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Official mpg figures overstate car fuel economy by 37%, says Professional Driver

PD website refueling 300- Comparison of 75 cars tested in real-world conditions by Professional Driver magazine reveals that no cars match the manufacturers’ quoted combined mpg figures

- Hybrids overstate fuel economy figures more than diesels, survey finds

- CO2 emissions also understated by “rolling road” tests

- Some mpg figures overstated by as much as 74%

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.

We have 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. “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.

“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,” said Mark Bursa. “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,” Mark Bursa added.

The 75 cars tested include current and superseded models road tested by Professional Driver since January 2011, and the figures were published in the Professional Driver Buyers’ Guide, 2014 and 2015 editions.

Mpg variances are calculated by using real-world figures as a base and calculating the percentage overstatement of the manufacturer’s official combined mpg figure for the each specific car.

PROFESSIONAL DRIVER REAL WORLD MPG FIGURES

ManufacturerModelFuelOfficial mpgReal mpgVariance %
Peugeot 3008 HYbrid4 Allure HD 74.3 42.7 74.00
BMW X5 xDrive M50d Auto D 42.8 24.6 73.98
Hyundai i40 Tourer SE Nav 1.7 CRDi 141 BlueDrive D 65.7 40.9 60.64
Skoda Octavia Elegance 1.6 TDI CR 105PS* D 74.3 47.1 57.75
Ford S-Max 2.0TDCi 180 Titanium X D 56.5 35.9 57.38
Ford Tourneo Custom 2.2TDCi LWB D 43.5 27.8 56.47
Infiniti Q70 GT 2.2D Premium D 57.6 37.2 54.84
Peugeot 308SW Allure BlueHDi 2.0 120 D 85.6 55.3 54.79
Mazda 6 2.2D 150 SE-L Nav D 67.3 43.5 54.71
Peugeot 5008 Allure 1.6 e-Hdi D 58.9 38.1 54.59
Volvo S80 D4 2.0D Lux Geartronic D 65.7 42.5 54.59
Volvo XC-90 D5 2.0D Inscription D 49.6 32.2 54.04
Volkswagen Passat SE Business 2.0TDI 150 D 64.2 41.8 53.59
BMW 730Ld SE* D 50.4 33.4 50.90
Ford Mondeo 2.0TDCI Titanium Business 163* D 54.3 36.0 50.83
Toyota Avensis Tourer Sports 2.0D-4 Business + D 62.8 41.8 50.24
Mercedes-Benz S350L BlueTEC SE D 50.4 33.6 50.00
Mercedes-Benz GL350 BlueTEC AMG Sport Auto D 35.3 23.6 49.58
BMW 318 Gran Turismo Sport 2.0D D 62.8 42.0 49.52
Peugeot 508 Allure 2.0 BlueHDi 150 D 72.4 48.6 48.97
BMW 520d Gran Turismo SE D 53.3 36.0 48.06
Mercedes-Benz E220 SE 7G-Tronic Plus D 58.9 39.8 47.99
Mercedes-Benz C300 BlueTEC Hybrid Sport Auto D 78.5 53.3 47.28
Mercedes-Benz S300L BlueTEC Hybrid AMG HD 61.4 42.1 45.84
Maserati Ghibli 3.0 diesel D 47.8 32.8 45.73
Toyota Auris Touring Sports Excel 1.8 Hybrid HP 70.6 49.0 44.08
Citroen Grand C4 Picasso Exclusive+ 150 D 61.4 42.7 43.79
Jaguar XF Sportbrake 2.2 163 Luxury D 55.4 38.7 43.15
