Ben Wojdyla does a good job of explaining how EPA fuel economy estimates are determined and testing a couple of todays more efficient compact cars, the Ford Focus and Hyundai Elantra.

Anyone comparing their real world mileage to the new car sticker must remember this, Your Mileage WILL Vary!

Both cars met or exceeded the label estimates but the conditions during the test were also pretty optimal with temperatures in the 40s that meant no air conditioning, heat or window defoggers were needed. The tests were also run during the day negating the need for headlights. All of these factors reduce the drain on the engine and the lack of traffic during the mid-day testing also eased the load.

I just have one small nit to pick with Ben's explanation of the EPA test procedure and it also affects real world efficiency. Ben described the fuel used during EPA testing as 100% gasoline. While Ben meant that there is no ethanol blended in as there is with most pump gas sold in the US, there is in fact no such thing as pure gasoline.

Gasoline as we know it is a blend of primarily heptane and octane (hydrocarbon compounds with 7 and 8 carbon atoms respectively) along with a number of other chemicals such as detergents and stabilizers. The exact blend of gas you get from the pump in various parts of the country varies depending on the location and time of the year. The blends are adjusted for factors like altitude, humidity and temperature to ensure easy starting in cold weather and thin air. The specific blend affects the mileage you get. However, the EPA uses a specific standard blend for all certification tests so that the results can be compared.

#fuelefficiency #mileage

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Mileage Moment of Truth – We Put 40 Mpg Claims to the Test
The 2012 Hyundai Elantra and Ford Focus SFE are among 20-plus cars that now claim 40 mpg highway. But given the peculiar way in which the EPA calculates its fuel economy estimates, do those mileage nu…

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