You're probably going to get higher than 'normal' operating temps on the track compared to the street. Therefore, to keep the temps as low as possible, you want to keep tire deformation (source of heat) as low as possible.

If you're tracking the car in the winter on summer tires, then that's a different story.

 

You're mincing words. Every rubber compound has an optimum temperature for producing friction. Too cold and it slides because it doesn't generate enough friction. Too hot and it's greasy with quick fade. You don't want to keep temperatures as low as possible. That would be as foolish as assuming your engine runs better at 160 degrees than it does at 180 degrees (or more.) You want the tire to run at the temperature producing the most friction. You adjust air pressure to limit sidewall flex so it generates enough heat to get into the best friction range but not so much that it doesn't flex enough and runs cold. Hence the term "optimum."

Rubber behaves with a hysteresis performance curve. Ideally, you want to be on the flat part at the top and stay there. Falling off the top means the tire is not performing best.

 

Ok guys, thanks for all the technical knowledge about proper tire inflation for track use. For those of us who don't plan to track our cars, just your ordinary everyday driving, here's a link that is less technical. You decide for yourself.

http://www.nbc6.net/news/5066742/detail.html

Just click on the play button and watch the video.

 

As lobuxracer stated previously we use N2 in aircraft mainly for its temperature stability. It is most benifical in the winter months that's why I run N2 in my winter tires and never had to top them off in my Highlander or IS. You guys in CA may never see the benifits on the street but in the North East I would run N2 in my summer tires as well.

 

Let me try again and put it another way:

Out of all the track days I've done on max performance summer tires (which include the PS2's, GS-D3's and S03's) I've exceeded the 'optimum' temp to the point the tires feel 'squirmy'/'greasy.' Those tires feel great in the first half of the 20 minute session and start to lose their grip in the last half/third of that session as they heat up.

This is the basis from which I am advising trying to keep the tire temp as low as possible on the track as you'll most likely go past the 'optimum' temp anyway. I hope I'm not 'mincing words' again and I'm making/made sense.

Just in case:
1. I agree that tires have an optimum temp where they have the most effective mu.
2. On the track on street (not race/R compound) tires, you'll most likely exceed the optimum temps to the point where you'll lose performance.
3. Keep the tire pressure up to reduce the heat generated by tire deformation and you'll also get the added benefits of sharper turn-in, etc.

 

Uh, I don't want to be a jerk or anything, but this thread is full of b.s. First, I'm under the impression that racers (big time--open wheel, F1, etc.) use nitro in their tires so that the pressure adjustments they make are more accurate (as mentioned, nitro more stable than oxy). Extending tire life sounds like crap to me. Second, as for inflation pressures...I'm sure that those of you who track your cars know the prime operating temperatures for your tires. Having said that, tire pressures are based on a "cold tire". So, to inflate (or deflate) to a point below the "cold" measure would seem to me to be putting you at risk for delamination particularly as you warm the tires. After that, you had better damn well keep those hides in the boil, or you could be in trouble, I would think. To me, it would make more sense to inflate (or deflate) to the minimum "cold" measure, and then go. I don't think that the tire would get so hot that all traction would be lost. If it did, you are simply on the wrong tire for the track. In that instance (and hold on here for the revelation of the century), you should get some purpose built track tires. Tah duh!!!!

Revman

 

Is putting in nitrogen that expensive in the U.S.?

Here, I now get it for free at a local tuning shop...but they would charge about $20 USD normally with lifetime refills. Last time I checked, Costco was doing it down here for about $12 USD.

I have never heard anything harmful about using nitrogen in the tires.

 

Revman - sounds like you've heard a lot. What have you actually experienced? BTW, once your tire goes greasy from overheating, it will never be the same again. I know this from experience, not what someone told me. Same as what I said about using N2. Experience, not what someone told me. If you think it's b.s., what have you experienced to back up that statement?

al503 - I agree with what you are saying with one exception - if you overheat the tires not only do you ruin them, but it's a clear indication you didn't have enough cold pressure. Even street tires will be OK on a track day as long as you recognise they have limits and you have enough sensitivity to what they are doing to know when you are exceeding those limits. In truth, there isn't anywhere near enough tire under a 2IS for track duty. A car this heavy should be rolling on at least 315s on all four corners, but that's a different subject altogether.

 

10-4. I've tried higher cold temps but I didn't like the way the tires broke away at the limit. I still consider myself 'intermediate' and I'll take a little trade-off in terms of losing some grip as the tires heat up v. not enough warning before the tires lose their grip, period.

You're right about the rubber on the IS. I'd settle for 275/285's all around.