Fuel Efficiency Numbers Overstate MPG More For Cars With Small Engines

whoever57 writes: All official numbers for fuel economy in the EU typically overstate the miles-per-gallon figure that drivers can expect to achieve in typical driving. A recent study confirmed this once again. However, what the study also found was that MPG figures are more unrealistic for cars with smaller engines than for cars with larger engines. Actual MPG figures achieved based on typical drives for cars with small engines could be as much as 36% under the official number, while those cars with 3-liter engines would typically achieve 15% less than the official figure. These discrepancies need to be accounted for if we're going to be serious about regulating fuel efficiency. But then, we should be using gallons-per-mile instead of miles-per-gallon, too.

Comments

metric you insensitive clod!

[louic]

"But then, we should be using gallons-per-mile instead of miles-per-gallon, too".

No. You should be using litres per kilometer. Especially so when talking about the EU.

Re:metric you insensitive clod!

[rgmoore]

that is exactly what the government does with the CAFE standards.

No, it isn't. The CAFE standards traditionally used the weighted harmonic mean of the mpg values, which gives exactly the same result as the weighted arithmetic mean of the economy expressed in gallons per mile. There are some other quirks- dual fuel vehicles are treated much more favorably than they probably ought to be, for instance- and the standards were recently changed to give bigger vehicles a break. But the larger point is that the EPA isn't completely stupid and does realize that the arithmetic mean is not the correct way of calculating average fuel economy.

Even simpler

[goombah99]

would it not be better to simplify a volume divided by a length to an area. Gallons/mile is best represented in represented in hectates or furlongs^2.

Original link has more data

[orzetto]

The study is by Emission Analytics, and here is the original link (as opposed to TFA from The Telegraph).

Note some misleading elements from TFA: they show only the three smaller classes for UK cars, seemingly indicating that small cars are the worst gas guzzlers, whereas cars with higher engine sizes are actually much worse according to the original study (see the graph). So the lesson is: still buy a small car, just not a very small one for best fuel efficiency.

Another interesting bit that is not in TFA is that the data for US cars is different: there, cars between 1 and 3 liters in volume (I assume this is the large majority of the car pool) have less than half the mileage. Also, the smallest US cars are actually the most efficient of any class, even though their efficiency is below UK average.