air vs nitrogen in tires...

Anybody have any real world data from their data sheets that demonstrate the differences between a tire filled with 'air' vs dry nitrogen? For instance... my cold pressures for Mosport with 'air' from my little portable battery powered Campbell Hausfeld compressor are:

LF 30 RF 31
LR 32 RR 33

Car weighs 1950lbs empty, 205/50/15 Toyo RA-1 tires.

'GENERALLY' ... Hot pressures are 40psi all the way around, but it varies on the humidity... maybe by a psi or two...

I'm interested in switching to Nitrogen because I'm likely going to keep a tank in the trailer for air tools. What do people experience and what is the difference in starting pressures that one sets from air to nitrogen to get to a desired end point?

Generally, using nitrogen instead of air in tires cut the cold-to-hot pressure differential in half, plus that change is much more consistent from event to event and track to track. - GA

What Greg said.

Isn't the car delivered from the factory with air in the tires? While wheels (within size) and tires (DOT) may be free, I can't locate in the rules where it permits me to change the filling medium. :lol:

I wonder if nitrogen is lighter than air ??? Hmmmmmm :ph34r:

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Originally posted by GregAmy@Nov 7 2005, 09:14 PM
Generally, using nitrogen instead of air in tires cut the cold-to-hot pressure differential in half, plus that change is much more consistent from event to event and track to track. - GA

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Also Eliminates the water that is carried in air. :eclipsee_steering:

That's actually what creates the variation in pressure change. If one could get 'dry air' it would be VERY close to nitrogen. The reason nitrogen is generally so dry, is that it can be taken from liquid nitrogen which is pure, so you don't get water vapour contamination. Dry air, on its own, has nearly the same R, as in PV=nRT - gas law equation... so the differences between dry air, and dry nitrogen as a gas to fill one's tires is negligible.

The catch is that the tires are mounted and inflated with air from a compressor, unless you have the facilities to do that yourself using only nitrogen. You can only rid your tires of the compressed air by breaking them down, however, it you deflate the heck out of them, then at least most of the air can be replaced by nitrogen.
You'll definitely remove the H2O factor from the increased tire pressure. In fact, they will vary only slightly from the start. However, some drivers factor in that pressure increase into their handling during the race.
FYI, a lot of pro rally teams use argon to inflate their tires to eliminate tire growth that would alter the odo readings. That could even be carried so far as to consider that increased pressure from heated, compressed air could alter the final drive. :blink:

Yep, it's the WATER in the air that causes the problem. If you can eliminate the water from the air in the tires, you'll greatly reduce your hot pressure buildup. The advantage of using nitrogen only is the nitrogen has no moisture in it to begin with.

However, even if you use nitrogen, you have to use some sort of vacuum pump to evacuate the moisture laden air out of the tire first, otherwise you'll still have moisture in the nitrogen/air mix in the tire. If you just pull the valve stems and let all the air out at atmospheric pressure (14.7 psi), when you refill to 30 psi in the tire (44.7 psi atmospheric), you'll end up with a 1/3 - 2/3 mixture of air and nitrogen. (PV=nRT)

You can get nearly the same benefits by using a vacuum pump to evacuate the tire first, and then refill with regular air using a moisture remover/dessicant in-line filter. I use the disposable in-line kind that NAPA sells for use with paint guns, one on the compressor and one on my portable air tank. I replace them regularly when the indicators change color. You can get fancier ones that will remove almost ALL the moisture if you want, but these seem to help with the hot pressure buildup. To me it's easier than carrying a nitrogen tank around and the associated expense of refilling. Air is "free"! And I'm cheap. :023:

MC

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Originally posted by racer14itc@Nov 8 2005, 06:09 PM
Yep, it's the WATER in the air that causes the problem. If you can eliminate the water from the air in the tires, you'll greatly reduce your hot pressure buildup. The advantage of using nitrogen only is the nitrogen has no moisture in it to begin with.



To me it's easier than carrying a nitrogen tank around and the associated expense of refilling. Air is "free"! And I'm cheap. :023:

MC

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Talk to your friendly nitrogen supplier and maybe you can work a deal equal to the "free" air. ;)

Key benefit of the nitrogen over the free air is the volume that can be put in a rather small tank and you have an "air" supply for tools at the track and tires that can last you months.

