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Old 06-25-2017, 09:13 AM   #1 (permalink)
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Anyone notice EPA data changes?

Hi,

I'm a fan of the EPA "Data on Cars used for Testing Fuel Economy":
https://www.epa.gov/compliance-and-f...g-fuel-economy

Recently I noticed that the 2017 Prius c had a distinct drop in rated performance:

Other than adding TSS-P, the radar and optical dynamic cruise control and collision avoidance, I was not aware of any significant changes. But look that MPG hit.

So I used the downloadable data for the 2016 and 2017 Prius c and found:
  1. 125 lbs added
  2. 82 hp -> 72 hp

Ok this begins to suggest what is going on. Car bloat on the weight but the loss of hp doesn't make any sense. Regardless, I plotted the highest mileage numbers and go this:

So the loss of MPG begins to make sense as it came from the more recent model. YECH!!

I also calculated the drag HP vs mph and found:

The car drag has gone up significantly. This does not make a lick of sense and suggests the 2017 Prius c has gone retro.

Has anyone else noticed changes in the EPA data?

Bob Wilson

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Old 06-25-2017, 10:01 AM   #2 (permalink)
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https://www.fueleconomy.gov/feg/ratings.shtml

https://www.epa.gov/fueleconomy/basi...onomy-labeling

https://iaspub.epa.gov/otaqpub/displ...d=35113&flag=1

Quote:
2017 Ratings Changes

EPA is updating its method for calculating the fuel economy shown on new-car window stickers starting with the 2017 model year.

EPA periodically updates its methodology to account for changes in vehicle technologies, driver behavior, and/or driving conditions. The 2008 changes (see below) were broad revisions to the entire methodology that affected every vehicle.

The 2017 change updates some of the calculations used to estimate fuel economy. The new calculations are based on test data from model year 2011–2016 vehicles. So, they better reflect today's vehicle fleet of more fuel-efficient vehicles and advanced technologies such as hybrids and turbocharged engines.

Most vehicles are not affected by the new calculations. Some fuel economy estimates will decrease by 1 mpg, and a small number may be 2 mpg lower.
The extra weight may have come from TSS-C and improvements for the small-overlap crash testing, but who knows really.
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Old 06-25-2017, 01:24 PM   #3 (permalink)
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Thanks,

I was aware of a change but a loss of 4 MPG (~8%) versus the EPA claimed "1-2 MPG" is a little much. But there were other changes that really gutted the 2017 Prius c.

I've sent a detailed note to the EPA curator with the specifics. We'll see what comes back.

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Old 06-25-2017, 11:06 PM   #4 (permalink)
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The last EPA link has more detail.

Quote:
In fuel consumption terms, the new regression line tilts relative to the previous analysis. Most label values are likely to be unaffected except those with higher MPG values, where the difference is most pronounced. Some high MPG vehicles may see a decrease in label values if they continue to use the derived 5-cycle values, but of course the actual impact will depend upon the results achieved with complete 5-cycle testing and whether a manufacturer opts for derived 5-cycle methods for determining label values. The difference relative to the previous equation is more pronounced for the highway derived 5-cycle value. Some low MPG vehicles may actually see an increase in label values, but the difference relative to current values is so small and subtle that any change would simply be the result of changes due to rounding of MPG values. The following figures illustrate the new versus old equations, both in terms of fuel consumption and MPG. Further, as a result of the equations providing a better fit with current vehicles, we expect a decrease in the volume of failures of the “litmus test” with a corresponding increase in the number of vehicles eligible to use the derived 5-cycle values.
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Old 06-26-2017, 07:42 AM   #5 (permalink)
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Understand that I am all for procedures that improve the accuracy but this one, in the case of the Prius c, is going the wrong way:


There are a statistically significant number of user reported mileage to show the 2012-16 was reasonably accurate. Even using a larger pool from Fuelly - Track and Compare your MPG

The earlier EPA estimates are pretty darn close. But the 2017 version is ~8% too low.

Speculation on my part but at one time the EPA applied a 'correction factor' to derate vehicle mileage. I'm wondering if this correction factor was applied to the more accurate results and thus driving it to error?

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Old 06-26-2017, 11:10 AM   #6 (permalink)
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Upon further review, it may be a moot point. The Monroney sticker is meant as a way to help people comparison shop cars. So I looked at small cars and found this ranking:



The only cars with higher mileage are plug-in. The nearest ordinary car is 7 MPG worse, 39 MPG versus 46 MPG for the Prius c. This also means the 2017 Prius c owners are likely to see significantly better MPG than the Monroney sticker. But unlike the TDI, no cheating.

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Old 06-26-2017, 10:27 PM   #7 (permalink)
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The Cruize diesel is 47 highway on the new standard no cheating. That is the car to get if you are a highway commuter. In the unadjusted old style highway EPA test it was in the 70 mpg range. I fully expect a hypermiler could do 80mpg tanks right off the showroom floor with good driving.
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Old 06-27-2017, 12:49 PM   #8 (permalink)
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Careful what you wish for:
Quote:
Originally Posted by Hersbird View Post
The Cruize diesel is 47 highway on the new standard no cheating. That is the car to get if you are a highway commuter. In the unadjusted old style highway EPA test it was in the 70 mpg range. I fully expect a hypermiler could do 80mpg tanks right off the showroom floor with good driving.
Source: Four major cities move to ban diesel vehicles by 2025 - BBC News
The leaders of four major global cities say they will stop the use of all diesel-powered cars and trucks by the middle of the next decade.

The mayors of Paris, Mexico City, Madrid and Athens say they are implementing the ban to improve air quality.
That would pretty well keep the Cruze on the highway and out of these cities. Sounds like a good plan, never bring the Cruze into the city. They could park on the edges and take an Uber Prius into the city. <GRINS>

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Old 06-27-2017, 12:59 PM   #9 (permalink)
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Quote:
Originally Posted by Old Tele man View Post
Which is more STUPID?

1) EPA not testing the same way that people drive?

or

2) Drivers not driving the same way that EPA does its tests?
I think it makes more sense to study the vehicle and systems. In particular look for boundary conditions. Then use the knowledge to tune the vehicle and optimize subsequent trips. The rest is easy.

Bob Wilson
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Old 06-27-2017, 02:41 PM   #10 (permalink)
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Quote:
Originally Posted by bwilson4web View Post
Careful what you wish for:

Source: Four major cities move to ban diesel vehicles by 2025 - BBC News
The leaders of four major global cities say they will stop the use of all diesel-powered cars and trucks by the middle of the next decade.

The mayors of Paris, Mexico City, Madrid and Athens say they are implementing the ban to improve air quality.
That would pretty well keep the Cruze on the highway and out of these cities. Sounds like a good plan, never bring the Cruze into the city. They could park on the edges and take an Uber Prius into the city. <GRINS>

Bob Wilson
Won't happen in the USA. The cars and trucks are already controlled in their emissions and the air is clean now in our cities. They aren't going to pick one minor source while ignoring all the rest. They could keep making the emissions of newly sold cars stricter and stricter, but the 2017 Cruize diesel will be on the road in every US location as long as the owner keeps it there. They will even run into constitutional problems if say Seattle trys to prevent me from driving my Montana licensed Cruze over for the weekend and using the federally funded roads. Seattle may be able to apply for a waiver to prevent the sale of diesel cars in Seattle, or Washington state could apply for a waiver for the whole state, but a car sold and licensed somewhere else or an older car licensed before the change will still be on the road for a good 30 years if not more.

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