Help -10% Mileage Drop with New Tires!

Discussion in 'Prius v Fuel Economy' started by Tonydavid, Sep 16, 2018.

  1. Tonydavid

    Tonydavid Junior Member

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    Two weeks ago I put 4 new Goodyear Assurance Fuel Max Tires on my 2014 Prius v. They replaced the original tires that had 50K miles on them and were very worn. I was consistently getting 44 miles/gal since I purchased car with 33K miles on it. With the new tires I am getting 39. I am frustrated because I thought I did my research and was told that the Goodyear Assurance Fuel Max Tires would get good mileage. Any thoughts, help or suggestions?
     
  2. fuzzy1

    fuzzy1 Senior Member

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    (1) We normally expect a temporary MPG reduction with new tires, until they are 'broken in'. Though 10% is too steep for that alone.
    (2) What is your tire pressure now? What was it before replacement?
     
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  3. Air_Boss

    Air_Boss Senior Member

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    Ditto the above remarks.

    It typically takes several thousand miles for the tire friction surfaces and siping to 'bed in'.

    Be sure the tire pressures are what you previously ran, if not the high recommended pressures we typically see quoted -- 38-42 psi front, 36-40 psi rear. (We run 42/40.)
     
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  4. rdgrimes

    rdgrimes Senior Member

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    From the marketing pitch:
    "offering long wear, wet traction and low rolling resistance"

    The sad truth is that there's no such thing as one tire that does it all. You get tread life or LRR, but not both. You get traction or LRR but not both. Goodyear is claiming all three in one tire - not likely. It may be a tire that offers tread life and traction with better MPG than most. Pump them up and see how they work out. Honestly, the difference in cost for a really LRR tire doesn't justify paying more for it unless gas is at $4/gal and the tire gives you 3-4 MPG more.
     
  5. bisco

    bisco cookie crumbler

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    need break in as mentioned, but also, new tyres have larger radius, affecting your screen average and miles driven. nothing you can do about that.
    put a few tanks on her and report back with hand calculated total average
     
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  6. fuzzy1

    fuzzy1 Senior Member

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    With modern steel belted radial tires, inflated and loaded to their normal working range, radius change has very little impact. The contact patch on the ground is flat, not round, so the normal circle equations don't work out as expected.

    What matters is the rolling circumference, controlled by the steel belts beneath the wear portion of the tread. This controls the "Revolutions Per Mile" specification on the tire's datasheet. A little bit of arithmetic will reveal that this doesn't match up with the turns you'd expect from the radius if the tire acted as a perfect circle.
     
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  7. farmecologist

    farmecologist Senior Member

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    I put a set of Michelin Defenders on our 2012 Prius v (wagon). Sure enough, I took around an 8% MPG hit. However, after a 5,000 mile road trip I'm happy to say that things are back to normal. So hang in there!
     
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  8. Rmay635703

    Rmay635703 Senior Member

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    Add more air to your tires until they “break in”
     
  9. Tonydavid

    Tonydavid Junior Member

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    THANK YOU so much for all your helpful replies! You guys are AWESOME! Each of you has such great experience and wisdom and are so generous in sharing it. I will test the tire pressure tomorrow and adjust as necessary. I will be patient - I did not know about "break-in period." Thanks again
     
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  10. Mendel Leisk

    Mendel Leisk 'Orrible Oracle

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    Everyone's piling on, saying new tires take time to deliver their best LRR. Maybe yes, maybe no, but several times I went to new EP20 and they REALLY hit the ground running, great mpg from the moment they were put on. So, I'm a little sceptical, and suspect the break-in adage is at least in part created by tire dealers, to blow-off customers.
     
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  11. Kenny94945

    Kenny94945 Active Member

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    There's some good answers above.
    Especially new circumference vs. old.

    Perhaps best for the OP:
    1) Report back in 5000 miles
    2) Bump air pressure a few pounds.
    3) Check wheel alignment, not mentioned, could be a good thing too.
     
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  12. farmecologist

    farmecologist Senior Member

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    Yep, we are all tire dealers here. :whistle:

    Seriously though...of course EP20's will give you great mileage. They are one of the premiere LRR tires on the market. We are not talking about that here. Rather, we are talking about going from the 'original' tires ( which I'm assuming were a 'good' LRR tire )...to new 'not so good LLR tire' that is certainly not one anywhere new one of the 'good ones'.

    • Edit: Question...I'm assuming Toyota does use a 'good LRR' tire as original equipment on the Prius v (wagon)? If not, that would certainly affect my reasoning. o_O

    I have never had brand new 'non LRR' tires get better mileage than what I previously had on. However, I'm basing this on Michelin tires ( usually Defenders ) that have an extremely high treadwear rating and a pretty deep tread. Perhaps that could have something to do with it? At any rate, I have had Michelin Defenders on three vehicles so far and have noticed that all three vehicles needed a 'break in' period.

    Of course, talking about tires is like talking about oil...or religion :D...so there is that! (y)
     
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  13. Mendel Leisk

    Mendel Leisk 'Orrible Oracle

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    Yeah I like the Defenders, got them for our son's Civic one time. They're a good balance. I drove his car across town to the airport, pretty much right after installing them, and found them very easy rolling. If they were available in 215/4R17 they'd be on my short list, too bad they aren't. :(
     
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  14. burnout8488

    burnout8488 Member

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    How does "break-in" actually effect rolling resistance?

    Do they get harder as they break-in? What exactly causes the better mileage some people report after a tire breaks in?
     
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  15. Air_Boss

    Air_Boss Senior Member

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    The tire contact patch becomes smoother and more 'LRR' as the mold flashing and sipes are -- for lack of a better analogy -- 'sanded down' by thousands of miles of road contact and a million or so revolutions (at 832 to the mile). Prior to 'smooth', deformation and hysteresis of the tire flashing and sipes as they come out of the mold generate heat, which lowers 'LRR' and MPG.
     
    #15 Air_Boss, Sep 17, 2018
    Last edited: Sep 17, 2018
  16. Merv Himself

    Merv Himself Junior Member

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    Are you sure you don't have a hub problem? I fixed a very similar problem by replaceing a wheel hub with bad bearings. If you are hearing any slight "scraping" sounds, this could be the culprit, not the tires.
     
  17. Tonydavid

    Tonydavid Junior Member

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    GOOD NEWS - UPDATE.....Hi guys....thanks for all the responses. I am happy to report that after that initial drop in mileage with my first tank with the new tires....that my mileage has returned to normal!!!! I was very relieved and thrilled. So, I know there was some skepticism about the "breaking in" theory but there is anecdotal evidence, at least in my case, that there is something that decreases mileage initially. As always, you guys are awesome....Thanks for the advice, recommendations and help.
     
  18. Air_Boss

    Air_Boss Senior Member

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    Glad to hear it's working out.
     
  19. farmecologist

    farmecologist Senior Member

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    Yep..I have noticed a similar 'break in' period with two sets of Michelin Defenders. However, it took more than one tank of gas for me.
     
  20. padroo

    padroo Senior Member

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    On my 2008 Prius every time I put new tires on it my MPG went down. The last set were a no name non LRR but the second set were Michelin A/S LRR tires, I forgot what model. I never hit 50 mpg in the summer again. With mpg on the decline I kind of lost interest in hypermiling.
    When I got my Gen 4 it all came back.
     
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