medtech

So the latest gimmick from the dealer is $40 for nitrogen filled tires. I know COSTCO and pep boys has been doing this for a while. Wanted to get your thoughts on this.

Meister Fahrer

I wrote a technical letter to Excellence magazine about this a few months ago after reading Johannes von Overbeek's article comparing the Flying Lizard race GT3 RSR vs a street GT3 RS.
In the article, he was complaining about the street car's handling went way off because the hot tire pressure went up like ~10psi because of all the moisture in the air in the tires.
Nitrogen doesn't have this problem which is why most (all?) race teams use it.

There's probably some chemists here, but nitrogen also apparently has larger molecules that means you don't need to add air every couple months.

Anyway, Excellence published my letter and recommends nitrogen for those reasons.....

justinbig87

My local radio station, tv news program and an email from Rusnak Porsche where I bought the car, said nitrogen was the way to go...plus it was free fill ups until the 14th of July. I like things that are free, work well, and apparently this does Only weird thing was they filled the tires 4 psi over the tire recommendation via Porsche instructions for nitrogen filled tires...does that make since?
edit: btw I ran my tires before on compressed air 4 psi less front/rear for better traction but the way the dealership filled the tires with nitrogen at 4 over, I seem to have a way more comfortable ride than before.....but haven't tested the traction on any twisties yet.

smackboy1

Apparently it's true that N2 molecules (78% of air) are larger and permeate through tire walls slower than O2 (21% of air). Also expansion and contraction differences of dry N2 vs. dry air are negligible. The benefit of filling tires with N2 is that it is dry whereas compressed air usually contains moisture.

I found this and much more on this site promoting N2 use for tires.

http://www.getnitrogen.org/deepscience/

For the average road driver, it seems a little bit of a sales job to me. You know, a little bit a science mixed in with a bunch of marketing. I note that they don't really mention that while the inside of the tire is "protected" from corrosion and oxidation, the outside of the tire is still exposed to the same 21% O2 air, moisture, and road hazards. Nor do the "savings" seem to factor in the cost and hassle of N2 fills.

MikeZ

Major inconvenience issue for those of us that have compressors at home and use air to adjust the pressure in tires.

Tippy

Do a search, has been discussed here before.

medtech

Here's my thing, my wife is a chemist so we are hotly debating this topic. If you look at the periodic table Nitrogen and Oxygen are right next to each other. In fact Nitrogen is apparently smaller than oxygen (at least by weight). Coupled with the fact that air is close to 88% nitrogen anyway. At this point I agree with meister. I think that the real benefit comes from filling the tires with filtered, dry gas.

Tippy

I believe that was the same conclusion that came from the last discussion about it. There is just too much moisture coming from the air compressors. Small dryers don't do much.

Ubermensch

The atomic radii of individual atoms and the bond lengths are very similar for diatomic nitrogen and oxygen. The technique used to measure or calculate the radius of the molecule impacts the results, but in general:

N: radius 65-75pm, bond length 110pm
O: radius 60-73pm, bond length 120pm

As others said, these differences are neglible and the real benefit is a dry gas source.

Chaos

How about propane !

smackboy1

Why stop at propane? Hydrogen would lower unsprung weight! Oh the humanity!

Leigh2

I use nitrogen in my MPSC tires on the track and solo 1; where I typically see a 6 to 8 PSI gain. I haven't noticed any difference between air or nitrogen. Dry air from the compressor at home works just fine.

Gaspasser19

Your wife is a chemist who thinks that air is 88% Nitrogen??? I hope that's a typo.

Eharrison

We all know it's 78%...NASA

JimB

Setting aside the debate over whether to use air or nitrogen, you should ask your dealer how much they pay for enough N to fill up your tires. I always have it around for race tires and the air jacks on the cup car. I think I pay about $20 a tank. I'd guess they are charging you $40 for $2 worth of nitrogen.

FWIW, I don't use it in my street cars.
Jim