The Nisan GT-R is the first car I ever owned that came with Nitrogen filled tires from the factory. There are a lot of myths and urban legend about benefits nitrogen filled tires. This is also a very confusing topic for many car owners.
So what is the main reason for my N2 setup - CONSISTENCY! and the second benefit I have found over the years is simply CONVENIENCE!
The typical advertised benefits of Nitrogen or N2 are often stated by greedy dealerships that will charge $6-8 per tire in an effort to turn N2 into a profit as: better mpg, doesn't leak, no low pressure warnings, longer tire life, etc. For everyday use all these are simply complete Bull$hit! Yes, in extreme cases each of these condition would apply true for using Nitrogen (e.g. better mpg because the tire pressure were correctly set with Nitrogen), but for the every day tire use, these are all false compared to just simply using air provided the proper pressure are maintained at all times. So why do I use N2 not only in my GT-R, but all cars and even bother? Read on....
With regards to proper pressure, that is the pressure which should be set in the morning at ambient temperature (as indicated on the door jam sticker - 29 psi for the GT-R - and not the pressure written on the tire as that is max pressure). This is to be done before the car is driven or driven less than 1-2 miles and the tires have not been exposed to direct sunlight say on side of the car. My going to the dealership 20 miles away to get this done and finding the time to do it is reason #1 for an N2 setup for convenience.
For every 10F drop or rise, the pressure in tires drops and rises by 1 PSI accordingly. So if you set the pressure on a nice 90F day and 3 weeks laster it is down to 50F, the tires will be 4 PSI lower and this is what causes bad fuel economy and reduced tire life. Starting the other way around can cause unsafe pressure increase and also a very uncomfortable ride.
The other issue is that when temperatures drop below 32F, water freezes, which means all the humidity that was in the air and had got transferred into the tires on a hot humid 90F day will freeze inside the tires causing an even further drop in pressures. That frozen moisture can lodge itself on the filler value of the tire. So having dehydrated or dehumidified air is the ideal, but is harder to get than N2 which is already dehumidified, and which is sold for many other industrial reasons, hence cheaper. This is reason #2 for me to use N2 from a tank - free of moisture content.
Normal air is already mostly nitrogen : ~78% nitrogen, ~21% oxygen, ~1% Carbon dioxide, argon, other gases and water vapor. Nitrogen is an inert gas, which means it does not react, whereas oxygen does react, so the theory is that by filling tires with nitrogen, this removes oxygen from tires and reduces the reaction with rubber compound. This is true, but unless you are landing an airplane with those N2 filled tires, or keeping the tires on for 10 years, or getting the tires so hot that every 1/10s per lap counts, the normal everyday car that has tires last 2-3 years or 1 year on the GT-R. This is not really a benefit. But the consistency of having all 4 corners go up/down exactly 1PSI with a 10F change in temp is wonderful to have when on a track. Reason #3 - more consistency and predictability.
It is true that N2 doesn't leak out as much, over 6 years of using N2, I was initially skeptical of this, and I am now a believer that slow leaks simply go away. I can set the pressure on my summer tires at 30psi @ 40F, store them for winter, take them out 5 months later and at 40F they will be the exact same pressure.
Lastly, it is so easy to top off air using a tiny little scuba-sized tank that can push out up to 200psi. It takes a few seconds of N2 burst on each tire to get up to pressure compared to sitting and waiting for a 12V air compressor. Also contaminating an N2 setup with regular air means wasting money later to get a flush and fill. I can do this at a much lower cost that any dealership. Reason #4 cost! If one is a Costco member, they fill N2 so it is a free way to get N2 top off if going to the dealership is out of question.
To make my garage setup, I got a 22cu ft steel tank from a local gas and welding supply dealer that did not require me to be a contractor to purchase it and refills. This cost me $45. These tanks come with 99.9% pure N2, as opposed to the on-site machine that some dealerships have which produce 90%-95% purity by extracting from the air. The tanks comes with N2 at 2200psi.
If one were to connect a 2200psi to a tire, it would cause a spectacular and deadly explosion. In order to make this useful, I bought a regulator rated at 0-4000psi to 0-200psi, so that I can "step down" the pressure from 2200psi down to about 40psi, which fills the tire up fairly quickly. This is an application of Boyle's law for pressure, volume and temperature. So at 2200 psi with this tiny tank, how many GT-R tires can be filled. to 29 psi...about 7 tires from completely empty! 1 tank was enough for me to fill, flush and fill my winter setup wheels.
To round out the setup a 4ft high pressure hose with an locking air chuck is connected to the end of the regulator and clamped in place. I could have got an air chuck pressure gauge combo, but already I use digital pressure gauge for that.
How long does a tank last me - about 1 year of fill-up and topping off tires on 2 cars, 1 truck and even a few toys. What is the cost of a refill tank exchange? - $7.95!
The net is that my N2 setup that I did as a way to "support" my DIY work on my GT-R has been a great investment with good returns. Finally, on Michelin PSS, I run 31psi front and 28 psi rear when cold.
