Nitrogen and Air tires on same car.

Discussion in 'Gen 3 Prius Fuel Economy' started by Reaper, Apr 24, 2015.

  1. Easy Rider 2

    Easy Rider 2 Senior Member

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    Not in any intelligent, unbiased debate.

    The ONLY real "problem" with plain air is that it is "wet".
    That is, it contains a high percentage of water vapor........due to being compressed.
    It is the water vapor that causes the biggest changes with temperature.
    It is the water vapor that encourages corrosion....if there really is any at all.

    Plain air that is properly dried is just as good as pure nitrogen.

    For those applications where tires are critical.......airplanes for instance......a bottle of dry nitrogen is easier to use and maintain than a compressor with a dryer.

    For common consumer vehicles it is great for ONLY one thing; boosting dealer profits.
     
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  2. Reaper

    Reaper Junior Member

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    So what you're saying is that If you go fill up your tire with regular air you're most likely going to get water in the tire. So over time it could cause the tire to go bad, wear out the tire, cause the tire to lose its integrity, hurt mpg, lose tread life, etc.... So nitrogen would be better for the tire then. You just answered my original question.
     
  3. Mendel Leisk

    Mendel Leisk Titanic Social Director

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    I think gas station compressors are "supposed" to dehumidify the compressed air, somehow. I don't know the first thing about it. I do know I've never had a problem with regular air. FWIW I always air up at Chevron, it's the old-fashioned, free air there.
     
  4. DoubleDAZ

    DoubleDAZ Senior Member

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    If you own a portable air compressor, they usually tell you not to leave air in it because of the condensation that occurs. That's why there's a valve on the bottom. The instructions for mine recommend opening the valve when pressure gets down to the last 20psi and sometimes there's a spot of water on the floor depending on how long I've used it and how humid it is. My guess is that any condensation that might form in a tire would be dealt with when the tire warms up through normal driving. When I worked in service stations part time and changed tires, I never noticed any moisture, though I wasn't really looking for it. I'm not sure the moisture would damage the tire, but I suppose it could damage old steel wheels if there was enough of it for a long period.
     
  5. wjtracy

    wjtracy Senior Member

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    Reaper- Consumer Reports has an article on this about 2008. The only cited benefit of N2 for regular cars is that it leaks more slowly. Let's say you did not re-fill your N2 tires until they lost 3 psi. At the same interval of time, your black sheep air tire might be down 5 psia. This will cause a slight drop in MPG, if and only if, you don't fill the tires with more pressure. Since oxygen does leak a little faster eventually you end up higher N2 anyways.

    Re: temperature effect: there is no difference betweeen air/N2 which is exactly what the text you posted says: no difference. You don't care much about moisture either, unless you're a race car driver. As the tire temperature approaches the boiling point of water (212F) your tire would gain pressure if you had water in it...this is unacceptable for race cars, but not for us mortals. Race cars and trucks benefit from the N2 also as a fire suppression if the tire catches on fire.
     
    #25 wjtracy, Apr 24, 2015
    Last edited: Apr 24, 2015
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  6. bisco

    bisco cookie crumbler

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    i still say, fill 'em with hydrogen, the car will practically fly.
     
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  7. CR94

    CR94 Senior Member

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    Right, and any excess water vapor similarly "leaks [permeates] a little faster" out of a tire than nitrogen does. Same result.
     
  8. PLSPUSH

    PLSPUSH Active Member

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    $30 a tire...wow...$5 here
     
  9. fuzzy1

    fuzzy1 Senior Member

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    My understanding is that the excess water vapor should diffuse out much faster than N2 and O2.

    Or, if one actually succeeds in making the interior much drier than the exterior, then water should diffuse in comparatively rapidly.
     
  10. bwilson4web

    bwilson4web i3 and Prime

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    I'm a pragmatist about nitrogen. It is dry and avoids oxygen effects on the tire interiors. Compared to a K&R filter, there are worse. I'm looking at this as a test setup. Document what happens to that tire versus the others including pictures when they are replaced. But I'm more impressed with the sub photo.

    I worked with a former sailor who told about a shake-out cruise where it was time to surface. Unfortunately one of the sailors closed the valve feeding the depth gauge. Up bow planes . . . depth did not change. More power . . . depth did not change. Blow the tanks . . . depth did not change. They broke the surface just as full nuclear power came on. They reported the front third came out of the water; tilted to max lean bubble, and; threw-up a rooster tail. I suspect the prop would have suffered cavitation damage. But then sailors are 'creative' as anyone in blue-water has to be.

    Bob Wilson
     
  11. wjtracy

    wjtracy Senior Member

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    I actually feel the bad MPG effect of low tire pressure is pretty good justification for filling new tires with N2. I wish more places were like Costco filling with N2. But I would go with regular air after the first fill. By the way, many tire companies support N2 for holding pressure better.

    Also I heard Maryland has mandated free air at some gas stations (but I have not seen this: I pay for tire air in MD) but that idea has merit to conserve fuel. I would like to see encouragement of N2 for new tires and free air for refills as fuel conservation step.
     
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  12. Easy Rider 2

    Easy Rider 2 Senior Member

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    No, I said no such thing.

