MPG decrease from 49.6 to 33-- Yokohoma (stock) to Assurance FuelMax?

Discussion in 'Gen 3 Prius Fuel Economy' started by blake schiafone, Aug 9, 2012.

  1. blake schiafone

    blake schiafone New Member

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    I replaced my stock 15" Yokohoma tires (30k miles) and put on stock 15" Michelin Assurance FuelMax. I've driven a little over 100 miles on the new tires and I am at 33MPG average. This coming from 49.6MPG, which was comprised of a 6k mile journey across the US (plus local driving after we moved to CA) with 2 passengers and 6 large suitcases.

    Something doesn't seem right. Nothing else has changed with the car. New tires were put on 3 days ago. I read others saying a break-in period, but that was factoring a 5MPG loss or so. How am I down almost 17MPG?
     
  2. ItsNotAboutTheMoney

    ItsNotAboutTheMoney EditProfOptInfoCustomUser Title

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    1) Check the tire pressures on your new tires. You could be running at low pressures. Tire installers often suck and set the pressure on the tires to the door jamb irrespective of current temperature, resulting in low pressure when you drive it. I forgot to check pressures when my new FuelMax's were put on and found them at about 30psi. My fuel economy improved noticeably once I pumped them up to where I wanted them.
    2) Maybe they screwed up in another way and your tires aren't properly balanced or something.
    3) You've moved so your driving conditions will have changed. If you're driving shorter trips in heavy traffic with the A/C on you'll be much less efficient.
    4) It could merely be a coincidence with the tires and now your 12V battery is shot or your new environment has exposed a problem. (Or maybe a neighbor is siphoning your fuel.)
    5) To be picky, "down 17mpg" is meaningless since the "value" of difference between mpg numbers depends on the starting point. You're up 0.01 gallons per mile. ;)

    PS I presume you meant Goodyear Assurance FuelMax
     
  3. MattPersman

    MattPersman Member

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    I never had the yokohama tires but stock Assurance FuelMax and am having no issues with MPGs. maybe if I get the yokos I can gain 17 mpg lol, i would buy today if that was the case
     
  4. jhinsc

    jhinsc Senior Member

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    You don't say where in CA you moved to and how your commute or local driving has changed from where you used to live. That could be a big factor in your mpg's.
     
  5. blake schiafone

    blake schiafone New Member

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    San Diego. But it doesn't matter and I'll tell you why...

    We've been here for 2 weeks now and driven 2,000 miles here locally. Doing manual calculations between fill-ups, I was averaging 50MPG. As soon as the new tires went on, and I'm talking literally driving a few miles, the onboard computer started dropping my remaining miles till fill-up fast. I think 270 to 230 within a few miles.

    Bought the car 6 weeks ago from a Toyota dealership. I never touched the tires inflation, but the dealership did. They had to fill one of the tires up with air before my purchase, and I'm assuming they did not inflate past a typical 30-33PSI. So with my new tires on, the PSI should be equal to what the Yokohoma's were. In practicality, if I inflated the old tires higher I would have 49.6MPG+.

    The car requires more pressure on the pedal to move. So to me this sounds like a rolling resistance problem? My girlfriend, who is car illiterate, even asked yesterday why at 40MPH on a slight downhill road was I not on full electric-- as we usually would be on this road in the past.

    My driving habits have not changed. I'm telling you, the only thing that changed were the tires.
     
  6. ItsNotAboutTheMoney

    ItsNotAboutTheMoney EditProfOptInfoCustomUser Title

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    If you don't know the previous tire pressures or the current tire pressures you don't know that only the tires have changed. That would just be an assumption. If they've had to inflate one of the tires you could have a slow puncture or slow leak in the valve. Please check your tire pressures. If they have to be raised get a new measure of fuel economy.

    (Also, are the tire sizes the same? Larger tires have higher rolling resistance.)

    But, even if you went from high pressure on old smaller tires to low pressure on new larger tires it's still an excessive drop.
    Anyway, please post answers here to the PriusChat mileage questionnaire (Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new | PriusChat) so people with more knowledge can help you.
    It might be a combination of things, including coincidental failure of your 12V battery.
     
  7. Codyroo

    Codyroo Senior Member

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    I'd guess something went horribly wrong with your tire change (no duh).

    1) Check your tire pressures. If you need to go out an get a pressure gauge, do so (they are useful to have).

    2) Regardless of what the dealer or other place may have done, set your tire pressures to what YOU want. Many of us, who like a combination of longer tire life and better MPG's fill the tires to Maximum cold PSI or close to Maximum cold PSI. I don't notice a difference in ride quality, but my Yokohamas lasted 50,000 miles and still had a little life in them when I traded tires.

    3) If, after checking and adding air to your tires, your MPG's are down, I would bring the problem to

    A) Shop A that put your tires on, to give them a chance to spot their mistake and make it right....OR
    B) Take it to Shop B and have them look at it. They will be much more willing to notice and point out Shop A's error since it will likely mean that you will frequent Shop B for your future maintenance or tire needs.

    It could be that when the tires went on, something else went wacky. A bad alignment, way underinflated tires, something went awry and you have brakes that are sticking, etc.

    I'd address what I could fix (1 and 2) and go to step 3 as soon as I could eliminate 1 and 2 as the cause.
     
  8. jhinsc

    jhinsc Senior Member

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    I suspect something happened to your Prius during your tire change, and that it's not the tires causing the lower mpg's. Could it be brakes, alignment, transmission or combo of things? Even non-LRR tires wouldn't cause this much of a drop.
     
  9. Codyroo

    Codyroo Senior Member

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    I agree. Taking care of the tire pressures will prevent them from saying "oh, the pressures were low, we filled them and it should be good to go". This eliminate one extra trip to the place that installed the tires, because

    1) the tire inflation will fix the problem (unlikely).
    2) It will prevent them from saying the pressure IS THE PROBLEM, when it is something else.
     
  10. GrumpyCabbie

    GrumpyCabbie Senior Member

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    I'm wondering how many miles were in the trip computer for it to display 49 mpg?

    Perhaps the previous owner had less of a lead foot? If the trip stored the last 3,000 miles at 49 mpg, then 6 weeks of you hammering around won't have reduced that much. Put new tyres on, reset trip and carry on driving as you have previously and all of a sudden your true mpg's are displayed.
     
  11. Insight-I Owner

    Insight-I Owner 2006 Insight-I MT + 2011 Prius

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    There are TWO versions of the Goodyear Assurance Fuel Max in the stock size for the Prius. The OEM one weighs 19lbs and has a pressure rating of 44psi. The other one weighs 18lbs and has a pressure rating of 51psi. The size is identical, and both are "LRR". You can see the difference on Tire Rack.
     
  12. F8L

    F8L Protecting Habitat & AG Lands

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    One is S rated and the other is H rated. The 185/65/15 only comes in an H rating I believe. That is kinda weird though since the 185/65/15 does not need such a high speed rating. lol
     
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