. No doubt the Yorkshire boy racer one is the E-Up Lad. And the Friday afternoon one that breaks down all the while is the Muck Up, or something like that. ;)
It is a very stupid name for a car. Then again, Aygo and Ka are daft too.
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Fuel consumption. - L'escargot
