[s-cars] Everything You Always Wanted to Know About Nitrogen, But Were Afraid to Ask

[Vincent Frégeac]

Hi All,

Since I had to dig into the Nitrogen in tires debate for my work, I thought
I could as well share my findings with you. So, here are some facts:

The FAA requires Nitrogen in Tires: TRUE
- After a plan crash, caused by a burning tire igniting a fuel line when the
landgear was retracted, the FAA conducted studies that concluded that the
time the tire burnt after the landgear was retracted would have been
noticeably reduced if the tire would have been filled with Nitrogen, since
this would have reduced signigficantly the volume of oxygen around the tire.
Conclusion for us: Except if you have upgraded your car with Mr. Fusion
engine and retractable wheels ala Back to the Future, you shouldn't care
about the time your tires will burn when your urS landgear are retracted.

The race cars benefit from Nitrogen in Tires: TRUE and FALSE
- The pressure in a race car tire will increase by up to 50% due to the
temperature. Predicting the increase in pressure is very important to
racers, so they want the same pressure to temperature correlation in every
tire they use in a race, whenever they have been filled. By filling a tire
with bottled gaz, they are sure to have the exact same gaz in their tire,
while outside air has a different humidity content when it's sunny and dry
than when it's pouring rain. On the other hand, they could achieve this
reproductibility with any dried bottled gaz, including air. The advantage of
nitrogen is it's the cheapest readily available bottled gaz with controled
content. Now, you can think that you're racing your car too, but a typical
car tire will increase it's pressure up to 10% when driven normally, up to
20% when driven hard, which mean that a 1psi difference in a F1 tire will
become a 0.4 psi in your tire when driving hard. Beside, you are not
changing your tires every few hours, just adding some air once a month, let
say, worse case scenario adding 5% of air (If you're adding more, you have a
slow leak and should do something to it). So, if this 5% of air is 100%
different than the air of last month, you will experience a difference of 5%
of 0.4psi when you're driving hard, aka 0.08psi. Now, if you're able to tell
by the way your car handle that your LR tire is at 33.48psi after the 3rd
corner after your home when last month it was at 33.40psi only, and this
difference in handling really annoys you, you should go with Nitrogen, but
for all of us who don't have a bionic seat of pants, F1 cars using it is not
a good reason to go nitrogen.

Nitrogen keep it's pressure over time: FALSE
A Consumer Report studies have compared leakage of 20 new tires when filled
with air an Nitrogen. The psi drop was anywhere from 1 to 8 psi over a
period of 1 year, depending on the tire. The difference between air and
nitrogen was between 0.2 to 1 psi. Now, this study was done with tires left
on a rack, so we cannot say the absolute psi drop would be the same when
driving. However, we can expect the ratio to be the same, which is nitrogen
filled tire will loose pressure at 80% of the rate of air filled tire.
That's better, but they still loose pressure. The difference of pressure
drop is 20% when switching from air to Nitrogen but up to 800% when
switching from one tire brand to another. So, first conclusion, choosing the
right tire is much more important than choosing the right gaz, and we all
know we choose our tire because of their handling, their fatness, their cool
factor, any reason but gaz permeability. Since we don't care about a 800%
difference in pressure drop over time, why should we care about a 20%
difference. Second, Nitrogen still leaks at 80% of the rate of air, which
means than instead of checking your tire pressure every month, you will be
able to check your pressure every month and a week (in an ideal world with
no nails, no leaking valve, no leaking mags, no tire monkeys, etc.)

Nitrogen protect wheels: TRUE and FALSE
Bottled Nitrogen is dry and somewhat inert. It won't promote rust or
oxidation even over a very long period of time. On the other hand,
compressed air, with its combination of oxygen and humidty, does a very good
job of promoting rust, which can have a visible effect with steel wheels.
Are you running on steel wheels!!!?!! Beside, IME, steel wheels rust much
faster on the outside than on the inside (below the tire) so even if the
nitrogen protect the inside of the wheel, you still have to change the
wheels because they're all rotten on the outside. Now, oxydation of
aluminium does exist too. It is much slower and produce a very fine white
powder, and Nitrogen will also stop aluminium oxydation. But have you ever
changed your mags because of oxydation of the inner part?

Nitrogen doesn't change pressure with temperature: FALSE
This is derivated from race cars using nitrogen. The reason they use
nitrogen is predictability. Bottled nitrogen is standard, so it will always
react the same way, but it is still a gas so the pressure is still more or
less _proportional_ to the temperature in Kelvin. The difference with air is
that air contain humidity and humidity will have an influence on the way
pressure change with temperature. So pressure change won't be predictable.
But as mentionned earlier, in our car, it means an unpredictability of
0.1psi each time we check and adjust the pressure. Do you really care about
a difference of 0.1psi in the 2-3psi variation of your tire pressure when
the tires warm up?

Nitrogen allows a longer life of the tire: TRUE and FALSE