/ 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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Flocker says:
6 May 2014

If the drag factor is not included, then how has the statement ‘to allow comparisons between different vehicle types and different manufacturers’ never been challenged as surely this would have succeeded no matter how big the motor industry is.

Which? has recognised that published fuel economy figures are not very useful. What consumers need is figures that are closer to reality. It would be better to underestimate rather than overestimate fuel economy so that the average driver can achieve or exceed the published figure.

Most car journeys start off with a cold engine, yet the EU tests are performed on engines at full operating temperature. If I recall, Which? does one of their two tests starting off with a cold engine. Perhaps it would be useful to do both with a cold engine.

I acknowledge the need to carry out tests on a rolling road, so that air resistance is ignored. I’m sure it would be possible to adjust the fuel economy figures to allow for how streamlined different vehicles are.

I would like to see all fuel economy tests carried out independently and not by manufacturers.

“EU tests are performed on engines at full operating temperature.” Not so – only the extra-urban cycle, that is continued after the urban, uses an initially hot engine. However, tests are done in high ambients. Dispel the myth that the EU tests represent real life- they don’t and are not claimed to. Just an attempt at comparing vehicles in a relative way. Use other data, as above, to get an idea of real life mpg (l/km).
“Urban cycle
The urban test cycle is carried out in a laboratory at an ambient temperature of 20°C to 30°C on a rolling road from a cold start where the engine has not run for several hours. The cycle consists of a series of accelerations, steady speeds, decelerations and idling. The maximum speed is 31 mph (50 km/h). The average speed 12 mph (19 km/h) and the distance covered is 2.5 miles (4 km).”

Thanks Malcolm. I stand corrected. I see the EU as part of the problem here.

Many of us are aware that the EU fuel economy figures are not representative of real life. That does not stop car dealers using these figures to sell cars. As I reported earlier, an experienced sales rep tried that one on me and he received a lecture about dishonest selling.

Flocker says:
6 May 2014

I have reply from a certain manufacturer that air tests/drag should and is taken into consideration this particular manufacturer. Anyone have a definitive test procedure to conform that drag is or should be taken into consideration.

As far as testing the particular vehicle is concerned there is no reason at all that the test cannot include a simulation of hills of different gradients. The test will certainly have a load applied to the drive wheels to simulate the rolling resistance of the vehicle under test on a level road, and they can simply increase the load to simulate the effect of gravity on the vehicle mass on inclines. It calculable. No need to take into account inertia as in free wheel mots engines shut off fuel flow.

This drag factor is the most important input particularly if its not taken into consideration. Need to know definitively that it is or isn’t.

I agree, Flocker. Even if the simulation is not perfect we could still have figures that are attainable.

One point I disagree about. Even when fuel is not being injected, the engine acts as a brake and thus affects fuel consumption. The way that I can sometimes achieve fuel economy figures similar to the published values is to allow the car to run down long gentle slopes out of gear so that there is no braking effect of the engine. The car remains in control and I don’t inconvenience other motorists.

Flocker says:
7 May 2014

Yes it will affect miles per gallon because the vehicle is moving but your not actually using fuel as you coast/idle down the gradient. On an injection engine in overrun (using the engine as a brake) fuel is effectively shut off so taking the car out of gear shouldnt make any difference to fuel consumption. If you have instant mpg indication, look at the reading it may show off scale say 99.9mpg and when your idling you may see gallons per hour.

But the test could easily provide a more informed guestimate of real world.

So anyone confirm that drag is supposed to be taken into consideration during the tests, anyone from which? This is to me the most crucial input to the loading in real world and if not included makes the official figures useless as a comparison other than comparing engine/gearbox/drive chain between cars under the specific mass load of the vehicle model being tested..