    The little bit of water VAPOR that is in the air stays as vapor under most conditions and the ONLY adverse effect is that the pressure varies a bit more with temperature. That's it. No big advantage with dry nitrogen.....or dry air for that matter.

    Were you asking a legitimate question or just trolling for a fight ??
     
  13. Easy Rider 2

    Easy Rider 2 Senior Member

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    What science book are you looking at which says that water vapor molecules are smaller than nitrogen molecules ????
     
  14. wjtracy

    wjtracy Senior Member

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    That's a good science question because none of the tire chemistry articles I have seen talk about the relative size of the water vapor molecule, and its ability to diffuse through the tire.

    Note that if we were membane engineers we could easily answer the question with all the equations, but here on PriusChat we are hoping to find an article by a membrane engineer to explain it for us.

    The closest thing I found so far is attached see Figure-1 it looks like H2O vapor is extremely fast diffusion vs. other gases, but this membrane is not a tire...we would like to see data for a tire. Interesting how slow He diffuses in this membrane, so this is Bisco's invention. I wonder where Argon fits in as that would be practical to isolate from air as 1% of air.

    See also Table 1 where H2O is shown to diffuse 300xN2 300 times faster than N2 in natural rubber.

    http://doc.utwente.nl/40766/1/thesis_Metz.pdf
     
    #34 wjtracy, Apr 25, 2015
    Last edited: Apr 25, 2015
  15. CR94

    CR94 Senior Member

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    ... and even that adverse effect is temporary, as has been pointed out above.
     
  16. CR94

    CR94 Senior Member

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    Here's an experiment you can do yourself to demonstrate the difference in permeation rates: Store a typical PETE (#1) bottle of bottled water for a long time, like years. The water will slowly permeate outward through the plastic, but air (nitrogen plus oxygen, mostly) can't get in as fast (if at all). As a result, the bottle slowly collapses, as if you were sucking the contents out. I have a couple of examples dating from before water bottles were as thin as they are nowadays, so results would become apparent more quickly now.
     
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  17. alekska

    alekska Active Member

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    Sorry I need to correct you here....
    1. Water vapor is gas, same as oxygen or nitrogen. It follows the ideal gas law in the same way, so it's pressure change with temperature is absolutely the same as long as there is no condensation happening.
    2. Water vapor (gas) can not encourage the corrosion. As soon as water molecule hits the metal it bounces off. It can not participate in electrochemical reaction which is called corrosion. Corrosion requires liquid electrolyte ( weak solution of carbonic acid in liquid water) oxygen and unprotected metal. Electrolyte provides path for electrons to leave metal. Water vapor can not provide path for electrons.

    I agree with the rest of your statements :)

    Alex
     
  18. ursle

    ursle Gas miser

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    wjtracy nailed it, nitrogen, while it may inhibit the disintegration of the inside of the tire, is great because if your valve stem isn't leaking, the tire will hold its air for six months or more, vs two weeks for "air" to go away.
    But if they won't fill the tires to 40 lbs and you have to top it off, pity
    And pity if you pay, usually it's included in the tire package, err, I wouldn't pay, but I will accept for free.
    At my local jobber, if you buy the road tire warrantee it comes with nitrogen, so for "insurance" you get the satisfaction of not worrying about air for six months.

    The color of the caps is moot, take off the windshield wipers and valve caps, .0000001 mpg is gained.
     
  19. alekska

    alekska Active Member

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    So imagine, you filled the tire with air (78% nitrogen, 21% oxygen). You claim nitrogen does not leak. So oxygen leaks out and leaves tire filled with 100% pure nitrogen, but at 20% lower pressure. You pump it up with air to the normal pressure again, and now you have ~ 94% nitrogen and 6% oxygen. But remember, you claimed nitrogen does not leak, so the minute amount of oxygen you have in the tire now leaks out and again you have 100% nitrogen at pressure just slightly lower than normal......do I need to continue?

    Alex
     
    #39 alekska, Apr 25, 2015
    Last edited: Apr 25, 2015
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  20. ETC(SS)

    ETC(SS) The other One Percenter.....

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    Cavitation isn't as big a problem when you have huge screws with lots of scimitar shaped blades moving relatively slowly. We were always much more worried about cavitation making noise
    Back in the day, submarines had 2 analogue depth gauges, 1 deep and 1 shallow, the later being isolated with a valve while deep. I've heard a lot of sea stories about boats forgetting to open (or shut) those valves.
    I've also heard of boats operating much deeper than intended due to non-operational depth gauges only to be nudged back into reality by an exited call from another part of the boat.

    I tend to believe that some of these stories aren't apocryphal, since we lost depth control on one dark and stormy night due to nothing more that the mid-watch being exhausted and inattentive.
    Waves slapping the side of the sail, or especially the bottoms of the planes make a distinctive sound impossible not to notice, and the skipper was NOT amused!!

    We frequently used N2 to calibrate gauges and pressure test all manner of items, valves, and piping exposed to sea pressure. Moisture in high pressure air systems is a VERY non-trivial problem for subs...
    [​IMG]

    For passenger cars?
    Not so much.
    It's a scam. They run the same scam on bikes and motorcycles.

    YMMV
     
    #40 ETC(SS), Apr 25, 2015
    Last edited: Apr 25, 2015
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