Just curious, are there associated DOT permits and placards you have to place on your trailer if you're hauling compressed gas tanks aboard your trailer? :unsure:

MC

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Originally posted by racer14itc@Nov 8 2005, 03:43 PM
Just curious, are there associated DOT permits and placards you have to place on your trailer if you're hauling compressed gas tanks aboard your trailer? :unsure:

MC

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That's absolutely an issue, as well as being restricted in terms of where you can travel (no tunnels w/ gas cylinders). And you're probably supposed to be placarded if you carry over a certain amount of extra fuel (didn't we have this discussion already??).

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Originally posted by racer14itc@Nov 8 2005, 06:09 PM
However, even if you use nitrogen, you have to use some sort of vacuum pump to evacuate the moisture laden air out of the tire first, otherwise you'll still have moisture in the nitrogen/air mix in the tire. If you just pull the valve stems and let all the air out at atmospheric pressure (14.7 psi), when you refill to 30 psi in the tire (44.7 psi atmospheric), you'll end up with a 1/3 - 2/3 mixture of air and nitrogen. (PV=nRT)

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Makes sense, most people, if one doesn't want to vacuum the old air out, one can get to a better percentage of nitrogen by going to atmospheric, filling and repeating once more. Then you end up with a 90% nitrogen fillled tires... for all intensive purposes that's pretty good.

I 've been debating getting a small compressor (my big one doesn't seem to work to well off my generator :) ) vs getting a nitrogen tank. I already bring a generator and my trailer is wired for 110 so that's not an issue for the compressor. The compressor probably won't be able to run something like an impact wrench (not that I've needed one yet, but you never know) since it won't have the volume, but I would think it should be able to run a pnematic socket wrench and smaller air tools. What can a nitrogen tank run as far as air tools? Does it have enough pressure/volume to run an impact wrench?

What else do you need along with the nitrogen tank? I'm assuming you need some sort of regulator to hook up to it. Can you get that at your local welding supply shop? There's a local welding/gas shop I go to to get co2 for my fish tank and I'm guessing I can get the nitrogen tank from them as well.

Thanks for any info.

David

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Originally posted by DavidM@Nov 8 2005, 11:53 PM
What can a nitrogen tank run as far as air tools? Does it have enough pressure/volume to run an impact wrench?

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Ya! It can run everything. This is the the way that all pro teams get air tools in the pits, as generators and air compressors are almost always prohibited in the pits. Think NASCAR, Grand-Am, ALMS, etc... all these guys use Nitrogen for everything in pit lane. Air jacks (lift car), air tools, etc... all of the things that one would do with air tools can be done with Nitrogen tanks. Rules of your series would define what you need. Yes, you need a regulator to take a tank down to 90psi, the regulator and valves generally need to be in a cage or contained well within your pit cart - so that it is protected from accidents. I'm just interested in having the nitrogen for the paddock. Air tools are crazy handy. For the number of times I've pulled out the generator and the electric impact gun in the pits would easily equal the usefulness of getting nitrogen tanks for the trailer.

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Originally posted by rmicroys@Nov 8 2005, 07:03 PM
Ya! It can run everything. This is the the way that all pro teams get air tools in the pits, as generators and air compressors are almost always prohibited in the pits. Think NASCAR, Grand-Am, ALMS, etc... all these guys use Nitrogen for everything in pit lane. Air jacks (lift car), air tools, etc... all of the things that one would do with air tools can be done with Nitrogen tanks. Rules of your series would define what you need. Yes, you need a regulator to take a tank down to 90psi, the regulator and valves generally need to be in a cage or contained well within your pit cart - so that it is protected from accidents. I'm just interested in having the nitrogen for the paddock. Air tools are crazy handy. For the number of times I've pulled out the generator and the electric impact gun in the pits would easily equal the usefulness of getting nitrogen tanks for the trailer.

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Cool. I'm just looking for something in the paddock as well. I'll have to ask the guys at the welding shop about it next time I'm there.

Thanks for the info.

David

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Originally posted by DavidM@Nov 9 2005, 06:44 PM
Cool. I'm just looking for something in the paddock as well. I'll have to ask the guys at the welding shop about it next time I'm there.

Thanks for the info.

