How close, in real life does one get to the official figures for fuel consumption?
This was highlighted by Rattle's answer to my fuel economy query on his Panda - around 38 mpg with mostly shortish trips. The Panda's combined figure is around 50mpg, so quite a difference.
Currently, with cold weather and no long trips, we are getting very close to the tdi Alhambra's combined figure of 43 point summat, at around 44mpg.
A car salesman to whom we were talking (looking at (used) a Panda, a Picanto and a Getz) said that "shopping trolley" cars struggled to reach claimed figures as their engines need to be hard worked.
He also advised us to keep our Alhambra and not to swap it for a little car!
On an aside as we will probably now hang onto the SEAT I've been pricing tyres and shuddering at the costs. They are 215/55/16/9/H /XL and it's going to be £99 a corner for Avon ZV5s in our size (Black Circles & a local fitter, within pennies).
Any recommendations for a budget tyre which isn't really vile?
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It might be worth you looking at HJ's site - he seems to be running a real world consumption thing on there, with readers inputting their own stats for their own make/model experience.
Last edited by: R.P. on Tue 14 Feb 12 at 16:37
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Goodness, I've nearly forgotten HJ's "other place", but I will look. Ta for reminding me.
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Within a short trip I sometimes managed to beat manufacturer's figure slightly :-)
But on average consumption over several months, my figures tend to hover around 80-90% of the quoted value.
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>> It might be worth you looking at HJ's site - he seems to be running
>> a real world consumption thing on there, with readers inputting their own stats for their
>> own make/model experience.
That will be only with the individual owners' interpretation of what constitutes a valid method of calculation. I only trust two sources ~ the manufacturer's and mine.
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Not sure that you will find a budget brand reinforced tyre. £99 each is reasonable
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www.honestjohn.co.uk/realmpg/
Filled it out.
37mls round town in this cold stuff better when warmer and nice when on a run.
Last edited by: Bigtee on Tue 14 Feb 12 at 17:14
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Within a short trip I sometimes managed to beat manufacturer's figure slightly.
Forgive me but how can you possibly know that? I have no idea what mine does on the one-mile downhill Worralling trip from a cold start on a Saturday morning, and wouldn't be any the wiser if it had a fuel computer. Any data collected over such a short period is meaningless.
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Ignore all the figures apart from the urban one. That's what you'll actually get. The combined is optimistic and the even higher one is total fantasy.
A small car with a bigger engine is ok. Don't get a lawn mower model and you'll be fine for ascending hills with passengers.
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It was easier in the old days when there was a constant 56mph figure, at least you could emulate that pretty accurately at the right time of day. A quick Google suggests the extra urban figure for my lovely Vectra is 41.5 mpg, which is pretty much exactly what I get on my daily commute up and down the A31/M27/M3.
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For a cheap tyre, decent enough quality and feedback reports check out mytyres.co.uk and the
Goodride SA-05 215/55 R16 97V XL
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Any attempt to match the quoted test results is, bluntly, a fool's errand.
Even if your personal measurements are averaged over a period of time, all you're establishing is the consumption of your duty cycle, under your particular environmental conditions: a meaningless figure to anyone but yourself.
The attempts to do this indicate a misunderstanding of the meaning of the official figures. This misunderstanding is usually accompanied by the claim that the tests are done in a lab, and therefore don't include the effects of aerodynamic drag. Of course, this is nonsense. The aerodynamic drag of the vehicle is measured, and the drag (as a function of vehicle speed) is added to the rollers on the test dynamometer.
Part of the problem has a chicken and egg nature to it. The test MUST be standard to enable the results to be compared between cars - to enable people to make buying decisions, and to set a meaningful baseline for taxation purposes. However, once the test is standardized, manufacturers will optimise the performance of their cars in that test - they would be foolish to do otherwize.
While "practical" people scoff at lab based tests, it is extraordinarily difficult to obtain good quality data when running a vehicle on the road - or even on a controlled test track. Trying to otain data which have any meaning in traffic conditions represents the very opposite of practicality in my view.
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Real world tests are needed too. There is a lot of deviation in some vehicles between quoted results and actual results.
I'd happily volunteer to test all the supercars and decent cars to see if they match ;)
Only way to test them in the real world is to collect data from real drivers actually using the cars under real world conditions. I can't imagine they can't hook up the car's ecu and get a readout of fuel economy. If you test enough cars over enough time with enough different people then you'll get a reasonably accurate figure.
It's like the guff mobile companies spout about standby and talk time. They're just utter rubbish as they don't reflect actual usage patterns at all. MPG figures quoted should reflect actual figures that a normal driver can achieve. Why do car manufacturers get away with being able to lie about things? We don't accept blatant misinformation for other products so why are cars different? Kettle manufacturers don't lie about how much electricity they use. Cooker manufacturers don't lie about how powerful their hobs are. TV manufacturers don't lie about electricity usage or features.
