Not entirely true. I have an old sports car with wire wheels (like this) and it needs tubes inside of the tires.
Nitrogen’s best use is it’s stability under varying temperature conditions. That’s why aircraft tires are inflated with it. There was a Mexicana flight in 1986 that crashed because a tire was filled with air instead of nitrogen and it resulted in an explosion/fire.
If a car tire is continuously losing pressure then there is either a leak in the tire from a puncture, a defect, a leak around the rim, or the valve. Spraying it with soapy water should reveal the problem.
Love those wheels! I am a bit of a car nut myself. My comment about tubeless tires was a general one.
Well that’s true N2 is fairly inert. (Which kind of explains why nitrogen based explosives are that powerful. I takes alot of energy to break it apart so when it comes back together alot of energy is release.) Also I could see that the O2 could do quite a bit of break down since O2 reacts quite vigorously with alot of stuff. (Like carbon and hydrogen which would be really common in a tire.) One thing you need to keep in mind is that I think a truck tire on a semi would have pressures in excess of 100psi. To give an idea how much O2 that really is that actually quite a bit more oxygen than pure oxygen at 1ATM which is very oxygen rich. (That’d be about 23 psi of O2 in the tire, a pure O2 environment at 1ATM is 14.7) Of course car tires are far lower pressure.(My tires are 30 psi so that works out to 9 psi) Oh if anybody is wonder why the math is different now I’m using absolute pressure here and gauge pressure in the other bit.
In answer to the OP’s question, tire material is porous, so gases will diffuse through it over time. There may or may not also be leakage at the junction between tire and rim.j
re: the ongoing discussion over nitrogen, this question came up repeatedly on a motorcycle website I frequent, so a few years ago I took the time to research the matter thoroughly, and ended up writing this web page to explain what I learned. Short summary:
-the inertness of N2 has advantages in aerospace and truck tires, where the high overall pressure results in high partial pressure of O2, which causes rubber oxidation (a major issue for truck tires which get retreaded) and a combustion hazard (major issue for aerospace where braking during landing can cause high tire temps).
-there’s virtually zero difference between the temperature response of N2 and air. Water (this includes both atmospheric humidity, and moisture in your breath) can cause major pressure swings if there is enough in there to condense into liquid at any time during service, but this is typically eliminated by taking air from a compressor that utilizes a storage tank. That is, a typical compressor with a 5-gallon storage tank will give you reasonably dry air due to condensation within the storage tank; a compact emergency compressor that runs from you car’s cigarette lighter and dumps air directly into your tire might not, if used in a moderately humid environment.
-N2 doesn’t leak out much more slowly than air; it only holds pressure about 1.6 times as long. Confirmed by theory and test.
re: the unfortunate Air Force captain who died to to a tire explosion, the article noted that they may have been dealing with a tire that was bulging. I’ve seen tires delaminate and result in a bulge that grows very slowly over time as air leaks slowly through tiny fissures in the tire carcass, only to be held back by a final layer. Eventually the bulge grows big enough that the bulge explodes. Possibly something like this happened, i.e. air slowly leaking into a space in the tire carcass and gradually increasing stress on the tensile materials in the carcass until the point of failure - unfortunately, in her lap.
Quick question, did you only fill once and check over time or did you also see what would happen if you replaced any gas that leaked? (Because like I wrote earlier when O2 leaks faster then a tire would basically be a N2 accumulator. The little thought experiment shows that what will happen is basically every refill with air just pushes it closer and closer to just N2 since you would be replacing mostly O2 with a mix that is mostly N2.)
Wasn’t me; it was Consumer Reports. 31 different brands/models of tires, one copy filled with air, one copy filled with N2, left alone for a year. Air tires lost an average of 3.5 psi, N2 tires lost an average of 2.2 psi.
The ‘Hype’ in using Nitrogen (N2) for tires is silly. Yes, long term studies from trucking and long haul companies see a benefit… why? Well, they are checking pressure regularly. As should everyone. Once a month at least. Is there a benefit? Well, perhaps. $5/tire worth? Nope.
As mentioned above, oxygen is reactive, and so will react (bind) with everything in the wheel… The rubber, the wheel itself, even the valve stem. O2 is actually a larger molecule then N2 is, so we can toss that argument out.
My shop compressor actually delivers 78% nitrogen (N2) to my tires. Which makes sense, the air we breath is 78% N2.
Slow leaks, in my experience, are caused mainly by poor rim bonding (the wheel rim must be extremely CLEAN before applying an EXTREMELY CLEAN tire to it. Dirt, a flake of rust, a scar in the wheel, will all cause a slow leak of air. Think about a bit of dirt at one tiny point of the rim… think that it only puffs out a tiny tiny bit of air every time 1/4 the weight of the vehicle is on it (or maybe at a different location in rotation)… You will see that you lose air a LOT in a car/motorcycle. The wheels on my boat/jetski/otherboat trialers? even my lawn tractor? They never lose air, except due to the difference in temperature season to season.
Okay, my lawn tractor was losing air in one tire, but there was a pinhole. Literally, a pinhole (had a pin in it). Drilled it out some, stuck in a plug, and it’s been fine, shop air from my compressor.
I’m too tired (and too lazy), to properly do the numbers now, but you should, just using atmospheric air (compressed) eventually have almost fully N2 filled tires (after the O2 has bonded away), aside from the minor atmospheric gases.
The one huge difference between “Pure” N2 (Pure being tire company ‘pure’ which is about 98%) and regular compressed air, is the water vapor content. The effect of water vapor, I can’t tell you.
Regards!
I use latex inner tubes on my cross-country mountain bike, and they leak like a sieve. They’ll keep a good pressure over a few hours (long enough for the rides I do), but need re-inflating the next day. Over the course of a week they’re almost flat. For the record, I put up with the inflation regime as latex tubes are lighter, more puncture resistant, and have lower rolling resistance than standard butyl rubber tubes. That’s worth a bit of extra pumping in my book.
I recall someone asking a mountain biking magazine whether inflating tyres with hydrogen would make for a lighter wheel. The answer was yes, a tiny bit lighter, but at the expense of faster pressure loss due to the smaller molecules.