After driving our 2013 Ford Fusion Hybrid to CA and back from MN I have a theory about how Ford achieved 47 MPG in testing when many of our results seem to belie that claim. This theory also explains why Ford is offering to work with the EPA to establish new testing standards for hybrid vehicles.
First off let me say that I have no affiliation with Ford or the automotive industry. I'm also not a journalist, I'm a Business Analyst and a math nerd. Because I have a form of autism called Aspergers I pay lots of attention to numbers and data and pick up on patterns in data subconsciously. My thoughts here are only a theory of how Ford could possibly have achieved 47 MPG in their EPA testing when many car owners are not reaching that number. Please let me know if you have any other theories or ideas.
First off, we need to understand how the EPA testing procedures work and the rules governing those tests. There are a number of different testing cycles used by the EPA. These cycles are designed to simulate “typical” driving patterns. Details of the cycles, including graphs, can be found at http://www.epa.gov/n...s/quickdds.htm. An explanation of the distinct cycles can also be found at http://www.cleanmpg....ead.php?t=1510.
What are the limitations of the EPA cycles? Let’s first examine the city cycle. The city cycle involves a lot of acceleration and braking. However, there is not much time spent idling as if at a red light. During this test the Fusion Hybrid could spend a lot of time in EV mode, possibly even often accelerating in EV mode depending on the SOC (state of charge) of the battery. The EPA test procedures call for very slow acceleration, unrealistically slow in fact. The maximum acceleration rate in the EPA testing is 3.3 MPH/second. At that rate it would take about 18 seconds for 0-60 MPH. That is not the constant acceleration rate, that is the maximum acceleration rate. At other parts of the testing the acceleration is even more languid.
The highway cycle also has its flaws. The highway cycle calls for a maximum acceleration rate of 3.2 MPH/second, even slower than in the city cycle. The highway test also does not measure fuel economy at a constant cruising speed. The graph looks more like what your speed would look like if you were doing pulse & glide for maximum fuel economy. The average speed is 48 MPH and the maximum speed is 60 MPH. This cycle includes no stops, no idling and begins with the engine already warm. All those factors will contribute to higher highway fuel economy.
To help offset these disadvantages the EPA created the high speed cycle in 2008. The high speed cycle includes faster acceleration and a top speed of 80 MPH. However, the average speed in the high speed cycle is only 48 MPH. If you look at the graph you can see that it includes multiple stops and time spent idling. The high speeds are sustained only for a very short period of time. This test also starts with a warm engine.
Then there’s the AC cycle with warmer temperatures. This cycle is designed to lower the overall fuel economy numbers to be more realistic with summer driving using the AC. The cold temperature cycle is a repeat of the city cycle except with the lab temperature lowered to 20 degrees. This test also includes a cold engine at the start.
What are the overall limitations with the EPA tests? The highway speeds are too low for starters. We now have roads with speed limits as high as 85 MPH and many highways, even in the city, are increasing their speed limits up to 65 MPH. The EPA highway cycle looks more like typical driving on suburban county roads for someone who lives out in the outer-ring suburbs. The tests also underestimate the amount of time spent idling in city driving. Most city commutes are going to have a lot more time spent idling than the tests show. The tests do not include the use of AC or heat. In many parts of the country AC is a necessity for most of the year, and heat for the remaining months. The tests also don’t account for winter driving conditions. Lowering the temperature in the lab to 20 degrees is not the same as driving in winter. There is more resistance in the winter due to snow, sand and salt on the roads. But, the biggest flaw though is the cycle length. In an 11 mile city drive the fuel economy will be markedly better than in a 5 mile city drive. An 11 mile city drive is much too long. Most of our trips in the city are less than 2 miles, with the occasional trip being between 5 & 10, but very rarely do we do a city drive more than 10 miles. This greatly affects fuel economy in the Fusion Hybrid because of waiting for the engine to warm up. The EPA does not state that the heat should be turned on for the cold temperature cycle. In a hybrid this is very important, as turning the heat on will keep the engine running thus lowering MPG results. Driving with the heat off in cold weather will raise the MPG numbers, but is not realistic. The EPA test cycles factor in the aerodynamics of the vehicle but not wind. Wind is a big factor in highway fuel economy. In some non-scientific tests that I have done with our Fusion Hybrid I have found that a 10 MPH crosswind can lower fuel economy by 2 MPG or more.
So, now that we understand the limitations of the EPA cycles we can focus on Ford. I fully believe that Ford also identified these limitations and built the Fusion & C-Max to take advantage of the unreal reality that is the EPA tests. For example, why program the Fusion and C-Max to do a maximum of 62 MPH in EV mode? Where does that number come from? Why 62 MPH and not 60? Or 65? Or 55? The answer can be found in looking at the EPA test cycle graphs. The city cycle includes a maximum speed of 56 MPH, in the highway cycle the max speed is 60 MPH, 54.8 MPH in the AC cycle and 56 MPH again in the cold temperature cycle. This means that in all those tests the Ford hybrids can potentially run in EV mode the entire cycle. And while we know that the car could not go the entire distance under battery power, we do know that as soon as the cycle calls for deceleration the Ford hybrids can switch over to EV mode for gas free coasting.
