/ Motoring

Car fuel economy claims are miles from the truth

Car wheel

We already know that ‘official’ car mpg figures are rarely possible in the real world – our tests show that. But choosing larger alloy wheels could see your fuel bills increase even more.

As part of the Which? Car team, I get more emails about fuel economy than anything else. They inevitably start by mentioning the official EU test figure, as quoted by the car manufacturer, then explaining how their car can’t get within 20 miles per gallon (mpg) of that number.

That’s why we think our mpg tests are more realistic. They include cold starts and motorway driving – both absent from the official EU cycle.

However, official figures could be even further from the truth – depending on the wheel-size of the car you buy. Opt for big alloys (as many style-conscious buyers do) and your fuel economy could drop significantly.

Different wheels, different mpg

At the moment, Toyota and its sister-brand Lexus are the only companies to quote separate economy and CO2 emissions figures depending on wheel size.

For example, buy a Lexus IS 300h in entry-level SE spec and it comes with 16-inch wheels. Quoted economy is 65.7mpg with CO2 emissions of 99g/km (grams of carbon dioxide per kilometre driven). However, stretch your budget to the Luxury model and you’ll also need to stretch your fuel allowance; its 17-inch alloys reduce efficiency to 64.2mpg (103g/km CO2).

At the top of the Lexus IS range is the F Sport version. This has exactly the same engine and electric motor, but with 18-inch rims its claimed economy is 60.1mpg (109g/km CO2). That’s an increase of nearly 10% over the SE model – almost entirely because of those larger wheels and tyres.

To put that in perspective, a driver covering 12,000 miles a year would spend £107 more on fuel for the F Sport than the IS 300h SE. Plus, annual car tax (VED) costs £20 – rather than being free.

Same car, different wheels

Now let’s look at one of the IS’s rivals. The BMW 3 series is the UK’s bestselling large car, yet its maker quotes identical fuel economy and CO2 emissions for all models, whether with 17, 18 or 19-inch alloys.

I believe Toyota and Lexus deserve credit for being upfront about fuel economy figures. It’s time other car companies followed suit.

Can you match your car's mpg claims?

No (69%, 784 Votes)

Yes (18%, 205 Votes)

I don't know (13%, 153 Votes)

Total Voters: 1,150

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Comments

It is well known that EU fuel consumption figures do not represent real-life consumption, and are not intended to. They are precisely controlled tests to compare different cars on an equal basis, and presumably to provide a basis for emmission taxation.

The way to get real-life consumption is from drivers reported information – and particularly, I suppose, from fleet operators. Honest John at the Daily Telegraph publishes these. So do Which? and other motoring publications.

Even then, your own consumption will depend on how you drive and your journey pattern, so it would be impossible to give a consumption figure that would apply to all drivers – only a range would make any sense.

For emmission, read emission!
Dear Which? When can you introduce editing of posts please? Even if it involves deleting your offending post and resubmitting it.

Please don’t worry about typos Malcolm – if you are concerned report your comment and I’ll fix the typo. Thanks

Colin Samson says:
15 September 2013

Ha Ha! “Emmission” stuck out like a sore thumb to me too. I’m glad that I’m not alone in finding such errors to be irritating. The spell checker usually shows that a word is misspelled when these posts are being typed, as the word “Emmission is highlighted as I write this now; so there should be no excuse.

“TV’s” is another error showing up on Which? reviews. There should be NO apostrophe as the abbreviation is plural (more than one television); it should spell as “TVs” or arguably “TVs.” with a full stop to show it is an abbreviation of “Televisions”. Unfortunately the daily press is usually littered with spelling & grammatical errors so it is no wonder that standards elsewhere are plummeting.

Hi Colin, Malcolm’s referring to the error in his own comment (sorry Malcolm!) However, if you ever spot a typo in something we’ve written please do tell us. Sometimes mistakes slip through, but we do like our copy to be error free. TV’s is an annoying one! Now, back on the topic of car mpg claims…

We could do with an easier way of reporting errors in the introductions to topics than using a Web-based form and putting in name, email address, subject and message.

Incidentally, the energy campaign logo has KWh rather than kWh. I’ve seen kW/h in an earlier Conversation. 🙁

Cheers

petty Dare I say

But accurate. We should preserve correct English – it has a purpose. Two things (well two of the many things actually) that irritate me are the misuse of apostrophes and beginning spoken sentences with “so”. Sorry to deviate from the topic.

