Do higher NO_x numbers explain Eco's much superior fuel efficiency?

We have an answer via e-mail received a few minutes ago:

Hi Bob,

It looks like there is a bit of confusion about which vehicles are represented on the Test Car List. Hopefully this summary will clear up most of your questions.

Vehicle 16-ZV2H is the Prius 2 Eco, and it is tested in Power, Normal, and ECO modes (16-ZV2H/0, 16-ZV2H/1, and 16-ZV2H/2 respectively).

Vehicle 16-ZV1H is the Prius 3, 4 with the Li-Ion battery. 16-ZV1H/1 represents the models with 17 inch wheels, and 16-ZV1H/2 represents the models with 15 inch wheels.

Vehicle 16-ZV3H is the Prius 2 with the NiMH battery. 16-ZV3H/1 represents summer tires, and 16-ZV3H/2 represents all-season tires.

You can find descriptions of the sales model codes in the certification applications available on the Document Index System:
Basic Search | Document Index System | US EPA

Here are direct links to the applications:
https://iaspub.epa.gov/otaqpub/display_file.jsp?docid=36706&flag=1
https://iaspub.epa.gov/otaqpub/display_file.jsp?docid=36707&flag=1

The information is in the section “Description of Vehicles Covered by Certificate”

Regards,
<name withheld upon request>​

I will update my posting pages later this evening.

Bob Wilson

 

What do they mean by "summer tires"? Since I use snow tires in winter, I thought about getting summer tires to use spring/summer/fall rather than all season, but found only one 195/65-15 "summer tire" on Tire Rack. And it wasn't clear to me whether it wold give better MPG than the OEM tires??? How would one find out, short of buying a set??

 

The summer tires did much worse than the all season tires on the NiMH. Summer tires were not tested on the Li-Ion, just 15" and 17".

Vehicle 16-ZV2H is the Prius 2 Eco, and it is tested in Power, Normal, and ECO modes (16-ZV2H/0, 16-ZV2H/1, and 16-ZV2H/2 respectively).

Six tests were run in each Mode. The average of the six tests are as follows:
16-ZV2H/0 Power Mode = 62.8 MPG
16-ZV2H/1 Normal Mode = 63.2 MPG
16-ZV2H/2 ECO Mode = 64.7 MPG





Merged

Actually, that is the reverse of what the test report says:
Note*1: AS : All-season tire
SM/SM#2 : Summer-tire

The average of the 16-ZV3H/1 is 53.8 MPG
The average of the 16-ZV3H/2 is 61.9 MPG

At this point it isn't clear which is which. All cars tested with the Li-ion were tested with all season tires.

 

So I looked at Tire Rack and searched for summer tires for the 2015 Prius Two (the 2016's aren't listed there yet). The only "summer tire" in the OEM size is the Pirelli 6000, which is not LRR. Apparently it's designed for some Porsche model so presumably grip was the primary goal, not fuel efficiency.
I looked at Discount Tire and all the LRR tires they offer in 195/65-15 are described as all season, or the blurb talks about winter traction.

Do actual LRR summer-only tires exist? What is this report talking about?

 

Wow Bob, you never cease to amaze.

Just want to say thank you for your enduring contributions to PriusChat, freely sharing your technical expertise, digging deep into these topics, and doing the grunt work to get real data driven answers.

It's contributions from folks like you who really enhance this forum and make it the great place it is to frequent and learn.

 

x 1000% agreed!

SM-G900I ?

 

Based on the e-mail:

. . .
Vehicle 16-ZV2H is the Prius 2 Eco, and it is tested in Power, Normal, and ECO modes (16-ZV2H/0, 16-ZV2H/1, and 16-ZV2H/2 respectively).

Vehicle 16-ZV1H is the Prius 3, 4 with the Li-Ion battery. 16-ZV1H/1 represents the models with 17 inch wheels, and 16-ZV1H/2 represents the models with 15 inch wheels.

Vehicle 16-ZV3H is the Prius 2 with the NiMH battery. 16-ZV3H/1 represents summer tires, and 16-ZV3H/2 represents all-season tires.
. . .​

	Test Desc\model	Prius 2 ECO_ Eco	Prius 2 ECO_ Nrm	Prius 2 ECO_ Pwr	Prius 2_ all-season	Prius 2_ summer	Prius 3_4_ 15”	Prius 3_4_ 17”
1	Cold CO	58	56.3	56.6	77.3	63.6	48.6
2	Cold CO (low)				52.3
3	Federal fuel 2-day exhaust (w/can load)	82.5	84.1	84.1		50.8	71.2
4	HWFE	78.2	78.2	76.9		46.9		71.1
5	SC03	59.6	59	58	76.1	64.9		66
6	SC03 (mid)				55.4	45.4
7	SC03 (low)		57.4	51	48.6	42.9
8	US06	58.5	51.1	50.1			78	45.5
9	US06 (low)	51.6	50.7

• There were two other Prius configurations in my spreadsheet, configuration 4 and 5, I'm still investigating .
• I am reviewing source documents to see if I've missed something.
  
