Is nitrogen worth it?

[Eyelise]

I'm about to change my track only set of tires. I'm going from OEM A048s to Robert's 225 Ms up front and 245 A032s in back. I noticed my local tire dealer offers nitrogen fills. I do mostly HPDEs and typically get a fair amount of pressure bleed. Is the nitrogen worth it?

[tesprit]

Nitrogen may be worth it for a couple of reasons. The pressure stability is a good reason, but the best reason for a street car is the lack of moisture compared to compressed air. It is quite easy to get "wet" air from an air compressor if the filters aren't maintained well and this can lead to rim corrosion over a long period of time. The downside to nitrogen is that you will eventually have to have your own tank to do pressure adjustments at home or the track and they aren't cheap or fun to handle due to their size and weight.

[Buz]

I have heard that nitrogen also has larger molecules so tires lose less pressure over time. It seems a welding supply shop could fill a tank or bottle for you.

[codymac]

Originally Posted by tesprit

Nitrogen may be worth it for a couple of reasons. The pressure stability is a good reason, but the best reason for a street car is the lack of moisture compared to compressed air. It is quite easy to get "wet" air from an air compressor if the filters aren't maintained well and this can lead to rim corrosion over a long period of time. The downside to nitrogen is that you will eventually have to have your own tank to do pressure adjustments at home or the track and they aren't cheap or fun to handle due to their size and weight.

For track use, I'd imagine a 3000psi paintball cylinder would work. With some quick and dirty math, I'm arriving at somewhere around just enough to fill four tires - should be enough to top off trackside and plenty transportable.

[Jim Itin]

Originally Posted by Buz

I have heard that nitrogen also has larger molecules so tires lose less pressure over time. It seems a welding supply shop could fill a tank or bottle for you.

Buz,
Not to pick nits, but air is 79% nitrogen, and the molecule is about the same "size" as oxygen. Any pressure loss for tires is due to mechanical issues
(valve stems, imperfect rims, etc.). The benefit of nitrogen from cyliners is
pretty much the lower moisture content, which allows more constant pressure as the tire heat cycles.
Jim

[Val]

Originally Posted by codymac

For track use, I'd imagine a 3000psi paintball cylinder would work. With some quick and dirty math, I'm arriving at somewhere around just enough to fill four tires - should be enough to top off trackside and plenty transportable.

Yep, you can also get 1+ litre 4500psi in very light kevlar

[Eyelise]

Originally Posted by Val

Yep, you can also get 1+ litre 4500psi in very light kevlar

Are these cylinders threaded? I have CO2 cartidges for my bike that would work for the track. Anyone know any reason not to use CO2 to top off the nitrogen? They are dirt cheap at the bike shop. I'm sure there is no appreciable water vapor in the CO2 cartridges. One added benefit is nitrogen is lighter than air. This is a Lotus we are talking about after all.

[Buz]

I thought paintball guns used co2. I have never heard of using c02 besides bicycle tires.

[Eyelise]

Originally Posted by Buz

I thought paintball guns used co2. I have never heard of using c02 besides bicycle tires.

Can you think of any reason not to?

[fastliz]

I know some (if not all) the local clubs who run track days have rules against compressed gas cylinders at the track.

Mike

[Val]

Originally Posted by Buz

I thought paintball guns used co2. I have never heard of using c02 besides bicycle tires.

lol maybe some sort of "aka military simulation" aka paintball for n00bs

competitive paintball uses either comressed air or nitrogen, usually 0.5-1.0 litre tanks at 4500-5000psi made from aluminium and kevlar.

Markers are electronic semi-automatic, often programmable. Firing rate upto 30 balls per second.

[codymac]

Originally Posted by fastliz

I know some (if not all) the local clubs who run track days have rules against compressed gas cylinders at the track.

Mike

Really? Any reason why?
What about air compressors? What about welding equipment in the shops?

[TimMullen]

There is no reason (other than cost) not to use nitrogen, but no real reason to use it either (unless you are a professional race team looking for every last hundredths of a percent improvement).

The only advantage of nitrogen is that it is dry - the moisture in regular air used to inflate tires can expand when heated more than a dry gas expands. It's not that big of a deal - figure out what tire pressure works and use that pressure. Yes, it's trial and error, but so is figuring out the nitrogen pressure to use.