Ah, but what about the high-speed cycle you say. Take a look at that graph too. Even though it calls for a maximum speed of 80 MPH, the time spent above 62 MPH is minimal. The test calls for cruising around 62 MPH and then acceleration up to 80 MPH for less than 60 seconds. Once that one minute burst of speed is over the cycle calls for speeds that are mostly below 62 MPH. I believe that Ford specifically identified the 62 MPH EV mode limit as the best way to maximize their results on the EPA cycles, not necessarily as the best way to maximize fuel economy for their customers.
In what other ways could Ford have manipulated the results? What about the battery SOC at the start of each cycle. The EPA doesn’t have strict guidelines for hybrids like there are for gasoline cars. While the EPA does specify for each cycle whether it starts with a cold engine or a warm engine, nothing specifies the hybrid battery SOC. From more unscientific testing that I have done, starting with a near 100% SOC is worth easily 5 MPG over starting with the SOC under 25% in short or medium length trips, like the EPA test cycles. This effect is magnified in highway driving because at higher speeds the engine spends a larger percentage of the distance running than in city driving. By watching the instant fuel economy gauge on the dash it is possible to see this effect while cruising on the highway. For example, cruising on flat ground at 60 MPH the instant fuel economy will show somewhere between 35-45 MPG depending on the ambient temperature if the battery is nearly full. When the battery SOC is low, the same conditions yield an instant fuel economy of 20-30 MPG. That’s a big difference, 15 MPG. So if Ford starts the highway cycle with the battery SOC near 100%, then the car will be able to spend more time cruising in EV mode and less time returning 20-30 MPG while recharging the battery.
My second theory is thus that Ford started the different test cycles with a battery with a SOC well higher than 50%. And, since the EPA has not established guidelines regarding the SOC of hybrid batteries for the test cycles Ford did not break any rules in doing this. Thus, Ford now offers to work with the EPA to develop new testing procedures for hybrids that would account for such measures. That offer is a smart move on Ford’s part because they can then say that they are working to satisfy consumers by “building a better mousetrap” as it were.
What can we do about it? In short, nothing. I don’t think the lawsuits will succeed, and unless the EPA finds that Ford broke some rule we aren’t going to see a refund like Kia & Hyundai were forced to hand out. There is a reason why the EPA mileage estimates come with the disclaimer: “Your mileage will vary”. This disclaimer is there because the tests have their flaws and limitations. What do we do then? Rather than complaining and trying to sue Ford, people need to grow up and learn to deal with it. Before we bought our Fusion Hybrid we test drove the Fusion & the Camry Hybrid. The Camry is rated much lower by the EPA for fuel economy (40/38/40). I wanted to see for myself. So my wife and I drove a specific route that simulated our normal driving. Our testing revealed 46 MPG overall in the Fusion and 45 MPG overall in the Camry doing the same driving route. “Your mileage will vary.” Does this mean that Toyota understated the fuel economy of the 2012 Camry Hybrid? No, it simply means that “your mileage will vary”.
The EPA fuel economy numbers are estimates. What is an estimate? It is a rough calculation or an approximation of a value. The EPA estimates that you will get 47 MPG. That means that if you drove the EPA test cycle 100 times you should come out with 47 MPG as the average. Some times you might get 50 MPG, other times 45 MPG, etc. This does not mean that you will get exactly 47 MPG driving to work, to the store, to the mall, etc. This means that if you follow the very specific guidelines the EPA sets forth, and drive in a lab, with no AC, with no wind, with no cargo weight in the car you will get 47 MPG. However, if you are not driving in a lab, with no AC, with no wind, with no cargo weight in the car and are driving to work, school or the mall, then “your mileage will vary”.
Really what is needed to find the solution to this conflict is not a lawsuit against Ford. Ford never states “you will get 47 MPG”, they merely hype the fact that the EPA test cycles return 47 MPG. And, what’s wrong with them doing that? It’s their right to advertise the EPA estimates of their cars. And it’s our responsibility as consumers to make wise decisions based, not on advertising alone, but on other factors.
So what if the EPA mileage is 47 MPG and you’re only getting 38 MPG? Have you considered all the factors that make your driving different from the EPA test cycles? Do you ever drive on windy days? Are you driving in warm weather with the AC turned on? Are you accelerating faster than 3.3 MPH/second? Are you driving faster than 60 MPH? If the answer to any of those questions is “yes” then you have your answer as to why you aren’t getting 47 MPG. Since none of us drive the EPA test cycle on a daily basis, is it any wonder then that we don’t see 47 MPG?
Maybe what’s needed here is a change in perception, a change in how we think about the EPA estimates; not of a lawsuit and a bunch of whining.
Edited by hybridbear, 28 January 2013 - 06:52 PM.