And I don't mean, why does my car only get 25mpg, if the figures say 42mpg.
The mpg figures are calculated from the emmissions tests. These are done in a laboratory (i.e. inside a building I assume) and therefore, any aerodynamic aids to economy that the vehicle may have will be useless, as the car is on a rolling road in still air.
So if you have two cars with the same engine and transmission and the same weight, but one is like a Ferrari and one like a london bus, in the real world, the economy will be different, but in the test they will be the same.
Am I right?
--
Espada III - well if you have a family and need a Lamborghini, what else do you drive?
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They program the rolling road to emulate the drag profile of that particular car.
BB
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While drag is always a factor, I imagine it's less of an issue at the relatively low speeds most of the test sequence is done at.
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Esentially you have the correct degree of scepticism.
It is a test under artificial conditions. The result can only be relied upon for comparison purposes when comparing two new diffrent cars. Ie A: will do more MPG than B: but what that MPG is lord only knows.
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TourVanMan TM < Ex RF >
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I have had consistent mpg figures more or less in line with manufacturers figures on a number of cars, namely two Peugeot 309s, a ZX and a Xantia. The C5 tends to underachieve, if it can be put that way, although I am not sure what mix of urban and extra urban driving makes up the official combined figure. What I do know is that the computer read out on the car has never got up to the manufacturer's official combined figure of around 39 mpg, when measured over a period of time required to take into account a reasonable mix of urban and extra urban motoring. The best it has done is about 37 mpg.
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>>but what that MPG is lord only knows.
But this only really matters to nerdy, fuel consumption spreadsheet keeping types. I think the figures are useful, helping people to choose between cars on their shortlists.
Number_Cruncher
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For the first time since I started driving I've found the figures to match reality. My Toyota Avensis 1.8 petrol has an offical combined MPG of 39.1 and in reality with shorter runs and a few motorway journeys I've got around that mark.
My old 1.8 Focus never achieved the same offical figure in all the time I owned it!
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"this only really matters to nerdy, fuel consumption spreadsheet keeping types".
I disagree, N_C. If you do (for the sake of argument) 10 mpl = 45mpg, and 10K miles a year, it follows that you need 1000 litres, which will cost you (or someone else) about 900 quid. That might lead you to thinking how many £££ you might save. Also perhaps about consuming less non-renewable resources - never mind the CO2 output.
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Isn´t the rule of thumb to go by the urban figure quoted by the manufacturer to get an idea of real-world MPG?
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Isn´t the rule of thumb to go by the urban figure quoted by the manufacturer to get an idea of real-world MPG?
I hope not and, thankfully, I have never returned overall figures as low as the official urban figure for any car I have driven.
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>>I disagree, N_C
Good good! - if we all agreed, this forum would be a dull place indeed!
I'm not saying the concept of aiming for fuel efficiency is not worth bothering with, I am saying that the figures provided by manufacturers may not be particularly meaningful in day to day motoring, except to anyone who is a bit of an anorak wearing Excel fiend.
The tests provide a meaningful standard by which cars can be compared. I think that the tests are done in a fair way.
This comparison between cars can just as well be done with a fuel efficiency rating. The absolute figure in mpg obtained by driving an ideal car over a ficticious driving cycle is not hugely important IMO.
The figure one obtains by driving a real car under real traffic conditions is important.
There may be a point to say that fuel is still not expensive enough because many people are not making fuel efficiency their top priority. I suspect many buyers are more interested in trim levels and the spec of the radio and alloys than the fuel efficiency.
Number_Cruncher
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I suspect many buyers are more interestedin trim levels and the spec of the radio and alloys than the fuel efficiency.
I suspect - if this forum is anything to go by - that fuel economy, performance, handling and running costs are not important.
What matters is how it looks!
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There may be a point to say that fuel is still not expensive enough because many people are not making fuel efficiency their top priority. I suspect many buyers are more interested in trim levels and the spec of the radio and alloys than the fuel efficiency.
Totally right, and the more premium the car the less it matters in most cases. Most of the BMW M5s and Audi S4s sold in this country will be bought on company money and include a company fuel card to run them.
As far as official figures go - I usually beat the govt figure for my A3 2.0TDI on the trip computer most journeys. Sometimes I can beat it by more than 10mpg. Tank to tank the Excel spreadsheet shows I've averaged 45mpg against the govt figure of 51. Most of my tanks are around there, with some in the high 30s and a few in the mid 50s.
Interestingly I find it much easier to beat the government figures in big petrol cars than in diesel econo hatches. I can get 25mpg from an A8 4.2v8 without really trying, and 28/29 if I do try. It's not even too tough on a trip of over 50 miles to beat 30mpg in an S4. Now assuming the computers in those cars are similarly over optimistic like my A3's, then I'm still hitting 25mpg from an S4 Cabrio. Beating 30mpg (actual) in a 3.2 A3 Quattro is easy.
Some of it is due to the huge power excess with a big engine though. Reigate Hill on the M25 will wipe 3-4mpg off the average figure on my A3. On the same journey in an S4 cab I've dropped less than 0.5mpg over the same stretch. The A3 usually showing about 52 at the bottom and 48 at the top having covered about 10 miles at that point. S4 was something like 28.6 to 28.2 I think. Both times average speed in the high 50mph/low 60mph range.
Trip computers are fun and fuel my geekiness...
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"But this only really matters to nerdy, fuel consumption spreadsheet keeping types"
You called. I have the figures for every car I've ever owned back to 1979. Sad, I know!
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Manufacturers' fuel consumption figures are the ideal - the reality is much different.
Devise an exercise with two drivers in the same model of car and covering a mixed roads test route of, say, 100 miles, their indiviudal fuel consumption figures will be some way apart.
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What\'s for you won\'t pass you by
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Manufacturers' fuel consumption figures are the ideal - the reality is much different. Devise an exercise with two drivers in the same model of car and covering a mixed roads test route of, say, 100 miles, their indiviudal fuel consumption figures will be some way apart.
Very True (bit like a politican) will only give you the best results ,The truth is that we don't drive cars in a sealed tunnel on the same machine used for the MOT - the rolling road.
We also have a variety of weathers to cope with - all electrical accessorys add up to destroy a good MPG.
But how meny people will turn the engine off if stopped at a level crossing ? (waiting for 3mins with the engine ideling could be a distance of 0.5 mile - taken from my Ford handbook) how meny at night Turn off the headlights when in a cue at say traffic lights or that junction that takes minutes to clear?
How meny will drive at say 56mph in a 50 zone (thus speeding) or the same on motorways
The trouble is we all drive differently some for speed some for economey those who want speed need deeper pockets though or parents who can bail them out!!
The final thing is the same engine in a heavier bodied car or van will make a difference to its performance as will whats in the boot number of passangers and the roads themselves
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>>how meny at night Turn off the headlights when in a cue at say traffic lights or that junction that takes minutes to clear? >>
I understand your reason for this suggestion - but it's actually illegal.
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What\'s for you won\'t pass you by
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