The Mustang Forum for Track & Racing Enthusiasts

Taking your Mustang to an open track/HPDE event for the first time? Do you race competitively? This forum is for you! Log in to remove most ads.

  • Welcome to the Ford Mustang forum built for owners of the Mustang GT350, BOSS 302, GT500, and all other S550, S197, SN95, Fox Body and older Mustangs set up for open track days, road racing, and/or autocross. Join our forum, interact with others, share your build, and help us strengthen this community!

Nitrogen tire fill

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

I will start using Nitrogen for my tires. I just bought a few sets of Conti G5000 slicks from the discount sale right now. As I understand, with normal air, you start 28 cold and aim for 36 - 38 hot. I may be off so feedback on those numbers would be most helpful.

The other question is, how much less pressure gain could you expect with Nitrogen. For example, if with air you gain 10 PSI, would you expect like 5 with Nitrogen? Or would it be more or less than that. I know a million factors are involved, just trying to get some generalized answers as to where to start teh Conti's on Nitrogen.

Thanks in advance.
 

Mad Hatter

Gotta go Faster
5,237
4,227
Santiago, Chile
I would not waste your time with Nitrogen.... Its hard to get a good "Dry" tire fill and it makes it harder to control tire pressure at the track. As it is going to the track on a hot day or cold day changes everything!! You would need to take a Ntrogen tank to the track etc.

I can't wait till my P2000 tires arrive, they were on sale as well! Looks like they use a little less air the the R7's
 

Mad Hatter

Gotta go Faster
5,237
4,227
Santiago, Chile
Looks like the G5000 runs at about 2psi less then the R7.

About the G5000...

" It will be a bit slower in speed when run on a flat road course compared to the P1000, or P2000 tire which is a Flat Road Course tire only. Actually the G5000 tires are made with the R7 tread compound, while the P1000 and P2000 tires are made with a cold blooded tread compound(harder) tires which take 1 – 3 laps to come up to operating temperature."

Thats what I got from Hoosier before.
 
6,363
8,187
There are a couple of aspects to this, one is that nitrogen is much more stable than regular air, partially because of all the crud that comes out of the air compressor, and two,partially because it's just more stable. So when a tire is mounted, you will get one "atmosphere" lets call it, inside the tire, so whatever that day is....100% humidity as it is here in Florida, then the "atmosphere" in that tire will be 100% humidity even before you put any air, or nitrogen in it. That can lead to issues, even when you use nitrogen, so you should at least purge that air out of the tire before you fill it with nitrogen. You don't have to suck it off of the wheel. just pull a vacuum on it, that should do it. There are devices for measuring things like that, but they are expensive and you probably won't need it.
For those reasons I can't tell you of how much "gain" you will get one medium vs the other, the nitrogen will be more... predictable..is a better word.
I don't post the pressures we run because they are proprietary, but I will tell you it's been my experience that the manufacturers are really high on the safe side of the tire, they seem to think adding pressure is the answer to all of a tire's issues. So whatever hot target you choose, subtract 8 psi from that and start there, if you are an AJ, then start with even less. The ideal plan is to come in after 5 or 6 hot laps and bleed the tires down to the target hot pressures.
There is a method for this which is covered elsewhere on this page.
https://trackmustangsonline.com/threads/tire-pressure-mapping.13121/
Don't forget that the useful life of that tire depends directly on how it is broken in..fast initial laps equals less longevity, slower initial laps mean longer life, and always use stickers for qualifying since the first 4 laps will always be the fastest.
 

Mad Hatter

Gotta go Faster
5,237
4,227
Santiago, Chile
Since our main track is relatively far from the sea and right next to the mountains.... its 5deg C and foggy when the track opens and by mid day is 24 deg C and dry... So to keep close to your tire pressure goal is a moving target all day, found it harder to do with Nitrogen then air (having a pump handy etc).

I look forward to trying out your AJ Hint!! I have been running my R7's at 38psi hot and was going to try 34psi for the P2000's... Planning on keeping better tire pressure logs next event.
 

Grant 302

basic and well known psychic
Everybody *should* be mapping their tire pressures...

I'm still using compressed air, but found out how bad humid air is for track use last year. It moved pressures waaay higher/faster than anywhere else on my map/chart.

You'll only know WTF is happening if you are able to look at your plotted data. Rob's advice has been priceless on this.

Dry air helps make everything predictable...
 
