Emissions Analytics measures the real life mpg of cars and the company has found that the gap between official miles per gallon and real world mpg has grown to 22%. This is up 5% since the company first started testing fuel economy almost three years ago.
The average official combined economy figure of the 459 passenger cars it has tested is 57mpg and this is increasing by approximately 1.7 mpg per year. Real world miles per gallon (TMPG) on the other hand, which averages 44 mpg, remains flat, thus causing an increase in the gap of about two percentage points each year.
MPG vs. Engine size
Broadly speaking, the mpg gap grows as the engine size reduces. If you buy a five-litre car you won’t get great mpg, but at least it’s likely to be close to the official figures. However, if you’re shopping for a frugal run-around, you’re better off looking at the one to three-litre engines which give the best absolute performance as well as a lower divergence from official figures than the superminis.
Fuel economy by engine type
Emissions Analytics’ data also shows that petrol engines, as expected, have worse fuel economy than diesels, but interestingly the gap between real life and official figures is also larger. Manuals return better fuel economy than automatics, but automatics have a smaller gap between their official and real-world figures.