Mileage Moment of truth: We put 40 MPG Claims to the test

[aneekr]

Yes, but that's not as pretty as a graph! :P

Here are some additional plots with vehicle speed on the x-axis and fuel economy on the y-axis.

 

1997 study by Oak Ridge National Laboratory:

 

2006 evaluation by Auto Bild:

[Captainp4]

Holy crap, I understand this. I get it, I majored in engineering before I decided it wasn't for me and I was sticking with the family business. I'm not an idiot. All I am saying is that there is a POSSIBILITY that Ford gears their vehicles to do well on the EPA testing cycle and not for real world where people drive 70+ on the highway. A lot of Fords that I have been in seem to be geared optimally to run around 65mph on the highway, which is about where the EPA test is. Yes, wind resistance is exponential, but it is not the ONLY factor in fuel mileage at highway speeds. As an example, there seem to be guys that are running taller tires (but not wider) effectively lowering (numerically) their gear ratio and increasing fuel mileage on some of the Ford truck forums that I'm on. While others, guys with the v10 it seems, have more luck with a deeper gear (numerically higher) and better fuel mileage.

Edited February 7, 2012 by Captainp4

[akirby]

Holy crap, I understand this. I get it, I majored in engineering before I decided it wasn't for me and I was sticking with the family business. I'm not an idiot. All I am saying is that there is a POSSIBILITY that Ford gears their vehicles to do well on the EPA testing cycle and not for real world where people drive 70+ on the highway. A lot of Fords that I have been in seem to be geared optimally to run around 65mph on the highway, which is about where the EPA test is. Yes, wind resistance is exponential, but it is not the ONLY factor in fuel mileage at highway speeds. As an example, there seem to be guys that are running taller tires (but not wider) effectively lowering (numerically) their gear ratio and increasing fuel mileage on some of the Ford truck forums that I'm on. While others, guys with the v10 it seems, have more luck with a deeper gear (numerically higher) and better fuel mileage.

 

Changing tire diameters is the same as changing gear ratios - it just changes the RPM at any particular speed. Generally speaking the lower the RPM the better the fuel mileage provided you have enough power to maintain speed and you're not having to downshift or lug the engine.

 

Any gear changes that help fuel economy at 65 is also going to help fuel economy at 70 - the RPM reduction is linear because you're in the same gear (6th in this case). This whole "tuning for the EPA cycle" is an urban myth at this point. Whatever you can do to increase EPA fuel economy will also increase real world fuel economy.

 

Once you're in top gear, RPM changes are linear; the weight is the same but wind resistance increases exponentially and is by far the biggest difference.

[rkisler]

Changing tire diameters is the same as changing gear ratios - it just changes the RPM at any particular speed. Generally speaking the lower the RPM the better the fuel mileage provided you have enough power to maintain speed and you're not having to downshift or lug the engine.

 

Any gear changes that help fuel economy at 65 is also going to help fuel economy at 70 - the RPM reduction is linear because you're in the same gear (6th in this case). This whole "tuning for the EPA cycle" is an urban myth at this point. Whatever you can do to increase EPA fuel economy will also increase real world fuel economy.

 

Once you're in top gear, RPM changes are linear; the weight is the same but wind resistance increases exponentially and is by far the biggest difference.

 

I agree with what you're saying and want to add a thought. It's true that "tuning for the EPA cycle" is a myth. For the other readers,

 

All manufacturers, including Ford, will want the label to be as high as possible. Since the resistance on the rollers is set by weight and coast-down criteria (which encompasses wind resistance, rolling resistance, and friction), manufacturers will do the best they can to decrease resistance and get the weight of the vehicle into the next lower ITWC class.

 

In each case, as you rightly pointed out, the actions taken to improve label fuel economy also help real-world fuel economy. However, in once case, where you are heavy with a weight class, there could be some difference between your product and one that is light within a weight class (the roller resistance for weight is the same, but in the real world you might be heavier than your competition).

 

Manufacturers also have a very delicate balance of fuel economy and driveability/performance. Manufacturers cannot have one engine/transmission calibration for certification and another for production. So, if a manufacturer wants to let the vehicle linger in a higher gear for fuel economy and it lugs, transmits vibration, or is to slow to shift down and accelerate, then they are likely to pay the price with reviewers and consumers.

