Hi folks,

Recently, a Honda advocate suggested that Toyota engineering designed the Prius just for good EPA mileage but in fact it delivers worse performance than the equivalent Honda Civic. As we were discussing the inflamatory nature of a "cheating the EPA" claim, I realized there was some information about the Prius that the Honda advocates might not be aware of. By discussing this from the Prius side, there is a chance for enlightenment not only for our Honda advocates but also Prius pilots who may be disappointed in their MPG performance.

Perception: Honda Civics get EPA numbers and Prius Dont

The Honda advocate believes that Honda Civic owners have a higher ratio of those getting EPA numbers than the Prius owners. His source, is the GreenHybrid.com database. So let's check the numbers.

We have two generations of Honda Civic Hybrids and two generations of Prius with CVT transmissions. Starting with the gross numbers:

Median mpg (US) Mean mpg (US) Middle 50% mpg (US) Standard Deviation Standard Error Cars in Sample

Honda Civic Hybrid I 2WD CVT (48/47 EPA)
46.0 45.4 42.4–48.9 5.2 0.3 424
Toyota Prius I (THS) 2WD eCVT (52/45 EPA)
45.0 45.5 43.1–47.6 3.5 0.5 55

Clearly the HCH I out performs the Prius I, 46 to 45 MPG. Yet the larger standard deviation suggests HCH I drivers are getting a larger variation or spread in performance. This may be due to the smaller sample set of Prius I. But the situation changes with the HCH II and Prius II.

Honda Civic Hybrid II 2WD CVT (49/51 EPA)
46.9 46.4 43.7–50.0 4.8 0.3 226
Toyota Prius II (HSD) 2WD eCVT (60/51 EPA)
47.7 47.7 45.3–50.4 4.4 0.2 683

The Prius II has a clear advantage, 47.7 to 46.9. With both vehicles having respectable sample sets, the Prius II has a somewhat smaller standard deviation suggesting slightly more consistent performance. But these numbers only apply if there is a normal distribution.

So this is the HCH II distribution:



Here is the Prius II distribution:


These charts suggest a lot of HCH II drivers are achieving the median and lower values and a few stars are achieving excellent results. The situation is reversed with the Prius II, many are at and above the median with a faster fall-off on the low side. Simular distribution curves exists for the HCH I and the Prius I.

So how do they compare to the EPA numbers?

Prius I - median and mean equals the lowest EPA number, 45 vs 45 mpg
HCH I - median and mean are below lowest EPA numbers, 46 vs 47 mpg
Prius II - median and mean are below lowest EPA numbers, 47.7 vs 51 mpg
HCH II - median and mean are below lowest EPA numbers, 46.9 vs 49 mpg

So what can we now assert:

• Prius I - the only hybrid to reach even the lowest EPA numbers
• Prius II - has the largest deviation, ~3 mpg, from lowest EPA numbers
• HCH I, HCH II and Prius II - all achieved lower than the lowest EPA numbers
• HCH I outperformed the Prius I
• Prius II outperformed the HCH II

Does this fairly state the facts? Later today, I'll try to edit the EPA expected values and differences. I believe this is calculated 40/60 highway vs. city, unless someone elses posts the values.

Bob Wilson

ps. Later, I'll offer a description about how the Prius architecture works versus the EPA and normal driving. Hopefully this will show there was no "cheating" or "designing for the test" but reveal insights that can be used to improve Prius MPG and meet the EPA numbers.

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Bob, very interesting. Now, you'll have to forgive me, but I want to twist your numbers to suit my pet theory.
My Theory- I'm convinced that HCH 2 owners are more committed to getting "great" FE than Prius owners.I'm also convinced that it is easier for an average criver to get outstanding FE with a Prius 2 than with a HCH 2.NOW I'M NOT SAYING THEY ARE CHEATING-NO WAY-I'M JUST SAYING THAT A HCH 2 OWNER ON THIS FORUM IS MORE LIKELY TO DRIVE TO MAX HIS/HER FE. It is a probably point of honor for FE fanatics to be scrupulous in respect to honesty.
How can I prove this?
Well,I can willfully over interpret your numbers and "say" that the fact that more than 50% of HCH 2 get better than average FE means that the HCH 2 data has more "committed" drivers-committed being defined as "better than average."
The Prius has exactly as many above and below average drivers-median and mean are the same.
Of course, the numbers are so close, they really don't support my claim very strongly.
My strongest evidence comes from the much hated CR numbers.CR drivers did much better with the Prius 2(city 35 hy 50 trip)48 than the HCH2 (26 47 45). CR doesn't use any FE tricks; many members of this forum do use FE tricks, and I think HCH2 owners use them more than Prius owners.

