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Ignorant new owner: 17" wheels, narrow sidewall tires and EPA mpg estimates

Discussion in 'Gen 3 Prius Fuel Economy' started by Badger2, Feb 24, 2014.

  1. Badger2

    Badger2 New Member

    Joined:
    Feb 24, 2014
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    Vehicle:
    2014 Prius
    Model:
    Five
    Greetings all!

    First, a hearty "Thank you!" for all I've learned the past two weeks since we took deliver of our 2014 Prius 5. Wish I had stumbled onto this forum before the purchase. Nevertheless, we're delighted with the Nautical Blue car, "Isobel."

    She came equipped with 17" wheels and Bridgestone P215/45R17 87V Turanza EL400 02 tires. I know nothing about tires, but was not unhappy to have the 17" wheels, thinking the larger the wheels the further the car rolls with each turn and, therefore, better mpg. Now I'm reading posts which tell me nope, that the 17" wheels, all other things being equal, yield poorer mileage. Where am I wrong? Is it because the narrow sidewalls make for a smaller diameter tire? Further, if it's true the 17" wheels yield poorer mpg should this not be reflected in the EPA estimates printed on the sticker? I drove the car home from dealer 50 miles in hilly country (Olympic Peninsula in Washington) and logged 50.1 mpg which I thought was pretty good first spin for someone who had never driven a Prius. Now, after 750 miles on the clock, am averaging just under 50 mpg in mostly country trips of 10 to 40 miles.

    I'm not a physics major, but the wheel diameter issue has me curious. Also can you enlighten me about how the EPA estimates mpg? Seems wheel diameter would be a pretty important variable.

    I love all the stats people throw around in this forum. Sloppy science, but my former chancellor always told me that without data, you're nothing but a guy with an opinion.:rolleyes:

    Thanks!
     
    #1 Badger2, Feb 24, 2014
  2. vskid3

    vskid3 Active Member

    Joined:
    Jun 23, 2013
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    Location:
    Texas
    Vehicle:
    2005 Prius
    Wheel size does not dictate the tire diameter. The tires that come with the 17" wheels are 24.6" in diameter, the 15" tires are 25". That's about a 2% difference and the transmission pretty much eliminates any advantage of diameter. Your tires are wider, though, which increases their rolling resistance and decreases aerodynamics by a bit. The wheel and tire probably weigh more, as well. That means it takes a little more energy to get them spinning.

    50MPG is good for a new owner, there are plenty of people who have had their car for years and still don't get that high. I wouldn't worry about the wheel size unless you don't like the way it handles. If you do want to swap, test drive a Prius with 15" wheels before deciding, to make sure you'll like it.

    The EPA tests don't have to be redone for minor changes, mainly just different engines and transmissions.
     
    #2 vskid3, Feb 24, 2014
  3. hybridbear

    hybridbear Member

    Joined:
    Aug 19, 2013
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    Location:
    Minneapolis
    Vehicle:
    2013 Prius
    Model:
    Persona
    The EPA window sticker applies to the trim level/wheel combination that is sold in the highest volumes. The majority of Prii do not have 17 inch wheels like yours or ours, and thus the EPA MPG figures are not based on 17 inch wheel MPGs.

    The Prius doesn't have any trim MPG variations even though the higher trim models likely would have lower MPG numbers because more features means more weight. The Camry has EPA numbers for both the LE and XLE hybrids. This is likely because the XLE hybrid is the higher volume model which is required to be tested per the EPA. But since the XLE is heavier and thus less efficient, Toyota decided to also test the LE model on the EPA cycles. The LE model has higher EPA MPG numbers which they can thus publish and promote, even though the XLE is the higher volume model.
     
    #3 hybridbear, Feb 24, 2014
  4. Badger2

    Badger2 New Member

    Joined:
    Feb 24, 2014
    3
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    Vehicle:
    2014 Prius
    Model:
    Five
    Thanks folks,

    OK, I may have purchased the wrong model, but I'm thrilled with the car. Can I live with high 40-low 50 mpg? Yes! It's a whole new driving experience and I like it. Not an old MG - much better than that, but the drive by the seat of your pants feel is surely there. Now to convince my wife that it rewards careful driving and punishes aggressive driving. In our little community of 300 families, there are over 30 Prii. I'm happy to have joined the club.

    Regards
     
    #4 Badger2, Feb 24, 2014
    hybridbear, retired4999 and F8L like this.
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