 

In addition:

 

ALL manufacturers have skilled "drivers" to follow the trace on the screen to ensure the best results with a given vehicle.

 

ALL manufacturers use prototype vehicles because the vehicle has to be certified before the vehicle is in production.

 

ALL manufacturers experience variability between individual vehicles, but less than it used to be due to tightening manufacturing tolerances and electronic engine/transmission controls. A prototype that is doing particularly well in testing is referred to as a "flyer". How manufacturers treat the certification of these vehicles which might not be representative of the population of that vehicle line is up to the manufacturer.

 

ALL manufacturers conduct their own tests with the EPA lab in Ann Arbor doing audits on 10-15% to keep everyone honest. I only remember one cheating episode (GM), and I believe it was actually brought to the EPA by GM voluntarily when they found out about it internally. So we have to assume that manufacturers aren't cheating.

[Captainp4]

Yes, I know that changing tire diameter is the same as changing the gear ratio, in fact, that's exactly what I just said in the previous post. I don't know why you two keep trying to explain things to me that I've either already said or are quite obvious, I didn't state anything as fact, all I said is that there is a possibility that Ford might gear their vehicles for optimal EPA results, not optimal real world results - and I never and said there was anything wrong with it if they do, why not try to get the best ratings possible when the .gov is forcing you to.

 

And no, it is not an urban myth. Tuning the computer and transmission shift points will help in both, but gearing can be changed to do well on the EPA test and not do well on the highway. If the EPA only tested city type driving, the deepest gears possible would be the most efficient becaues it would give the engine the most mechanical advantage and you wouldn't have to worry about bouncing off of the redline on the highway because it would never go that fast. If they only tested highway and accelerated extremely slow to get to those speeds, you want the numerically lowest gearing possible so that the engine is turning at a low rpm on the highway, or the most efficient rpm for desired speed. Any gearing changes that helps at 65 will not necessarily help at 70, if it puts the engine out of it's most efficient RPM range at one or the other, then no, it won't help both.

 

Of course they don't test like this, but my point is if they are using a gear set that is efficient at getting the vehicle up to 65mph and everything below that it will be turning very high RPMs when it gets up over 70, 75+mph. If they used a gear set that had very low cruising RPMs at 80 mph, depending on the number of gears in the trans and how it is geared it may decrease city mileage because of the increased load on the engine getting the vehicle moving. Now obviously different motors will have different results, but this is generally how it works.

 

Let me ask you this, if this wasn't the case that the goal is to have lower RPMs at highway cruising speeds while also lessening the load on the engine while accelerating, why do they keep adding more gears to transmissions and adding either more or deeper overdrives?

Edited February 7, 2012 by Captainp4

[jpd80]

Let me ask you this, if this wasn't the case that the goal is to have lower RPMs at highway cruising speeds while also lessening the load on the engine while accelerating, why do they keep adding more gears to transmissions and adding either more or deeper overdrives?

Acceleration in lower gears, first gear is around 4:1 in a 6 -speed auto where as in a 4-spped auto it was around 2.7:1

A 6-speed auto has smaller gaps between all gear ratios enabling smoother transition of power and lock-up in mid gears.

[Captainp4]

Which is effectively the same as using a lower (numerically higher) final gear set for the first few gears - it increases your city mpgs.

[RichardJensen]

why do they keep adding more gears to transmissions and adding either more or deeper overdrives?

To keep the engine operating in its 'sweet spot' at a wider range of speeds.

 

And to your earlier remark, I think you're reading far too much into a poorly designed test.

 

Yes, it's possible that Ford gears its vehicles to have terrible mileage at interstate speed limits, but it's also possible to win the lottery. Possibility is not probability, and I don't see a high probability in Ford engineering their vehicles to do considerably worse than the competition at cruising speeds.

 

Understand that manufacturers test fuel efficiency across a wider spectrum of environments than the EPA test regimen.

[Edstock]

Considering who was testing, maybe if they'd shifted the Focus into 6th?

