When you look at a new or used car, one big factor that helps you make the right selection is fuel economy. If you travel a lot, this is crucial. Even if you don’t, you still want the best possible fuel economy for your usage. However, experts claim that the difference between official fuel economy figures and those from real world use could be as much as 42% – with the real-world figures being the higher of the two.
The changing face of fuel economy
According to the International Council of Clean Transportation (ICCT), there is a massive 42% difference between the official fuel economy figures that are given out by car manufacturers and the results from real-world tests. This is a huge leap from 2001, when the difference between the two sets of figures stood at just 9%.
This misinformation could be costing drivers an average of £350 a year in extra fuel bills, the report revealed.
(Credit – Robert Couse-Baker)
Economy and emissions
The latest analysis is based on the official figures and also those achieved during controlled laboratory tests by the ICCT. It measured both CO2 emissions and the miles per gallon fuel efficiency. According to official figures, the CO2 output for new cars has been in gradual decline since 2008. However, the real-world tests from the ICCT painted a very different picture – the figures have changed little in the last five years.
This contrasts starkly with the information provided by car manufacturers. Official tests since 2012 show that the new car outputs of carbon dioxide have dropped by nearly 11%, to a new, lower average of around 120g/km. However, the real-world tests show that in the same period, the reality is a drop of only around 2% meaning cars hover at an average of 170g/km, polluting the atmosphere much more than drivers are led to believe.
The effect on fuel
Even if the effect on the environment isn’t at the forefront of drivers’ minds, the effect on fuel consumption and the resulting increased cost of running the car certainly will be. Higher emissions mean that cars use more fuel. The difference of 42% between official and real-world figures could be hitting drivers in the pocket to the tune of around £350 a year in extra petrol or diesel.
The news will no doubt particularly irritate diesel drivers, who are currently being scapegoated as the cause of all pollution around Britain’s towns and cities. With their vehicles classed suddenly as ‘dirty,’ after years of government advice to switch to this fuel type over petrol, as it is less polluting, many diesel drivers feel betrayed by the government’s change of direction.
Abject failure
According to Greg Archer of Clean Vehicles at Transport & Environment, the tests show the abject failures of the current CO2 regulations. The regulations were agreed in 2009. Since then, just 40% of the promised improvement has been delivered, with little real-world change to emissions for the last five years.
In addition to the new figures from the ICCT, the new WLTP test cycle is being introduced from September. This is part of EU measures to have stricter new CO2 targets by 2030. The test isn’t mandatory until September 2018 but should produce more realistic figures. It replaces a test – the NEDC – which itself hasn’t been updated since 1997.
Performance gap
The ICCT says that while the new test will help the problem, more needs to be done to address the vast discrepancy between the official and real-world figures. It is also concerned that the new test could have ‘loopholes’ that could permit the performance gap to increase once again.
The European Commission has just released new targets for the next ten years, by which time 30% of all new vehicles should be electric powered. It also looks for the average CO2 output for vehicles to fall by 15% between 2021 and 2025 and by 30% by 2030. However, unless more accurate figures are achieved, it will be almost impossible to know if these standards are being met.
Are you surprised by the difference between official figures and the real-world data? Does your vehicle achieve the fuel economy that it should? Leave a comment to let us know.
For my part I’ve never believed a manufacturers figures regarding fuel consumption. In my personal road test use I’ve even found my old P6 Rover 3500 with SD1 5-speed gearbox could always return 28+mpg, whereas my much newer BMW 330i could never better 24mpg, given that the BM had a higher performance in speed and acceleration.
Much of this pollution worry could be off-set if more car drivers thought about using a motorcycle for their, mostly, very short journeys. According to more knowledgeable persons than myself, if only 10% of motorists switched to motorcycle use for their commute/longer journeys this would reduce congestion by 40%, which would obviously reduce the amount of rubbish cars pump into the atmosphere while waiting in their self-made traffic jams going nowhere.
The other plus would be that the more motorcycles being used would also improve road use and manners and therefore possibly reduce the carnage currently suffered onour roads today.
No I’m not surprised at all. This is old news! The buying public has been tacitly playing along with the deception because if the fuel consumption and CO2 figures were accurate, we’d all be paying more Vehicle Excise Duty! WLTP will help, but even in that drive cycle you don’t use full power at any point in most cars – something which I think most of us do at some point or another when driving. I certainly do! Like any target-based system, the manufacturers will optimise the cars for whatever the target requires and pay less attention to the parts of the operating envelope that are not assessed. That happens in all walks of life. It’s certainly not peculiar to the car industry. The RDE (Real Driving Emissions) tests coming along the following year will make a greater difference again. Between the two, I anticipate a VERY significant reduction in tailpipe pollutants but unless the public calls off its witch hunt against diesels, a rise in CO2.