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>> Real world tests are needed too.
No. I think you're drawing the wrong conclusion.
>> There is a lot of deviation in some vehicles between quoted results and actual results.
Yes, and this shouldn't be a massive surprise. To ask ONE standard test to cover the whole range of vehicles and usages is asking too much.
>> Only way to test them in the real world is to collect data from real drivers actually using the cars under real world conditions. I can't imagine they can't hook up the car's ecu and get a readout of fuel economy. If you test enough cars over enough time with enough different people then you'll get a reasonably accurate figure.
Who's going to pay for that?
>>MPG figures quoted should reflect actual figures that a normal driver can achieve.
It's a question of practicality. The best we can do at the moment is to use a very carefully controlled standardized test.
>> Why do car manufacturers get away with being able to lie about things?
No one is lying about anything. You are being told the pure undiluted truth.
>> why are cars different? Kettle manufacturers don't lie about how much electricity they use. Cooker manufacturers don't lie about how powerful their hobs are. TV manufacturers don't lie about electricity usage or features.
All the examples you give there represent technically trivial measurements where the usage of the device is well defined or completely out of the control of the user, where the results do not show a significant change under differing atmospheric conditions where there's no equivalent of varying traffic, where the electricity doesn't vary if you buy it from a different supplier, where the device cannot be serviced (or mis-serviced). That's why cars are different.
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Everything is being compared against each other, using the same test, its all relative. Doesn't matter what the test is or how accurate is in in the real world, its comparative guidance.
Alas the manufacturers don't want you too look at it like that. They want you to believe the actual numbers. The numbers should be something that you cant relate to.
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>>its all relative
Yes, I agree.
>>The numbers should be something that you cant relate to.
Like an energy rating, A to Z, perhaps?
>>They want you to believe the actual numbers.
They are the figures which you can quote from the mandatory tests. That people don't understand them and how to react to them is hardly the manufacturers fault.
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>> >>The numbers should be something that you cant relate to.
>>
>> Like an energy rating, A to Z, perhaps?
Little restrictive - only 26 ratings. Something giving you a 4 digit number would be good.
>> >>They want you to believe the actual numbers.
>>
>> They are the figures which you can quote from the mandatory tests. That people don't
>> understand them and how to react to them is hardly the manufacturers fault.
Its no accident that the test comes out with the type of rating it does. A lot of work (lets be kind and call it work) was put in by the manufacturers to ensure the tests involved a "marketable" number.
Last edited by: Zero on Tue 14 Feb 12 at 22:05
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>> being able to lie about things? We don't accept blatant misinformation for other products so
>> why are cars different? Kettle manufacturers don't lie about how much electricity they use. Cooker
>> manufacturers don't lie about how powerful their hobs are. TV manufacturers don't lie about electricity
>> usage or features.
>>
Manufacturers of cars don't lie - they tell you what was achieved by a model in a specific set of circumstances.
Kettle manufacturers AFAIK do not conduct a test to see how much energy is used to boil a specific amount of water at at a specific starting temperature and a specific ambient temperature
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You want to try the word "unlimited " in the context of mobile phone data if you think car consumption is a fairytale..
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>The combined is optimistic and the even higher one is total fantasy.
Mine is pretty accurate for the combined figure but then my 25 miles each way daily commute is probably the definition of "combined".
Urban going through Basingstoke, then about 12 miles of extra urban on the A33 followed by four miles of dual carriageway and another three or so miles of urban on the outskirts of Reading.
I average 25mpg (measured brim to brim) which is 1mpg short of the official combined figure for my Jag. The 1mpg difference is probably due to permanent climate control, bum warmers and occasional forgetfulness of the speed limit.
The extra urban is supposed to be 35mpg but I've never achieved more than 29mpg on long trips. I've no doubt 35mpg would be possible if I tried though.
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>> Any recommendations for a budget tyre which isn't really vile?
>>
Not sure what your load rating is Roger, one figure is missing, probably 93 or 97 is the rating?
However Camskills are showing Avons at £76.60 and Kumho's at £64.10, both heavier 97 rated...there will be a tenner postage on 4 and you will need to find a local fitter.
I'd be happy to fit these...
www.camskill.co.uk/m62b0s292p6372/KUMHO_TYRES_CAR_KUMHO_KU31_ECSTA_SPORT_KUMHO_KU_31_-_215_55R16_97W_XL_TL_
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If speedos over-read by 5%, does that mean the fuel computer is also 5% opimistic?
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Depends whether the odometer overeads - the only sure fire way is a careful brim to brim test - stopping at the the first click of the pump. Still dependent on a odo reading. Garmin SatNAvs provide trip meters which is probably as accurate as it gets.
