Prius FE Answers buried in the EPA Test Car Database

Thanks again for your analysis. FYI - I work for EPA in the early seventies and witness some of the early testing on dynamometers. We found the first defeat devices ...Sorry. A brief stroll down memory lane!

 

worked and witnessed. no need to apologize, we're all cheaters, in one way or another.

 

One last question.

Can you determine from the data whether the FE penalty would also affect the Four (non-touring)? The four has a few safety feature and convenience features that are interesting as well as fake leather seats while still useing 15 inch wheels. Another last question, do think that adding the safety option package would add enough additional weight to affect FE?

I guess what I'd like to know is whether the FE penalty is mostly from the 17 inch wheels or if the weight of the additional options is a significant contributing factor.

I want my toys and my FE, too.

 

One of the unanswered questions is why the 17" wheels look to underperform on MPGs.

Is it their weight?

The extra 20MM of rubber on the road? More wind resistance cause by the 10% wider tire width? The different suspension on the Touring models?

Or perhaps it is the brand/class of the tire itself?

If it is the brand/class of tire (which I suspect could be a huge factor), could some of the penalty be recaptured when it comes time to buy new tires? Do they even make a lower rolling resistance P215/45/17 tires? Perhaps tires with the similar mileage/tread life/noise/performance characteristics of those which come with the other models? Are the 15" tires equal or superior on all those metrics to the 17"?

Regardless, shame on Toyota for making this discussion possible -- and kudos to krousdb for the same reason!

 

Yes by the inertial mass. The wheel has a substantial amount of mass moved out 2" in diameter. The inertial mass (i.e., spinning momentum) increases by the 4th power of the diameter. Also, the 17" tires weigh more with the mass again further out, again the 4th power of the diameter.

Now there is a smaller increase in the linear momentum due to the absolute weight of the wheel and tire but we're talking small potatoes. It is the spinning mass that kills efficiency especially when it leads to more brake losses.

FYI, I use this with our 2003 Prius to increase linear stability in our 2003 Prius. By mounting over-sized, tires the increased moment of inertia (i.e., gyroscopic forces) has fixed the neutral stability problem.

Bob Wilson

 

CR must drive very aggressively in their city tests. I could get 60-70's mpg in my '13 Prius c going with the flow around Denver. CR got 44mpg in their city tests. Obviously they spent a fair amount of time with the pedal to the metal, and then they bitched about motor noise. Well, duh . . . .

 

Ive said this on another thread here, I read a British website that said that Toyota offers the 15" on all trims because their government CO2 emissions test show that the 17's produce 83 grams C)2/kilometer vs some mid 70's grams with the 15's, and that complies with some sort of driving restriction rule there.
Pretty obvious that the 17's are not so LRR.

 

For Gen3, CR got (approx numbers) 33 city 55 Hwy (44 avg)...the 33 is other-worldly (way too low) but they seem to hit other cars with the same crazy brush

 

If all your braking was pedal to the metal panic stops, you would lose all the regent. It would hurt all hybrids worse than conventional cars

 

Just FYI, ANL has a Downloadable Dynamometer Database providing some detailed test data.
Downloadable Dynamometer Database | Argonne National Laboratory
Looking forward to their results with Prius Gen. 4.