The NEDC (New European Driving cycle) was devised when cars were less powerful and so acceleration was gentler than now. So the cycle needs updating. There is a report produced by the Joint Research Centre (JRC) that supports EU policy making that you may find interesting:
The current cycle appears, on average, to underestimate fuel consumption by around 10-15% for petrol, and 12-20% for diesel compared with “in use” driving. For drag (including air resistance) it seems the dynamometer settings that simulate this are based in ideal data that underestimates its effect. The report says:
“5.6 Type-Approval optimization
Although this is not directly an outcome of the study, this is an important conclusion from relevant work that should be re-iterated. Type-approval tests of fuel consumption are conducted on chassis dynamometer using resistance settings provided by the manufacturer. These settings are derived from coast-down vehicle tests. It appears that resistance of actual vehicles measured by independent test centres are higher than the ones submitted by the manufacturers for the type-approval tests. There are several reasons why this can be happening, i.e. manufacturers test vehicles in ideal conditions (tarmac condition, weather, vehicle run-in, configuration such as
tyre dimensions, trained drivers to perform the test, etc.). Unfortunately, type-approval resistance settings are confidential. Using of real vehicle resistances instead of type-approval resistances has been shown to lead to fuel consumption increases of up to 17%. This is even beyond the in-use over type-approval fuel consumption ratio developed in this report. As a minimum impact this means that maybe the NEDC is not a bad (underpowered) cycle to report fuel
consumption but that maybe the actual test is an idealistic one. It can be recommended that vehicle resistance settings become public together with the type-approval fuel consumption value, so that independent authorities can check both whether these represent reality and whether the type-approval test has been conducted as required.”
I would suggest that it is the test rules and conditions that need strengthening, both to reflect the performance of modern vehicles and to avoid the loopholes that can, and will, be exploited by all manufacturers.

Flocker says:
7 May 2014

Thanks for that, I suspect someone got paid handsomely for that lot.

NEDC does state that drag/air resistance is included from a look up table.

Flocker says:
11 May 2014

It is interesting that comparing a car sold in the EU with the same car sold in the US, the US actually provide an estimated mpg. The estimated mpg is nearer the real world figure. I did the comparison by comparing the exact same Eco boost engine (petrol as Diesel option wasn’t available) and the weight was the same within a 20kg. With the old and now antiquated test being adhered to and vehicle manufacturers clearly wanting defending its use and probably reluctant to move to a more realistic results.

I’m just having a discussion with a manufacturer who I won’t name, but having changed from a 2008 140psi Euro 4 engine saloon car, to a 2014 163psi Euro 5 engine all-wheel drive crossover as they call them (which by the way I’m very impressed with) from the same manufacturer, the official figures amazingly are comparable in fact the Euro 5 engine gives a slightly better urban and combined figure the extra urban is within 2 mpg. I thought it not unreasonable that while the official figures are wide of real world, I could expect the new car to return similar real world figures. Having travelled the same commute this past 2 years of 142mile round trip covering almost 36000 of what is better than combined driving of literally 40, 60 and 70 mph the 2008 car returned 46mpg. The new car travelling the same route now for 5600 mile returns 38/39mpg. Ah, one may think that the new engine is not run in, well I’d like to think so too, but 1 year owners of the same car and engine having driven 15000 mile and probably like me a repeatable sustained journey, also get around the 38mpg.

The sales brochure states “The applied standard test procedure enables to compare between different vehicle types and different manufacturers”. (Their grammar by the way). In my change of car I would expect a drop in fuel economy, but the brochure actually showed there wouldn’t be. Clearly the test doesn’t give a comparison between different models within this manufacturer never mind other manufacturers too. I have now queried this with the manufacturer.

Flocker says:
11 May 2014

BTW, the real world combined consumption of the crossover is the same as the urban consumption and the official urban consumption is 39.7mpg. This shouts something very significant to me.

Flocker says:
18 May 2014

Well here’s an update. A reply from the manufacturer say I cannot compare the two cars as one has a bigger engine and has had to meet more stringent emissions control so could reduce mpg, it has bigger wheels (that a joke surely, both are 18”, Hatch has 234/40 SUV 235/50). Here’s the comparison official fuel figures of the hatch in 2008 and 2014. I can’t see where bringing the engine up to Euro stage 5 has increased fuel consumption there.

2008 Euro 4 140 psi 37.2mpg 57.6mpg 47.9 mpg
2014 Euro 5 163psi 46.3mpg 67.3mpg 57.7mpg

So I have replied indicating that they themselves have compared the 2 vehicles by testing them to the same specification to provide a comparison under controlled laboratory conditions between vehicle types and that the type of vehicle should be factored in to the test to enable a comparison to be made, otherwise then figures don’t mean anything.

This particular manufacturer does have a habit of exhibiting a contemptible attitude to owners of their products, but they know we’ll still buy their cars.

