I'm the beneficiary lightly used slicks for practice from several friends who race the GT3 cup series w/Imsa. I mount and fill those used sets with air since it's for practice only. I mount, bleed twice, and then refill my race sets with nitrogen. The difference in track temp gains is significant. I can count on a cold fill of nitrogen 23F/21R to come in within 1lb. of my target pressure of 30 degrees hot (as long as we're running hard). With an air fill at those temps cold, it's always a crapshoot. Usually the rears will get to 32-33 and require trackside bleeding, while the fronts remain more stable probably because of less weight....

 

Nitrogen from a tank is totally dry (no liquid water) that is why it is better- it's the ONLY difference between pure Nitrogen and air from an air pump.

 

I'm thinking through the issues I had this weekend with air pressure going up so much. I've never had this much of a swing in pressure. The cups aren't as sensitive as slicks but they don't work well at 40lbs when you want 36lbs.

I just had the MPSC's put on Thursday. It's been kind of wet here and I'll bet the compressor that filled them had a lot of water in in. It's usually dry enough here that many don't fit a drier if they aren't painting. I'll let all the air out and fill off of my compressor which I have drier on.

Still thinking about putting an N2 tank in the trailer instead of a compressor. If I can get some life out of the bottlesrunning an impact wrench off of it as well I'll probably do it. Thanks.

 

The amount of water in the tire does make a significant difference on the pressure change from hot to cold. The amount of water that gets into your tires depends on whether of not you have a filtration system, how often you drain your tank, etc. When I switched to nitrogen I had to increase my cold pressures by 2 to 3 pounds to achieve proper hot pressure, and they were way more consistent than they were with air, apparently the various compressors I had been using to fill my tires had a lot of moisture in them. As mentioned in the other thread dry air should expand at essentially the same rate as nitrogen (since air is 70%+ nitrogen), but I don't know too many tire shops or garages with dry air systems.

Here is the other Nitrogen post:

https://rennlist.com/forums/showthre...light=nitrogen