[akirby]

Tuning the computer and transmission shift points will help in both, but gearing can be changed to do well on the EPA test and not do well on the highway. If the EPA only tested city type driving, the deepest gears possible would be the most efficient becaues it would give the engine the most mechanical advantage and you wouldn't have to worry about bouncing off of the redline on the highway because it would never go that fast. If they only tested highway and accelerated extremely slow to get to those speeds, you want the numerically lowest gearing possible so that the engine is turning at a low rpm on the highway, or the most efficient rpm for desired speed. Any gearing changes that helps at 65 will not necessarily help at 70, if it puts the engine out of it's most efficient RPM range at one or the other, then no, it won't help both.

 

Of course they don't test like this, but my point is if they are using a gear set that is efficient at getting the vehicle up to 65mph and everything below that it will be turning very high RPMs when it gets up over 70, 75+mph. If they used a gear set that had very low cruising RPMs at 80 mph, depending on the number of gears in the trans and how it is geared it may decrease city mileage because of the increased load on the engine getting the vehicle moving. Now obviously different motors will have different results, but this is generally how it works.

 

Let me ask you this, if this wasn't the case that the goal is to have lower RPMs at highway cruising speeds while also lessening the load on the engine while accelerating, why do they keep adding more gears to transmissions and adding either more or deeper overdrives?

 

I see your problem. You SAID you can tune for better EPA results vs. real world but what you MEANT is that you can tune for better city mileage at the expense of highway mileage and vice versa - and that is true. But that holds true for both EPA and real world testing.

[rkisler]

Acceleration in lower gears, first gear is around 4:1 in a 6 -speed auto where as in a 4-spped auto it was around 2.7:1

A 6-speed auto has smaller gaps between all gear ratios enabling smoother transition of power and lock-up in mid gears.

 

jpd, you said the magic word. You really want the transmission to be able to lock up whenever possible to get rid of the losses from the torque converter. For fuel economy, you generally want to get into the next gear as soon as possible (i.e., lower rpm) and get locked up. But to ensure good driveability and good NVH, you might have to delay the shift somewhat. And of course, going in and out of lockup has to be handled carefully to avoid shudders or other undesireable effects. More gears can help the powertrain to meet these objectives. I could be wrong, but I seem to remember that Ford's transmission can lock up in any gear?

 

Designing a calibration that performs well in the CAFE certification (not to mention emissions) and also performs well on the road is part science and part experience/art. But the fuel economy test is representative enough that I don't think a manufacturer could completely game the test, hold the same certification, and have acceptable on-road behavior. So it's a give and take with program management, development engineers, and powertrain (certification) engineers toward the tail-end of the program that gets to the best possible result for label and customer acceptance.

[Ralph Greene]

In addition to our new Edge.....I also have a 2010 Honda Element....bought mainly to haul my bikes and grandkids. Compared to some other "sorta" similar vehicles, it gets poor highway fuel economy. And I 've spent some time figuring out why....especially since it has basically the same 2.4 L engine Honda uses in other vehicles that have excellent highway numbers well into the 30's.

 

First.....It's brick. And while it will get about 30 MPG cruising easily at 55 or so, with AC off..... at 70 with AC on, it gets about 25-26. In addition to the lack of aero efficiency, runing the AC compressor makes a big difference.....at least 1 MPG, which is more than I thought. It's geared to turn about 2300 @ 70. Maybe Accord turns less...it needs less gear since it's more aero efficient. I know each 5% in cruising RPM (roughly 100) is worth about 1 MPG usually. These engines are tuned so closely, that any drag.....aero or mechaincal, makes a big difference in real world driving MPG. Things like aftermarket mud flaps, tall antennenas, wide front tires, low or marginal tire pressure, agressive tire treads, soft compound tire rubber, large side mirrors, raising vehicle up off ground a fraction of inch with taller front tires, pre-electric power steering, all can add up to more than you realize. Then there is weight of passenger, and whatever else you are carrying. Thow in winter gas, also. So many variables.

Edited February 7, 2012 by Ralph Greene

[Captainp4]

To keep the engine operating in its 'sweet spot' at a wider range of speeds.

 

And to your earlier remark, I think you're reading far too much into a poorly designed test.