Mercedes-Benz ML350 BlueTEC SE Executive* D 39.2 27.4 43.07
SEAT Alhambra SE Lux 2.0TDI CR 140PS DSG* D 49.6 34.8 42.53
Mercedes-Benz E300 BlueTEC Hybrid 7G-Tronic Plus HD 65.7 46.3 41.90
Audi A7 3.0TDI Ultra Quattri S-trnic SE D 54.3 39.0 39.23
Skoda Superb SE 2.0TDI 140* D 61.9 44.6 38.79
Porsche Panamera 3.0 Diesel D 51.4 37.2 38.17
SEAT Leon ST FR 2.0TDI 184 D 65.7 48.0 36.88
Volkswagen Passat SE Bluemotion 2.0TDI 140 DSG* D 54.3 39.7 36.78
Lexus GS300h Luxury HP 58.6 42.9 36.60
Skoda Octavia Greenline 3 1.6 CR 110PS D 80.7 59.1 36.55
Land Rover Discovery 3.0 SDV6 HSE Lux D 36.7 27.0 35.93
Audi A6 Ultra SE 190 S-Tronic D 64.2 47.3 35.73
Kia Carens 3 1.7CRDi D 56.4 41.6 35.58
Peugeot 508 Allure 2.0 HDi Auto* D 49.6 36.6 35.52
Range Rover 4.4 TDV8 Autobiography LWB Auto D 32.5 24.0 35.42
Lexus LS600hL HP 32.8 24.3 34.98
Audi Q7 3.0TDI Quattro S-Line 272PS tiptronic D 47.9 35.7 34.17
Toyota Prius+ T4 HP 68.9 51.4 34.05
Honda Civic Tourer 1.6 D-TEC SR 120 D 72.4 54.3 33.33
Mercedes-Benz V250 BlueTEC Sport 7G-Tronic Ex Long D 44.8 33.8 32.54
Mercedes-Benz Viano 3.0CDI Ambiente Extra Long D 32.8 24.9 31.73
SEAT Toledo 1.6TDI 105 Ecomotive D 72.4 55.0 1.64
Ford Mondeo 2.0TDCI Titanium 180 auto D 56.5 43.0 31.40
Volkswagen CC R-Line 2.0TDI BlueMotion 177 DSG D 54.3 41.6 30.53
Jaguar XJL 3.0D Portfolio D 44.8 34.5 29.86
Audi A8L 3.0TDI SE D 47.1 36.3 29.75
Skoda Superb SE Business 2.0TDI 150 D 68.9 53.2 29.51
Range Rover 3.0 TDV6 Vogue SE Auto D 37.7 29.3 28.67
Chrysler 300C Executive 3.0D V6* D 39.2 30.6 28.10
Chrysler Grand Voyager 2.8 CRD Limited* D 37.8 29.8 26.85
Ford Galaxy 2.0 TDCi 163 Titanium X* D 49.6 39.6 25.25
Jeep Grand Cherokee 3.0 CRD V6 Limited D 37.7 30.2 24.83
Volkswagen Sharan SEL 2.0TDI 140PS DSG D 49.6 40.1 23.69
Hyundai i40 Tourer 1.7 CRDi 136 D 47.1 38.1 23.62
Maserati Quattroporte 3.0 Diesel D 45.6 37.0 23.24
Volvo XC70 D4 2.0D AWD SE Nav D 44.1 35.8 23.18
Audi Q7 3.0TDI Quattro SE 204PS* D 39.2 32.0 22.50
Vauxhall Insignia SE 2.0 CDTi 163 Auto D 58.3 48.6 19.96
Volkswagen Phaeton 3.0 TDI 4Motion D 32.2 27.0 19.26
Porsche Cayenne Diesel 3.0TDI D 39.2 33.6 16.67
Mercedes-Benz Vito Tourer Select 114 BlueTEC Long D 43.5 37.8 15.08
Toyota Prius T-Spirit 1.8 Hybrid HP 70.6 62.0 13.87
Volkswagen Caravelle Business 2.0BiTDI 180 D 32.1 28.3 13.43
Infiniti Q70 GT 3.0 V6 Premium D 37.7 34.0 10.88
Infiniti QX70 GT 3.0d* D 32.8 29.8 10.07
Kia Optima2 1.7 CRDi 134 Auto D 47.1 43.9 7.29
Skoda Rapid Elegance 1.6TDI CR 105PS D 64.2 60.2 6.64
ALL CARS     53.75 39.12 37.39
ALL DIESELS     52.66 38.41 37.11
ALL HYBRIDS     62.86 45.09 39.42

NOTE: Vehicles denoted with * are models that have been superseded in production
KEY: D = Diesel; HD = Hybrid Diesel; HP = Hybrid Petrol

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