• When the source materials sorted out, I'll start a fresh thread titled something like,"EPA tests and 2016 Prius" and include tables with more metrics and useful graphs.

Bob Wilson

 

Bob,
The actual document shows this is reversed:
Note*1: AS : All-season tire
SM/SM#2 : Summer-tire

Can you get your resource to comment on this?​

 

The load is determined from the roll down test. Tires with a higher rolling resistance will result in a higher load for the test dynamometer.

 

This is my most recent version:

	sales\test	Cold CO	Federal fuel	HWFE	SC03	US06
1	Prius 2 ECO (Eco)	58.0(gas)	82.5(gas)	78.2(gas)	59.6(gas) 58.5(E10)	51.6(gas)
2	Prius 2 ECO (Nrm)	56.3(gas)	84.1(gas)	78.2(gas)	59.0(gas) 57.4(E10)	51.1(gas) 50.7(E10)
3	Prius 2 ECO (Pwr)	56.6(gas)	84.1(gas)	76.9(gas)	58.0(gas)	51.0(gas) 50.1(E10)
4	Prius 2 (NiMH 15")	56.3(gas)			58.8(gas) 58.1(E10)
5	Prius 2 (NiMH 17")	51.7(gas)			51.9(gas) 51.3(E10)
6	Prius 2 (NiMH all season tires)	55.4(gas)	77.3(gas)	76.1(gas)	52.3(gas)	48.6(gas)
7	Prius 2 (NiMH summer tires)	50.8(gas)	64.9(gas)	63.6(gas)	46.9(gas) 45.4(E10)	42.9(gas)
8	Prius 3_4 (15")		78.0(gas)	71.2(gas)		48.6(gas)
9	Prius 3_4 (17")		71.1(gas)	66.0(gas)		45.5(gas)

1. Prius 2 ECO (Eco), Federal fuel, 82.5(gas) - this is the only data point that appears inconsistent with the other data points for the modes (Nrm) and (Pwr). Upon closer inspection, the "FE Bag" averages are lower this point than the other two. However, the test driver quality metrics, "DT-Inertial", "DT-Absolute", and "DT-Energy", are significantly different than the other two with both sign and magnitude differences. Speculation, the (Eco) mode remaps the accelerator and this may have surprised the driver who has to follow a specific speed protocol.
2. "Prius 2 (NiMH 15")" and "Prius 2 (NiMH 17")" - were e-mail tagged as "Prius ECO" LiON models but their weight matches the "Prius 2". Also, "Prius 2" has the "summer tires" and "all season tires" tests which makes more sense for a compare and contrast than tossing strange tires on the "Prius 2 ECO." I could be wrong but IMHO this change makes sense.

	sales\Federal fuel	RND_ADJ_FE		AVG BAGS	FE Bag 1	FE Bag 2	FE Bag 3	FE Bag 4		DT-Inertia Work Ratio Rating	DT-Absolute Speed Change Ratg	DT-Energy Economy Rating
1	Prius 2 ECO (Eco)	82.5		87.7	60.78	110.49	68.97	110.49		-0.47	-0.22	-0.35
2	Prius 2 ECO (Nrm)	84.1		90.7	61.24	110.52	66.44	124.53		0.08	0.15	-0.16
3	Prius 2 ECO (Pwr)	84.1		90.8	58.80	119.51	68.51	116.34		0.44	0.3	-0.18

1. Bag 1 and Bag 3 - start of each run, the cold MPG
2. Bag 2 and Bag 4 - end of teach run, the warmed MPG

This is the driving profile:

EPA testing is well defined so anyone can replicate and achieve similar results by following the driving profile. A simpler approach is to set the cruise control to the equivalent speed avoiding the acceleration and braking loads. So just find a place where you can drive on cruise control at 25 mph for a distance of 10-11 miles . . . like the outer ring of a large shopping center or a business park loop. In the USA, drive making right-turns and exploit, 'right on red' and use low traffic periods, say 2-3 AM.

Bob Wilson

ps.

This is the best I've got for now.