What You Thought You Knew About MPG Ratings Is Probably Wrong

Do you remember me telling you that advertisements lie, how the marketing people (as well as the product manufacturers themselves) think you’re a sucker and how their goal is to target gullible people who believe everything they see and hear? Well, it’s still true, and nothing is going to change that.  This time, my ire wasn’t drawn to companies claiming to be the “best” or “highest quality” or any other subjective claim.  No, lately I’ve been more annoyed specifically with car companies and their practices for pitching their automobiles among stiff competition.  My beef with them centers on their non-stop talk about how you should buy their cars because of their fuel efficiency ratings.  Contrary to what many people believe and what we are allowed to think, the government doesn’t actually run the tests that determine the fuel economy advertised by car companies.


The thing that really gets me is that in all of the advertisements I have seen and heard, the number being used is the estimated highway mileage estimate.  The way it is presented, it is being made to sound like the higher of the estimates is what you can expect to get when you purchase a particular car.  Never mind the fact that a more moderate figure is readily available (the combined mileage estimate), but the big issue I have is that not only do car ads misuse the published estimates, or the fact that they make the figure they throw out there seem like a solid guide, but mostly the fact that most don’t even mention the term “estimate”, nor do they mention the biggest fact of all…


Let’s start with a simple fact: 

The auto manufacturers are the ones that determine fuel economy ratings


Yes, what you just read is 100% true.   There is no independent lab tests or specialized third party firms that do the testing.  It is the manufacturer of a vehicle that creates these estimates.  And, in most cases, the tests are done on pre-production models, and not even on the exact models that come off of the line and to the dealerships–the ones you will actually be buying.  The federal government, by way of a joint venture between the Department of Energy and Environmental Protection Agency, established a website to educate consumers on fuel economy and to help them make informed choices on the matter (as well as maintain their vehicles).  It also provides standardized guidelines for testing, but it’s active involvement essentially ends there.  When they are done with the tests, the auto manufacturers will send their reports to the agency, which then will review only 10-15% of the results.


Faulty assumptions in testing phases

First, this key piece of information essentially results in your having approximately a 1-in-10 of purchasing a vehicle that was verified as having the same fuel efficiency rating as is advertised.  It also means that there can be significant deviations between your actual experiences and those estimates.  The biggest reason is the fact that any number of events can happen between the testing phase and the end of the production process which can change these estimates. Think of it like a movie with bonus deleted material and extended scenes–not everything makes it to the final product completely intact, sometimes things are removed, added, or changed during the production process.  The same can happen during the manufacturing process of any item.  There is always room for change or improvement, and there is no guarantee that the models which are shipped for sale are the exact specifications of the ones used in pre-production testing.


Secondly are the ways that the tests are conducted: inside a lab, with the car on a dynamometer simulating “typical” trips.  All this means is that they put the car on rollers while the car is being driven at a speed determined by the simulator program.  Variables such as temperature, wind resistance, and more recently the use of air conditioning are then accounted for by the use of mathematical supplementation.  It is a purely speculative means of testing, while at the same time giving consumers false expectations and incomplete information since much of this is not common knowledge.



Impact on you as a consumer

What does this mean for you?  Well, for starters, it means that you will most likely never experience the same mileage ratings in terms of fuel economy that the window stickers claim on new cars.  In fact, since the testing methods changed in 2008 which lowered estimates across the board, it became even more difficult to shop for used cars which were tested using old, outdated standards.  The reasons for variances between actual and estimated fuel economy are significant and very important to understand.


The basic premise of these fuel economy estimates is a 55/45 split in terms of the percentage of highway/city driving.  In essence, these numbers can skew the picture greatly depending on where you live.  People who live in metropolitan areas with heavy traffic during most of their drive time will see greatly reduced results whereas those who do most of their driving on open highways with little impediments will see opposite results.  Fuel is burned more efficiently at constant speeds rather than continual stopping-and-starting, so the traffic patterns play a significant role in the results one would see in real world scenarios.


Another factor that is not specifically factored into the estimates is the style of driving.  Those who have what is known as a “heavy foot” will see reduced fuel economy as the amount of gas used to accelerate at an abrupt rate is greater than a gradual increase in speed.  Also of importance to fuel efficiency is the manner of activity.  Those who make frequent stops to complete driving tasks requiring the disengaging, then reengaging of the engine will also see diminished fuel efficiency, as an engine burns fuel more optimally when properly warmed up.


Weight and accessories play increasingly important roles in fuel efficiency as well. With more and more electrical components being included in cars, such as large displays, touch screen navigation, built-in monitors, etc. the less efficient fuel will be used.  Even carpooling can have a negative impact on fuel economy.  While being touted as an environmentally friendly transportation method, it may be more costly to the individual doing the majority of the driving, as increased weight requires more fuel to move the care at the same rate of speed as when driven alone.


Solutions to the problem

It’s pretty difficult to return a car if you realize it is not getting the fuel economy you thought it would when you originally bought it.  There is no way to take it home for a 30 day home trial like you can do with some other consumer products.  Fortunately, there are a few ways to protect yourself.  One way is to check out what others are saying about their own fuel economy results.  This resource is provided for people to report their own real-world results, and edmunds.com states that the reports are fairly accurate and reliable.  Another way to go about it would be to check out independent research authorities like Consumer Reports, or auto & financial magazines that run their own tests on vehicles.  Along those same lines, you can ask people who have purchased the same vehicle you are considering.  Although the last two methods still leave room for error, as personal driving styles will vary it is still better than not having any other resources other than the figures the auto manufacturers provide.


This post was featured in Carnival of Personal Finance: The Color Wheel Edition