David

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Now, as was mentioned, transporting compressed nitrogen is a 'dangerous good' so you must adhere to state/federal (US) or provincial/national laws for the transportation of these goods.

In Canada, I know that there is personal exemptions allowed - one has to read the Dangerous Good Transportation Act. I think we're allowed to transport up to 150kg gross weight. As per the act...

http://www.tc.gc.ca/acts-regulations...T/tdg/menu.htm

I have no idea about the US, but this may have been already dicussed in a thread here.

I use Nitrogen in my tires because I am Cheap too. Consistency in predicting starting pressures aside, the price of the empty tank (e-bay) and new regulator was less than the smallest 110V compressor you can find. I can fill the tires extremely quickly and am not driving my paddock neighbors crazy with generator and noisy air compressors. Don't squelch the sound of the race cars :D

A small (I think 55cf??) tank lasted me 9 race weekends this year. Cost me $7 to have filled. Takes less space and weight than a compressor. To me it is a no brainer.

I don't use air tools at the track. I would think that the consumption would be quite high.

What affect does the dry air have on air tools? Obviously you don't have water displacing the oil and no rust issues. But does the dry air increase/decrease life of tool...or frequency of needing to oil them?

Nitrogen has no effect on air tools.

Lubricity is an issue outside of the power medium. Even with compressed air, the tools need externally added lubrication.

Pretty much, I dont like any self oiling systems either because it gunks up the hoses. But just a quick drop or two for every hour of use so far has kept all my tools happy.

BTW, I was up getting a new bottle for my stainless mig so I asked the guys if I did a 160lb nitrogen bottle to use at the track for air tools and whatnot would I need to run with a placecard. He told me DOT and MDOT (maryland) laws go by weight and they said over 500lbs you need to run a non-flammable, over 1500lbs you need a HAZMAT before they will even sell you that many bottles.

He said the rules for VA and WVA are the same but he doesnt know about if other states have renched down on the DOT information.

Does anyone have any solid data that switching to N2/dry air vs ambient air will significantly reduce psi flucuations? This weekend at Roebling I was experiencing variations of 15 psi in the front and 10 psi in the rear (FWD 225 Hoosiers). The link below would suggest that it does not. But then again the discussion is based on some opinion and some physics calcs with no real world application.

http://www.eng-tips.com/viewthread.c...=120996&page=1

Humidity is key.

Also, unless you are able to mount the tire with Nitrogen (or somehow evacuate all the air so used for that purpose) you do not get that great effect .

With regard to humidity, H20 in a vapor state should still follow the PV=nRT rule meaning that water vapor would react the same as a dry gas. There is so much conjecture out there that I just wanted some first hand knowledge before I dropped $200 on a cylinder and regulator.

The thing is the system can not be evaluated by the ideal gas law. It is too complex with feedback mechanisms.

Doing so presumes that the gas temperature for a tire filled with commercial nitrogen and another with wet air will abosorb and release heat from the system at the same rate. All you need is for the humidity in the air to more readily absorb heat into the system and less readily release it and the temperature of the gas in the wet air tire is higher than the commercial nitrogen. Once that happens the pressure is higher, once the pressure is higher the feedback of pressures and temperatures in the system are completely different between the two. (And the characteristics of water vapor vary quite a bit with pressures IIRC.)


We aren't talking about containers where the gasses are heated from the same static temperature and pressure to the same higher static temperature raised and maintained in a controlled environment and then the pressure change from original is measured.

This is a good read:

http://forum.specmiata.com/cgi-bin/ultimat...0009;p=0#000000

I used Nitrogen for the better part of a year. You don't need to vacuum out the tires. Just deflate them then over fill them. I was running my tires in the ~31 PSI range so I put 45 PSI in, then deflated them down to the level I wanted before I went on track. That will get most of the water out and it'll work almost as advertised.

My experience was that it was about half the pressure increase relative to air. So instead of starting with 31 PSI for air I started with 34 PSI for Nitrogen to get to a hot pressure of 37. I never noticed a big enough on track difference to say it was worthwhile.

One thing I did note, with Nitrogen it was a lot harder to warm the tires on cold days. I had a morning qualifying session in the fall where the rear tires never developed any grip and I ended up stuffing it in the wall. I think I had run 5 or more laps before I crashed.