Managing tire PSI on track
 

Backdrop: I’ve been running MPSC2s consistently on track and have religiously set cold tire PSI at 26F/28R for the 1st session. I then bleed air between subsequent sessions to try and maintain 29-30F/32-34R. However, in a few track-focused threads I’ve read of folks who,

(1) set the same cold PSI for all FOUR tires (e.g., 25F/25R)
(2) don’t bleed any air at all between sessions

I will be trying the Dunlop SR Maxx 2s for the first time this DE season and I want some help understanding if one approach is better than the other on track. Is the same hot PSI F/R ideal vs. maintaining a 2-3 PSI difference between F & R and whether to bleed or not to bleed air between sessions? The argument being that continually bleeding air causes excessive overheating of the tires and degrades the tires faster. Any input on how your tires have performed at the track in either scenario above would be greatly appreciated. Thanks

FWIW, I’ve been coached by an experienced Porsche racing support shop to do what you have been doing....successive bleeds immediately after cool down lap.

I've been doing DE now for 17 years, and I've heard the opposing arguments you've mentioned. The only specific article I know is the pdf file put out by Michelin about the care and feeding of MPSCs. Everything else seems to be hearsay. So, I start off 26/28 on cold tires, then bleed the tires down to the desired pressures at the end of each run, the sooner the better. I check the tires again the next morning, and usually have to pump them up again to 26/28. As to equal pressures all around vs pressure differential between front and rear, that depends on what suits your driving style, tire wear and camber settings.

Glad to hear, if an experienced Porsche racing support shop recommends the same then I’m no hurry to change

Thanks, I follow a similar routine. The only difference is that I add back about 10-15 PSI to each tire at the end of the first track day for the drive back to the hotel/dinner etc. (the hotter the day, the more air I had to bleed). Next day I reset to 26F/28R for the new session, same as you. I run a fairly standard track alignment around -2.5 F/-2.0R camber (I forget the toe settings etc but it’s nothing wacky) and my tire wear is fairly consistent. On driving style, I’ve never run with equal pressures all around so I have no idea if it suits my driving style better, maybe it’s worth trying it out once, for reference.

I too run MPSC2 on my GT3 and my RS before it. I subscribe to the bleed b/w each session (as needed) approach. I also try not to remove more than about 2 lbs at a time.

The start really low and try to avoid bleeding approach works too but you'll wear the sidewalls

I agree with your approach and found Dunlop Maxx Race 2 to be happy with the same settings as the MPSC2. 34-35psi will make the tires very greasy feeling, so watch pressures when pushing hard before the tires are stabilized.

Thanks. This makes me wonder whether the “start really low and avoid bleeding approach” is a West-coast, south Florida phenomena where higher ambient & track temps means that tires gets hotter quicker and PSI rise faster so it’s easy to gain 10+ PSI in the outlap and avoid sidewall wear. Some have posted starting cold as low as 22 PSI in these climates.

Thanks, good to know that target hot pressures are similar for the Dunlop Maxx Race 2, makes life easier. On track, I keep the PSI gauge on the right dash cluster to keep an eye on it. I’ve found the car’s psi monitor to read about 1-2 psi higher than my Longacre tire pressure gauge.

Any thoughts on equal pressures all around? Would the lower rear tire pressures possibly help with rear grip (ability to get on throttle sooner on corner exit)?

25 years porsche racing and I can tell you that you are on the right track (no pun intended) but bleeding should be done as follows:

1. Have someone in pit lane with pressure gauge waiting.
2. Come in HOT, not after cool down lap as tires lose pressure quickly and you will not get true readings.
3. Bleed down as needed in the pit lane, driving slowly to your pits loses pressure and again will not get true readings.
4. If just DE’s time yourself (time on track not lap times) and come in a lap or two early so you can stop in pit lane, bleed and go park it.
5. You should only have to do this once all day as long as your session was with your true fast laps. Possibly do again after lunch break as weather may change and we all go faster after lunch. ��

Thanks ohniner, this is a great tip. I’ve been doing the standard, stay on track (gotta get every lap in...LOL), spot the checkered flag, back off and do the semi-parade cool down lap, pit, drive to my spot in the paddock and then check tire pressures! :-o I’ll be sure to try this approach.