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I've always worked on combined figure less ten percent. Seems to give a ballpark real world figure for most cars I've owned or driven for any length of time. Until the two newer (2008 on) cars came along, which stretch this to nearer twenty percent. I presume this relates to marketing / tax pressures to nail low "official" CO2/consumption figures.
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>> Until the two newer (2008 on) cars came along, which stretch this to nearer twenty percent.
>> I presume this relates to marketing / tax pressures to nail low "official" CO2/consumption >>figures.
>>
I suspect the 'reality gap' will indeed get bigger for this reason.
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>> ......... the only sure fire way is a careful brim
>> to brim test - stopping at the the first click of the pump.
That's only for that fill-up. In any case, fuel consumption varies with all sorts of things ~ journey lengths, terrain, traffic, driving style, load in the car, weather etc etc.
Last edited by: L'escargot on Thu 16 Feb 12 at 08:24
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>> If speedos over-read by 5%, does that mean the fuel computer is also 5% optimistic?
The speedo in my Mondeo over-reads by about 4% compared to a GPS speed readout, but if I hold a steady speed then reset the trip computer, after a few seconds the average speed shown on the computer is close to that on the GPS.
I used to drive a Sprinter van which my employers had asked the Mercedes dealers to electronically speed limit to 75mph. The speedo needle would read a fag-paper under 80mph but according to GPS the speed of the van was an accurate 75mph. I understand that speedos are deliberately set to display an inflated figure, but that an accurate value for speed is used by the vehicle's ECU.
I've found the mpg function of the Ford's computer to be pretty close when compared with brim-to-brim calculations; the computer settles at 52.4mpg, pencil and paper works out at 51.7mpg. Both better than the book figure of 48.7mpg.
Last edited by: Dave_TDCi on Wed 15 Feb 12 at 14:31
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My 2 litre petrol Focus's overall consumption is slightly better than the official combined figure. My calculation is a genuine overall, recording every drop of petrol bought over the last 64,000 miles. It's a waste of time calculating over short distances or short time periods, brim to brim etc, which is what most drivers do.
Last edited by: L'escargot on Wed 15 Feb 12 at 09:27
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Yes, l'Es, and I can say the same for my car. But, as NC explains, all that tells us is what our respective cars achieve the way we each use them. It's useful for our own budgeting, because we can predict what a trip is likely to cost in fuel, and perhaps as a warning of a problem if the figure changes suddenly, but that's about all we can take from it.
What I do find curious is that, while I regularly 'over-achieve' in my Volvo, the same driving style in the Verso seldom achieves 90% of the Combined figure. Maybe I secretly thrash it through some subconscious urge to get out of the beastly thing.
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I get the same mpg for my Pug diesel as the quoted figure. I have bettered it on a long drive however by keeping it under 70mph and accelerating slowly and it didn't affect journey times with any noticeable difference.
Are car makers obliged to publish mpg figures? Maybe they should scrap them and just publish the CO2 figures.
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CO2 and MPG figures are inversely linked to each other so they pretty much reflect the same result of the test.
CO2 levels are higher for the same MPG when comparing diseasel and petrol vehicles, because the black stuff contains more carbon per gallon (thus makes more CO2 per gallon burned).
And yes, the makers are obliged to publish the figures.
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Used to beat the book figures on my Passat TDI on a regular basis by about 10%.
The 120d, on the other hand, averages 46MPG on the motorway at 70mph as opposed to the quoted figure of 60+. Winds me up no end - in fact, on this basis I've already decided my next car will not be BMW.
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If manufacturers started using "real world" mpg figures then the price of car tax would increase substantially overnight.
Auto journalists constantly bleat on about not being able to match the manufacturers figures, then in the same paragraph say how "willing" the car was at 80mph or whatever.
A recent review of the Fiat 500 multiair was one of the worst I have seen in this respect. It went on about how fun it was, liked to be revved etc.. then said how disappointing it was to get 45mpg over the course of the test.
Also people like to say how amazing it is nowadays to have a car (eg BMW 330d) that can do 0-60 in 6 odd seconds and achieve 48mpg. Well not at the same time they can't!!
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Regarding filling brim to brim - have I read somewhere it makes a difference on the volume of fuel you get if you fill up in colder temperatures because the stuff is more dense?
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>>the stuff is more dense? >>
not as dense as some who believe the mpg they calculate for their car. ;)
Last edited by: John H on Thu 16 Feb 12 at 13:22
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If the fuel you fill up with is colder and therefore denser, you get the same volume of fuel in a full tank but a greater mass of fuel. Presumably you would get improved mpg.
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Cold fuel tanks shrink so you get less volume but the same mass of fuel.
..../walks away whistling
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Any more thoughts on non-vile cheap tyres?
