Nitrogen, yes, or no and why?

[Wbonsell]

We would use nitrogen in our race car because you could manage tire temps much better, but unless you are driving at freeway speeds in 100+ temps all the time, its a waste of money IMO unless its free.

[jerome951]

Originally Posted by Wbonsell

We would use nitrogen in our race car because you could manage tire temps much better, but unless you are driving at freeway speeds in 100+ temps all the time, its a waste of money IMO unless its free.

There's the key. A dry gas (like nitrogen or dried air) has a lower rate of expansion than 'moist' air as it is heated, so dry gas sees less of a pressure increase when traveling.

This can be critical when you're trying to hit very specific hot pressures (such as in a race car, where 1-2 psi makes a big difference in handling) but shouldn't be a big deal in a motorhome. In my race car, I see ~6-7 psi increase when using nitrogen (this is from stone cold to ~170F), and ~9-10 psi increase using undried compressed air. The more consistent pressure increase of nitrogen takes some of the guesswork out of setting cold tire pressures to achieve a desired hot pressure.

Dry gas does have the benefit of slowing corrosion of steel components such as pressure sensors and steel wheels, which is why some auto manufacturers recommend it.

[Scatterbrain]

Originally Posted by jerome951

.........

Dry gas does have the benefit of slowing corrosion of steel components such as pressure sensors and steel wheels, which is why some auto manufacturers recommend it.

Bingo. This is exactly why it's recommended by some manufacturers. Internal wheel sensors. It's all about preventing corrosion.

Most shops should have a desiccant filter on their air system, but I can remember working at a dealer in Fl where I'd have water shooting out of the exhaust port of my air tools. That level of humidity in a tire with an internal sensor is not a good thing. Granted the next dealer I went to had two large dryers on the compressor and another one at each techs station. No issues there.

Personally, I don't worry about it. I replace my air dryers regularly and consider that to be enough. Every internal TPMS sensor I've replaced due to damage was actually due to either someone damaging it during a tire change or the valve cap seizing onto the threads. I'd recommend putting a wee bit of anti-seize on the cap threads to prevent trouble down the road.

[LDMcL]

There have been several previous comments relating to 100% nitrogen being able control air pressures in tires better than compressed air.

Although its been nearly half a century since I opened a physics book, I thought that for any gas, pressure*volume/temperature was a constant (P*V/T=C) when using the proper scientific units for pressure and temperature.

This equation does not make any reference to the makeup of the gas whether its oxygen, nitrogen or water vapour.

Would anyone care to offer a scientific explanation for their assertion that 100% nitrogen creates more stable tire pressures than compressed air?

Thanks for any comments that you may have.

[MartinP]

Not sure why it is more stable with temperature swings but I have been told the leak down rate is slower than compressed air due to the larger molecules. It is used in aircraft tires and air/oil struts. Inert gas and dry. I use it only because I have a nitrogen bottle sitting at home from my aircraft maintenance days.

[frankdamp]

Nitrogen in commercial airplane tires is an FAA mandatory requirement. When I was at Boeing, I did a lot of research on the subject of in-flight tire bursts. The near crash that got the mandatory requirement imposed was a 727. It took off with a dragging brake, which over-heated the tire. At around 18,000 feet, there was a tremendous bang followed by rapid decompression of the cabin.

After landing, the inspectors found a hole, close to 18" across, in the aft wheel-well pressure bulkhead with two mailbags jammed in it. If those mailbags hadn't jammed, the airplane would probably have crashed. The over-pressure was the result of gases in the tire's inside casing material. The explosion failed the tire beads, which we calculated would take about 13,000 psi.

If your RV can accelerate to 150 mph with a dragging brake and you can then put the hot wheels in a closed box and climb to 18,000 feet, then you should use nitrogen. Otherwise air is just fine.

[jerome951]

Originally Posted by LDMcL

There have been several previous comments relating to 100% nitrogen being able control air pressures in tires better than compressed air.

Although its been nearly half a century since I opened a physics book, I thought that for any gas, pressure*volume/temperature was a constant (P*V/T=C) when using the proper scientific units for pressure and temperature.

This equation does not make any reference to the makeup of the gas whether its oxygen, nitrogen or water vapour.

Would anyone care to offer a scientific explanation for their assertion that 100% nitrogen creates more stable tire pressures than compressed air?

Thanks for any comments that you may have.

It's not the difference in expansion rates between air and nitrogen, it's that air usually contains more moisture, which expands at a greater rate than the gasses when heated. Well-dried air and nitrogen would act about the same. Sorry, I failed physics first time through so can't provide the technical explanation.

I've also chatted w/ a former Michelin tire engineer who supported pro race teams on the weekends. They used nitrogen, but he commented that unless you fill & bleed the tire about ~3 times w/ nitrogen you still have enough moisture inside that will affect pressure increases (this is at the 150F temp swings of a race car; much less temp increase when driving on the highway). Their solution was to install 2 Schrader valves opposite each other to flush the tire through w/ nitrogen.