So from the above, the manufacturer’s technical liaison team either don’t know the real reason the NEDC test is carried out and what the results are used for, or they think or hope the owners of their vehicles don’t know either.

Flocker says:
18 May 2014

As someone already stated, wish we could edit posts, but excuse the spooling mistooks

234 should be 235 of course

It’s not just mpg – electric cars’ range is overstated too.

I bought my Mitsubishi Outlander PHEV on the basis that of the manufacturer’s claim that it would do ‘up to 32 miles’ on electricity only. Actually it only does about 20. I think that overstating by 50% is actually fraudulent.

jdsx says:
23 April 2015

I didn’t buy my Mitsubishi Outlander PHEV on the basis of the manufacturer’s claim – only a fool would do that, surely. I looked at the claims, read a bit about the type of driving I would do, investigated further and made my decision.. I am currently getting 140mpg (excluding electricity costs, of course).

David Ludlow says:
22 April 2015

Whilst it is correct that ‘test’ figures do not reflect real driving I have to say that my previous car, a Mondeo 2.0 litre diesel did better than Ford quoted, achieving 51 mpg, worst 49mpg best 52mpg, and I’m not recognised by friends as a slow driver. Given the difference is size (vehicle and engine, this is close to my current Focus 1.6 diesel that achieves 54 mpg with stop start & other economy toys. Sometimes technology is not as clever as people think!!

I am surprised that Which? is making such a fuss about manufacturers’ published mpg figures. Surely we all know that the Euro tests not only bear little relation to real life conditions, but also that actual consumption figures depend to a considerable degree on the individual driving style. The published figures provide a good initial guide to which make or model fares better or worse than another model, but for a purchaser to assume the he/she will achieve the manufacturer’s figure is surely extremely naive. If actual fuel consumption is important to a purchaser, it is sensible to read tests in motoring magazines and Which? Even then, it would be a miracle if any individual was able to match these test results exactly. I rather resent the statement made by Which? that “we each spend an average of £133 more on fuel a year than we expect to”. Many (if not most) of us understand that the manufacturers’ figures are a rough guide, only.

Hi Peter, we believe you’ve forgotten the difference in how much some cars miss their claims compared to others, though?

When our Cars Team tested the Mazda3 Fastback, it had a naturally aspirated 2.0-litre petrol engine. It matched the mpg claims in our test. However, the plug-in hybrid Mitsubishi Outlander PHEV used 120% more fuel than the claims suggest. Therefore, the claimed figures presented to consumers are most certainly not comparable – a Mazda3 2.0-litre petrol owner is being given a far more realistic impression of fuel costs than a Mitsubishi Outlander PHEV buyer.

We’d also disagree about your comments about most knowing about manufacturers’ figures – We think there’s plenty of consumers who do not know this.

Andrew, as far as I am aware the EU figures are not portrayed as mpg (l/km) “claims”. They are results of tests under very specific and consistent test conditions for a particular purpose, which is not to tell you what you will get in practice.

The DfT state “The fuel consumption figures quoted in this guide are obtained under specific test conditions, and therefore may not necessarily be achieved under ‘real life’ driving conditions. A range of factors may influence actual fuel consumption – for example, driving style and behaviour, as well as the environment and conditions under which the vehicle is operated. Furthermore, since several different specifications (variants or versions) of a given model may be grouped together in the list, the figures used in this guide should be treated as indicative only.

A definitive figure for a given specification of vehicle will be available at the point of sale.

As a recently retired ADI, fuel consumption was an important cost element. I found that strangely my first car, a Mazda 323 diesel, was marginally more economical than my second/third cars, both Renault Modus 86 dCi diesels. The Modus has a fuel consumption mode in its on-board computer which generally shows 54mpg + or – 3mpg. Checking this against a calculated full tank to full tank consumption, it was 5 to 10 % optimistic, i.e. real mpg was around 48.
Whether this is better or worse than the manufacturer’s figures does not bother me. It is still a very economical figure.
As a matter of interest I calculated how much the Mazda had saved me over 110,000 miles compared to what a petrol version loaned to me for 2 days would have burned. The answer was of the order of £2,500.

David says:
23 April 2015

Real world Driving Economy, but whose real world driving economy are we talking about.

my wife & I can drive the same car on differnt days and get very differnt results.