 

Yes, it's possible that Ford gears its vehicles to have terrible mileage at interstate speed limits, but it's also possible to win the lottery. Possibility is not probability, and I don't see a high probability in Ford engineering their vehicles to do considerably worse than the competition at cruising speeds.

 

Understand that manufacturers test fuel efficiency across a wider spectrum of environments than the EPA test regimen.

 

 

Yes, this is a poor test, yes I'm probably reading too far into it. I guess what I should have started with was a question; do other people seem to get the same results in their Ford's when exceeding 65, 70mph, which is their mpg seems to drop significantly beyond those speeds? If we seemed to get a lot of people with the same results, across several different vehicles, I think at that point we could say that it is possible Ford designs their gearing to acheive better fuel economy at speeds closer to the EPA test, which is below 65 or so from what I've gathered. (is that correct? or does the EPA go above and beyond 65 in their testing?) IF the EPA test is generally below or around 65 and we see Ford's with gear sets that seem to have a "sweet spot" at or around 65 then I don't think it is too far off to say that Ford designs their gearing with the EPA test in mind and not so much the "real world" where people frequently go above and beyond that speed. Of course it is still anecdotal, and probably not worth much, but I was more thinking out loud than anything "Focus dropped off a cliff at 70, my superduty dropped off a cliff at 65-70, I wonder if there is something to that in the way Ford designs their gear sets?" Nothing more than that, nothing less.

[Captainp4]

I see your problem. You SAID you can tune for better EPA results vs. real world but what you MEANT is that you can tune for better city mileage at the expense of highway mileage and vice versa - and that is true. But that holds true for both EPA and real world testing.

 

And if the EPA tests are generally at a lower speed than real world driving? ....

[RichardJensen]

the EPA test, which is below 65 or so from what I've gathered. (is that correct? or does the EPA go above and beyond 65 in their testing?)

Would probably be a good idea to review the tests. There are over an hour and a half of tests.

 

http://www.fueleconomy.gov/feg/fe_test_schedules.shtml

Edited February 7, 2012 by RichardJensen

[rkisler]

And if the EPA tests are generally at a lower speed than real world driving? ....

 

Go here to look at the test cycles:

 

http://www.fueleconomy.gov/feg/fe_test_schedules.shtml

 

The EPA highway test goes to 80 mph.

 

There is nothing in Ford's gearing that should cause a big dump after 70 mph -- or at any rate a bigger dump than one might receive due to the non-linear drag and friction associated with the increase in speed.

 

Maybe I didn't understand you correctly, but are you saying that the EPA test is a poor test? If so, I don't agree. The cars are run for 1 1/2 hours total during testing and the tests simulating a number of conditions. These tests are run at very highly controlled laboratory conditions, and all of the gasses are collected to determine fuel economy. All-in-all, the results of the test appear to be reasonably representative of real-world results.

 

But...let me expand on your question. What if it's at a lower speed? I could add "what if it's warmer out when you start the car?" What if you drive more aggressively than the test? What if you drive more gently? What if you brake more rapidly? What if anything? It's a standardized test and, as they say, your results might vary. All that those designing the test can hope for is a test whose results will represent a reasonable mean around which there is a reasonably tight distribution of actual results. Very tough to do in a big country with lots of different climates, geology, population, and driving habits.

[akirby]

IF the EPA test is generally below or around 65 and we see Ford's with gear sets that seem to have a "sweet spot" at or around 65 then I don't think it is too far off to say that Ford designs their gearing with the EPA test in mind and not so much the "real world" where people frequently go above and beyond that speed.

 

Wow. Just wow. "Sweet spot"? Once you're in top gear with the torque converter locked that's it - the only thing that will vary is the RPM - and it will do that linearly based on the speed. Anything you can do to increase effficiency and fuel economy at 65 mph will also increase efficiency and fuel economy at 70 and 75 and 80 mph. You can't tune a car to perform well on the EPA test but not in real life - at least not since they changed the tests a few years ago. As Richard pointed out the highway test goes all the way up to 80 mph now.

 

And if the EPA tests are generally at a lower speed than real world driving? ....

 

So what? That just means that real world driving might be slightly lower in highway fuel economy than the EPA estimate. But that's why it's called an estimate and it's only to be used for comparisons between 2 vehicles - not as a prediction of your actual mileage.

