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Vehicle manufacturers look likely to have to qualify their fuel consumption figures following an Advertising Standards Authority (ASA) ruling against Audi, upholding a consumer complaint against a combined 68.9 mpg claim for an Audi A3 TDI.
Future disclaimers are expected to highlight that quoted mpg figures may not reflect real world fuel consumption figures, something all drivers have been aware of for some considerable time.
The problem stems from the fact that fuel economy figures are established under controlled laboratory conditions, hardly reflective of real life driving situations.
The European regulations governing these tests date back to the Seventies and while they have been updated, they are still short in length, involve long periods of idling, slow acceleration and low engine loads.
Motorway speeds are hardly reached and air conditioning, lights and other electrics that drain power are all switched off. No passengers accompany the tester in an otherwise empty vehicle.
The test is even conducted in an ambient temperature of between 20 and 30 degrees. The New European Driving Cycle (NEDC) even involves cars remaining stationary for around 10% of the test.
Hardly reflective of real life - or UK weather.
Unsurprisingly, vehicle manufacturers optimise performance during the rolling road test to get the best possible urban cycle and extra-urban cycle figures.
The former involves a prescriptive stop/start cycle from cold covering around two and a half miles at an average speed of 12 mph, briefly topping out at 31 mph, while the latter involves acceleration, deceleration, steady speed and idling over a distance of 4.3 miles at an average 39 mph, topping out at 75 mph.
The official combined fuel consumption is arrived at from the weighted average of the two.
Recent research by the International Council on Clean Transportation (ICCT) found that, on average, real world fuel consumption figures for new cars was 21% worse than the figures quoted by the vehicle manufacturers. Back in 2011, the difference was only 8%.
To get a realistic mpg figure today, the AA suggests you can't go far wrong with assuming a car will do 25 per cent less than that officially claimed by the vehicle manufacturer.
A campaign is presently underway to adopt a new global test, the World Light Duty Test Procedure (WLTP), which on the driving cycle alone sees fuel consumption figures on average 5% higher.
If adopted by the EU, it could be applied to new type approvals from 2016/17. However, it could even be delayed to 2020 when new CO2 targets are due to be introduced.
And if you think vehicle manufacturers do not have a vested interest in optimising the official combined fuel consumption figures, let me disillusion you, because CO2 vehicle emission figures are entirely reliant on these.
The CO2 for petrol vehicles is 6740 divided by the official combined fuel consumption figure while for diesel vehicles 7440 is the magic number divided by the official combined fuel consumption figure.
Official fuel consumption figures therefore determine in which benefit-in-kind band vehicles fall. From a vehicle manufacturer's perspective more is at stake than you imagine.
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