If I was working in a hole in the ground, I would like to know whether the hole would consume 1 man day or 1 man/day . There is a difference.
In scientific reports, it is important to get the units correct. Wrong units cause confusion and make it look like you don’t understand what you are saying.
Apparently our new street lights will save several kW per year. On that basis, perhaps the contractor’s new lorries will save several horse power per week.

Malcolm,
Of course you are quite correct manufacturers figures will always be compiled in absolutely ideal conditions to give the best result possible. After all they want to sell cars. The car buyer has very little chance of matching these consumption figures, but because all manufacturers do it the numbers still offer valuable comparison information.

And lets face it no one drives the same or is as diligent about the cars condition so accurate figures for consumption even if independently derived would still at best only offer a comparison.
So there cannot be any real solution to this situation.
However most of us will realize these manufacturers figures are “optimistic”, but we can still make an informed buying decision based on comparison.

Not much to debate really is there?

Chris, I think it would have helped if Which’s introduction had spelled out exactly how EU figures are derived and that they are not created to represent real life, only as comparative data. Instead it rather suggests they are misleading. | wish that Which? would not employ the sensationalist (tabloid) approach quite so much – it should be objective.

MalcolmR,

Completely agree.

Hello Malcolm and Chris, we’ve debated mpg claims on Conversation quite a few times now, which means we are now simplifying the argument for why we think our tests are more accurate. Here’s our original, more detailed Conversation: https://conversation.which.co.uk/transport-travel/cars-mpg-claims-tested-car-miles-per-gallon-fuel-economy-petrol/

What Tim wants to debate here is specifically the issue of wheel size and mpg.

You can also read a more detailed summary of how we test mpg in our guide, and why we think the EC tests don’t represent real-world driving: http://www.which.co.uk/cars/choosing-a-car/how-we-test-cars/how-we-test-mpg/

I read somewhere that the official figures are rigged to be higher than real life, because a manufacturer will rig the car in favour of a better result, Whether its removing (the now non existent ) spare wheel, to switching off things like air con, disconnecting the alternator ( as why would they need to charge the battery) etc so what they end up testing doesn’t resemble real life at all.

The tests should be carried out on the exact spec and condition a car is likely to do be used in the real world and if anything should be done with a large weight in the boot too

The test is done on a rolling road, so I don’t think weight would have much effect. Drag is definitely excluded since it is not moving through the air. As I understand it the tests are very specific, so unlikely the manufacturer could cheat by disconnecting the alternator. I would think running without aircon would be sensible as long as all cars were tested the same way.
However, these are comparative tests. Perhaps the adverts and literature should make it quite clear that these are not representative of real-life performance. The only way to get this is to refer to the sources above.

Not sure they are done on a rolling road as that would eliminate air resistance.

I’ve read a similar, or was it the same, story. If true manufacturers remove every bit of excess weight, remove the drive to anything that might absorb power, remove door mirrors and even tape over gaps in the bodywork.

Must have been the same story as taping over the gaps in the bodywork rings a bell.

The tests are done on a rolling road. Taping over the bodywork gaps would have no effect. The tests and caveats are described on the following link:
http://www.dft.gov.uk/vca//fcb/exhaust-emissions-testing.asp

Where?

When tests are conducted in a laboratory on a rolling road an electrical fan must be used to simulate air resistance otherwise the tests would be producing even worse results than they do now, especially at higher speeds.

http://www.telegraph.co.uk/motoring/green-motoring/9241054/Fuel-economy-why-your-car-wont-match-the-official-mpg.html

Air resistance is not part of the test. These are laboratory tests for the specific purpose of producing comparative results, not real-life figures, and have never been purporting to do otherwise. For what you might achieve in practice you need real data from cars on real roads, doing real journeys driven by real drivers – and even then there will be a range within which your car with you driving might fall. Which publishes these, as does Honest John.

Air resistance has to be part of the test otherwise the test is useless. The fact that the manufacturers figures can’t be replicated in real life but are supposed to be realistic is the whole point of this conversation although some makers are still claiming that they are realistic and can even be exceeded by careful drivers!

Phil, the whole point is the tests are not realistic, nor claimed to be. I don’t see that the intro to this conversation suggests otherwise. There are moves to improve the test. If you want realistic results then use accumulated drivers reports for a good guide.