This is due to many factors that cannot be replicated in a laboratorys test conditions.

Traffic; heavy left foot, Ambeint Temperature.

I have always used a simple calcuation for the last 20+ years and been within 1-2% accuracy.
Add the Urban + the combined figures and divide by two.

this has worked for me to calculate worst case “real world” economy for many vehicles I have driven over the years before buying them and I have always bettered that MPG with my driving style.

Which? magazine’s promotion for the May edition reads
“False fuel economy
Did you know your car fuel could cost up to £854 more a year than expected because official fuel-economy figures are economical with the truth. Try as we might, it seems even a magician couldn’t produce the same rates stated on manufacturers’ websites. Find out why the system is broken…”

A pity I think that Which? resorts to this kind of publicity. It is well known and acknowledged officially that the EU test cycle does not, and is not claimed to, represent real life economy but to produce comparative data under strictly controlled conditions. It is not “manufacturers data” but EU data they are obliged to use. It also includes emission data which is necessary for cars to be appropriately classified for which standardised conditions are essential. Which? should make this clear instead of rubbishing it just to make publicity. If you want a better idea of what you might achieve in practice use the information published by the good motoring press and Which. But a lot still depends upon factors outside the testers control – your driving style, your journey patterns, the sort of topography where you live for example.

I have yet to read the article, but hopefully my postman will arrive soon.

I acknowledge that EU tests are carried out under standard conditions and most of us are unlikely to achieve similar figures for fuel economy. Thus they are unrepresentative but of value in comparing the fuel economy figures of different cars when deciding which to purchase.

An obvious way of making the EU test results a better indicator of what the motorist could expect to achieve would be to use the same multiplier to produce fuel economy figures that are more realistic. That would mean that some drivers would produce higher and others lower fuel economy than the published figures.

The most helpful results for the motorist would be to produce a spread of values between which most drivers would expect to find their own consumption. I don’t see multiplying an unrepresentative EU figure by a single factor makes them any more representative. Some do already get mpg (l/km) near the published values – I do on my Espace – but others don’t. Real life testing has rather different objectives from the EU test cycle. Another way is to test a car over a day or a weekend before you buy to see if the it lives up to expectations.

The fact that the present EU test is unrepresentative of real life is the problem. Having now seen the magazine, Which? refers to it as an obsolete test. Until we have official tests that are more representative of what motorists are likely to achieve, scaling the EU figures as I have suggested would give more realistic figures. Like the ‘up to’ figures for broadband speeds, we need more realistic figures and I am grateful that Which? publishes these.

What I have never understood is the effect of temperature on fuel economy, which I have seen with both petrol and diesel cars. I can understand why a car performs less efficiently until the engine has reached operating temperature, but after that there is still a marked difference. Yesterday I made a journey of 50 miles, mainly on A-roads, and at the end of the journey the meter showed 73 mpg. For the same journey in January, the figure was about 55 mpg.

First, the EU test conditions lag behind vehicle development – for example acceleration capabilities are much higher than when the test cycle was devised. So the test certainly needs updating; a problem with all standards is the time they take to agree paticularly in an industry that can changes fairly quickly.

That said, the mistake is to portray the EU consumption test as something they do not set out to be – suggesting that is simply to mislead. They have a particular purpose. Use published “real life” figures to get nearer what you will achieve – but don’t expect those to be accurate for you either.

According to the US Dept of Energy:
Cold weather affects your vehicle in more ways than you might expect:
•Engine and transmission friction increases in cold temperatures due to cold engine oil and other drive-line fluids.
•It takes longer for your engine to reach its most fuel-efficient temperature. This affects shorter trips more, since your car spends more of your trip at less-than-optimal temperatures.
•Heated seats, window defrosters, and heater fans use additional power.
•Warming up your vehicle before you start your trip lowers your fuel economy—idling gets 0 miles per gallon.
•Colder air is denser, increasing aerodynamic drag on your vehicle, especially at highway speeds.
•Tire pressure decreases in colder temperatures, increasing rolling resistance.
•Winter grades of gasoline can have slightly less energy per gallon than summer blends.
•Battery performance decreases in cold weather, making it harder for your alternator to keep your battery charged. This also affects the performance of the regenerative braking system on hybrids.

Hard to see that increasing your fuel consumption by 25% – perhaps you had a heavier foot!.

