These days, we’re pretty sure that most car drivers know that the EPA-approved gas mileage ratings you see displayed on every new car at the dealer are for guidance only.

In short, your mileage may (and probably will) vary from the EPA ratings, but by how much? And what effect does poor maintenance and driving style have on your gas mileage?

To find out, General Motors sent two of its Chevrolet engineers out in identical 2012 Chevrolet Cruze LT cars on a typical rush-hour commute, measuring the fuel economy of each car over the course of the trip. 

The results are truly shocking. 

40 percent difference

In a properly maintained 2012 Chevy Cruze LT, complete with correct pressure tires and no extra weight on board, one engineer completed her commute with an average gas mileage of 37 mpg, bettering the official EPA 30mpg combined gas mileage estimate. 

In a poorly maintained 2012 Chevy Cruze LT, with around 240 pounds of shopping in the trunk and under-inflated tires, the same route yielded a gas-milage of 21 mpg. 

In terms of cost, at 15,000 miles a year and $4 a gallon, the properly maintained Cruze LT would save an impressive $1,236 in gasoline a year and be able to travel an additional 250 miles further per tank of gasoline than the poorly maintained one. 

Simple things

2012 Chevrolet Cruze

2012 Chevrolet Cruze

GM’s experiment neatly highlights some of the biggest contributors to poor gas mileage. 

Aside from poor maintenance it advises, carrying unnecessary loads, especially roof racks, will dramatically affect gas mileage. 

Alongside that, aggressive acceleration and speeding will certainly diminish gas mileage, while waiting in line at the local drive-thru for 15 minutes consumes the gasoline equivalent of paying a dollar extra for your meal. 

As we’ve advised in the past, GM also says that bundling errands together and winding windows up also help improve fuel efficiency, while cruise control can help keep a constant, smooth speed and gas mileage on longer trips. 

Have you carried out any similar tests in your own car? What’s the largest difference in gas mileage that you’ve witnessed, and what caused it? 

Let us know in the Comments below. 


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