It is essential that cars are tested under standard conditions for fuel economy figures to be comparable. To overcome cheating by manufacturers, the cars to be tested should be purchased in the same way that Which? does when carrying out tests of products, and not using cars chosen for tests by the manufacturer.

Late one night I observed a policeman filling his car with diesel. After I had offered him a lift to the local nick, he told me that he was getting 25mpg on average. My last tank full delivered a verifiable 46mpg. We are both supposed to get an average of 56mpg from our cars. Scalded cats apart, the manufacturers’ claims are of no use to anyone; that’s why the latest Which initiative, among others, is so good. It now needs to be comprehensive, officially recognised and mandatory information for any new car spec.

I pay attention to the fuel consumption gauge on my car to help me drive in a reasonably economical way. Even if it is inaccurate, it gives me a useful indication of how cold starts, crawling in rush hour traffic and driving at 70 mph on motorways all use more fuel than longer journeys on reasonably quiet roads out of built-up areas. At the moment, I’m averaging over 60 mpg, but only because I am able to avoid doing many short journeys.

Whilst manufacturers have made good progress with increasing the efficiency of their engines, they are constantly tweaking other aspects to improve MPG figures – eg airflow, lowering the ride height, taller gearing, stop/start etc. Most of these tweaks have little effect on real life fuel economy. For example, with higher gearing, you need to change to a lower gear more often to compensate for variable driving conditions (traffic, bends, junctions, hills, speed limits etc). It’s only constant steady speed driving that will benefit from higher gearing and the scope for that is ever decreasing.

I’m very glad that car manufacturers are constantly tweaking their designs to improve fuel economy.

All the tweaks have given us cars that will easily deliver 50-70 mpg, despite the fact that many of us are driving more aggressively than in earlier years. If you do not like changing gears, there are good automatic transmissions that will do the job without greatly affecting fuel consumption, very different from the early automatic transmission systems using inefficient torque convertors.

That’s the problem – people are not getting such MPG figures in their every day driving. Figures reported in by drivers proves that these claims by car makers are not being achieved. You have completely misunderstood what people are saying. Do some brim to brim testing to find out what you are really getting.

AQ – I am NOT refuting the fact that manufacturers are being dishonest about fuel economy. I think this is dishonest and disgraceful. My point is that the cumulative effect of car design changes have greatly improved actual fuel economy over the years.

I will try to remember to measure my fuel consumption over a few thousand miles, but on the basis of one fill-up, I am achieving nearly 60 mpg at present, with my diesel car. I don’t expect this to be maintained during the winter months or if I start to do a lot of short journeys.

My fuel economy on journeys I make regularly can change by 25% depending on how I am driving and the traffic on the roads.

wavechange /AQ, if you are suggesting that when manufacturers quote EU test figures for fuel consumption they are being dishonest then you are being unfair. They are not claims for what you will get, but report the results of these “laboratory” tests. These tests are done for comparative purposes only and are not intended to represent real life. I posted a link above the goes into some detail on these tests.

Out of interest, I went to Devon on a mixture of rural roads and motorways, with the usual slow traffic at holiday time, in my 2.2 diesel Espace – not a light car. My on-board consumption meter showed 43.5 mpg – just on the extra urban EU figure. And when I returned and added a lot of local driving it dropped to 38.3 – well above the mixed figure. I always fill to a full tank and the consumption calculated from this matches the computer.

Malcolm R – Neither of us were accusing car makers of being dishonest. However, given the specifics of the prescribed EU testing methodology, manufacturers are exploiting the potential to achieve better and better results in such tests – and they have a legal obligation to publicise these test results in their advertising material. Whilst a good many of us know that these figures are unlikely to be achieved on the road, there are probably a much greater number of people who will “trust” this information when making their car buying decisions. Whilst we could criticise the test methodology, because it is so unrealistic, the difficulty is prescribing an alternative which would have so many variables that comparability would be impossible – hence the “laboratory” approach. Perhaps manufacturers should put a disclaimer in their publicity “believing EU inspired statistics can damage your wealth”.

Malcolm and AQ

When I bought a new car last year I looked at the published fuel consumption and read the small print in the brochure explaining that “The driving style, road and traffic conditions, environmental influences and vehicle condition can in practice lead to consumption figures which may differ from those calculated with this standard”. I asked the sales rep what fuel economy I could expect and he quoted the published information, without the disclaimer. That was an experienced sales rep at a VW main dealer.

