Boulder GT3

How much less does nitrogen expand vs. compressed air? If I go to the track on a cool morning of 60 degrees, by the time I get to the middle of the day at 80 degrees I will have bleed off 10-12lbs or so. What would the pressure build difference be if I was using nitrogen? Thanks.

mhm993

Admitting I have no factual knowledge, I wonder, since air is mostly nitrogen, can there be a big difference?

Boulder GT3

That's what I wonder. That said, the big advantage of nitrogen is that it does not expand and contract as much with heat. Making me a bit more skeptical is that our colorado air is low humidity to start with. nevertheless, if nitrogen will cut the pressure build up some amount I may try using it.

38D

I believe that the difference has more to do with water vapor than anything else. Compressed Nitrogen has very little water vapor, so it expands very little. You can probably also put a drier on you compressor to get some benefits.

Alan C.

There was a good thread on this not long ago. One of the items noted was that it is not just simply letting the air out and filling with N2.

Do a search and you will find it. It was 2 pages long.

Boulder GT3

When I looked at the threads I could find references to the "supposed" benefits of lower pressure build up but I can't find anyone who knows from experience. Certainly most pro teams use it but is that for a small benefit or does it really cut down on the expansion and contraction?

I'm trying to figure out if it is worth hassle of mounting a tank in the trailer and not a compressor.

Alan C.

From what I gathered you had to bleed the tires several times and the pressure change was then minimized not eliminated.

Boulder GT3

Roger that. I was picking up up 4lbs in a 30 minutes session starting with tires in the 140 degree range.

Dbltime

My experience with Nitrogen was mixed. From zero expansion to 10#. Contamination from various sources maybe but basic pump air is predictable and Nitrogen is not.

Boulder GT3

Thanks Bill. I didn't want to load the question but that's what I've heard.

AW

Nitrogen, just like basic air, expands with heat. However, unlike basic air, nitrogen expands consistently.

By using nitrogen, you can precisely predict your hot pressure from a cold pressure and ambient temperature.

As many said, basic air contains random moisture which makes this prediction impossible.

If you do driving events, you can probably use some air and adjust your pressure throughout the day.

However, if you are racing and need your tires to be absolutely perfect for a race and you have no opportunity to adjust the pressure once the session is started, nitrogen is a must have.

AW

Tom W

I do not believe that nitrogen will make a significant difference. I'm a scientist and refuse to believe anecdotal information that conflicts with basic physics.

P = nRT/V is fundemantal physics for an "ideal" gas. While air is not "ideal", it's pretty close (and close enough for the race track). What it means is that your pressure will vary in direct proportion to the temperature (as Volume is fixed) and the actual type of gas will not matter. Now, I've listened to the "water makes a difference" crowd and agree that water (and not water vapror) would make a difference as it changes from liquid to vapor. If when you have your tires changed you see liquid water inside the rims, then it might be time to switch to nitrogen. On the other hand, water vapor is a gas and obeys the same laws of physics that nitrogen does.

Alan C.

This is why I enjoyed this thread so much the last time

AW

Tom,

As you know I'm no scientist. But with the cup car I have to get the michelin slicks within a range of 2 psi hot or the car feels really bad. For me, using nitrogen made a very big difference in term of being able to predict expansion from cold pressure / temperature.

With air I can easily see expansion of +2-3psi which is just pushing the tire outside of its operating range.

AW

Nordschleife

as you point out there is a big difference between theory and practice. In practice Nitrogen is the way to go.

R+C