New MPG index highlights inaccurate fuel economy figures

Fuel economy figures quoted by manufacturers have long been recognised as being overly optimistic at best, and a new EQUA MPG Index launched my Emissions Analytics show just how inaccurate those claims are. Typically, cars return 25 per cent less fuel economy than the official figures when driven in real world conditions, with some models as much as 40 per cent less.

Independent vehicle testing firm Emissions Analytics has revealed information on MPG figures for more than 66,000 models - almost every car on sale in the UK in the last five years. Only two models produced better MPG figures than officially quoted according to Emissions Analytics forecasts - the Aston Martin Vantage with 21.5 MPG (+5%), and Nissan's 370Z at 26.8 MPG (+1%).

The highest fuel economy for a tested car is Honda's Civic 1.6 litre diesel, achieving 61.8 MPG - -21% on official figures - with Citroen's DS3 1.6 diesel in second place at 58.1 MPG, and the Toyota Auris 1.8 litre petrol hybrid in third at 58.1 MPG. All of these models are from 2013 and conformed to the old Euro 5 engine standard.

Of the current Euro 6 standard models tested, Audi's A3 1.6 diesel performs best outright with 57.8 MPG - at least -14% below quoted figures - with the Dacia Sandero 1.5 diesel at 57.7 MPG (-28%), and the Hyundai i20 1.4 diesel with 55.5 MPG (-19%).

Worst performers compared to quoted figures were the Fiat 500 0.9 petrol - down 46% with 39 MPG compared to the official 71.7 MPG; Ford's Fiesta 1.0 petrol at -43%; and the Ford Focus 1.0 down -42%.

Porsche's Macan Turbo offers the lowest outright fuel economy of Euro 6 models at 22 MPG (-31% vs the official 31.7 MPG), while the worst return of any Emissions Analytics tested car is the Range Rover Sport SVR at 17.5 MPG (-21%).

The reason behind the variance in official and real-world results is that quoted fuel economy is calculated from tests carried out in a laboratory, with a set cycle of different speeds run on a rolling road. There is a new test set to come into force next year in Europe - the Real Driving Emissions test (RDE) - which will be more accurate as it uses portable measurement software fitted to a car driven on public roads.

The problem is that the new test need to be more accurate since the gap between quoted and achievable fuel economy figures is increasing. The image below shows the extent of the problem from its findings, with the percentage difference between real and official MPG figures hovering around the 20-22 per cent mark for petrol, but increasing for diesel from 15 per cent in 2010 to 26 per cent in 2016; and hybrid figures are worse still, from a difference of 23 in 2012 to 34 per cent in 2016.

Emissions Analytics EQUA MPG Index

Image courtesy of Emissions Analytics

Drivers can visit the Emissions Analytics EQUA MPG Index website to find information for their car, while for additional information, search for the model on Next Green Car's MPG Calculator.

Chris Lilly

Author:Chris Lilly
Date Updated:2nd Sep 2016

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