If the alternative is to have the EU test figure or something more realistic, I think we can guess which most consumers would prefer.

There are so many cases where products and services are not as good as they appear. For example, my ISP used to advertise the broadband service I use as ‘up to 24 Mbps’, and I have never managed to better 7 Mbps. Now that they have dropped the ‘up to’ figure, I am much happier. If VW had published a fuel economy figure of 50mpg, I would be very happy indeed because I can achieve that or better throughout the year.

I’m prepared to retract my claim that the manufacturers are being dishonest on the basis that the small print exists, but maintain that using these figures in marketing is despicable, because they know well that they are not typical of what the motorist can expect to achieve.

Thank goodness that Which? and others publish fuel economy figures that are more realistic.

wavechange – I agree with your view on their use in marketing and sales. It would be difficult, though, to devise a standard test that gives truly realistic data. However, realistic data exists, as we have said. Maybe some of this is authoritative (carefully collected over a range of scenarios) perhaps from fleet operators. If so, I wonder if there is a way such data should be included in advertisements and literature. I’m a bit dubious.
As I have suggested elsewhere the government should help educate consumers deal with the sales and marketing hype exuded by lots of industries and services that seek to mislead us. Tax advertisements to provide the funding. Perhaps this could then educate everyone to consult sources of real-life fuel consumption before visiting the car sales emporium.

You mentioned taxing advertising when we were discussing unhealthy soft drinks, Malcolm, and I can see plenty of potential for raising revenue for education. In this case it could help consumers deal with manufacturers’ hype.

As a scientist who has spent years trying to present information in a clear and unbiased way, the deceit and misrepresentation that is prevalent in advertising really annoys me, but I have long given up hoping for the situation to improve.

Johno Shaft says:
14 September 2013

please explain why bigger wheels mean less mpg….

I would’ve thought it would be the other way round.

for me the main issue is tyres. compare mpg on a motorway with winter tyres vs eco tyres, unbelievable

It’s not specifically the size of the wheels, it’s the overall size of wheel and tyre. When bigger wheels are fitted, it’s usually to take lower profile tyres (to sharpen the handling, but it makes the ride harder). So it’s the circumference right round the tyre that needs to be compared. Normally, there would be very little difference between standard wheels / standard tyres and bigger wheels / lower profile tyres, but there can be occasions when the latter results in a smaller overall circumference, which results in slightly shorter overall gearing (MPH per 1000 revs) and thus the fuel economy – but it is very marginal.

It is far more complicated than that … .

If you look at the range of standard vs. low profile tyres available for the Lexus IS300, you will see that standard 205/55R16 tyres come with a wide range of Energy Label ratings – typically “C” or even “B” ratings. The low profile 255/35R18 tyres fitted to the rear of the Sport model only come in “E” or “F” ratings. In terms of economy, the effect of fitting these less energy-efficient tyres is similar to fitting winter tyres to a normal production vehicle.

Why? In theory, wide low-profile tyres should be more economical than standard profile tyres as there is less deformation of the tyre. However, there is more material, the tyres tend to be heavier and the rubber composition of the tyre may be more geared towards grip than economy, all factors that increase rolling resistance.

In practice, it is probably a recognition by manufacturers that people who buy low profile tyres for looks simply don’t care about fuel economy.

Top marks to Toyota for pointing out the difference, but another Convo opportunity missed to point out the importance of checking the tyre energy label and the tyres’ significance in fuel economy?

… Simply put, tyre rolling resistance accounts for about 10%-20% of the fuel used, so a small change here (different rubber, profile, tread pattern, etc.) can have a noticeable effect on consumption.

Em – yes I know there are lots of other factors concerning tyres that will have an impact on fuel economy. However, I was replying specifically to the comment made on the effect of bigger wheels, particularly in relation to diameter.

if you are buying a top of the range car – you have more money than sense and thus it is obvious you are not really concerned about the cost of fuel or economy

Andi, in principle I agree that by choosing a large-engined heavy car you are not putting economical fuel consumption top of your list. But I disagree that they have more money than sense – as if only by choosing economy can you be regarded as sensible. You could argue that flying abroad for holidays is not sensible (fuel used) for example – we all have the freedom to use our disposable income as we choose! -:)

small car man here – my motorcycle is my statement
my byeline: I’ll stop driving when petrol is as expensive as beer

Andi, at £20 a gallon I think you make a good point!

