Fuel Consumption – Can You Trust Official MPG Data?

If fuel consumption is an important factor in deciding your next car purchase, do official MPG figures from manufacturers live up to your expectations?

If fuel consumption is an important factor in your next car purchase, it’ll help to know if you can trust official MPG statistics. Unfortunately, this hasn’t necessarily been the case. In 2001, the average gap between the fuel economy you get in the real world and official figures that car manufactures must quote was around 8%. By 2014, however, it was as much as 40%.

It’s not that manufacturers are being underhand. The tests used to define official MPG figures were first developed in the 1970s and no longer accurately represent modern driving habits or vehicle performance. Car makers have been obliged to test each new model they’ve developed using this outdated method, and it means consumers aren’t getting the full picture.

In the New European Driving Cycle (NEDC) test that was used until late 2018, a car is driven over a standard cycle on an independent laboratory rolling road to determine fuel consumption and CO2 emissions. From the test procedure and driving cycle, 3 official fuel consumption figures will be produced – urban, extra-urban and combined, which is a weighted average of the other 2.

Car makers must quote these figures – and only these figures – on their marketing materials. The CO2 emissions figure is also included in a car’s registration documents and determines its rate of vehicle tax.

Since September 2018, however, all new cars have been measured using a new test procedure called the Worldwide Harmonised Light Vehicle Test Procedure (WLTP). It’s expected that this new test will lead to more realistic, and more achievable,official fuel consumption figures that you’ll be able to trust when buying a new car.


What Is The MPG Likely To Be In The Real World?

A 2017 study by independent environment think tank ICCT claimed the average gap between official figures and real world fuel consumption and CO2 emissions was 42%. As a result, car owners were paying around £350 (€400) per year in extra fuel costs. So if a car’s advertised fuel economy is 45mpg, it might actually only achieve 26mpg.

The figures produced using the new WLTP test should be much more realistic in terms of reflecting real-world driving conditions. But how you drive will still have a significant effect on your fuel consumption.


What Did Fuel Economy Tests Not Cover?

For cars tested before September 2018, the testing procedure didn’t adequately cover modern driving habits. For example, cars being tested only briefly reached motorway speeds. The air conditioning and other electrical loads weren’t turned on either, while testing took place in a relatively high 20-30°C ambient temperature. Not accurate if you drive in colder conditions.

No single test can tell you exactly what rate of fuel consumption you’re likely to experience. Your driving style, the weather and traffic conditions are among the variables that will have an impact on how much fuel you use. While you can’t necessarily rely on the MPG figures quoted in marketing materials, any such figures will still be representative and can be useful when comparing different models.


Fuel Consumption Rules Of Thumb

If you’re buying a car first registered in 2019 or later, the figures quoted should come from the WLTP test – and careful driving should enable you to get close to them. For cars registered between 2010 and 2018, you shouldn’t be disappointed if your fuel consumption works out at around 25% worse than official figures. For older cars, meanwhile, around 10% less than the quoted combined figure should be about right.


How Can I Improve My Fuel Consumption?

The gap between MPG and real-world fuel consumption figures may be unhelpful, but there are still ways that motorists can save around 20% on their fuel costs. All it takes is for drivers to adopt some simple improvements to their driving style. Here are some tips to help you improve efficiency and reduce fuel consumption:

  • Read the road – Be proactive to avoid harsh acceleration and/or braking
  • Reduce drag – Remove bike racks when not in use or keep windows closed at high speed
  • Keep tyres inflated – If all tyres in use are correctly inflated, it’d save UK drivers £265m in fuel costs every year according to Michelin research
  • Remove excess weight – Take out unnecessary items for a cheap and easy way to save fuel
  • Be energy smart – Open windows at lower speeds instead of using air-conditioning
  • Consider a driving efficiency course – Invest in a driving efficiency course that will pay for itself long-term through the savings you’ll make putting theory into practice
  • Regularly service your car – Simple maintenance can make an important difference to fuel consumption as your engine will be under less stress
  • Buy a newer vehicle – According to official figures, today’s cars are around 23% more efficient than they were 10 years ago

Image courtesy of iStock.


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