It is a good illustration of the difficulty in giving “real life” fuel consumption, isn’t it 😀

The trouble is that the EU test figures are used in the real world to mislead us.

When I last bought a car I told the dealer that I was most interested in two models (and that I would not consider anything without a spare wheel). Within five minutes I was being told what mpg I could expect. He received a pre-prepared lecture about his dishonesty and I referred him to the sales brochure which briefly explained that the published figures were not representative of what a driver could expect to achieve.

The fact that the sales brochure explained that the EU tests were not “real world” is honest. Hard to legislate for an individual being either ignorant or dishonest, and not grounds to condemn a test regime designed with a particular purpose.

Malcolm – Ask motorists if they are happy with the official fuel economy figures and most people will say that they are not. We need something more realistic, fit for the 21st century.

The mpg figures I quoted were just for a recent comparison of fuel economy. The effect of ambient temperature is not usually so great but I do wonder why the mpg improves so much in warm conditions. I had assumed that engine oil temperature might be significantly different between summer and winter motoring, but not according to the gauge in my present car. I check my tyre pressures weekly but temperature could still affect rolling resistance.

“Malcolm – Ask motorists if they are happy with the official fuel economy figures and most people will say that they are not. We need something more realistic, fit for the 21st century.”

Then don’t perpetuate the myth, by articles like this, that the EU tests are somehow dishonest. They give results from standardised tests that manufacturers must publish. They have a particular purpose, including emission data, but were not designed to generate real life claimed performance. New tests are being devised to be more representative of current car technology and driving situations but will no doubt still give comparative data by virtue of their need for standardisation.

It is a pity Which? resorts to being “economical with the facts” to apparently gain publicity. I wish it operated in a more objective way otherwise it is in danger of damaging its credibility as an independent consumer watchdog.

It would be better if Which? gave an objective explanation of the facts so people can know to look at either their results, Honest john’s, or other motoring press sites for so-called “real life” consumptions. But will you achieve these? Of course not – your driving style, journey type, topgraphy, tyre inflation, etc will all influence significantly the consumption you get. The range will be quite large. No such thing as a real life consumption – it will be a real life range within which you have a probability of falling.

We will have to agree to differ Malcolm. I support Which? in alerting us to the large difference between published fuel economy figures and what we are likely to achieve. It’s clear to me that the EU is listening to the manufacturers rather than consumers, otherwise we might have standard tests that better reflect average use.

DfT state the following, literature states it, so “alerting us” as if it was a calculated deception is a distortion.

“How Representative of Real Life Driving are the Standard Tests?
Because of the need to maintain strict comparability of the results achieved by the standard tests, they cannot be fully representative of real-life driving conditions. Firstly, it is not practicable, nor is it viable to test each individual new car. Only one production car is tested as being representative of the model and this may produce a slightly better or worse result than another similar vehicle. Secondly, there are infinite variations in driving styles, as well as road, car and weather conditions, all of which can have a bearing on the results achieved. For these reasons the fuel consumption achieved on the road is unlikely to be the same as the official test results. The purpose of the official fuel consumption test is to provide data that will permit a comparison of the fuel consumption of different cars, rather than to provide an estimate of average, on-the-road, fuel economy.

It is recognised that, for a variety of reasons, the fuel consumption achieved by the majority of motorists is poorer than that suggested by the standard tests, and work is going on with the intention of introducing a new test cycle which will better represent the way in which most people actually use their cars.”

Of course there are numerous reasons why there will be substantial variation in the fuel economy achieved by drivers. The problem is that the way that the official tests are carried out mean that they generally produce figures that are substantially above what most motorists would achieve in practice.

Why not design tests so that they correspond to the average or the median of what motorists achieve? If they are carried out under standard conditions then the comparison between models should remain valid.

In defending the motor industry, can you really justify manufacturers over-inflating tyres to help improve the fuel economy figures for their cars?

It would make us all feel a bit better if the tests were designed as you suggest, or even to a slightly lower benchmark, so that we could derive some satisfaction from out-performing the standardised performance test results. So long as the tests were truly standardised and regulated to prevent distortion the actual values would become less important [while at the same time becoming more meaningful] but the relative positions of different cars would become more credible and reliable thus assisting purchasers to make their choice.

