Nitrogen in TM tires?

[kdrickard]

Anyone had their TM tires filled with nitrogen?

The last couple of sets tires I've bought for our car/TV have been filled with nitrogen out of the shop. Since heat and low pressure seem to be the main TM tire issues (& age due to UV), on the surface it seems like filling the TM tires with nitrogen would be worth doing.

Thoughts / Experiences?

Thanks,

Kevin R.

Kevin

I think this is a great idea.

The thermal conductivity of nitrogen is something like 4X that of air. We used it in some space packages to improve internal cooling by conduction through the gasses and the difference was dramatic. What we were doing is moving heat from hot spots (like semiconductors) to cool spots (like the metal frame of the modules and the outer walls of the box. In the tire structure, we would be moving the heat from the heated rubber to the exposed metal rim of the wheel. I can imagine adding fins in the rim to improve the thermal path!

Another thing to consider is that ozone is the primary factor in breakdown of the rubber. That is what causes the cracking and why tires should not be run beyond 4 years. This breakdown is not only on the outside of the tire but inside as well. Puting nitrogen in there would eliminate the ozone and thus ozone induced damage inside the tire.

Since you are saying dealers are putting this in tires, there is probably some research published on the internet that would explain the advantages of nitrogen. Of course, one has to find something other than Madison Ave hype. One has to find the results of carfully controlled tests.

[kdrickard]

Originally Posted by BobRederick

Since you are saying dealers are putting this in tires, there is probably some research published on the internet that would explain the advantages of nitrogen. Of course, one has to find something other than Madison Ave hype. One has to find the results of carfully controlled tests.

Thanks Bob for your thoughts/input -- and exactly the reason I was asking. As you note, on the surface it seems like a good idea, and what I can find on the net supports that so far. But as you note, it is mostly from tire resellers websites you see the list of reasons why it is a benefit. (less heat, slower loss of gas, less moisture inside the tire, and less ozone).

The other issue I've noted is that you pretty much have to go back to where you bought your tires if you want to top them off up to pressure with nitrogen -- something you can't always plan. Interestingly, I did run across on the Internet a company selling to service stations nitrogen generator / compressor with the 'market angle' of being to serve the needs of those who have recently had their new(er) tires filled with nitrogen.

Kevin

[shunter917]

Maybe this is a dumb question, but what would be the problem with topping off a nitrogen filled tire with regular air?

[Bill]

shunter917 -

Since plain ordinary air is 80% nitrogen, the answer would be "Not much".

Air does contain some small amount of moisture, and fans of nitrogen regard this as a no-no. It won't hurt the rubber, but it can eventually rust the steel wheel, I suppose. Bear in mind, of course, that tires have been filled with plain old compressed air since tires were invented, and rust won't be any worse now than it ever was. Incidentally, there is almost no moisture in compressed air from an old-style compressor with a tank. This is because the moisture condenses inside the tank, and is drained out of the tank as a liquid. Virtually none is passed on to the tire. "Modern" tankless compressors (the ones you have to feed quarters into down at the Qwik-E-Mart) don't remove moisture, so whatever is in the air due to local humidity is passed on to your tire. But compressors don't "cause" mositure in any way - it is just whatever was in the original air.

The amount of ozone in a small amount of air is negligible.

Of course the outside of the tire is continually exposed to everything - moisture and liquid water, ozone, chemical pollution, and sunlight. By using nitrogen, you may end up after three years with a tire that is pristine on the inside, while the outside has aged a full three years from pollution, ozone and sunlight, just as tires have always aged. Personally, I'm not convinced this result is worth much, but YMMV.

Bill

I used to pressurize the landing gear struts on airplanes with nitrogen for all the reasons mentioned, but the main reason was so moisture in the strut would not freeze at high altitudes or on the ground. Also, these struts used an "air and oil" mixture. Oil and even a small amount of oxygen under pressure can be an explosive combination. We got the nitrogen from our welding gas supplier in a high pressure tank and then regulated it. The struts reuired a pretty high pressure, depending on the plane. I think tires and wheels on land based vehicles get plenty of wear and tear from the exterior and filling the tires with nitrogen is overkill. But to each his own.
Bill

Here is a post I found on the Internet written by a chemist, hopefully it will answer some of the questions on this subject:

1. Air is 78% nitrogen, N2, and 21% oxygen, O2. So even if you put air in the tire, it's already 78% nitrogen. Many of the so called nitrogen generators don't produce much more than 90% nitrogen.

2. At relatively low pressures (ie tire pressures) N2, O2 and water vapor will all behave as ideal gases, and follow PV=nRT. Pressure will increase or decrease to the same extent as the temperature increases or decreases regardless of which gas is in the tire. (Even at 300 psi, which is about 20 atm, there is little deviation from ideality.) Therefore the comments about N2 not changing in pressure as the temperature changes are without merit.

3. The rate of effusion (or diffusion) of a gas through a porous membrane depends on the molar mass and to some degree on the molecular diameter. N2 and O2 are almost the same size and N2 is lighter than O2 (28 g/mol vs 32 g/mol) so if either gas were to effuse out of the tire, nitrogen would do it more quickly. Luckily, tires are designed not to be porous membranes.

4. N2 and O2 both have essentially the same specific heat capacity, about 1.0 J/gK, and thermal conductivity, about 0.00026 W/cmK. Water vapor has a specific heat capacity of about 2 J/gK. But remember, water vapor will constitute less than 1% of the air in the tire. So the idea that N2 has different heat handling properties is also without merit.

5. The ozone, O3, in the atmosphere, which is a ground level pollutant, will do a great deal more damage to your tires than the O2 inside the tire. For instance, don't leave a condom out in the air in Los Angeles for a few days. It will develop lots of tiny holes and weaken.

spdracer22 says that dry air is preferably to air with a lot of water vapor. As a tire heats up, the very small amount of H2O present will be in the vapor state which may contribute to the overall pressure very slightly.

Several have suggested that N2 in a high pressure tank is more portable and requires no electricity. That would make sense, particularly for aircraft tires.

I find no reason to believe that N2 is going to produce a "better ride" or "better handling".

The bottom line is that for general passenger car tires or truck tires there is nothing to be gained (other than portability) by using nitrogen rather than air. The biggest gain will be $$$ by the companies that sell nitrogen handling equipment and the tire merchants that appeal to ignorant customers. And who is the biggest loser? Yep, the consumer.

[kdrickard]

Great info all! Exactly the reason I asked here.

Here is my take so far. There are benefits to nitrogen, but for everyday Tow Vehicle or Trailer use they are somewhat limited. If it costs me a few bucks to have a new set of tires inflated with nitrogen -- great, but I will not break a sweat if I need to top them off with "local" plain air. The "outer elements" as well as tire pressure (internal) continue to be the main issues with the TM tires.

Thanks all,

Kevin