I’ve heard all kinds of stories about the lengths that the manufacturers will go to to gain the mpg figures like:
removing brake pads, so there is NO friction, putting on thinner tyres with massive pressures to reduce the rolling resistance, massive weight reductions by having minimum fuel, nobody actually in the vehicle etc etc and I’m sure there are a lot more marginal gains that we don’t know about.
And I can’t believe only VW/Audi has the CHEAT CHIP, in a trillion pound business.
Why are we so worried about our CO2 output, di you know that;
India produce more CO2 in a day than we do in a year, as does China and America, so that’s 1/1095 or 0.091% out of just these few, and as ours is decreasing theirs are accelerating exponentially. (Figures about 4years old now). Our output is insignificant, do you think if dropped our CO output to Zero the World would even notice?
This interesting article does not include potential fines when the speedo states a 5% difference when compared to sat nav speed. Over the years I have checked 4 different sat nav’s and 5 different cars. I still don’t know which is correct. Are car manufacturers falsifying the speed readout to give the appearance of better fuel consumption or getting it wrong thus causing potential speeding fines?
By Law the speedos HAVE TO READ MORE THAN YOUR REAL ROAD SPEED, but by how much varies from car to car, I’ve had up to 13% on an old Audi A4, comparing it to a road side camera speed display (assuming that was right).
I guess they have to take into account various factors like, tyre pressures varying from cold to nice and warm on a longer run and the subsequent external circumference of the tyre, wear within the gear box, etc etc.
So to sum up if a Police officer was to ask you “Do you know what speed you where doing Sir?” the accurate answer would be “No Sir, by law I’m only allowed to know an approximate over estimate of my real road speed, sorry.”
I have an app on my phone which i fill in every time i put fuel in and I have a 10% difference compared to the cars mpg reading for every tank full over the past 5years.
Law allows manufacturer to rig the figures.
Bob.
It is a little known fact that all European car speedometers read low by law.
An EU Directive from around 2003 (if I recall correctly) states that the speedo must read at least 2.5% low.
I have noted the same differences – generally, the sat nav will be correct over a reasonable distance (say, half a mile).
Try plotting a route on Google, door to door, and then setting the mileometer to zero and calibrating the mileage – this often agrees with the speedo and has a notable error.
Paul
It`s obvious mpg figures are wrong, the only way to check is to fill the tank, zero the trip and see how much fuel is needed to fill up again, then repeat several times. I have a Peugeot 308 (1.6l), true diesel consumption 62mpg whereas the dashboard says 67! My previous car a vauxhall Astra gave similar figures. Tony
I’ve used this model of fill up & record consumption, using an Excel Spreadsheet for the last 30+ years now across some 10 cars.
I’ve NEVER had a car that gets withing 20% of the claimed MPG for a variety of different cars. Ironically the closest match was for A Renault Megane Diesel. I’m not a fast or ‘hard’ driver so heaven only knows how much worse the figured would have been were I to drive more vigorously!
Doug, I would love to see your figures. Are they online anywhere?
I would be interested in these figures too
Doug you should publish the figures. I too have started to keep a log of miles covered and volume of petrol filled to calculate MPG.
I have a Toyota Avensis Diesel eatate 58 reg and have always noted my mileage and fuel costs, for the 82000 miles I have done the cumulative MPG is 49.58 which is good for a 2litre diesel but not as good as the 59 MPG that the car computer claims. When I queried this with the Toyota main dealer he insisted that the computer was accurate, I asked him to check for fuel leaks to find the discrepancy, no leaks found. I then emailed Toyota and was told that the computer made an estimate bases on the time the injectors were open! Still a great error, someone who didn’t check would be convinced that the car was more ecomomical than it really wss.
Too many people belive all advertising blurb and believe it all is true A fact !!
My Civic 1.8 trip computer always tells me my mpg is 5,6,7 or even 8 better than I know I get by recording distance and fuel used. It was the tripometer figures from the half day test drive I had that convinced me to buy the car. The tripometer figures are nearer the published figures in the handbook. That is no surprise!!
When I quizzes the Honda dealer they told me that the speed shown is always 10% over actual to “help me avoid getting speeding fines”.
I have never noticed lots of Honda’s travelling slowly on the motorway…..It sounds like a fable.
or all the other Honda drivers ignore the Speedo?
