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Akunob

I've never heard of ADDING air when tire pressure rises at the track. I run Michelin Cup 2s and the recommended street tire pressures are 29F & 31R (psi COLD). I typically start the morning sessions around 25F & 27R (cold psi) and bleed air (as needed) to maintain close to 30-31F & 32-33R (hot psi) throughout the day. Most of my adjustments are in 2 psi increments (or slightly more on really hot days) based on the hot psi readings taken right after piting at the end of a session. It's not NASA moon landing precision but it generally works to maintain hot tire psi in the desired range.

CDinSing

^ This ^ I start the day at 26-27 and keep them at 31F-32R as they heat up on track. Any pressure over 35 and the Cup 2s are slippery. That may be fine for easy street driving but not track or fast twisty mountain roads. Starting a drive at normal (recommended in the door jam) pressures and monitoring for a rise above 35, and dropping them back down is reasonable thing to do if you are pushing the handling limits. Remember if the car is a daily driver, when the tires cool after the spirited driving, the pressures will drop and you will need to inflate them to proper safe recommended level. When my car comes off the trailer and into the garage I add back the 5-7 psi I took out at the track.

FourT6and2

Ok double checked today. Upon startup, when cold, my tires are 29psi front, 32psi rear. I was mistaken before. Cruising on the highway, they got up to 33 front, 36 rear. When pushing it on a hot day through some twisty mountain roads, they got up to 38 front, 41 rear. So they seem to be fairly consistent in terms of the front/rear differential of 3psi. But 41 seems a bit high, no?

This is for street driving. I can't really bleed the pressure during a fun drive through backroads and then add air when they cool again. I'd have to stop at every gas station I pass to constantly keep the tires at optimal pressure. So I guess I'll keep 'em where they are and try not to go crazy when the temps get super high. When they hit 41psi, it was pretty hot out and that's the first time I really saw lots of melted rubber on my fenders. I could also try dropping 2-3 psi and starting, cold, with a lower pressure.

Joe@Fabspeed

Michelin sport CUP/ CUP2 as others have stated above need to start with a measured COLD pressure when being used hard on a race track or sustained hard cornering on the street.
FRom my experience Michelins LOVE the extreme heat and temperatures verus any other brands provided you have the cold pressures set-up and monitor the hot side.

I raced PCA for 20 years ..........but over the last 12 I have not done much track stuff. Last year I took my Mclaren with Sport CUP 2 installed and in a Rush I forgot and I inflated the tires up to the recomended sidewall pressures. The 570S was absolutely terrible............ was on damn ice skates.

Bleed them all around and it was hot as hell.............she was velcroed to the track. I was like old times and alot better than my 993RS all around thats also been in Hoosiers and CUP tires.
Try what the gentlemen above offered
COLD front-rear 26-27 and keep them at 31F-32R

Dougr743

Outside temp for air will change, the nitrogen should stay static when outside temp changes, not driving on the tire, just sitting there. That is what I am trying to say concerning nitrogen, so your starting pressure will be the same if its cold or hot out. Air will drop as it gets could, so your pressure on cold days will be less when you start.

Yes, I have had many years on the track, both cars and cycles, 10 years Pro AMA, WERA, CCS etc etc. We are talking about tire pressure due to conditions and time. IF you drop your pressure and delaminate the tire, over heat it, and it cannot shed rubber, it will become greasy. IF you plan on burning a set of tires every time you go to the track or on an aggressive weekend, go for it. But if you want to understand operating temps, you have to keep the tire within its range for it to properly wear, shed, and sustain heat cycles.

I can roach a set of tires in 10 laps and get the best performance out of it by dropping the pressure to a level that the tire cannot sustain over time. or you can manage the pressure to get optimal function and life out of it. The tires are not designed to operate outside of a small temp window, so keeping them within the tolerance will allow the tire to perform and respond correctly.

Call any race tire distributor, ask them, Cars and bikes all respond the same way to temp and performance. Compounds are designed to give you balance. so my qualifing tire is only good for 10 laps, but my endurance tire for 50 min, maybe 100 min depending on all the variables. Same with the car. these cup2 tires are a balance of compound, siping, tread depth etc etc, they are to work in multiple environments. This is the reason everyone would perfer to have 3 or 4 sets of wheels, rainy day rubber, hot day rubber, cold day, track day. The cup2 is trying to be all those days.lol there is no perfect, but keeping the tire from over heating will create consistent results over a longer timeline. hope this helps

ExMB

And here is your biggest argument failure. Your believe in SHOULD versus reality. Park your car in your non climate controlled garage and take a pressure reading of your nitrogen filled tires lets say at 5 am when the temp in it has cooled and stabilized over night. Now go back and take another reading after the temp has increased in it after being heated all day from the summer sun. Take a reading at 5 pm now and compare that reading with the one you got at 5 am. Remember not to drive your car during that time interval; leave it parked. Come back and tell us what you got.

Nitrogen is a gas and behaves IAW with the gas law. Failure to believe otherwise is an old wife's tale that has been perpetrated to get people to pay $xxxx. I hear this constantly: but my mechanic told me it wouldn't change, blah, blah, blah.

e6tme

Guys, a couple of important points:

1) Tire pressure is not an indicator of tire temp. The proper pressure is a good baseline, but doesn't take many factors into account.
On a hot day (90 degrees+ ambient) Cup2s with hot pressures set at 30-32psi the tires WILL get greasy after a lap or two, depending on how hard you are pushing.
The Cup2 is a phenomenally flexible tire that works in a wide variety of conditions, but you can't expect it to be as resilient and fast at 90 degrees ambient as it was at 50 degrees.

