Max tire pressure question

Discussion in 'Gen 3 Prius Fuel Economy' started by TNGator, Jan 2, 2013.

  1. TNGator

    TNGator Junior Member

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    Last week I switched my wheels and tires out from OEM 15 x 6 wheels with 195/55R15 Good Year Fuel Max tires to 16 x 7 Drag DR9 wheels (16.55 lbs.) with 205/50R16 Good Year Fuel Max tires. ( I wanted a different look) At first I didn't notice any change in mpg's, but that soon changed. The temps went down into the 20's for lows and 30's for highs. I went from 48 - 50 mpg to 41 -43 mpg in just a few days. I assumed that the drop was due to the cold weather. This morning I decided to check the tire pressure in the new tires. 32 psi all the way around. I asked the guys that installed the tires to fill them up to 44 front, 42 rear. I guess that never happened. Anyway, I looked on the sidewall of the tire to check max pressure and I was shocked (51 psi). I ran 44 front, 42 front on my old set, because that was what I was advised to do by our members. Should I run 51 front, 49 rear on this set? Any thoughts? Also, I did block the lower grill 100% today.
     
  2. retired4999

    retired4999 Prius driver since 2005

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    You can set them at any thing you wish from 51 psi and below. just a ruffer ride is all. :)
     
  3. retired4999

    retired4999 Prius driver since 2005

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    Just remember 2 pounds less in rear.
     
  4. TNGator

    TNGator Junior Member

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    I've been told to do that, but I'm not sure why. Do you know?
     
  5. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    I adjust mine to get even tire wear, always staying below the max printed on the tire. Better MPG but wearing out the tire sooner is a false economy.
     
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  6. retired4999

    retired4999 Prius driver since 2005

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    On wet roads, snow ect. helps the car to track straight..:)
     
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  7. F8L

    F8L Protecting Habitat & AG Lands

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    At such low temps I would not suggest going too high unless your roads are very smooth and you generally travel at lower speeds.

    At temps below 45F your all-season tires become less pliable and they do not grip road irregularities as well as they do in warmer temps. This reduces grip and can actually cause a loss of mpg due to the tires skipping across those parts of the road and reducing forward momentum. It could also increased stopping distance.

    I would try running them at your usual 44/42psi for now and see how things go. The mpg increase from 44psi to 51psi would be very small anyway. Why risk yourself, others and your comfort for such a small gain?

    Here is a visual of what happens to all-season or summer tires in cold temps.
     
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  8. TNGator

    TNGator Junior Member

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    Thanks, I always wondered why. I'm going to run 51 front, 49 rear for now. I'm going for max mpg.
     
  9. xs650

    xs650 Senior Member

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    The manufacturer selects the air pressure the gives their desired handling and ride characteristics. The heavier end of the car usually, but not always, gets a little higher pressure.
     
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  10. TNGator

    TNGator Junior Member

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    Thanks man. Its getting too damn cold. I'll run them a little lower to be safe.
     
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  11. Judgeless

    Judgeless Senior Member

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    I have run 49 front 47 rear since Oct 2010. I have close to 100,000 miles on the car. Average MPG is 55. In the winter it drops because of differnt gas and my remote start.
     
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  12. TNGator

    TNGator Junior Member

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    Thanks Judgeless... How much does it drop in winter? I'm new to this and want some sort of baseline comparison.
     
  13. F8L

    F8L Protecting Habitat & AG Lands

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    Depends on your location and commute type. I lose 5+mpg and I live in a pretty mild climate. The more rain and freezing temps you have to deal with the worse the hit.

    In short you have to deal with:
    Winter fuel
    Longer warm up times
    Dense air is colder thus increasing aerodynamic drag
    Tire rolling resistance goes up in cold temps
    Rain/water on the road dramatically increases rolling resistance
    Heater/AC use (exessive) dramatically reduces mpg
    Time spent idling to warm up car and/or defrost windows
    More time spent idling trying to keep the engine and emissions system hot

    For more check this thread.
    Why mileage gets worse in winter | PriusChat
     
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  14. TNGator

    TNGator Junior Member

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    I was worried about that. My wife took my car out tonight. My mpg's are way off now, thanks hun!!! LOL!!! It really is like a video game. I'm a 43 yr old teenager still playing pac man. My new years resolution is to get into the 600+ club.
     
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