How does the EPA determine average MPG?

[FX4Offroad]

There's a ton of posts about MPGs and I can't seem to find how city/Hwy MPGs are determined.

In the case of Highway MPG... Do they run the vehicle at a specific speed... 55, 60, 65?

I know when I run mine at 55... I get 28/29 MPG. At 70, it's closer to 21/22.

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[P. A. Schilke]

There's a ton of posts about MPGs and I can't seem to find how city/Hwy MPGs are determined.

In the case of Highway MPG... Do they run the vehicle at a specific speed... 55, 60, 65?

I know when I run mine at 55... I get 28/29 MPG. At 70, it's closer to 21/22.

Hi Jim,

I am not familiar with the exact calculations, but it is done during the Federal Test Procedure for emissions testing. The goal of EPA was to present more real world estimates than were done previously in order to allow customers to make informed decisions on what was important to them. At the time of $4.00 gasoline, fuel economy was a huge determiner and the Auto companies strived for max Fuel Economy numbers, so the actual published numbers are from the emissions test cycle. It is a complicated algorithm. It does allow apples to apples comparisons between Manufacturers and for different models and powertrains of a vehicle for a particular manufacturer. Do these mirror real world? Not really but do allow comparisons as all vehicles are tested the same.

Why do we have auto stop/start? Well....in the Federal Test Procedure there is a significant period of time the vehicle sits on the emission dyno rolls at idle and if the manufacturer turns off the motor, then significant gains in fuel economy can be achieved. So if Ford does auto stop/start, other manufactures competitively need to also do this.

There are a number of key metrics that affect the emission performance. When Ford went Ecoboost, the industry was caught flat footed. Out of the park power and fuel economy. Now everyone is coming to the table. So Ford knocked it out of the park again with the all Aluminum F150...both for trailer tow performance but also fuel economy. There is this pesky little metric of the Federal Test Procedure called DPA. Dyno Power Absorption. The higher number of the DPA the worse fuel economy performance and maybe even emissions. We always had to strive for reduced DPA and Inertia Weight Class specs. Any time we could achieve weight reduction, we were heroes. So this whole thing is a game we play with EPA and other Manufacturers. So as they say...Mileage may vary.

In my day at Ford with the Corporate Average Fuel Economy requirements, Ford would invest $100,000,000 if CAFE could be improved by one tenth of a MPG. Ecoboost met this objective!

I am sure there are websites that can explain in more detail than I have and maybe the engine calibrators here can chime in and expand or correct what I have said....

Best,
Phil Schilke
Ranger Vehicle Engineering
Ford Motor Co. Retired

 

[FX4Offroad]

Thanks Phil.

Always a wealth of information.

 

[Chris M]

And now the government ups the ante regarding average mpg for the industry to meet:
https://www.wsj.com/articles/u-s-ra...rements-for-cars-and-light-trucks-11640016001

 

[CB750F]

Phil is wrong, they use a dart board.
@P. A. Schilke , apologies for calling u out. ?

 

[THLONE]

Its not Phil fault. He is a real engineer. Companies have marketing engineers that meet in secret and figure out ways to fool the dumb government. Kind of like the global warming scientists that start with a goal/agenda and work backward.

 

[CB750F]

Its not Phil fault. He is a real engineer. Companies have marketing engineers that meet in secret and figure out ways to fool the dumb government. Kind of like the global warming scientists that start with a goal/agenda and work backward.

Well, holy geez! Ya learn something everyday.

 

[jthompson48]

I was wondering this on my holiday road trip where I got 19 mpg at 75 mph on cruise control fully stock over 800 miles. There was cross wind and hills. It seems especially sensitive. Thankfully my 30 mile commute to work at 65 gets about the advertised mileage.

 

[CB750F]

I was wondering this on my holiday road trip where I got 19 mpg at 75 mph on cruise control fully stock over 800 miles. There was cross wind and hills. It seems especially sensitive. Thankfully my 30 mile commute to work at 65 gets about the advertised mileage.

Wow, you think this would have been the time to get great mpg!
I did 1 vacation this yr & it's the only time I got to see the posted numbers.
Filled up yesterday & hand calculated 14.4l/100km or about 16 mpg, winter
gas & 300 lbs over the wheels, it's just bad.
I wonder if bringing it in & resetting would be useful?

 

[slowmachine]

I was wondering this on my holiday road trip where I got 19 mpg at 75 mph on cruise control fully stock over 800 miles. There was cross wind and hills. It seems especially sensitive. Thankfully my 30 mile commute to work at 65 gets about the advertised mileage.

Drag force = 1/2 * air density * flow velocity (speed)^2 * drag coefficient * frontal area

Drag force increases with the square of the speed, so speed has the greatest effect on total drag, You’ll save fuel by slowing down, as long as you don’t have to downshift. In my Ranger, that happens at about 50 MPH. I live in an area where most of the driving is 45-55. MPG is excellent for a truck.

 

[dtech]

MPG is excellent for a truck.

Yeah I'm happy with the mpg for a fairly weighty vehicle, had mine on a scale last fall and it weighed in at 4745, my 190 lbs included.

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