6,363
8,187
Since our main track is relatively far from the sea and right next to the mountains.... its 5deg C and foggy when the track opens and by mid day is 24 deg C and dry... So to keep close to your tire pressure goal is a moving target all day, found it harder to do with Nitrogen then air (having a pump handy etc).

I look forward to trying out your AJ Hint!! I have been running my R7's at 38psi hot and was going to try 34psi for the P2000's... Planning on keeping better tire pressure logs next event.

I think, if you map your pressures, you will find the goal not so much of a moving target, and you will be much more consistent. Once I set pressures in the AM, the only time I change them is for a tuning problem, unless a drastic temp rise or loss happens..usually those are the next day events, which again, I set in the AM using a formula for temp changes, but except for that correction, are the exact same pressures.
 

Mad Hatter

Gotta go Faster
5,237
4,227
Santiago, Chile
I will give it a try being more diligent with my logs... Did notice in summer (our summer is in Jan and feb) I could leave the tire pressure alone and everything settled in ok, But just got new tires and longer race events in a new series so am still getting used to it (running around in a panic is another way of describing it). Found I had left my shock on full soft for the last event....... Thats what happens when you work on your car all night!!!
 
I have a friend who will fill and purge my tires several times to get as much air out as possible, so that is not a problem. Nitrogen is inert while air itself is not. I want to have more sonistent pressures. Plus, once the tires are filled, I am sure the 11 gallon tank I have would last a whole weekend (probably a lot more if tires don't bleed) of topping off if needed. Air's main problem is water, which expands via PV=nRT. Oxygen itself is also less inert than Nitrogen as well. As is CO2. So, it is really not a big deal for me to run Nitrogen, so I will. I suppose I can expect 4 - 5 PSI increase with hot temps vs. 8 - 10 PSi with air. With the G5000, I will be shooting for 35 - 36 hot and see how they feel. I have never wun them before.

For me, it's just that air fluctuates so much throughout the day, that it is worth getting the Nitrogen. Here in So CA, the tracks could be fully humid and 50 degrees in teh morning and then completely dry and 80 - 90 degrees by 11:00 AM. Especially in the winter months.
 

Grant 302

basic and well known psychic
Air's main problem is water, which expands via PV=nRT. Oxygen itself is also less inert than Nitrogen as well. As is CO2

That's not correct. All gasses just have a different 'R' value or gas constant.

O2 actually has a lower R than N2. Water is almost double N2. And that's why humid air is a problem.

None of them are inert gasses and aren't more or less inert than the other.

Hope that clarifies.

The issue I had with humid air was actually when we were out at Chuckwalla. The day before was foggy in OC, and I filled both the tank and tires with that air.
 
That's not correct. All gasses just have a different 'R' value or gas constant.

O2 actually has a lower R than N2. Water is almost double N2. And that's why humid air is a problem.

None of them are inert gasses and aren't more or less inert than the other.

Hope that clarifies.

The issue I had with humid air was actually when we were out at Chuckwalla. The day before was foggy in OC, and I filled both the tank and tires with that air.

True. I meant inert compared to water vapor. I should have clarified. And I know, same happened with me at chuckwalla.

Buy yes, R values for H2O vapor is 2760 and N2 is 1775. Those values are for ATM and under ideal conditions, but of course it still shows the huge difference. And the number of moles of H2O vapor becomes a huge factor because you multimply n and R. So, the relative molar density of H20 compared to the other gasses in air becomes exponetially worse as the number increases. Hence, I want Nitrogen for it's purity (lack of H2O) rather than R value.

Thanks for sparking my brain into explaining more. I did not sleep well last night. LOL


Sent from my iPhone using Tapatalk
 
Last edited:
6,363
8,187
One of these charts I created, the other is from the internet..the 225/18 (I call it that because I never changed the name) chart, you can see the difference between the same size tires at different pressures.. pretty predictable
jgoieBpl.jpg

Here's the issue with using just air in a tire that has not been purged
ImNhLgbl.jpg

as you can see there is a huge variance with compressor air and if the temperature does spike it can really effect pressures. I've seen a 5 psi increase with air on the one tire that gets the most abuse, this happened at Road America, and is what got me started on this whole pressure /temp crusade.
 
Last edited:

Grant 302

basic and well known psychic
That's exactly it. With moisture in it, the tire would be capable of jumping between those plotted lines in the first graph. And as I've found out over 5 psi on the *expected* gain to hot pressures. That's like jumping over two of those lines.
 

TMO Supporting Vendors

Top