in my bar that would be more of £40 to the Gallon – so I will be driving for a while yet I think

Jim Simpson says:
14 September 2013

This 13 reg is my 3rd 1.8 Prius : the first two averaged 65.0mpg over 20K, using “Eco” mode usually but switching to “Power” for overtaking when necessary. The current one is following the same profile. “Eco” is more than adequate in town and for motorways and gives a smooth and quiet performance. This mpg equates pretty well with Consumer Reports’ (USA) mpg when converted from US gallons. Pretty early you can adapt your driving style and I usually outperform most cars from the stoplights while maintaining or slightly exceeding the limit. Most car reviewers seem to drive impetuously and so get poor mileage.

Gerard Phelan says:
14 September 2013

It is very difficult to get repeatable “real world” fuel figures, because the “real world” is so variable. Some 35 years ago my employer, an oil company, was trying to validate US results that a new engine oil blend improved the mpg by x%. So 100 brand new cars were bought, 10 each of different models across the ranges. Each group of 10 cars were driven in convoy by experienced drivers, along routes that were the classic mix of motorway, urban, rural, flat and hilly. The order was fixed such that car #3 was always third and car #9 was always ninth, in case the mattered. Odd cars received engine oil A and even cars engine oil B taken from tanks just marked A and B. No-one in the UK knew whether oil A or B was supposed to be the better. The cars were fuelled from a single petrol tanker, so that the same batch of petrol applied throughout the trials. High precision fuel meters and odometers had been added to allow reliable petrol usage and distance travelled data to be logged daily for each car for the few weeks the trials ran.

My role as a fresh faced postgraduate fresh from studying mathematical modelling was as part of the team analysing the results, looking for the step change in mpg we were told we should find. The big problem was the variability of the data, which reflected the complexity of driving in convoys in the “real world”. In towns they got snarled up in traffic, some were held up by traffic lights whilst others escaped into the distance, sometimes they lost the car in front or behind (this is long before mobile phones or sat navs) so some cars would go faster or slower to allow the convoy to reform. Occasionally drivers would forget themselves and overtake others in the convoy, so getting out of their designated position.

Overall a massive variability of data, even before we tried to identify the improvement we were expecting to see. Therefore although as a driver myself I am sympathetic to the desire to see published “real world” mpg figures, I saw just how hard it would be to obtain anything that would be repeatable.

I can certainly relate to research being a bit frustrating at times, Gerard. 🙁

I presume that most cars now have a fuel economy gauge, so most drivers should be aware of the many factors that can affect their fuel consumption, and hopefully realise that providing realistic estimates is not a precise science. The problem is that far more people achieve less than the published mpg than those who manage to exceed it. If lower figures were published there would be fewer dissatisfied motorists and some very happy ones.

It seems daft that you are probably more likely to get a measure of fuel economy by asking friends with the same car than by studying the manufacturer’s data.

Every car I’ve owned over 30+years has returned something resembling the MPG for mixed driving conditions – until I got a jaguar XF 3.0 diesel. I struggled to get 30MPG on a car that is supposed to return 40+ MPG with mixed driving. I complained to Jaguar & they were useless. I took it the the dealer & they filled the tank to the brim, took it for a spin & claimed they got 40+MPG. When I insisted they must have fudged the results & questioned them firmly, they owned up to switching off the air con etc and taking it down the A3 at 55 MPH, and of course staring on a hot engine as I’d just dropped it off. I complained to the top & even the MD of Jag UK didn’t give a stuff.

There is no such thing as a single ‘real world’ fuel consumption figure for a car but rather several such figures with a very big difference between them! One of the major factors in the fuel consumption being achieved is the way the car is driven with the actual road/weather conditions for the journey running close behind. The figures published by the manufacturers are achieved under well defined test conditions, they should be used simply to compare car A with car B and not regarded as indicative of actual ‘real world’ performance.

As is so happens, my car usually returns a consumption figure not too far from the published value during the warm summer months but noticeably lower in the winter. On a recent journey from Birmingham to west of Ipswich I was surprised to see that I had actually bettered the published figure – and I had an appointment to make so was not hanging about!

There seems to be one lesson we can all take away from this Convo; never under-estimate the benefit of an extended (24 hour) test drive. Since nearly all cars now have a trip computer, it is possible to get an accurate real-world estimate of fuel consumption from a typical day’s usage.

