Campaign group Transport & Environment
says carmakers exploit loopholes in EU law to achieve favourable but unrealistic miles/gallon results.
They suggest the official fuel consumption cited by car manufacturers is on average almost 25% lower than that achieved in reality, and in some cases 50% lower.
The EU commission's consultants believe that 30% to 50% of the drop in claimed CO2 emissions between 2002 and 2010 "does not result from technology".
Article is here
Full report is here
Interestingly,the tricks manufacturers use are listed as including:
- disconnecting the alternator
- overinflating tyres
- taping over gaps in the bodywork and sealing the radiator grille
- using special low friction lubricants
- wheel alignment to minimze rolling resistance
- testing at altitude (low air resistance)
- using higher gears
- testing at unrealistically high temperatures
- using super slippery test track surfaces
- using a rolling road and misprogramming it for a lighter car
- Moving brake pads away from disks (not braking during the test)
- Deliberatedly under-reporting CO2 results by 4%
- Deliberatedly exploiting the testing tolerances (under speed, longer stops)
Also worth pointing out that the manufacturers do not make their raw data public either...
The upshort appears to be that much, perhaps most, of the improvement in EU car fuel economy and emissions over recent years is fictional, and that current models probably perform very little better than their (often smaller, lighter) predecessors!