Always remember that each pressure gauge will read different, once you start with one gauge you have to use it the entire weekend unless you want to start from zero again.

Read my op in this thread on how to deal with the Dunlop2 tires.

https://rennlist.com/forums/991-gt3-...rack-talk.html

The downside on the Dunlops is that they take 3 laps to really get the heat into them so they will stick and the first session is pretty much a throwaway session trying to get them up to pressure and temp. Warning: they do not grip at all when totally cold. Unlike cup2 which grip right away.

I love the Dunlops

Agreed. I use the Longacre as my primary gauge all weekend. The TPMS monitor in the car is just for reference when i would fell the MPSC2s start to breakaway/slide/get greasy. Now that i think about it, the tire's breakaway may have been partly due to the characteristics of the N1 Cup 2s progressive falling off as heat cycles added up.

"Plan on your first session of the day as a throwaway warmup session. Unlike the cup2s, which are good to go right away after one lap, the dunlops need one session to get up to temp and pressure. I start out with 26psi dead cold on all 4 tires. The tires WILL slide everywhere if you try to push quickly, unlike the cup2 which grip right away. It will take several laps, but each lap will be faster and faster and faster. At the end of the first session pressures will be around 36psi in the front and 38 psi in the rear. Drop the pressures down to 33psi in front and 34 psi in the rear and then leave it alone for the rest of the day. The car will be super consistent. On cup2s I would usually get 3 laps to get a fast lap before the tires start falling off. On dunlops I would need 2-3 laps before they really started to grip, but I was getting fast laps on lap 3 and lap 12 with no dropoff after that. Tire pressures with constant hard driving for 30 minutes would never go above 35F/36R and that was fine."

Thanks orthojoe this is perfect from your .2 3RS thread. I had not seen this thread as I've been more focused on the .1 & .2 GT3 track threads. Good to know about the first session "throwaway" and the 3 lap warm up thereafter! i would have definitely been pushing it after one lap (similar to the MPSC2s), and would have likely reported that the Dunlop Race Maxx 2s sucked big time if they were sliding everywhere early, relative to Cup 2s! I'll try this next week (I'm at Limerock) albeit with an initial staggered cold setup and shoot to maintain 32psi F / 34psi R and report back. The promise of consistently fast performance 'till they cord is why I'm giving Dunlops a try this season. Constantly "managing the tire" with MPSC2s was getting tiring...no pun intended.

For those who haven't read orthojoe's .2 3RS Thuderhill track thread, the video alone of the chase/follow by the ZL1 1LE is worth its weight in gold!! Thanks Joe!

Reporting back with updates

1. The Dunlops Race Maxx 2s are superb track tires and inspire confidence...they grip! Ran them at 2 events (2 weeks apart, Limerock & NJMP Lightning)
2. Starting cold pressures were 26F/28R (psi) (ambient temp about 50 degrees) and bled down to 30F/33R (psi) and they performed great. Ambient temps were slightly warmer for the 2nd event so starting cold pressures were 25F/27R
3. Noticed that the Dunlops weren't as "greasy" at 36psi in the rear as the MPSC2s which suggest that higher psi's might be OK for the Dunlops. Will explore (32-33F / 34-36R) (psi) at the next event
4. Tire temps, measured with a Pyrometer were even across front and rear (around 115 degrees), tire wear was consistent and even throughout over 4 track days
5. Biggest challenge was getting readings quickly after coming off track (kept the gauge in the glove box to speed things up)
6. Overall - great track tire. I was a bit cautious and took 2-3 laps to warm up the tires, however grip seemed decent after the 1st out lap. Interesting note, I didn't hear much tire squeal in the corners which suggests either that (1) I wasn't pushing hard enough or (2) these tires don't communicate as much

https://cimg8.ibsrv.net/gimg/rennlis...68bd95db89.jpg

https://cimg9.ibsrv.net/gimg/rennlis...378966d1b5.jpg

https://cimg0.ibsrv.net/gimg/rennlis...d609a2d038.jpg

Hey those BBS look so so good! What are your alignment settings for the Dunlops? Thanks Mike