Wednesday, January 8, 2020

Nitrogen Fill of Tesla Tires (and Spare)

My Nissan GT-R is the first car I ever owned that came with Nitrogen filled tires from the factory and required N2 fill for tracking the car. There are a lot of myths and urban legend about benefits of nitrogen filled tires, especially at a cost. This is also a very confusing and controversial topic in the automotive community.

So what is the main reason for my N2 setup - consistency. The second benefit I have found over the years is simply convenience. Lastly, I have concluded after 12 years of using N2, on my motorcycle and winter tires that degradation is reduced considerably specially when tires life outlast thread life.
This tiny little Nitrogen tank lasts over 1 year, with 4 cars and 1 motorbike.
The Wh/mi of the Model 3 seems to be rather sensitive to tire pressures, so having a quick and convenient way to ensure consistency is helpful. 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! Why?

So, in extreme cases these would ring true for using Nitrogen (i.e. better mpg because the tire pressure were correctly set with Nitrogen or better tire longevity for stored tiers), 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 on my GT-R, but all cars and my Tesla?

With regards to proper pressure, it is the pressure which should be set in the morning at ambient temperature (as indicated on the door jam sticker - 42 psi for the Tesla Model 3 - 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 a stealership many miles away to get this done and finding the time to do it is reason #1 for an N2 setup - i.e. so convenient to be able to fill up in the garage without pluging in pump, going to a gas station with a bad nozzle or anywhere else.

As I am a stickler about getting the right pressure in the tires at the right temperature, and since I happen live in a place where the summers can be can get up to 100 F and the winters can get down to -14 F. There is a vast pressure difference that can exist for these i.e.almost 14 PSI variation.

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 later it is down to 50F, the tires will be 4 PSI lower and this is what causes increased Wh/mi and reduced tire life. Going the other way around,  can also cause unsafe pressure increases and also a cause a ride  to be harsh and uncomfortable ride. The other issue is that when temperatures drop below 32 F (freezing point for water), all the humidity that was in the air and got transferred into the tires on a hot humid 90 F 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 ideal, but is harder to get than compressed than N2 which is already dehumidified, and sold for many other industrial applications, hence cheaper. This is reason #2 for me to use N2 from a tank - always free of any moisture content.

My garage in winter stays between 30-40F while outside can be 0-10F. So I have to often account for ambient outside temperature by increasing the pressure accordingly by a few PSI, escpeally if I know the car will be outside most of the day.

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 reacts with rubber, 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 which need N2 filled tires, or keeping tires on for 5+ years, or getting the tires so hot such that every 1/10s per lap counts, the normal everyday car that has tires last 2-3 years is fine with air. 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 - reduced degradation.

It is true that N2 doesn't leak out as much, over 12 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. Awesome.

Lastly, it is so easy to top off pressure using a tiny little scuba-sized tank that can push out up to 200 psi. 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 and top off  N2 for free, but still need to go there ans wait in line to get N2 top off. Going to the dealership and paying $ is out of question.

To make my garage setup, I got a 22 cu ft steel tank from a local gas and welding supply dealer that did not require me to be a contractor to purchase it and get refills. This cost me $45. These tanks come with 99.9% pure N2, as opposed to the onsite N2 machinese 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 2200 psi 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 2200 psi down to about 50 psi, 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 Tesla Model 3 tires can be filled up to 42 psi? About 6 tires from completely empty! 1 tank was enough for me to fill, flush and fill my Model 3 tires. 

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.

Of course the setup would not be complete without adding some plastic (not metal) N2 value stem caps:
N2 plastic caps for the Model 3
How long does a tank last me - about 1 year of fill-up and topping off tires on 4 cars, 1 motocycle. 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 for all my cars including my Tesla Model 3.