Does the Model V really get 2 MPG less?

You are correct sir.

15" Compare Tire Search Results

17" Compare Tire Search Results

 

I watched far too much video about The 2010 Prius on YouTube, so sorry I can't link or remember the exact clip, but at some Prius introduction event the Chief Engineer himself admitted a slight mileage hit if you choose the 17 inch wheels.

It get's debated as anywhere from 2-4 MPG.

It just make sense to me that you would take a hit. It also makes sense to me that driving style and other permutations and additions to any Prius can affect mileage. It's my opinion that one approach the addition of the 17 inch wheels with an advantage viewpoint not a disadvantage. For many people the 17 inch wheels offer a better look and drive feel and stability so it's an advantage they want. The straight across Mileage difference it might "cost" vs. and identical Prius with 15 inch wheels is in my opinion so slight that "if" you want the bigger wheels it shouldn't make a difference.

 

It may be better to compare the low rolling resistance tire sizes since this is what the majority of Prius owners will be purchasing.

 

...and don't forget that the CO2 emissions are worse with the 17" wheels too. In the UK CO2 increases from 89g/km (15" wheel on the Prius T3) to 92 (17" wheel on the T4 and T Spirit). As already mentioned above MPG is worse on the 17", a sacrifice I'm prepared to pay for the MUCH better looking bigger rims.