Prius II,III,IV vs. V Fuel Economy

and yet, strangely, the stickers say they are the same.

 

What is your average mileage on the V if you don't mind posting?

The EPA does not seem to note any difference so I wonder if this is a flaw of the rating system.

 

More like a loophole or allowance that the car makers strive to fit through.

 

I get about 45mpg in my V, but I'm still experimenting to try to improve on that. For example, I'm keeping eco mode on all the time now, turning off a/c, etc. Increasing tire pressure up to the rated 40psi max of my tires didn't seem to help all that much. If all you do is make 10min rides, to and from work, you'll never get 50mpg because it takes 10min of driving to fully warm the car up to get a mileage in the mid-40's or better.

 

I've been wondering about this for a while. I've read where there is a difference between the II,III, and IV's and the V's in terms of mileage, I thought I also read where the overall circumference of the 15's and 17's were close to the same.
I'm still reading up on this car. This is the first definitive side to side comparison between the 2 sub-models..
I don't blame you. The wheels on the V's give the car a much better look, although if I were to spend that much on a car, I'd probably just revert to my gear-head roots and get a Camaro, or another Miata!...

 

I have read somewhere that the MPG rating is based on an average for similar models within a manufacturers product line. The numbers that I saw way underestimated Prius V sales so the average given is closer to what the II-IV are rated at than it should be.

I can't find my source for that so take it all with a bigger grain of salt than you would if I had quoted a source.

Edit:
This isn't specific enough but does talk a bit about averages. The details are probably buried someplace else in the CFR
http://edocket.access.gpo.gov/cfr_2010/julqtr/pdf/40cfr600.510-08.pdf

 

Consumer Reports repeatedly found a 2MPG diff with the 17" wheels on the last Gen Prius, so I think 2MPG worse is a safe bet. Since this is averaged over all Priuses, that means my level II is slightly better than the sticker In any case, a barrel of oil is now double what it was 2 years ago, so I'm VERY happy i have a Prius.

 

They are able to use an average instead of lowest common denominator.

 

Just use the basics:

With all specs the same except accessories, which ever vehicle weighs the most, will get less fuel economy.

If yours has a sunroof/heavier wheels/Amps with speaker boxes. And one thing most do not take into account, YOU. Your weight? Your passengers weight? The weight of your storage area?

So, with all things being equal (same tires/same PSI/same accessories), to gain more MPG....lighten your load.

 

Most folks on PriusChat seem to agree that the V gets worse mileage, by about 4-7%, because of the larger wheels.

For those of us to whom this makes no intuitive sense, why is this so?

 

Primarily a difference in tire rolling resistance, the wider tire also contributes to poorer aerodynamics but that might not be significant.

That sounds high until you work the the numbers.

If you assume it takes rear wheel horsepower 15 hp to move a Prius at 55 mph, that is 102 lb of total drag plus rolling resistance. 4% of that is 4 lb, or 1 lb extra rolling resistance per tire per tire.

 

The larger rims are also heavier. This contributes to the unsprung weight, which is a greater detriment (by about 4x, I think) than sprung weight, like the load inside your car.

 

The official EU test that are used for taxation of vehicles says its worse for the 17" tires:
17" tires 4.0l/100km (58.8mpg)
15" tires have 3.9l/100km (60.3mpg)

The EU test cycle gives quite optimistic numbers, but the procedure to conduct the tests is quite rigorous. So the numbers are in that sense quite reliable.

 

That 2% difference is entirely consistent with the 2-3% difference Toyota's chief engineer stated when the car first came out. Based on my short-trip driving, I usually only get 40 to 42 mpg (sometimes even less in cooler weather). Looks like I would only raise that by 1 to 1.5 mpg if I switched wheels. That's not enough for me to justify giving up the looks and greater stability the 17" wheels give me, though there are days I think I might prefer the softer ride of the 15" tires.

 

Rotating weight on the wheel/tire will be less than 2X th eeffect of non-rotating weight unless it's right smack on the tread surface in which case it will be 2X.

They are called the laws of physics and not the suggestions of physics for reason.