Nitrogen doesn't corrode rims an more or less than dry air - it's the moisture in the air that does any corrosion. But since the only steel wheel that I have that's corroded is on my old wheel barrow, I'm not worried.

If you use air (hopefully dry air) you can adjust the pressure simply and easily anytime. If you use nitrogen, it becomes much more difficult. I had nitrogen used in my tires on my Accord the last time I bought new tires (that what they used at Costco as a "selling point"). Did it make any difference to my tires or the cars handling? On difference is that they used a green tire valve cap to signify nitrogen.

By the way, the 13 year old Honda's steel wheels that has used air all it's life are just fine with not sign of rust prior to the installation of nitrogen in the last year or so.

I'm certainly not going to empty out the nitrogen, but I wouldn't go out of my way to use it either...

[ChrisH]

Options for dryer air:

a) Fill your tires when it is cold outside, and preferably low humidity. Why cold? Air holds less moisture when cold. Humidity is a percent of the water vapor capacity of the air at the current temperature. Hence, 50% humidity at 10 C is much less actual water content than 50% humidity at 40 C.

b) Hook up the intake of your air compressor to your freezer. Allow a small air opening to the freezer so you don't create a vacuum in the freezer. Same reason as "a" above.

c) Use a commercial inline moisture filter (e.g., dessicant) with your compressor. This has been discussed in other threads (last year?).

d) Combine a+c or b+c.

I could see a problem with liquid water in the tire if you filled it with air on a hot, humid day, and then it got cold. You would then have liquid water in your tire. If you filled with more air while cold, then you could get some overpressure when the tire got hot again as the water evaporated. Of course, even without the water, the tire pressure would go up as the temperature increased.

[fastliz]

Originally Posted by codymac

Really? Any reason why?
What about air compressors? What about welding equipment in the shops?

If you bring a compressed gas cylinder, it has to be in a container that prevents it from tipping over. I guess they're afraid of one falling, the valve getting knocked off, and turning into a missile.

Mike

[TimMullen]

Originally Posted by ChrisH

even without the water, the tire pressure would go up as the temperature increased.

The point of it all is that the air pressure in the tire will not go up any more than the nitrogen pressure. It's the moisture in the tire that rapidly expands with heat. Moist air in the tire will cause the pressure to increase as it warms up. Dry air or dry nitrogen will increase at about the same rate (not much).

I simply use a filter on my regulator and have fairly dry air coming out of my air hoses. Dry enough that it doesn't make much difference.

[Eyelise]

Originally Posted by TimMullen

The point of it all is that the air pressure in the tire will not go up any more than the nitrogen pressure. It's the moisture in the tire that rapidly expands with heat. Moist air in the tire will cause the pressure to increase as it warms up. Dry air or dry nitrogen will increase at about the same rate (not much).

I simply use a filter on my regulator and have fairly dry air coming out of my air hoses. Dry enough that it doesn't make much difference.

O.K. how about CO2 to top off the tires at the track?

[fastliz]

If you want super-dry air, use a scuba cylinder filled at a dive shop. It's what I've been doing for years. Not so much because it's dry. Rather, because I had a scuba tank not being used and it will fill tires for a long time.

Mike

[ChrisH]

Originally Posted by TimMullen

The point of it all is that the air pressure in the tire will not go up any more than the nitrogen pressure. It's the moisture in the tire that rapidly expands with heat. Moist air in the tire will cause the pressure to increase as it warms up. Dry air or dry nitrogen will increase at about the same rate (not much).

...

By moist, that means there has to be liquid water in the tire (even tiny droplets), not just humid. Water vapor expands at the same rate as nitrogen and oxygen. They are all just gases and pretty much obey the ideal gas law: PV=nRT.

But, it is easy to end up with liquid water in the tire if you fill up on a day that has a high water vapor content, and then it cools.

[Eyelise]

Originally Posted by ChrisH

By moist, that means there has to be liquid water in the tire (even tiny droplets), not just humid. Water vapor expands at the same rate as nitrogen and oxygen. They are all just gases and pretty much obey the ideal gas law: PV=nRT.

But, it is easy to end up with liquid water in the tire if you fill up on a day that has a high water vapor content, and then it cools.

I think it has more to do with the fact that water vapor provides a greater heat capacity. The greater heat capacity, the hotter the tires gets and higher the pressure. If you lower the heat capacity of the gas in the tire, you decrease the tendency for the tire pressure to raise.