 

And it would be lower FOR ALL BRANDS across the board.

 

Whatever point you keep trying to make here - it's not correct.

[Captainp4]

You're just not getting what I'm saying. Seeing that test goes to 80 my whole point is invalidated anyway, so whatever. Rear what I wrote again if you don't get the point I'm trying to make.

[akirby]

You're just not getting what I'm saying. Seeing that test goes to 80 my whole point is invalidated anyway, so whatever. Rear what I wrote again if you don't get the point I'm trying to make.

 

But with a 6 speed transmission you can make it more efficient at both getting up to speed and running at higher RPM. You don't have to sacrifice one for the other any more.

[jpd80]

jpd, you said the magic word. You really want the transmission to be able to lock up whenever possible to get rid of the losses from the torque converter. For fuel economy, you generally want to get into the next gear as soon as possible (i.e., lower rpm) and get locked up. But to ensure good driveability and good NVH, you might have to delay the shift somewhat. And of course, going in and out of lockup has to be handled carefully to avoid shudders or other undesireable effects. More gears can help the powertrain to meet these objectives. I could be wrong, but I seem to remember that Ford's transmission can lock up in any gear?

 

Designing a calibration that performs well in the CAFE certification (not to mention emissions) and also performs well on the road is part science and part experience/art. But the fuel economy test is representative enough that I don't think a manufacturer could completely game the test, hold the same certification, and have acceptable on-road behavior. So it's a give and take with program management, development engineers, and powertrain (certification) engineers toward the tail-end of the program that gets to the best possible result for label and customer acceptance.

Thanks Austin, FoA went for the ZF 6HP transmissions because they can lock up in all forward gears in normal running, an exceptional box,

I can't recommend it high enough, new Falcon Ecoboost (April) with ZF scored similar fuel economy to 200 lb lighter Mondeo Ecoboost with

darling Powershift...

 

Finally, we might soon be able to start comparing performance and economy of Falcon-Mondeo-Fusion-Taurus EB engine combinations.

[Noah Harbinger]

Wow. Just wow. "Sweet spot"? Once you're in top gear with the torque converter locked that's it - the only thing that will vary is the RPM - and it will do that linearly based on the speed. Anything you can do to increase effficiency and fuel economy at 65 mph will also increase efficiency and fuel economy at 70 and 75 and 80 mph. You can't tune a car to perform well on the EPA test but not in real life - at least not since they changed the tests a few years ago. As Richard pointed out the highway test goes all the way up to 80 mph now.

 

Do you (or does anyone) happen to know at what speed the Focus drops into 6th, if you're accelerating as slowly as possible?

[jpd80]

That's EPA HWY

 

 

 

High Speed Test

 

 

 

Air Cond Test

 

 

Cold Temp Test

Edited February 8, 2012 by jpd80

[akirby]

Do you (or does anyone) happen to know at what speed the Focus drops into 6th, if you're accelerating as slowly as possible?

 

I don't know for sure but it has to be around 50 - 55 mph max.

[mackinaw]

Do you (or does anyone) happen to know at what speed the Focus drops into 6th, if you're accelerating as slowly as possible?

 

I can probably give you a more definite answer later today, but if I accelerate like I'm stepping on an egg, I'm guessing my 2012 Focus will shift into 6th gear at about 35 mph.

Edited February 8, 2012 by mackinaw

[svtenthusiast]

In real world highway driving, I can get 40 MPG out of my 2012 Focus (non SFE) by driving between 60-65 MPH. I just drove a long trip getting 468 miles on 11.32 gallons which comes out to 41.4 MPG with 25 miles in city. I drove another trip a few months ago with the cruise set on 70 most of the time an got 39 MPG. Car is fully broken in at over 10K miles.

 

 

Daily 80 mile county highway drive to work with little in town, but with stop lights I average around 38 MPG. Speed between 58-62.

 

 

Car is rated at 27 city 37 highway and my lifetime combined average is over the EPA highway number.

 

 

I don't do any major hypermiling, but I do drive smartly and look ahead to stoplights to maximize coasting. This car puts down the MPG if you drive smart. Here is my fuelly account that I started when the car was new:

 

 

 

Edited February 8, 2012 by svtenthusiast