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Old 11-07-2008, 08:02 AM   #11
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Who can provide data on thermal expansion/contraction of nitrogen vs. oxygen, and how the volumetric change affects pressure? I'd be interested to find out if there was really anything to it, though I have a hard time believing it without hard data.

Air is (by volume) 78.0842% nitrogen, 20.9463% oxygen, 0.9342% argon, 0.0384% CO2, and 0.0020% other (according to Wikipedia and backed up by Encarta). For the purposes of tire inflation, nitrogen and oxygen are the only significant components -- even if argon and CO2 completely exited the tire you probably wouldn't be able to measure the difference.

So, at 40psi, just how much expansion/contraction is required of oxygen and to make a big difference, when you factor in the expansion/contraction of nitrogen?

The other proposed benefit is seepage through the tire. If nitrogen doesn't manage to get through the tire, and you lose all the oxygen once (a 20% drop in volume -- I don't know my physics that well, would that also be a 20% drop in pressure?) then fill it with air again, now you've only got 4% oxygen. The next time, you've got under one percent, almost pure nitrogen in your tires.

So, you could pay for nitrogen, or just let them naturally balance to 100% nitrogen.
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Old 11-07-2008, 08:08 AM   #12
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Quote:
Originally Posted by PaleMelanesian View Post
According to NASA's studies, higher pressure is better against hydroplaning. I believe it correlates with 1/sqrt(pressure), so it's a diminishing returns thing. However, lowering the pressure would make it more likely to hydroplane, not less.

Snow may very well be another story. I can't comment on that.
Higher pressure would definitely help against hydroplaning, but wet pavement can be slippery before you hydroplane, in my observation. If I run 80 PSI in my truck's rears, I have to be very careful (when the pavement is wet) at low speeds on sharp turns or any time I step on the gas. If I knock it back to 72 psi it handles more predictably.

For snow, it's known that narrower tires cut through better. If contact patch is affected by inflation in radials the same as it is in bias ply, that indicates using more pressure in snow. Based on my big tire pressure thread, I'm not sure that contact patch is affected the same way.

I don't have many years experience optimizing tire pressure for FE, but I have been running the same high pressure habits for ten years (for wear and handling, not FE), with lots of snow driving. I never stopped to think about how pressure affects snow handling until I posted this thread. I'd say that it's probably not much of a worry.
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Old 11-07-2008, 08:10 AM   #13
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People on this board are an exception ie regularly checking tire pressure and taking care of their vehicles. For the most part people don't want the "hassle" of doing things like that. They want the little lights to stay off and they don't want to have to do anything beyond bring it in for an oil change which is how we can charge $40 for nitrogen and $30 for a full service oil change where we check all the fluids and top them all off including washer fluid.
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Old 11-07-2008, 08:19 AM   #14
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They definitely don't want to be bothered with having to check things or deal with lights...I just question whether 100% nitrogen could really accomplish that goal so much better than 78% nitrogen. What's worse than them not checking is them believing that they don't even need to care anymore. The people who didn't care and didn't check were the ones whose Firestone tires exploded on their Ford Explorers.
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Old 11-07-2008, 08:29 AM   #15
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Surely you don't expect people to be responsible for their own actions and well being?
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Old 11-07-2008, 08:34 AM   #16
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I just realized I've turned into my dad.
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Old 11-07-2008, 08:43 AM   #17
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Holy Cow - interesting about your truck's wet driving performance. Real World point taken.
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Old 11-07-2008, 11:43 AM   #18
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Quote:
Originally Posted by theholycow View Post
They definitely don't want to be bothered with having to check things or deal with lights...I just question whether 100% nitrogen could really accomplish that goal so much better than 78% nitrogen. What's worse than them not checking is them believing that they don't even need to care anymore. The people who didn't care and didn't check were the ones whose Firestone tires exploded on their Ford Explorers.
Great point, and so very true!!!

I have worked in the tire industry for about 5 years. For a few years I was a tire adjuster, determining the cause of failure and determining if a manufactures warranty is applicable. I am far from an expert on tires, but I do know a few things.

The biggest advantage of nitrogen is the molecule is bigger then a oxygen molecule. Because of this, tires will lose air at a slower rate. Just like theholycow said, YOU STILL NEED TO CHECK YOUR PRESSURE.

As far as the add or subtract air for winter, that is all up to you. Max sidewall pressure will provide the best hydroplaning resistance, but you will have a trade off with traction in the wet. On a snow covered road a properly inflated tire will help "cut" the snow and gain traction. Deep snow is another story, for that drastically lowering your air pressure will cause a "floating" effect, just like with mud and sand. Just make sure to keep speeds low and don't try turning to fast with drastically lowered pressures

When it comes to tire safety, a slightly over inflated tire is WAY safer then under inflated. There is a term we use called "run flat". Most people call it a blow out, but it is quite the opposite. Simply put it means the tire was ran too long in an under inflated condition. When tires are low the sidewalls flex more as they rotate. This flexing causes a hot spot on the INSIDE of the tire. The damage that is being done is not visible from the outside. Over time the tire will heat up and the inside of the sidewall will start to disintegrate into rubber dust until a hole or weak spot develops. After that the tire is toast and you find yourself on the side of the road.

I have found the worst offenders of not checking tire pressure are people who have run flat tires. Some run flat tires will look properly inflated even when they are down to only a couple psi. This is a very dangerous condition as run flat tires are only designed to be ran for around 50 miles @ 50mph when flat. They will "blow out" from running low just like any other tire.

That's just my .02
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Old 11-07-2008, 11:51 AM   #19
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Quote:
Originally Posted by T.P. View Post
When it comes to tire safety, a slightly over inflated tire is WAY safer then under inflated. There is a term we use called "run flat". Most people call it a blow out, but it is quite the opposite. Simply put it means the tire was ran too long in an under inflated condition. When tires are low the sidewalls flex more as they rotate. This flexing causes a hot spot on the INSIDE of the tire. The damage that is being done is not visible from the outside. Over time the tire will heat up and the inside of the sidewall will start to disintegrate into rubber dust until a hole or weak spot develops. After that the tire is toast and you find yourself on the side of the road.
[...]
That's just my .02
That's worth a lot more than $.02. Too bad people don't understand, most people only ever think of overinflating a bicycle tire and figure that's how it works. Folks on this forum tend to be the exception.

When you worked as an adjuster, did you see any failures attributable to overinflation? If so, what can you tell us about them?
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Old 11-07-2008, 12:02 PM   #20
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I have to replace one of my tires because it wore out real fast on the drive wheel. I attribute it to over inflation. So I probably didn't save myself any money by over inflating (but it was still fun to get 70mpg). Granted it was a cheap tire from Walmart. I wouldn't replace it but it won't pass inspection. I also notice I have terrible traction in the wet with overinflated tires. I imagine it would only be worse in slush and snow. Going right now to replace the tire and then to deflate them all to about 45psi.
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