EPA vs Prius c puzzle

About a month or so ago, I came across this:

I was not aware of a refresh for the Prius c so it didn't make sense why the 2017 took a nosedive. I contacted the EPA web curator who assured me there was no problem. I also notified @Prius Team in case there was a problem, nothing yet.

Today, I picked up the EPA 'test car database' for 2016 and 2017 and may have stumbled across the problem. For the 2017 data, Toyota submitted new test data for the 2017. The only change I knew of was TSS-P and I found in the data, the weight went from 2,750 lbs to 2,875 lbs, an increase of 125 lbs. HUH? Just to make TSS-P standard?

So I took the two highest mileage, test results, and plotted the results:

• HWFE, four distinct results for each model year.
• FTP (Federal fuel 2-day exhaust (w/can load), four distinct results for each model year

So what happened is Toyota submitted new EPA metrics for model year 2017, a different test car, and now the results are significantly lower. That 125 lbs could cause this loss of MPG doesn't make a lot of sense but now we know why the EPA metrics were lower.

Sometimes manufactures will make incremental improvements to safety or other systems and these can lead to minor weight gains that DO NOT require retesting. But adding the TSS-P might have pushed the weight over a threshold requiring retesting. It is also possible that Toyota improved their testing protocol and we are seeing in 2017, perhaps more accurate results? Possibly the effect of EPA tweaking their testing protocol?

EDIT: I'm finding the Coef A appears to come in two flavors that vary by a factor of 1000 and this is not limited to just the Prius c nor is it universal for other cars. Once I figured out what was going on, I generated this HP vs mph:

• 82 hp - listed for 2012 Prius c
• 72 hp - listed for 2017 Prius c

The EPA rating shows the drag is up and rated power down for the 2017 model Prius c over the 2012 model. This still has me puzzled and I don't own a Prius c nor am I a likely buyer.

I'm still scratching my head about the 2016/2017 Prius c changes. If the weight increase has led to more safety both TSS-P and accident, GOOD! But it also raises a question about earlier model year Prius c perhaps not having as good of MPG results as the earlier EPA data suggested (remember your mileage may vary.)

Bob Wilson

ps. I'm still looking at the 2017 data not just for the Prius c but across the board. Some of the 2017 data does not make a lot of sense.

 

FYI, I'm discussing the technical aspects in another forum:
Anyone notice EPA data changes? - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

Bob Wilson

 

Perhaps you might consider following @mojo:

• Both users often post insults
• Both users make claims not supported by facts and data:
  • @Sam Spade without citing sources
  • @mojo citing sources with obvious errors and then not defending them

In a perfect world, you two would 'follow' each other and loop-post yourselves into oblivion. For me, 'ignore user' is close enough. <GRINS>

One of the better features of PriusChat is the 'ignore user' option that is accessed by clicking on the offensive username in a thread. In the pop-up, click on 'Ignore' and signal-to-noise level instantly improves:


Every now and then, I check my user profile page to see if the ignored user is still around and stinking up PriusChat. Sure enough this troll is still around so we'll put him back on the ignore user list. Like we used to say in the Marine Corps, don't get mad, get even.

Bob Wilson

 

That would make sense in Europe and Japan because the official vehicle testing protocols are too optimistic. I just don't see it in the USA as our EPA has consistently been harder to sandbag.

I tried a Google search and didn't have any luck. Do you remember where you saw Toyota make this claim? Context often helps.

Bob Wilson

 

I did a quick check and even the derated value may not really be a problem:

The only cars with higher ratings are plug-in hybrids and the nearest ordinary car is 46 - 39 = 7 MPG worse. So as far as competing in the market place, the 2017 Toyota Prius c is no slouch. The funny thing is new owners will be getting superior MPG, much better than the Monroney sticker but unlike VW diesels, Toyota didn't cheat.

Bob Wilson

 

I remember finding a Toyota paper about reporting hybrid HP that is based on the net power, not the traditional engine on a test-stand and dyno. This led to reporting lower HP than the sum of the engine and electric motor, a much more honest approach.

We used to own a 2003 Prius and I remember learning how to drive it to achieve the original EPA metrics. Then in September 2008, the EPA downgraded the performance:

	Metric	2003 Prius < 9/08	2003 Prius >= 9/08	2012-16 Prius c	2017 Prius c
1	combined	48	41	50	46
2	city	52	42	53	48
3	highway	45	41	46	43

Athough I 'got the memo', I still maintained 52 MPG in our 2003 Prius. I suspect the new Prius c owners will be pleasantly surprised.

Bob Wilson