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Old 08-07-2006, 03:58 PM
Diesel User
Join Date: Aug 2006
Posts: 12
It's not the weight of the nitrogen, or anything specific in the nitrogen itself. It's the lack of moisture inside the tire that makes a difference. When tires get hot, the moisture turns to steam, and the pressure inside the tire increases a LOT. This happens most noticeabally on preformace cars and racers whos brakes heat the wheels significantly (since they're bolted together). Having pure nitrogen in tires contributes to a more stable (and very predictable) pressure across different tire temps. This COULD in a consumer car lead to an increase in milage, but it would higly depend on driving conditions. Anyone driving their car hard enough to notice would most likely already be using nitrogen. The one added benifit for a consumer of using nitrogen rather then air is tires rot a LOT less without moisture inside of them. When parked, that moisture sits on the bottom of the tire and rots out the inside, where you can't see it until the tire completely blows out, not just goes flat. This happens even if your car is stored inside for long periods. If your tire was filled from an aircompressor with a lot of moisture in it, leaving the tire to sit for as little as six months could rot it out, it happened to me.
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Old 08-07-2006, 05:46 PM
I told you so!
Join Date: Jun 2002
Location: Motor City, MI
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If moisture is the issue, then we could essentially DIY most of the same result by purging the tires in Michigan with air during January, when the dew points are near 0F. That's pretty dry!

As far as gaining 2 mpg... if this was true, cars would be leaving the factory that way, unless EPA rates the car mileage on some kind of dyno test.
95 E320 Cabriolet, 147K
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Old 08-07-2006, 06:31 PM
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Join Date: Mar 2006
Location: Sonoma Wine Country
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Originally Posted by Kestas View Post
As far as gaining 2 mpg... if this was true, cars would be leaving the factory that way, unless EPA rates the car mileage on some kind of dyno test.
True. The claimed mileage gain is a self-fulfilling prophecy, probably due to
(a) checking and maintaining tire pressure regularly, a good thing for all of us to do
(b) driving "carefully" (perhaps even without realizing it) and leaving the lead shoe at home
(c) otherwise keeping the car in a well-maintained condition, again perhaps unconsciously

The water that often contaminates "inexpensive" compressed air is definitely a problem for users such as NASCAR and the commercial airlines. In a race car, tire pressure is critical; moisture in the tire will turn to water vapor and raise the pressure. In an aircraft tire, the same moisure will freeze at altitude, putting the tire out of balance. You don't want that when you land at 170 MPH.

Finally, water and oxygen at high pressure and temperature cannot be good for tires (or anything else). Both water and oxygen are highly corrosive, especially in conditions above STP.

For us average Joes, a question might be, how long does this supposed accelerated rotting process take? If one drives enough to wear down the tread in two years, does it really matter what is inside the tire?

"Buster" in the '95

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Old 08-07-2006, 06:35 PM
Diesel User
Join Date: Aug 2006
Posts: 12
Well, you'd have to completely drain your aircompressor of any moisture in the bottom and fill it when the humidity is really really low, but that would work pretty well. Remember that even on the dryest of days the humidity is 10-20%, and that always gets compounded by aircompressors. As air leaves the compressors, the pressure drop causes the condensation in the tank to become airborne and leave via your air hose. Dry nitrogen (pure nitrogen is by deffinition dry) is a perfect 0% moisture content. Again, for the 1-2mpg, I'm skeptical, but truth is stranger then fiction.
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Old 08-07-2006, 06:35 PM
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You might get an aditional 2mpg with a smart car, but I don't think your going to get serious return on your investment on your average car. Unless you have a bus or 18 wheeler where rolling resistance is a much bigger factor its not going to save you much money.
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Old 08-07-2006, 06:53 PM
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Join Date: Mar 2004
Posts: 375
Most tire places apply a nice little dose of soapy water to the rim prior to installing the new tire. That stuff stays trapped inside the tire for good, with or without Nitrogen, if moisture is bad for your tires, you will have it no matter what.

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Old 07-06-2018, 11:59 PM
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Join Date: May 1999
Location: Lehigh Valley PA
Posts: 1,329
My wife's Mazda3 was sold with nitrogen in the tires.

I spoke with a service advisor at a Mazda dealership today.

I asked the guy what the deal was, since I had to top off her tire pressures the other night.

He said that they actually pull a vacuum before inflating with nitrogen.

That "should" get rid of any water vapor in the tires, similar to pulling a vacuum in AC lines, I would think.

He wasn't sure of the cost but it sounded substantial from what he said: "$79 or $99."

I did check into the cost of a tank if I bought one from a local gas distributor; $165 would buy me a 60 cubic foot tank filled with dry nitrogen, which is about 3 feet tall, and would cost $37 to refill.

That doesn't include the regulator (I don't think) but eBay has several choices.
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Old 07-07-2018, 10:28 AM
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Join Date: Jan 2012
Posts: 6,380
Nitrogen filled tires are somewhat of a placebo, there is a benefit but the cost is rather high for an on the road car.

Race car teams started to use nitrogen because high pressure nitrogen bottles are convenient where compressed air is not available. For a racing application, dry gas is critical in keeping tire pressures at expected levels. ( Water throws off the expansion curve )

Nitrogen is a larger molecule so tire leak rates will be lower but, if a tire is filled with regular air, eventually you will end up with a higher concentration of nitrogen / lower leak rate as the oxygen and other gasses leak out.

As an experiment, I used bottled CO2 to fill a slightly leaky tire, as the CO2 concentration rose, so did the frequency of refilling.

Regular dry air will be just fine.
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