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>> Any more thoughts on non-vile cheap tyres?
>>
I've just chucked some Nexen Roadstones on the front of the C5. So far so good - cant say I have noticed any difference between them and the Michelins that came off.
I paid £70 odd quid for 205x60x16's - not reinforced though
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>> I've just chucked some Nexen Roadstones on the front of the C5. So far so
>> good - cant say I have noticed any difference between them and the Michelins that
>> came off.
Good tyres, I have a pair on the back that have been swapped from the front. They were excellent on the front in last years blizzards.
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It matters not if the fuel is more dense. If your car is not level side to side and front to back.. then "brim to brim" filling will not be the same volumes.. Also the fuel cut off point is measured by a pressure sensor .. which will have varying values pump to pump..
I brim to brim but there can be differences of 2-3 litres in 40..(think filling up the fuel pipe or not as the case may be.
I trust my figures as accurate - measured over 7 years..:-)
Anyone who thinks a cold petrol engine - or one on a really cold day - driving round town - is going to get anywhere near the urban figures is - how shall I put it delicately ? - the kind of person who thinks politicians tell the truth..
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I can't understand this fixation on fuel consumption, If a car is properly maintained the main fuel consumption control is your right foot. You use your car, it uses fuel, fact of life.
That is NOT an excuse to mimse! Buses are for mimsers. :-)
Last edited by: Old Navy on Thu 16 Feb 12 at 15:22
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I agree. Can't see the point in knowing your exact fuel consumption . It is what it is.
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I would like to know if a potential purchase is going to cost me £60 or £90 per week at the pumps!
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The key word is "exact". There is no such thing, but we all have a "ball park" consumption. Mine does about 120 miles per quarter tank, what more do I need to know?
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Ah... okay. I know my pug will do 550 minimum per tank, but upto 630 sometimes.
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Yes, I understand that but once you have bought it surely then the fuel consumption is only of passing interest. All this brim to brim stuff and keeping records of fuel purchases is, well just a bit trainspottery?
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Agree Norwich I never do this brim to brim what's the point? Computer says about 54 and a bit mpg.Why diesel cost more in this country I don't understand should be cheaper easier to refind.Robbing so and so's.
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I don't think I could achieve the official urban figure for my car. I know if I mimse I'd get near it but I tend to accelerate briskly. What's the point of having paid for the more powerful version of a car and then drive it slowly :-)
On the way home from Liverpool on Sunday there was some fog so slowed down to an indicated 65ish... mpg was rising steadily.
On a run to Edinburgh and back recently I noted a big enough difference between an indicated 70mph and 85mph (slower in the real world then)... but not enough to make me drive 70 everywhere. It takes long enough to get to/from say Edinburgh from Manchester as it is.
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Me to rtj70 If on m/way 75 to 80 mph.Depending on weather you be a fool in fog or heavy rain to drive to fast.In winter depending on conditions slow down.
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I slowed down appropriately and left plenty of room all around especially in front. Idiots were coming charging past at way above the limit and driving far to close to the other cars in front... visibility was poor. Only one of them needed to brake hard to cause a pile-up.
For my Passat CC 170PS diesel I can easily get 700 miles to the tank without mimsing. So a lot more if I did. Not around time of course.
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Nice motor Passat the old mans favorite when he was still alive..>:)
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Still the favourite of plenty of old men, Dutchie, not all of them still alive.
[Removes crumpled shortlist of estate cars from pocket. Sees familiar name in pencil at bottom. Walks away, affecting air of nonchalance.]
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Affecting air of nonchalance nice one.>:)
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Not considered a Pastit since they started putting those silly handbrakes on them. Bit Masonic anyway.
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>> Not considered a Pastit since they started putting those silly handbrakes on them. Bit Masonic anyway.
Yes foot operated parking brakes are much better ;-) Especially if they push the pedals to the right in right hand drive cars.
Last edited by: rtj70 on Fri 17 Feb 12 at 10:19
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>> Used to beat the book figures on my Passat TDI on a regular basis by
>> about 10%.
>>
>> The 120d, on the other hand, averages 46MPG on the motorway at 70mph as opposed
>> to the quoted figure of 60+. Winds me up no end - in fact, on
>> this basis I've already decided my next car will not be BMW.
>>
Interesting. I've often looked at the BMW figures and thought that some looked a bit to good to be true
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This site www.fuelly.com/about/ does not do anything that one cannot do oneself, but it is a novel way of recording a car's economy - or otherwise.
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I was going to point out that as it's American the gallons in everyone else's consumptions would be the smaller transatlantic variety (would only affect comparisons with others).
But you can set units to UK, where you enter fuel quantity in litres and get consumption in miles per imperial gallon.
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Fuel consumption figures. - R.P.