A good example of where a car simply didn’t suit my journey pattern or deliver anything like the manufacturer’s stated mpg was the Toyota Prius. If I lived in a city, then great. But although it was very economical around town, the petrol hybrid system wasn’t of any benefit on motorway journeys, where the Prius was overweight (all those batteries) and underpowered.

Re. another Convo: attempting to accelerate a Prius out of danger at 70 mph going up hill in the fast lane is not a good option. A conventional Diesel-engined car turned out to be just as economical for me – and “safer”.

Up until I had my company car I have always bought second hand cars, in order Mini 1L 1983, 1300 Metro 1985, Rover 216 Si 1997, Volvo 740 2L Estate (petrol no turbo) and in all of those cars I could readily exceed the official MPG without even trying too hard – sometimes by more than double the official figure – and without driving like an old dear. I then had a Volvo V50 2005 2L diesel and this, just met the figures, albeit only when I was being careful. Now I have an 61 plate Astra Sports Tourer, which supposedly should do about 67mpg. The best I ever had when I emptied a tank on a motorway and did 62mph all day constant, was 62mpg. If even constant speed at most efficient revs (90 KPH and 100KPH equate to approx 56mph and 62mph and are the tested limits for Europe because of common speed limits there) can’t match the official numbers, then there is something seriously wrong with the official test.

Just read the TestLab feature (Oct 2013) I notice all/most vehicles are diesel which unless the user drives some 10K per year, or at least has regular travel, at speed, over some 10/20 miles then they are liable to suffer particulate filter problems, and the maintenance costs will thence cost more than any fuel saving over petrol.
I feel Which has failed to warn peoples of this problem in their Lab feature

Regarding insurance costs of the Mazda CX5, I see in your Test Lab article you quote £619 as a typical price. However, my wife pays just £149.50 for fully comprehensive from Sainsbury’s Bank, and we don’t live in a particularly low risk area. I read on another website that the collision avoidance radar on the car has led to large reductions in premiums. Maybe your information is a little out-of-date?

Regarding the poll on this topic – “Vote in our Poll Can you match your car’s mpg claims?”.
This presumably refers to the EU figures that by law must be published by the car-makers? Figures that are well known not to claim to be representative of real-life motoring, but not stated explicitly here.
It would be fairer to ask perhaps if the EU should also collate real life data and publish that , at least to give a better indication of performance. Difficult with a brand new model or engine, which is no doubt partly why laboratory testing is necessary.
I am all in favour of real life data – aren’t we all – but we must be careful not to lead people into thinking they are being mislead.

Joe Cash says:
11 November 2013

In yankee doodle land if cars do not meet the mpg stated by the manufacturer they are heavily fined. A well known Korean manufacture had its wallet emptied of millions of dollars because of this “dodgy” dealing.

Flocker says:
5 May 2014

Just a quick question, do they manufacturers include an air resistance factor (remember the drag coefficient in the 70s) in the simulated tests. As someone mentioned above, without this being factored in, there can not be a comparison of the vehicle with other vehicles even where they have the same engine and drive train.

The answer is no they don’t include it for fuel consumption tests – they can’t do this in a “laboratory” type test, in just the same way they cannot effectively simulate hills and bends or other factors that would influence a real life result. However, given two cars with the same laboratory results, the car with the lower drag coefficient is more likely to give better MPG results in real life driving – all other factors being equal. The EU testing methodology is exploited by manufacturers to tweak settings, gearing, ride height, tyre rolling resistance, weight saving etc to stretch the MPG figures in the test as far as they can so that they can quote the results in their publicity – and the more they do this, the less likely anybody will get anywhere close to their figures. Whilst “economy” versions of cars (eg blue motion, greenline etc) will publicise consumption of say 15 to 20% less than the standard car, owners are more likely to achieve results hardly any better than the standard car. Best to use the figures as nothing more than a rough guide.

The DfT point out: “The fuel consumption testing scheme is intended to give potential car buyers comparative information about the relative fuel consumption of different models in standard tests.” They are not intended to represent real life, but to allow some comparison between different cars. Tests must be standardised for this comparison to make any sense. Individuals will get widely differing results anyway in practice, depending on their journey types, geography, driving style etc. I think the best you can do is to look at published average real life data (such as Honest John and Which?) to get an idea of what you might get near, and treat the EU figures for what they are -comparative and relative only. Moves are afoot apparently to make them more related to normal motoring but use.