Apart from the point that no two vehicles off the same production line will perform identically, no car will perform the same in two or three years’ time as it did when new and might well have diverged markedly from any proximity to the declared fuel consumption figures for that model. Since sales of used cars far outstrip sales of new cars there could be a case for checking whether there is a ‘standard’ deviation over time for any particular model from its norm in comparison with the deviations of models that were orginally similar. Or it might just all be too random and abstruse and not worth bothering about, letting anecdote and hearsay prevail; those who keep fuel and mileage records at least have something to report when the question is asked.

John wrote: “It would make us all feel a bit better if the tests were designed as you suggest, or even to a slightly lower benchmark, so that we could derive some satisfaction from out-performing the standardised performance test results.”

I agree. It is always a pleasant surprise when something proves to be better than expected, for example a really good meal, a tradesman’s bill that is less than the estimate, an unexpected act of generosity. In many respects, cars can exceed our expectations but fiddling economy tests is as bad as advertising one price and charging more.

With the current standard methodology for determining the official mpg figures, the incentive is for manufacturers to outdo each other in ratcheting up these results for the test, rather than to produce cars which will be genuinely more economical on fuel in day to day driving.. In theory, one might reasonably expect a car with a claimed 75mpg to be, say, 25% more economical than a car with a claimed 60mpg. However, in real life, the difference between the two is probably rather less and might even be worse, depending on driver and conditions. Road tests by motoring journals are, of course, focusing more on the performance achievable, so the mpg results take a real dive and bear absolutely no relationship to the official mpg figures – often showing that the claimed more economical car is thirstier in their hands than the claimed more economical car. Readers have to draw their own conclusions on which car will deliver the best real life results, which might not be what they thought by reading the official results.

10th/11th line should read “than the claimed less economical car”.

AQ – I have no problem with a manufacturer that designs a car to perform well in fuel economy tests. If it is more streamlined than other cars I can check if that affects space inside the car or the boot. If they decide to leave out a spare wheel, that’s fine as long as I am made aware, so I can avoid buying the car.

What I object to is carrying out tests on any car that has been modified in any way.

As you say, motoring journal tests may be focusing on performance rather than reflecting normal driving. The ‘real life’ tests may be of highly variable standards. Some drivers will take great care to base their measurements on careful long-term measurements whereas others will report what is shown on their car computer from a single fill-up. That’s why we need proper testing of unmodified vehicles under controlled conditions. As has been said several times there are many factors relating to how the car is used that will determine what figures you and I can achieve.

As I see it, preparing a car by over-inflating the tyres or taping-up the doors is equivalent to changing the price label in a shop, so that the sales assistant charges less than the intended price. One of the reasons that we have bar codes and tills that show a description of the goods is to tackle the fact that we have some dishonest customers. Most customers are honest (I hope) and would not resort to this or other form of dishonesty. I hope we have some honest car manufacturers that test cars that have not been prepared in any way. The problem is that we hear about the ones that cheat.

Oops – that should read: “The ‘real life’ tests may be of highly variable MEASUREMENTS.”

If you look at the proposals for the new test regime this should allay some of the concerns about loopholes as well as the test being more aligned with both current car technology and current driving conditions. Remember though that the key issue seemingly behind the standard test is not to produce fuel consumption data only, but primarily to address the impact vehicles have on climate change by reducing allowable emissions. It seems that the argument over the proposed new test regime is not the test procedure – it seeks to put all on the same level playing field – but may be the reduced emissions the EU seeks to impose, levels that may not be attainable in practice in the timescale.

Politicians have to find ways of making policy that can be sensibly achieved, otherwise it will be discredited.

I would like to know more about the factors in this argument. Simply heaping the blame on manufacturers is, I think, popular with some but may be misplaced. Let’s ascertain the facts. I’d be happy then to s**g off whoever is at real fault.

I accept that emissions present a problem and that pragmatic solutions are needed to make progress. If there is a problem with implementing new emission standards then their introduction could be delayed, as we have seen with the planned phase out of halogen bulbs.

What I will not accept is manufacturers taking cars that you or I could buy and preparing them in a way that will return artificially high fuel economy figures.

I agree that our policy makers deserve criticism, but that is not a reason for modifying cars before testing. I would like to know if there are any manufacturers that do not modify their tests. That would gain a lot of my respect.