Report: Fuel Economy Rating Gap In Europe Now 31%

The average difference between the official fuel economy ratings for new cars in Europe and their actual efficiency soared to 31% last year from 8% in 2001, according to this year's Mind the Gap report by Brussels-based Transport & Environment.

The advocacy group says the gap could grow to more than 50% by 2020 unless regulatory agencies adopt a new standard. T&E backs the Worldwide Harmonized Light Vehicles Test Procedure, which the EC has recommended be phased in three years from now.

In the meantime, T&E estimates the current gap represents an average additional annual fuel cost of €500 per new vehicle.

Mercedes-Benz is the worst offender, with fuel economy ratings about 37% higher than real-world performance, according to the report. BMW and Ford follow with gaps of about 33%. T&E found no companies whose fuel economy rating was less than real-world results.

The gap is growing as manufacturers become more skilled at manipulating the test procedure to gain the best result, according to the report. It says carmakers bolster ratings by fitting test cars with special tires, altering wheel alignment, using special ultra-low-friction lubricants, taping over body seams and disconnecting the engine's alternator.

Manufacturers don't admit to manipulating the tests. But they agree that the government-mandated procedure leaves plenty of room for interpretation. Mercedes adds that independent studies indicate driving style can produce a 30% swing in fuel economy performance.

T&E says the widening gap means that half the gains in official fuel efficiency rating since 2008 are "hot air."