The figures quoted do not add up. A drop of 11% to 120gm suggests a start point of 135gm. Therefore a drop of 2% gives a result of 132gm not 170gm. Dodgy reporting, twisting the stats or a simple error. make up your own mind.
I am not suprised at all by these figures, i bought a Volvo estate (diesel) where the fuel figure was given as 68.4 mpg I actually achieve 38.8 mpg in the real world of driving I wont be buying another Volvo
1. With a good GPSr in a good position in a vehicle, i.e. not loosing fixes, will give a more accurate indication of speed when driving at a constant speed. The law requires a speedo to never display a slower speed that true speed. Thus as a speedo will have a tolerance in it’s indications it will always display a faster speed, than the true speed.
2. Manufactures will test their vehicle’s performance when driven by professional careful drivers. This will produce the best results. Owners will generally accelerate faster and brake harder, thus producing a worse result.
I bought Automatic Toyota Auris 1.8L running on Petrol and achieve 30MPG, mainly for town driving, far less than manufacture figures. The dashboard figure for MPG is a suspect too and the error between this and one calculated based on miles driven and petrol cost is at least 10% out.
Law does not allow any claim for false claim. So it encourages manufacturer to falsify the claim.
Whilst it is old news, I am surprised that the car manufacturers have been allowed to get away with this false advertising for so long. I had hoped that after the VW scandal the figures would be truer to reality – should have been more pessimistic!
I recently made a complaint to the ASA about this and the apparent photo shopping of pictures to make wheels look larger.
was told they wouldn’t do anything.
I think we need to somehow start a petition to claim compensation for this, maybe a solicitor will take it on like is the US.
The big difference between 2001 and now is the use of stop-start and hybrid, especially plug-in hybrid technologies. Stop-start, especially if twinned with soft hybrid (enables the alternator to be disconnected) can give a significant improvement in economy from the NEDC, but has little effect in practice because many drivers switch it off so that they can sit in their 4 wheeled offices either having lunch, or making telephone calls. The way hybrids are tested means that they always get better results than reality. Especially with plug-ins, it is not possible to give a meaningful figure. It could vary from zero mpg to 40 or more. All a manufacturer needs to do with a plug-in, if a higher mpg figure is needed is to fit a larger battery. I see no indication in the new tests that this will change. Plug-ins should not be included in comparisons because they are so variable and will severely accentuate the”Gap”.
I am surprised by the number of readers with inaccurate trip computers. I have been amazed just how accurate the one in my Peugeot 207 Hdi is. Over 70, 000 miles, I always fill the tank to the top and record volume bought and distance and put this in a spreadsheet. I operate in metric (L/100 km) which is what most trip computers do and the actual consumption is nearly always the same as the trip computer says. It is also up to nearly better than 10% better than Peugeot’s claimed economy. That is over 7 years and 70,000 miles
Car computer mpg is not obtained using a fuel flow meter but is calculated by a mathematical algorithm. Includes variables such as instantaneous speed, engine revs, throttle opening, acceleration, ambient temperature etc etc. Probably shared with other manufacturers. My Corsa 1.4 90, (petrol) very gently driven and with only one occupant, does a true 46 – 53 mpg depending on time of year and journey length and conditions, and assuming milometer accurate. Computer readings give a further 10% approx. Official average is around 54 mpg. It is difficult to calculate the true readings since current fuel gauge does not have 1/4, 1/2, 3/4 and full marks but is a nasty block gauge. If you do it for long enough (my checks are continuous) you can still get a good set of consistent true readings. Never do brim to brim since it depends a lot on gradient in filling station – they are rarely level. Do 3/4 reading, later fill, 3/4 reading, later fill etc. If gauge pointer moves more rapidly down near full mark or 1/2 mark use those marks instead. With a decent fuel gauge and similar journeys (and the same driver) your readings will agree to 1 mpg!
I’ve never even considered a diesel (higher initial and maintenance costs) for only modest improvement in mpg..
For my part I’ve never believed a manufacturers figures regarding fuel consumption. In my personal road test use I’ve even found my old P6 Rover 3500 with SD1 5-speed gearbox could always return 28+mpg, whereas my much newer BMW 330i could never better 24mpg, given that the BM had a higher performance in speed and acceleration.
Much of this pollution worry could be off-set if more car drivers thought about using a motorcycle for their, mostly, very short journeys. According to more knowledgeable persons than myself, if only 10% of motorists switched to motorcycle use for their commute/longer journeys this would reduce congestion by 40%, which would obviously reduce the amount of rubbish cars pump into the atmosphere while waiting in their self-made traffic jams going nowhere.
