The truth about official fuel economy figures

Toyota Prius+

Car makers have been ordered to make it clear in advertisements that claimed fuel economy figures are unrealistic.


The ruling by the Advertising Standards Authority comes after a customer complained to the ASA that their Audi A3 1.6 TDI was not returning the advertised combined fuel consumption figure of 68.9mpg. 
The Volkswagen Group, which owns Audi, argued that all manufacturers use official laboratory-derived MPG figures, which are widely known not to reflect figures achieved in real-world driving conditions. 
However, the ASA said it was 'unlikely to be clear to the average consumer that the figure quoted was based on a standardised test and was not necessarily representative of what they would achieve when driving the car themselves.'

The ASA has instructed Audi and all other car manufacturers to include a suitable disclaimer in all adverts published from now on. 
Not getting your official mpg either?
In fact, very few cars manage to achieve their official fuel economy figures. That's largely because the official tests are conducted in artificial, laboratory conditions. 
Meanwhile, a recent report by the environmental organisation Transport and Environment (T&E) claimed this difference was also due to loopholes in the test procedure that allow manufacturers to use special techniques to get the best possible economy from their vehicles. These techniques include sealing gaps in doors and grilles, overinflating tyres and testing at high altitude or at unrealistically high temperatures. 
So which figures can you believe?
Last spring, What Car? launched its True MPG test programme, which measures cars' fuel consumption when driven on real roads, in real traffic and real weather. 
This first year of testing has found that 95.5% of cars tested failed to reach their official 'combined' mpg figure (calculated using a car's urban and extra-urban mpg results), and on average cars use 17.3% more fuel than official figures suggest. Based on an average of 12,000 miles a year, that equates to around £660 more than you'd have expected to spend on fuel. 
True MPG
The True MPG programme uses specialist equipment to measure mpg
That said, some cars actually performed better than their official figures – for example, both the Volvo XC90 2.4 D5 200 and Ford S-Max 2.0 TDCi 163 auto returned slightly more mpg than claimed. 
The report also confirms that the most economical cars are hybrids, closely followed by diesels, with petrols in third place. However, the average real-world economy for hybrids of 49.2mpg is a gaping 24.5% lower than their average official figure. Petrol and diesel cars fall nearly as short – almost 20% less– with average True MPG returns of 48.1mpg and 38.0mpg respectively. 
Volvo XC90
Volvo's XC90 is among the few cars which give better economy than promised
It's not all bad news, though. While most cars are unable to achieve their official mpg figures, the True MPG tests showed that many cars are still impressively efficient never the less, with figures upwards of 60mpg in everyday driving. 
It also turns out that, on average, automatics are only 3% less efficient than manual cars, compared to the 6.9mpg that official figures give.
What the past year's results prove most of all is the importance of checking a car's achievable fuel economy when estimating it's real-world running costs – and this is what True MPG allows you to do. You can even personalise the results according to the way you drive and the type of roads you drive on. 
True MPG top five  
From the 199 cars tested under the True MPG programme to date, the following five cars have proved the most economical in real-world driving conditions:
1. Kia Rio 1.1 CRDi 1 Ecodynamics 5dr - 70.6mpg

2. Citroen C3 Picasso 1.4 e-HDi 70 Airdream VTR+ – 70.3mpg

3. Ford Fiesta 1.6 TDCi 95 Econetic (previous model) – 62.1mpg

4. Fiat Panda 1.3 Multijet 75 – 61.0mpg

5. Mercedes-Benz A-Class A200 CDI Blue Efficiency – 59.6mpg