2016 Prius Two MPG changed after switching 15" rims to factory 17" ones

Ultimately it seems that intelligent customers have a responsibility for making rational decisions. Sadly the laws of physics are pretty hard to get around. It's well known in the car world that larger wheels are not the hot ticket for efficiency, but they definitely improve handling responsiveness. Given Toyota's extreme obsession with reducing weight and drag with these cars (heck, my car doesn't even have a rear wiper), how could anyone believe that going from skinny high pressure 15" tires to wider lower pressure 17" tires not hurt fuel economy?

 

Oddly on 2016, Prius Car and Driver got both higher skidpad speeds and shorter stopping distances with the two Eco with 15 inch wheels than the Four touring with 17 inch wheels.

 

If you look for the Thread in Priuschat regarding tires and mpg, you will find that extensive research has been done on this by are esteemed members here. Make sure you put aside some long reading time, as you will need it.

 

Lots of useful data by all who posted before me. Appreciate all those who
offered their expertise, comments, charts!

You have to think that whatever you add or modify from
the your Prius from the dealer, will reduce your mpg, then you won't be surprised by any drop
in mpg.

From the poster's original numbers, using $2.50 per gallon, driving 12,000 miles per year,
the 5 mpg loss for having nicer rims/tires, costs about $60 more per year. Not a whole lot
for improved stance/appearance. 6 less Starbucks visits!
I wanted the 4 Touring initially, but wife wanted moonroof. Had to get the 4, and 15" tires.
Getting 60 mpg, so all is good!

With other manufacturers catching up to Toyota on mpg numbers, Toyota engineers
are looking for areas to improve mpg efficiencies. Drag coefficient, weight, rolling resistance, etc.
All this while trying to have an appealing external appearance, so they can sell their cars.

stt

 

Be sure you have the correct MIJ/OEM tires and try 42 PSI.

You should take a slight hit but my MPG has been phenomenal so far.

 

Yep, hard to have hard facts without hard facts.
Tires that are made in different factories by the same company have different results. When I am careful how I drive I get 74MPG easy even with AC and cargo. If I drive like an idiot I can get in the 60s. Rain and high speeds kill MPG more than anything. Hard rain (100 proof) will drop me in the 50s depending on how fast I drive.

I bought the touring because of how the car feels when I drive it. It is a pleasure to drive BTW.

 

Can we start drinking now?

 

now that would just spoil everything. must wait until seven o'clock... must wait unit seven o'clock... must wait...

 

Hot donuts Friday. 4.95 a dozen at Krispy Kreme. Wonder if the extra Krispy Colonel eats Krispy donuts?

 

do they have a supercharger?

 

In my case, I relied on the fact that Toyota published the same fuel economy standard for my 4 Touring with all its many features as that of the other (non-eco) models.

Your point that common sense should have trumped that claim has some merit.

Everything else being equal, one should probably assume that the extra weight of a sunroof on the 4, or different tires on the 4 Touring would reduce the fuel mileage some, right?

The thing is, everything else was not equal with those models. Not only do they lack a spare tire, in my case the front door windows are a lighter weight laminated glass.

In the case of the extra weight of a sunroof, the mileage delta (thanks to physics) seems hardly noticeable.

In the case of the 17" tires (you know, the ones picture in all the ads) the mileage penalty is pushing 10%.

Was it my responsibility to know that before I bought tha car when Toyota claimed this model was equivalent to the others?

Shame on Toyota.

 

until i learned about it here, i sometimes wondered why all models with different packages had the same mpg. especially on my wife's 2008 hycam, which came with larger than standard wheels, but showed the same mpg as the base.
i don't think it should be the buyers responsibility, that's why we have the epa and the maroney. but it takes political action to overcome mfg.'s desire to hide the truth.

 

I will throw out this idea. When there is water on the road, a wider tire has to plow through more water and thus more resistance to be overcome, and thus more fuel burned.
A possible analogy, cross country skis are very narrow. The skier is providing the motive force and the less resistance the better. Alpine skins are much wider, and can be because gravity is doing the work for the skier.

 

Logical. I think 4 donuts would really improve MPG but not my health. Who can eat just 4 hot ones anyway.

 

I once read that each test costs in the neighborhood of ~$250k by people who know what they are doing. So many things such as as compressed natural gas conversion kits are not available in the USA because of the testing costs. However, sometimes the EPA conducts the tests and we see there is a range of MPG as a function of model and other variations:

We've got better models but as VW has shown, the system can be fooled. It is a problem of regulations and costs and I don't have a good answer. But I know the effect is testing costs have become a barrier to better technology in the market place.

Bob Wilson

 

It is interesting to note that England takes the mileage (and attendant increased greenhouse emissions per mile) hit of the Prius' 17" tires so seriously, they they tax those who buy those tires hundreds of dollars more every year.

To me it is not so much a testing issue, as a presentation of the findings issue.

I would be more or less OK with a single EPA estimate, if there was a notation stating that actual mileage will be significantly impacted by one's choice of equipment and/or model number.

My problem is that Toyota assigns a specific mileage estimate for a model that by definition includes only 17" tires, when they know full well (as evidenced by thier experience in England) that those tires decrease mileage by up to10%.

Make no mistake about it, that impact is not trivial. Prius buyer's value the engineering that goes into these cars, and to tack on pretty wheels without disclosing the impact on mileage (and greenhouse gasses!) is just plain wrong.

This is legal, but in some ways akin to the mind-set that VW is paying for now. Leadership at Toyota (and the automotive press) should simply not tolerate it.