The other plus would be that the more motorcycles being used would also improve road use and manners and therefore possibly reduce the carnage currently suffered onour roads today.
No I’m not surprised at all. This is old news! The buying public has been tacitly playing along with the deception because if the fuel consumption and CO2 figures were accurate, we’d all be paying more Vehicle Excise Duty! WLTP will help, but even in that drive cycle you don’t use full power at any point in most cars – something which I think most of us do at some point or another when driving. I certainly do! Like any target-based system, the manufacturers will optimise the cars for whatever the target requires and pay less attention to the parts of the operating envelope that are not assessed. That happens in all walks of life. It’s certainly not peculiar to the car industry. The RDE (Real Driving Emissions) tests coming along the following year will make a greater difference again. Between the two, I anticipate a VERY significant reduction in tailpipe pollutants but unless the public calls off its witch hunt against diesels, a rise in CO2.
I’ve heard all kinds of stories about the lengths that the manufacturers will go to to gain the mpg figures like:
removing brake pads, so there is NO friction, putting on thinner tyres with massive pressures to reduce the rolling resistance, massive weight reductions by having minimum fuel, nobody actually in the vehicle etc etc and I’m sure there are a lot more marginal gains that we don’t know about.
And I can’t believe only VW/Audi has the CHEAT CHIP, in a trillion pound business.
Why are we so worried about our CO2 output, di you know that;
India produce more CO2 in a day than we do in a year, as does China and America, so that’s 1/1095 or 0.091% out of just these few, and as ours is decreasing theirs are accelerating exponentially. (Figures about 4years old now). Our output is insignificant, do you think if dropped our CO output to Zero the World would even notice?
This interesting article does not include potential fines when the speedo states a 5% difference when compared to sat nav speed. Over the years I have checked 4 different sat nav’s and 5 different cars. I still don’t know which is correct. Are car manufacturers falsifying the speed readout to give the appearance of better fuel consumption or getting it wrong thus causing potential speeding fines?
By Law the speedos HAVE TO READ MORE THAN YOUR REAL ROAD SPEED, but by how much varies from car to car, I’ve had up to 13% on an old Audi A4, comparing it to a road side camera speed display (assuming that was right).
I guess they have to take into account various factors like, tyre pressures varying from cold to nice and warm on a longer run and the subsequent external circumference of the tyre, wear within the gear box, etc etc.
So to sum up if a Police officer was to ask you “Do you know what speed you where doing Sir?” the accurate answer would be “No Sir, by law I’m only allowed to know an approximate over estimate of my real road speed, sorry.”
I have an app on my phone which i fill in every time i put fuel in and I have a 10% difference compared to the cars mpg reading for every tank full over the past 5years.
Law allows manufacturer to rig the figures.
Bob.
It is a little known fact that all European car speedometers read low by law.
An EU Directive from around 2003 (if I recall correctly) states that the speedo must read at least 2.5% low.
I have noted the same differences – generally, the sat nav will be correct over a reasonable distance (say, half a mile).
Try plotting a route on Google, door to door, and then setting the mileometer to zero and calibrating the mileage – this often agrees with the speedo and has a notable error.
Paul
It`s obvious mpg figures are wrong, the only way to check is to fill the tank, zero the trip and see how much fuel is needed to fill up again, then repeat several times. I have a Peugeot 308 (1.6l), true diesel consumption 62mpg whereas the dashboard says 67! My previous car a vauxhall Astra gave similar figures. Tony
I’ve used this model of fill up & record consumption, using an Excel Spreadsheet for the last 30+ years now across some 10 cars.
I’ve NEVER had a car that gets withing 20% of the claimed MPG for a variety of different cars. Ironically the closest match was for A Renault Megane Diesel. I’m not a fast or ‘hard’ driver so heaven only knows how much worse the figured would have been were I to drive more vigorously!
Doug, I would love to see your figures. Are they online anywhere?
I would be interested in these figures too
Doug you should publish the figures. I too have started to keep a log of miles covered and volume of petrol filled to calculate MPG.
I have a Toyota Avensis Diesel eatate 58 reg and have always noted my mileage and fuel costs, for the 82000 miles I have done the cumulative MPG is 49.58 which is good for a 2litre diesel but not as good as the 59 MPG that the car computer claims. When I queried this with the Toyota main dealer he insisted that the computer was accurate, I asked him to check for fuel leaks to find the discrepancy, no leaks found. I then emailed Toyota and was told that the computer made an estimate bases on the time the injectors were open! Still a great error, someone who didn’t check would be convinced that the car was more ecomomical than it really wss.
