Mpg decrease after getting new tires?

Discussion in 'Gen 2 Prius Fuel Economy' started by MindHalfGone, Feb 13, 2019.

  1. MindHalfGone

    MindHalfGone New Member

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    Hello, I'm sure there are tons of forums on this but have not been able to find any good responses or fixes. About a month ago I changed the back tires from good year assurance tires to Hankook st 88t tires, the mileage did not decrease until about a week ago I had the front 2 assurances replaced with another set of 2 hankook st 88t tires. Since then I've seen a pretty bad drop in my MPG, it is winter but I live in socal so the temps dont go lower than 50 until late at night/early morning. I change my oil regularly (synthetic) just put a new air filter, had the Hybrid battery changed with a 5 year warranty. The tires seem to be the culprit, would breaking these tires in cause my mpg to drop so significantly, I was getting over 400 miles per tank and now I'm getting 340 to 350...

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  2. bisco

    bisco cookie crumbler

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    welcome!

    i hate to say it, but it's more likely the rebuilt hybrid battery, but.

    the best way to track your mpg's is a manual calculation every time you fill up. then watch the long term averages.
    the gen 2 has a fuel tank bladder which wreaks havoc with capacity, and thus, tank miles or mpg calculations.
    and 50 degrees is nothing to sneeze at, batteries start to lose performance under 70 degrees, not to mention engine warm up and temp maintenance, along with any cabin heat you may be asking for.
     
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  3. litesong

    litesong Member

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    On our two Elantras (auto & manual), we have Goodyear Assurance Touring tires on one & a mix of Hankook 431s, Yokohamas, & Kumoh Solus tires, all of greater tread width & sometimes, greater height than the Assurances. As I have changed the various brands, I have NOT determined any greater fuel consumption among the three & can NOT state that I find them, either more or less, efficient than the Assurances on the other Elantra. I have always gotten good MPG with my cars, whether the cars &/or the tires have been new.
     
    #3 litesong, Feb 13, 2019
    Last edited: Feb 13, 2019
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  4. George W

    George W Active Member

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    With new tread it's possible you could benefit from a wheel alignment.
     
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  5. dolj

    dolj Senior Member

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    I hate to say it as well, but I agree with bisco. It is your rebuilt battery that is the most likely cause.
     
  6. MindHalfGone

    MindHalfGone New Member

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    Thanks!

    Why would you assume its the rebuilt battery? I still have a 4 year warranty on it so if that's the case I can get it swapped, I was getting great gas mileage before i switched the front 2 tires, I was also told I do need an alignment but am fighting with my insurance company to have it fixed because of issues I had last year. Could having the 2 new tires put on with my alignment off cause the MPG to drop and i'm noticing it more with newer tires? (Odometer is 137k+) miles.

    Also I checked the 12v With the diagnostic menu the car offers, It was at 14 volts when the car was turned on and running. I do also know that the cold can cause a MPG drop but it just seems so SUDDEN, If it is the Rebuilt Hybrid Battery I'll be taking it in to my mechanic and have him test it to make sure that the rebuilt battery is still working as it should.

    What PSI do you recommend? I'm just going with what the car says with 35front and 33rear.
     
  7. MindHalfGone

    MindHalfGone New Member

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    Yes, I have been told this. Waiting on my insurance to have this problem fixed, do you think I would notice the MPG drop more with newer tires and the alignment being off? Because the alignment has been off even before the 2 new front tires, new tires = more noticable?
     
  8. dolj

    dolj Senior Member

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    That is fine. Just remember to check them often and particularly when the weather changes. When it gets cooler the pressure in your tires will fall. It only takes 1 or 2 PSI lower than what you're running to affect the MPG.
    There shouldn't be any effect because of the alignment. The only way you would notice anything would be the new tires, and the MPG would only be less if the new tires had a higher rolling resistance when compared to the previous tires.

    If the Hankooks are the Kinergy variant, then they are supposed to be LRR, but they still might have a higher RR than the GoodYear Assurances.
     
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  9. bisco

    bisco cookie crumbler

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    if it happened when you put them on, it would make sense. but dropping after month doesn't.

    rebuilt batteries can be sub par, affecting mpg, but not throwing a code.

    i think it would be best for you to track a few tankfuls and calculate your mpg's.

    how long have you owned the car?

    the 12v volt needs to be measured with the car not in ready
     
  10. MindHalfGone

    MindHalfGone New Member

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    I understand rebuilt batteries can be sub par depending on where you get them, My mechanic is a Aes certified mechanic and he has been amazing to take my car to. I've owned the car around 2 years now.

    I just measured the 12v when the car is not in ready and it dipped to 11.7-11.9 (did I find my problem)

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  11. The Electric Me

    The Electric Me Go Speed Go!

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    I think it's the tires.
    New Tread has a higher rolling resistance.
    If originally you had new ONLY on the back, and didn't notice a decrease until putting new on the front? I'm going with the tires, as the Prius is front wheel drive. The new tires on the drive wheels have lowered your MPG. I would expect it to improve with better weather and as the tires break in.

    If it was your Hybrid battery, I'd expect some inconsistency on your battery charge display and/or some codes. You don't seem to be displaying any other symptoms BUT lower MPG.

    I could be wrong. But I'm putting my money on tires. Also..maybe an alignment would help.
     
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  12. The Electric Me

    The Electric Me Go Speed Go!

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    Please note, I said I could be wrong.
    The good news (bad news) would be, if it is your Hybrid Battery, you'll eventually know that for sure. As your mileage will not improve and more symptoms will arise.
    But let's be optimistic and just hope it's the tires.
     
  13. George W

    George W Active Member

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    it made a noticeable difference in my case, and I only had 1 wheel off by 2 degrees
     
  14. George W

    George W Active Member

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    Many here use a balance of 42 front, 40 rear. The tires` max psi is stenciled on your sidewalls. In my case the 16" tread has 55psi max, so I use the 42/40 to minimize road contact, but not high to create the bouncing sensation.
     
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  15. bisco

    bisco cookie crumbler

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    borderline 12v. more testing would be needed, probably a load test. how old is it?
     
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  16. MindHalfGone

    MindHalfGone New Member

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    Older than I know, lol. It's been in the car since i bought it.

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  17. willakwin

    willakwin New Member

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    it happens some time i also feel this issue in 24 Hour NYC Towing Services truck, i was thinking that maybe there some issue in the vehicle after some research i realize that it's normal. no need to worry about this.
     
  18. bisco

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    worry about what?
     
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