On the subject of Toyota tuning the Prius to produce "Great" EPA FE. FE that -in respect to city mpg- is far, far removed from real life. OF COURSE TOYOTA DOES THAT-WHAT COMPANY WOULDN'T? Now does this mean they have to give up some "real world" FE to achieve their "fake" numbers?Of course not; that is the beauty of having fairly complicated ECU with lots of memory,and having EFI with O2 and air mass sensors that give many,many readings/second. You can set it up to give great "fake" numbers while not giving up anything real world. We aren't dealing with a carb that can give good FE at one throttle opening/load/altitude, but has to give up FE/power everywhere else to achieve it.
I'm biased, but I'm also convinced that your numbers indicate that the HCH 2 data indicates that more of them are FE fanatics than Prius owners.It is easier for an uncommitted driver to get good numbers with a Prius 2 than a HCH 2. Thanks,Charlie
PS If I was even more biased,and had even less of a life, I would check the total number of posts by HCH 2 data providers-get the average, and compare it to the average numbers of posts by Prius 2 data providers.
If the numbers showed that HCH 2 data providers post more than Prius 2 data providers, I would immediately claim that AVERAGE NUMBER OF POSTS IS A PERFECT MARKER FOR FE FANATICISM,and claim my theory as proven.If the numbers don't show that-then I wouldn't report it,since I'm a typical biased cheater!!Just kidding about the last part.

Hey - just as another fact:

EPA "does not test every car they rate."

About 15% of the time they actually TEST the car THEMSELVES. The other 85% of the time, they rely on test results given to them by the carmakers.

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

There was a debate on Edmunds Forums for the last couple of years about whether or not the EPA actually DID the tests on the Prius II. Apparently, the EPA will not divulge that info, so no one REALLY knows.

If the tests came directly from Toyota, then who knows what happened in the testing? Only the people who were there.

<conspiracy freaks unite>

Hi Charile,
I don't think this is a defendable hypothsis from the data sources provided. I'd rather see a more direct metric of hypermiling commitment and nothing really jumps out from this gross data.

Actually, this is my ultimate goal, to go over the changes between the NHW11 and NHW20 and review the EPA test protocol and ordinary US traffic patterns. By hopefully a conservative, open investigation, we can draw attention to the effects of Prius engineering changes and give our Honda friends insight and a "clue by four" for our Prius friends.

Measuring motivation is hard although posting habits MIGHT provide some indication. Just that type of analysis from the GreenHybrid.com database is beyond the scope of my time budget. But there is another, indirect indication.

Recently, a vehicle independent web site, CleanMPG.com, started up addressing a broader question of any vehicle MPG performance. I noticed when reviewing their MPG entries that there are about the same number of Prius and non-hybrid posters, 3-4. In contrast, it seems to be over represented, >80%, by Honda hybrid advocates. As a measure of motivation, this is a number hard to ignore . . . BUT IT IS NOT DEFINITIVE . . . and these are just rough counts.

If you are interested in this hypothsis, you might 'do the numbers' and let us know.

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
Free speech, dialog and knowledge thrives without the poison of SPAM.

Bob, why did you leave my car (Honda Civic Hybrid with MT) out of your analysis?

To compare simular Continiously Variable Transmission vehicles. Anyone who can drive a Honda CVT can handle a Prius CVT. But manual transmissions require skill and physical ability. They are a 'horse of a different color'.

We would have the same problem with the MT Insight or for that matter, any MT vehicle. To a greater or lessor extent, it was also one of the problems found with the test methodology of the "Autoweek" article:

Let me suggest this. Quote my first posting and add the relevant data and assertions. Just be sure to caveat them as introducing a "manual transmission" and there won't be a problem. Say adding "(*)" by each of these elements would be great.

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
Free speech, dialog and knowledge thrives without the poison of SPAM.