Too many people belive all advertising blurb and believe it all is true A fact !!
My Civic 1.8 trip computer always tells me my mpg is 5,6,7 or even 8 better than I know I get by recording distance and fuel used. It was the tripometer figures from the half day test drive I had that convinced me to buy the car. The tripometer figures are nearer the published figures in the handbook. That is no surprise!!
When I quizzes the Honda dealer they told me that the speed shown is always 10% over actual to “help me avoid getting speeding fines”.
I have never noticed lots of Honda’s travelling slowly on the motorway…..It sounds like a fable.
or all the other Honda drivers ignore the Speedo?
The figures quoted do not add up. A drop of 11% to 120gm suggests a start point of 135gm. Therefore a drop of 2% gives a result of 132gm not 170gm. Dodgy reporting, twisting the stats or a simple error. make up your own mind.
I am not suprised at all by these figures, i bought a Volvo estate (diesel) where the fuel figure was given as 68.4 mpg I actually achieve 38.8 mpg in the real world of driving I wont be buying another Volvo
1. With a good GPSr in a good position in a vehicle, i.e. not loosing fixes, will give a more accurate indication of speed when driving at a constant speed. The law requires a speedo to never display a slower speed that true speed. Thus as a speedo will have a tolerance in it’s indications it will always display a faster speed, than the true speed.
2. Manufactures will test their vehicle’s performance when driven by professional careful drivers. This will produce the best results. Owners will generally accelerate faster and brake harder, thus producing a worse result.
I bought Automatic Toyota Auris 1.8L running on Petrol and achieve 30MPG, mainly for town driving, far less than manufacture figures. The dashboard figure for MPG is a suspect too and the error between this and one calculated based on miles driven and petrol cost is at least 10% out.
Law does not allow any claim for false claim. So it encourages manufacturer to falsify the claim.
Whilst it is old news, I am surprised that the car manufacturers have been allowed to get away with this false advertising for so long. I had hoped that after the VW scandal the figures would be truer to reality – should have been more pessimistic!
I recently made a complaint to the ASA about this and the apparent photo shopping of pictures to make wheels look larger.
was told they wouldn’t do anything.
I think we need to somehow start a petition to claim compensation for this, maybe a solicitor will take it on like is the US.
The big difference between 2001 and now is the use of stop-start and hybrid, especially plug-in hybrid technologies. Stop-start, especially if twinned with soft hybrid (enables the alternator to be disconnected) can give a significant improvement in economy from the NEDC, but has little effect in practice because many drivers switch it off so that they can sit in their 4 wheeled offices either having lunch, or making telephone calls. The way hybrids are tested means that they always get better results than reality. Especially with plug-ins, it is not possible to give a meaningful figure. It could vary from zero mpg to 40 or more. All a manufacturer needs to do with a plug-in, if a higher mpg figure is needed is to fit a larger battery. I see no indication in the new tests that this will change. Plug-ins should not be included in comparisons because they are so variable and will severely accentuate the”Gap”.
I am surprised by the number of readers with inaccurate trip computers. I have been amazed just how accurate the one in my Peugeot 207 Hdi is. Over 70, 000 miles, I always fill the tank to the top and record volume bought and distance and put this in a spreadsheet. I operate in metric (L/100 km) which is what most trip computers do and the actual consumption is nearly always the same as the trip computer says. It is also up to nearly better than 10% better than Peugeot’s claimed economy. That is over 7 years and 70,000 miles
Car computer mpg is not obtained using a fuel flow meter but is calculated by a mathematical algorithm. Includes variables such as instantaneous speed, engine revs, throttle opening, acceleration, ambient temperature etc etc. Probably shared with other manufacturers. My Corsa 1.4 90, (petrol) very gently driven and with only one occupant, does a true 46 – 53 mpg depending on time of year and journey length and conditions, and assuming milometer accurate. Computer readings give a further 10% approx. Official average is around 54 mpg. It is difficult to calculate the true readings since current fuel gauge does not have 1/4, 1/2, 3/4 and full marks but is a nasty block gauge. If you do it for long enough (my checks are continuous) you can still get a good set of consistent true readings. Never do brim to brim since it depends a lot on gradient in filling station – they are rarely level. Do 3/4 reading, later fill, 3/4 reading, later fill etc. If gauge pointer moves more rapidly down near full mark or 1/2 mark use those marks instead. With a decent fuel gauge and similar journeys (and the same driver) your readings will agree to 1 mpg!
I’ve never even considered a diesel (higher initial and maintenance costs) for only modest improvement in mpg..