In December last year, a consumer watchdog petitioned the Environmental Protection Agency EPA to re-test the gas mileage of the 2011 Hyundai Elantra amidst complaints from owners that it did not achieve anywhere near its advertised 40 mpg in real life.  

But can cars listed as getting 40 mpg or better really achieve that in real-life, or have they simply been engineered to get good gas mileage in the EPA’s gas mileage test cycle?

Enter Popular Mechanics, test routes totaling nearly 200 miles, two cars, and some accurate scales.

Using the city of Detroit as a base, the magazine took two cars with a claimed EPA gas mileage of over 40 mpg -- the 2012 Hyundai Elantra and 2012 Ford Focus SFE -- on a series of test routes to see how each car compared to its laboratory-derived EPA rating. 

Accurate Measurements

Before leaving on the 133 miles of highway and 64.5 miles of city driving involved in the test, Popular Mechanics weighed each car to record the amount of fuel in each tank. 

2011 Hyundai Elantra

2011 Hyundai Elantra

Because the same amount of gasoline has a different volume dependent on temperature, weighing the amount of gasoline in the car is much more accurate than simply measuring volume of gasoline going into the tank. 

With a gallon of standard E10 gasoline weighing in at 6.4 pounds, the team could then weigh each car at the end of the test and calculate the exact amount of gasoline burned on the trip -- and thus the gas mileage. 

Regular Driving, Real-World Test

Although Popular Mechanics drove the highway routes during the middle of the day to ensure the roads were at their least congested, the test was carried out under real-world conditions. 

During the tests, the team reported the outside temperature was around 40 degrees Fahrenheit, meaning there was no need to use air conditioning. 

Starting with the highway test, both cars drove around the city of detroit, once, at 55 mph, and once at 70 mph. 

Following on, the cars were then taken on a shorter city test loop, complete with the usual stop/start traffic you’d find in any city.

As for driving style? 

“We made no effort to be overly frugal -- no drafting, not excessive coasting -- and we made a point to keep up with traffic,” wrote Popular Mechanics’ Ben Wojdyla. “Sure, we were a little light with the pedal, but slowpokes we were not.”

2012 Ford Focus

2012 Ford Focus

40 MPG possible, More at Lower Speeds

Unlike the many 2012 Hyundai Elantra owners who claim they can’t get anywhere near its 40 mpg EPA rating, the Popular Mechanics team noted that both the 2012 Hyundai Elantra and 2012 Ford Focus SFE nearly averaged 50 mpg during the 55 mpg highway test.

On the faster 70 mph test, neither quite managed the 40mpg of their EPA rating, but in the words of Popular Mechanics, “they were close.”

For city driving, each car hovered around 35 mpg. 

Your Mileage May Vary

As Popular Mechanics notes, the gas-mileage of a car in the real world depends on so much, from its design through to tire friction, vehicle weight, air density, speed and weather to name a few. 

In other words, gas mileage figures should be only ever used as a very rough guide -- not a promise of guaranteed fuel efficiency.

2012 Ford Focus

2012 Ford Focus

More importantly perhaps, the test also proves that under regular conditions, it is possible to get gas mileage that matches the EPA’s official ratings for your car even if you keep up with traffic. 

The key? Like we’ve said before, good maintenance, reading the road ahead, and a smooth, controlled driving style


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