2) If you filled your tires at a shop or out of a canister at home you have no idea what the actual N content of the gas in your tires is.
Normal N continent in the air we breathe is ~79%. If you "fill" your tires with nitrogen, you don't magically get 100% nitrogen in your tires, it's much more likely N content is in the low to mid 80s, which won't make an appreciable difference in tire performance and stability.
Did you measure the nitrogen content? How many times did you purge?
Pro racing teams go to ridiculous lengths to ensure max nitrogen content in race tires, and most of them are just guessing!

The only way to tell if you have a meaningful proportion of N in your tires is to fill them with something like this: https://www.jdltechusa.com/motor-sports/

3Series

+1

I've only see folks add air if they let too much out....by mistake

In my 997, I'll start 28F and 29R. Let the temps rise and try to stay at 32F/34R.
As the day progresses, I'll let more air out to maintain the temp. Sessions 2+, I'll also bleed maybe 2psi per wheel.
At the end of a 4 to 5 session day and after a long cool down ~2 hours, I'll add ~15 pounds for the ride home.

I run in the fastest/advanced groups, PCA, SCCA, BMWCCA in my region which means I'm not new and am putting the car/tires through a workout. .

Dougr743

I ignore the letting out or adding, if you have too much pressure due to temp being too high, its due to increased temp, add air, the temp will lower, the tire will maintain the proper temp better, by removing more air, you raise temp, raising temp causes higher pressure. so you keep raising the tire temp until it bakes. the temp needs to maintained, thats all related pressure when cold, and pressure when hot. The tire should not increase by 10 to 12 lbs

Dougr743

Is anyone checking tire temp? If you had a set of tire warmers, you would set the temp, then adjust the pressure, when starting cold you are guessing, excessive heat is a problem and is caused by low tire pressure, or improper tire pressure, that temp increase will cause all these side affects, greasy tires

orthojoe

^listen to this man. He knows what he is talking about

boxer-11

In case it helps anyone else, I found some of the advice in this doc quite useful. It does talk about starting cold pressures and target hot pressure ranges but it also focuses on getting the temperatures in the right ranges when up to speed. It also talks about distribution of temps across the tread and what that might mean for pressure or even setup changes; not enough to really make me feel like I know enough...more like just enough to make me sure that I don't know enough about this topic!

I do have a contact pyrometer and try to use it although probably not often enough. The question I'd ask for the experts here is this: given an HPDE environment where normally you can't expect to stop mid session and take temps in a hot pit setting the best you can do is wait out the cool down lap and get back to the paddock and then measure...so for measurements taken that way am I wasting time doing it all because the tires will have cooled too much or is there still value in the readings?? I guess more generally what advice would you suggest to someone doing HPDE on how to go about checking tire temperatures??

Bonus point question (probably relevant to less people, I know)...on my car I can get and log the internal air temp of the tires as I run around the track. I know that's not the carcass temp but I'm wondering if there is some relationship between that temperature and operating temperature of the tire carcass that would help me set the pressure better. Since I can log these values at all 4 corners I can look at the values from laps at speed during the session so perhaps that's better data than contact pyrometer readings taken "too late" back in the paddock??

Dougr743

this is my suggestion, get to 80% of your normal track tempo, make sure the car feels solid and is responding consistently. as soon as you come off your hot lap, check temp. so cold pre track, called static temp, then you last stable, solid lap, if you are within 6 to 8 lbs, you are close, then adjust. the key to tire warmers is being able to get the tire to proper temp then adjust, car, weight, tire choice etc etc are key too, but way to difficult without a purpose tire, and conditions perfect for that purpose tire. I don't even know what the recommended temp on a cup 2 is. probably don't have one. The slick will.

These things will consistently change. If i was doing a lot of track days, i would have 4 sets of wheels and tires, and warmers. keep logs and repeat so i could get the total performance out of whatever tire i was running. so track days are limited to 80% or you roach tires and fiddle with poor setup and lose your mind trying to figure it out. Bikes are similar but you have no room for error and you can adjust your body position and weight to help control tire wear. The car has so much contact patch, you have so many different compounds and surfaces and load on all the different surfaces, it can drive you crazy trying to figure it out. I run factory settings in normal conditions on the road and cannot find a time that they are fading or under temp etc etc. although I can understand how the car should feel and drive it accordingly, this could be a large part of learning the car at abnormal pressures. This leads to poor judgment on how the tire is suppose to perform vs how it actually is.

Ex. I would run my super stock 750 dunlop 207, 208's at soft, soft 30 front, 27 rear (this was 04, 05 06) burn them up in 8 laps knowing they would over perform for that limited period of time. but never in a race, and never over a track day. I would heat cycle per day, always leaving the tire at temp the entire day with warmers. So warmers are a bargain if you want 3 or 4 track days out of car tires. plug them in, set them and forget them, the tire never cycles that entire day. I don't do many track days, and if i get the itch, i will buy a dedicated car for it. My .2 was a mid life crisis purchase.lol I just like to drive the mountains, talk cars with others and enjoy the views. I think the cup2 tire is overkill for the street. Its probably a great tire for the track if you take the time to figure its best temp performance range

boxer-11

The doc I linked above is I think for the gen 1 Cup tire. It calls for an ideal temp in the range of 160-220F. I suppose it's possible that the cup2 would be a lot different but if I had to guess I'd imagine the range for that is similar to the older version given same family and design brief.

There's obviously a lot to the business of optimizing performance out of tires, not to mention understanding how to trade off wear. I think I followed just enough of what you said to know this is all way over my head still. And some of it is out of practical reach to -- I drive the street car to the track and there's no practical way to carry 4 sets of wheels and tire warmers and so forth...I can see how that approach would make good sense though.