Tuesday 22 May, 2012. The Green Piece Column.
It has long being been accepted that most motorists will see a notable gap between their cars official MPG rating and what they really achieve. But with motorists now ever more squeezed by prices at the pumps it seems that there is a renewed disgruntlement with the erroneous official figures.
But just because most motorists won’t achieve close to the official figure, doesn’t mean they can’t. And while perhaps not a true reflection of a car’s economy, the official NEDC figures are a least a standardised test meaning that the results are a least a fair way to compare one model to another.
However motoring champion, Honest John set up a The Real Life Fuel Economy Register which, in just over a year, has collected the real fuel economy findings of over 25,000 motorists over (www.honestjohn.co.uk/realmpg) proving that drivers seem to want to know the truth about their cars. What’s more Honest John isn’t the only one taking an interest in this. What Car? also recently launched its True MPG online tool to (www.whatcar.com/truempg) which also helps motorists figure out what they can truly expect to get from their car, factoring in their driving style, mileage and the driving conditions they usually endure (from free-flowing to heavily congested).
As these motoring websites seek to help uncover the truth about fuel economy, we ask is the current system really so bad? And if it is so unsatisfactorily and wildly inaccurate, then what, if anything can the EU do about it?
Europe-wide
Official fuel economy figures are obtained through the New European Driving Cycle (NEDC) tests to produce the combined, urban and extra urban and the CO2 emissions figures. They are a legal requirement for cars sold in Europe.
One of the problems with the NEDC tests is that these laboratory tests are supposed to represent a typical drive in Europe. A typical drive in Europe! Just what exactly is that? From mountainous regions like the Alps to the blisteringly hot conditions of southern Spain to the freezing cold, Arctic conditions in northern parts of Norway and Sweden, there is nothing typical about a road in Europe. That’s even before you consider the different ways in which individual countries maintain and manage their roads and the traffic flow on them. There is huge variety in the amount each Government will spend on their roads and just how much traffic uses them.

So how exactly do you come up with a fair-standardised test? One way would be to produce a worst case scenario, assuming that an urban road is heavily congested, that the cold-start is much colder than the current test requires (20-30 Celsius), let’s say 10 Celsius, which is still very warm compared to average winter temperatures in some parts of Northern Europe.
What’s more NEDC tests were developed at a time when European cars were typically lighter and less powerful, meaning that the tests are now looking very dated.
The car makers are require by law to publish their official NEDC fuel economy ratings, so their intention is not necessarily to mislead the public, but obey the law.
However, it is true that carmakers optimise their cars to perform well in these fixed parameter tests, something that has been dubbed ‘cycle beating’. As the test primarily are designed to test the emissions of a car, and because tax is based on CO2 emissions, and because carmakers have to meet a fleet average of 130g/km CO2 by 2015 or face fines from the EU, manufacturers work hard to ensure that their cars fit under certain CO2 thresholds when tested in these fixed tests.
What the NEDC involves:
The tests are conducted in a laboratory at an ambient temperature of between 20-30 on a
flat rolling road. A machine is used to simulate wind resistance and account for vehicle mass inertia. Any sort of energy-sapping auxilliary functions such as the radio, air con and lights remain switched off and windows are closed.
The urban test involves accelerating and slowing down several times, with speeds varying between 9mph and 31mph. The extra urban test is mostly conducted half the time at a steady speed, with some acceleration/decceleration and engine idling. It is conducted at an average speed of 39mph and a maximum of 75mph.
The official combined figure is the average calculated from the urban and extra-urban tests.
Change afoot
However there is hope on the horizon, earlier this year it emerged that the European Union and the United Nations are working on new proposals to draw a new Worldwide Light-duty vehicle Test Cycle (WLTC) which would set a standardised test which could be applied across across Europe and parts of Asia too. It will be a while before this could be implemented, the review of the proposals is not expected to be completed until 2014, and it will be years thereafter before it can be introduced.
Getting the real fuel economy story
We won’t patronise you with the usually guidance about how to boost your fuel economy if you want to get near the official figure, you likely know the basics (make sure tyres are inflated to the correct pressure, remove excess weight and unnecessary vehicle racks, avoid harsh braking and acceleration, look ahead and anticipate slowing traffic etc)-it is all common sense.
However using online tools such as those mentioned above should at least help you gauge the difference between the published figures and the real thing. Sadly, for now its seems that the fuel economy figures will remain where they are.
Let us know how your car performs compared to its official fuel economy figures by leaving a comment below.
Faye Sunderland.