Bob, yes,I agree that the numbers don't fully support HCH 2 drivers being more committed FE drivers than Prius 2 drivers. Now there is a hint of support there in the higher number of above average mpg drivers(median a little higher than mean), and in CR's numbers for both vehicles.If we assume that CR's drivers just drive to the specs of their test, then we do have to ask why their city loop for the HCH 2 was just 26 mpg(just 55% of our posters numbers) while out HCH 2 drivers get ~47mpg. CRs city loop with the Prius 2 was 35 mpg(73%) vs the 48 mpg we get here.
Another possible explanation is that HCH 2 drivers(here, on this forum)) might do more hy driving,and less city driving, than Prius drivers(forum drivers/posters).
If I get a bit more time,and have even less of a real life, I might sample some HCH 2 drivers post count vs Prius 2 post counts. Prius 2 counts should be a lot higher since they have been out since ~2004. I should probably do post counts per unit of time(months maybe) to control a bit for time.
On to the subject you are interested in which I'll paraphrase as "why does the Prius 2-a heavier, faster , bigger car-get better mpg than the Prius 1."
Do you have the relevant #s posted in any single place:
1)Weight
2) 0-60 1/4 mile
3)Claimed hp for ICE
4)Claimed HP for electrical motors
5)Total max storage capacity in watt hr for the 2 vehicles.
6) How much the batteries can be drained? 70%
7) Max "regen" energy pre 5 minutes.The Prius 2 manual says 200 watt-Hr per 5 minutes is the most it can display.I'n not sure that is the actual max it can regen, but maybe it is.
Have you been able to figure out how much of the Prius's 1 or 2 regen braking is actually from real "hitting the brake pedal braking", as opposed to the Prius's computer deciding to add subtle braking when the driver rolls off the gas, but doesn't hit the brake pedal??
I would be willing to bet that Toyota added more of this "unasked for braking" to the Prius 2. How else could they supply the extra electrical energy that the Prius 2 must use?
My 1st thought is that this " unasked for braking"would require a bigger program that would take more memory(of whatever type of memory this would need), and you could check memory "size' of the Prius 1 vs Prius 2. On second thought, this might not be so.Maybe Toyota just did something simple like" add regen braking whenever the pedal changes position 20% instead of 30%". A command like this wouldn't take any more memory. Besides , the memory of all vehicles increases with each new model; it would be impossible to make anything out of an increase in memory of program size. We couldn't/can't assume that it is for my pet idea.
Do you have any idea on how we can measure regen. on the Prius 1 and Prius 2(per unit of time or distance on a set course)?
Do you have any idea on how to measure electrical energy used(per unit of time or distance-on a "set" drive of course, by the electrical motors on the Prius 1 vs Prius 2??
It is possible-maybe likely-that the Prius 2 actually has more efficient ICE , electrical motors, lower aero drag,lower rolling resistance, lower drivetrain losses(better bearings, thinner grease,lower vis oil). Toyota also might have increased the amount of energy it could regen during hard stops that required both types of "brakes"-use electrical braking instead of friction braking???I still think that some of the improvement is due to more unasked for brake regen.Bigger, more powerful electrical motors/gens should be able to brake harder-right?
The downside of doing more unasked for brake regen is obvious-if Toyota added more braking in situations where the driver doesn't need more braking, then it would actually hurt efficiency because the driver is going to have to use more energy to get that speed back. I would bet Toyota has a program that predicts when a roll off throttle indicates that braking will very likely be needed. The computer then " works faster than the human" and adds braking. I wonder if Toyota could/did access this info from Prius 1's when they did maintenance on them? Toyota might have used this real world info to improve the regen brake program on the Prius 2??
Hmmm,I'm running on.Sorry.Thanks,Charlie

Hi Charile,

Last week, Ken posted some URLs that I added to the Prius FAQ that describe many of the differences and improvements for the NHW20 over the NHW11. Take a look at those URLs and then ask your questions. But I'll give you a hint:

- more efficient transaxle --> replaced bushings with bearings on one gear. Furthermore, the higher voltage, lower current minimizes I(2)R losses in MG1/MG2

- more regenerative braking --> regeneration stays on longer and mechanical braking is held off longer

- improved coefficient of drag --> better high speed performance. This includes limited 'belly pan' panels

- ICE coolant thermos --> quicker warm-up by using previously stored coolant minimized energy lost during the warm-up

There may be more changes but these are the ones that come to mind quickly.

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
Free speech, dialog and knowledge thrives without the poison of SPAM.

Bob this is not strictly true. First of all I'm not a Honda advocate. I like the Prius every bit as much as I like any Honda car. I don't really care for Honda's belt and pulley CVT. If I had to choose between a Honda Civic CVT and a Prius 2 I'll likely take the Prius. You can compare a Prius to a CVT HCH if you like but the comparison is meaningless to me because I favor the Prius already anyways.

My beef is with people who insist the the Prius is better than my car (MT HCH). People who start spouting terms like "full hybrid" and spout off EPA figures even though they themselves are not getting EPA figures. I consider my car roughly equal to the Prius.

The MT HCH is rated 46/51 and the average in the database is 48.2 which is above the lower EPA figure and just about exactly what the EPA combined mileage is. It seems to me like Honda designed and tested the MT HCH to be driven in real world conditions. The way all the numbers agree within a few tenths seems very honest to me.

OTOH the way the Prius 2 database numbers falls far short of the Prius 2 EPA figures seem a little fishy to me....I've speculated that Toyota designed the Prius to maximize the EPA tests but I have no idea if that is actually true. I prefer the database to the EPA figure because the database seems more "real world" to me. I'm not trying to insult Toyota or the Prius, only pointing out data that all are free to check for themselves and speculating on the reason for the Prius descrepancy between the database and EPA.

Bob,

Good analysis. The only thing I might add is that the HCHII database probably should not be treated as "stable" until the cars have been around for at least one full year to accurately reflect its performance in all weather conditions.