Official MPG figures overstated by 37%

Manufacturers’ quoted fuel emissions figures overstate real-world miles-per-gallon performance by an average of more than 37%, according to data collected by Professional Driver magazine.

Professional Driver, the highly respected business magazine for the private hire and chauffeur industry, has road tested 75 cars, including mid-sized and large saloons, MPVs and SUVs, and has compared road test results with manufacturers’ published combined-cycle mpg figures.

The average overstatement is 37.39%, with some cars having a quoted figure as much as 74% above the real-world test figure. Not one of the 75 cars evaluated matched or bettered the quoted figures, which are calculated in laboratory conditions using a rolling road.

Mark Bursa, Professional Driver editor said, ‘While this is not as serious as the manipulation of the US pollution tests by Volkswagen group, it does highlight the fact that the manufacturers’ quoted mpg figures in every case overstate the fuel economy you might expect to get from your car.’

Mark Bursa continued, ‘Professional Driver is aimed at private hire and chauffeur operators, for whom operating costs are of paramount importance. So unlike some consumer magazines, we’re not testing the cars round a track, at the limits of their performance. We test in real road conditions, as a fleet operator might drive, with fuel economy in mind. This gives the car the best chance of matching the quoted figures – yet only a handful of vehicles even come close.’

The majority of the cars tested are diesels, as these remain the most popular cars for the private hire sector. But a number of popular hybrid models have been tested too, and in fact some of these fare even worse than the diesels – the average over-statement for hybrids is 39.42% when you compare Professional Driver’s real-world test results with the quoted mpg figures.

Mark Bursa believes the results highlight the weakness of the testing process used to set benchmark figures for the car industry. He said, ‘The simple rolling-road tests are simply not rigorous enough to simulate driving conditions in the real world. There are no hills or even corners on the tests, and the tests only last for a few minutes.’

‘And the manufacturers are able to prepare their cars so they perform to the maximum – reducing weight and electrical features and to optimise fuel economy. And the short nature of the tests favours hybrids, especially those which offer a high proportion of electric drive when driven gently. It’s no coincidence that the Peugeot 3008 HYbrid4, a diesel hybrid car, has the most overstated fuel economy compared to real-world testing: 74%.’

The tests are also used to calculate the CO₂ emissions for all cars, and CO₂ emissions are used to calculate the Government’s Car Tax rates.

Mark continued, ‘There is a direct link between fuel economy and CO₂ emissions, and that means all the cars we’ve tested are certainly emitting more CO₂ than claimed. Some would certainly be in a higher tax band if real-world figures were used. The Government could be missing out on tax revenue as a result.’

The cars that performed closest to the bench tests were two smaller-engined diesel models, the Skoda Rapid Elegance 1.6 and the Kia Optima 2 1.7, where the official figure was 6.64% and 7.29% above the real-world test return. However, there is no clear pattern, with some larger-engined cars, including cars from manufacturers, including Infiniti and Volkswagen, also performing within 10% of the official mpg figure in real-world conditions.

‘The rolling road tests are the same for all cars, and it may be that some cars simply perform better than others under the specific test routines,’ said Mark Bursa. ‘As a comparative test between cars, the official combined mpg figure is not a bad guide. But the actual mpg figures are unachievable in the real world.’

‘On the positive side, the average mpg figure of all 75 cars we’ve tested is still an impressive figure – 39.12mpg. As we’re only considering cars that can be used as private hire vehicles, we only test larger cars, SUVs and MPVs with at least four doors.’

‘There are far worse causes of pollution in Britain’s cities than cars, for example trucks, buses, London black taxis and construction equipment,’ added Mark.