Remove spare tire, how much mpg gain?

Discussion in 'Gen 2 Prius Fuel Economy' started by carbon, May 1, 2013.

  1. carbon

    carbon The Knight Templar

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    Baiscally the title. If I removed the extra weight the spare tire is giving me, would I see a significant mpg increase? I have roadside assistance so I really don't need that thing in there I suppose.
     
  2. -1-

    -1- Don

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    :ROFLMAO:Interesting. You have regular Prius owners removing their spare tire to reduce weight and improve fuel mileage. Plug In owners adding spare tires to their Prius. I did. Are we confused?
     
  3. nh7o

    nh7o Off grid since 1980

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    Weight matters less on flat land. So it all depends on the terrain you drive.
     
  4. Rokeby

    Rokeby Member

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    I'm guessing that the donut spare weighs ~30 lbs. max.
    Add the jack, maybe 35 lbs total.

    Weights removed affect mpg when accelerating, basically from stops and up hills,
    although changing the direction of a vehicle is an acceleration. That said:

    "...if the vehicle weight decreases by about 156.26 pounds (or roughly 150 pounds),
    the fuel economy will increase by 1 mpg."

    This figures out to a 0.22 MPG gain for a 35 lb weight reduction.
    Another source says 0.4 MPG.

    It's far more likely that you'll be seeing meaningfull passive MPG gains as the result of
    rising Outside Air Temps ( up to ~80 degF)...

    or from actively changing your driving by trying "driving without brakes," inflating
    your tires to 42front/40 rear, or lowering your typical cruising speed by 5 MPH.
     
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  5. uart

    uart Senior Member

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    35 Lb is about 1% or the cars mass, so I'll estimate about 0.5% improvement in MPG. So yeah, about 0.25 MPG sounds good.

    Edit: Trying to add an adjustment for "typical" hills and descents, or acceleration and deceleration, I'll add another 0.2% to that estimate.

    So I'll estimate 0.7%, which I guess is going to be around 0.35 MPG savings for the average driver.
     
  6. Mike500

    Mike500 Senior Member

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    Gut the interior of the car and get rid of every ounce possible. You'd surely increase MPG's.

    NOT for me.

    Getting towed for just a flat tire, even if you have road service is NOT an option for me.

    I even bought full size spare.
     
  7. boppo

    boppo Active Member

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    How much does the engine weigh? :)
     
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  8. iClaudius

    iClaudius Active Member

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    I was carrying a full size spare over the winter and didn't notice much difference in mpg when I removed it.
     
  9. F8L

    F8L Protecting Habitat & AG Lands

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    Aye, it's not worth the inconvenience or risk of being stranded. If you are competing then go for it. Otherwise keep the spare.

    Just buy more efficient tires when the time comes. ;)
     
  10. wjtracy

    wjtracy Senior Member

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    ^^^ here is an equation I stole from the Chevy Cruze chats.
    My intent was to post this this on the spare tire thread but I will offer it here.
    Think it says +50-lbs is -0.6 MPG at 50 MPG for 3165 car weight (PiP).
    <:ASIDE>
    ...here's an equation that approximates the WT vs. MPG trade-off:​

    (MPG2/MPG1) = (WT1/WT2)^0.72
    ...where:​

    MPG1= prior fuel economy, mpg​
    MPG2= new fuel economy, mpg​
    WT1 = prior weight, lbs​
    WT2 = new weight, lbs​


    addendum: equation is valid for vehicles in the 3,000± weight class (per GM engineer).​

    Read more: http://priuschat.com/threads/better-economy-at-the-top-of-the-tank.123507/page-2#ixzz2Sa7lhW00
     
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  11. uart

    uart Senior Member

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    So if you put the weight of the Prius (about 3400 lbs assuming typical passenger + luggage loading), and the added weight of the spare at 35 lbs as estimated above, this equation gives a result of 0.73% loss. Almost exactly the same result as my previous estimate. This proves I'm good, haha :cool:
     
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  12. F8L

    F8L Protecting Habitat & AG Lands

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    We already knew that. :p
     
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  13. wjtracy

    wjtracy Senior Member

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    Only proves you qualify for work at Government Motors. If you have not yet received an email from Toyota, that probably means the Toyota engineers have a better equation!

    Made me realize part of our MPG problem is our Prius is now in serious GP (grand parent) service. We have two hefty car seats - must be 50-lbs each empty - and a big stroller in the hatch. GP service also means shorter trips. But we like it.
     
  14. dbcassidy

    dbcassidy Toyota Hybrid Nation, 8 Million Strong

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    WOW, if one could always drive downhill - what great mpgs!
    Seriously, removing the spare tire do not increase mpgs.

    DBCassidy
     
  15. Mochabuzz

    Mochabuzz Junior Member

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    It shouldn't make much of a difference to reduce the cars weight by 35lbs
     
  16. bisco

    bisco cookie crumbler

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    less than 1 mpg i'd venture...
     
  17. TheEnglishman

    TheEnglishman Member

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    Even if it really did improve mileage by 3 MPG I don't think I'd feel safe parting with it. I have triple-A roadside assistance and a cell phone, but what if I'm in a location where my cell phone doesn't work? I'd be stranded, possibly for hours. I'm getting about 51 MPG average right now and I feel like that's a lot to me. I won't sell my peace-of-mind for a few extra cents in savings at the pump.
     
  18. N3FOL

    N3FOL Member

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    I will not leave my spare tire. LOL.
     
  19. PriusGuy32

    PriusGuy32 Prius Driver Extraordinaire

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    This is a funny thread because I did remove the spare tire on my old departed SUV for weight savings BUT if you can get 35lbs out of the Prius you gain about .73mpg? I just lost 21lbs over the past 4 months. So if I lose 14 more, I will gain .73mpg just from that? lol
     
  20. uart

    uart Senior Member

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    No, the estimate was about 0.7%, so realistically more like around 0.3 to 0.35 MPG.

    BTW. It's interesting that the "googleleadservices" ad at the top of this thread is now showing a fat/weight loss ad for me. Oh well, at least it's a change from how they usually "profile" me and display ads to "meet mature women". :D
     
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