Cool topic. First off, We run compressed air in our machine.
Many varied opinions on why to run N2, most common reason not run N2 is money.
Consistency is a big reason to run N2. Racers, need predictable and repeatable settings. Compressed air could work but it varies from each time a tire is serviced and will give a different result on the track. Often moisture is the culprit. If racers had a better choice, they would likely use it.
Never measured a N2 Molecule, but word is they are larger. If you run tube type tires, this is a big factor, less important on the modern tubless tire but they will not bleed down as quickly. Therefore tire pressures remain up longer.
As for TPSM, I learned something with that, and honestly it is certainly a viable reason.
The post that mention how to purge the air, I agree, however we use two partial fills, and then a final fill.
I enjoy the comments about why aircraft run N2 in tires. We run N2 for a number of reasons, not one sole reason.
First, many of the tires are inflated to pressures not easily attained by the typical air compressor. So it is far easier for me to service a tire with N2 bottles. FWIW, when we do this maintenance task, for safety, we do not get positioned anywhere except facing the tread. This way if the flange fails, and they do, the metal fragments will fly away from you (hopefully).
Second, the brakes on most aircraft are able to absorb a lot of heat. The heavier aircraft from corporate jets and up have fuse plugs. These plugs by design will release the tire pressure at a given temp. The idea is that if the fuse plug releases, the temp may be worthy of a fire or tire explosion. N2 will not add to the combustion as the gas is released. his reduced fire hazard is also good for racers.
Third, like the TPSM already mentioned having corrosion concerns, aircraft wheels are often made from either certain alloys of cast aluminum or magnesium. With the heat and corrosive dust from the carbon or metal brakes the wheels tend to see abuse. We make all attempts to control corrosion as the pits could become stress concentrations and cause cracks, either in the tie bolt holes or flange radius.
Forth, we do not often get too worked up about pressure loss as the tires are checked often. We do deal with huge temperature shifts from say leaving a southern runaway with asphalt temps near 150f, enduring a flight at -40f and then landing on a snow covered runway. The N2 helps in these large temp changes.
Also, we use N2 to service pretty much all the accumulators and blowdown bottles. Often for similar reasons.
In smaller aircraft such as single engine piston types and often in twin engine piston aircraft, the smaller shops will use compressed air. Not all but many do this. Often, these aircraft have inner tubes, and it does make a difference in how quickly the pressure drops.
Is N2 worth it in a Spyder... A lot depends on how readily available it is and the cost. Myself I have N2 bottle in the garage for rebuilding shocks, yet I still grab the air hose and gauge and fill the three tires with compressed air. I'm just being lazy.
Cool topic.
PK
