Independent, Expert EV Reviews & Advice Since 2006

Real life mpg v official mpg

ford-fiesta-econetic-000.jpg The New European Drive Cycle (a driving cycle designed to assess the emission levels of car engines and fuel economy in passenger cars) has long been accused of providing figures unrepresentative of real world driving.

A lax testing procedure allows car manufacturers to manipulate the tests to produce low results in terms of CO2 emissions and mpg figures which are unachievable in the real world. Car manufacturers are known to disconnect the battery during the test, minimise the weight of the car, use special lubricants that are not supplied with the production vehicle and test the car in unrealistically hot temperatures amongst other tactics.

‘Emissions Analytics’, amongst others, have investigated by running a real world test cycle by gathering data from 90% of new cars sold in the UK. Of these cars tested, 98% failed to achieve published figures with an average failure by 25% but some up to 40%.

The MPG marathon, the best known economy driving event, also came up with some interesting findings to demonstrate which cars perform well economically in the real world. Bristol Street Birmingham’s Ford Fiesta
ECOnetic 1.6 TDCi, achieved 88.69mpg, followed by the Renault Clio dCi 90 with 87.36mpg and the Honda Civic 1.6i-DTEC in third place with 84.87mpg.

However, it’s not just the testing procedure that prevents cars from ever achieving their official figures, research shows it can also be affected by wheel size and other additions to a car.

What about EV or hybrid cars?

Pure electric vehicles (EVs) don’t have mpg figures that can be measured but problems arise in hybrid cars where energy efficiency figures are often exaggerated.

Take the Volvo V60 Plug-in Diesel Hybrid, which has an official combined fuel economy figure of 155mpg. However, in typical real-life driving, a V60 Plug-in Diesel Hybrid owner is likely to achieve an average of around 50 miles per gallon over a year, or 12,000 miles, which is a drastic difference! The reason being is that the NEDC test is conducted on charged batteries rather than the car’s diesel engine, which is unrealistic of real-life driving.

It’s therefore really important to do your research if you’re considering going green.

Do Petrol/Diesel cars affect mpg?

Diesel cars have historically been known for being cheaper to run, for their energy efficiency and mpg. However, as car manufacturers have made the cars smoother and more powerful, more people have purchased diesel cars and, subsequently, diesel prices have overtaken petrol.

Research undertaken by Emissions Analytics also showed that small petrol engines are the worst performers with an average surplus of 67% CO2 compared to official emissions, and diesels with a larger engine range perform closer to the official figures given.

Added extras

Do the extras you buy for your car also affect whether or not your car will be able to reach the official mpg given by car manufacturers? That’s probably not something the car salesman told you when you bought the car – unless you bought a car from Toyota or Lexus.

Toyota and Lexus quote different economy and CO2 emission figures depending on the size of wheels. The Lexus IS 300h in entry-level SE spec with 16-inch wheels has a quoted economy of 65.7mpg with CO2 emissions of 99g/km. The higher spec model in the Lexus IS range , the F Sport version, has exactly the same engine and electric motor, but with 18-inch rims its claimed economy is 60.1mpg (109g/km CO2).

Added luxuries such as air conditioning (which can worsen fuel economy by over 10%) and heated seats when in use can all affect whether or not the car will perform to the official figures.

Calls for an update on the NEDC test continue to be demanded from the general public and will hopefully be addressed soon.