Car fuel economy claims are miles from the truth

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.

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.

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.

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.

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.

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.

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

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.

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.

“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.

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.

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:
http://publications.jrc.ec.europa.eu/repository/bitstream/111111111/22474/1/co2_report_jrc_format_final2.pdf
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.

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).

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.

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.