[JazzCatGab]

I went to my second HPDE sponsored by the KYPCA at Putnam Park Road Course in Indiana. It was great fun and I added to my knowledge and experience of the first HPDE in June. As per my signature, I was driving my 2019 base Cayman with PASM and SC, with 18" wheels and stock Pirelli P Zero tires. I decided to torque my own lugs this time (dealer mechanics are on hand and would do it for free) and I am figuring out my tire pressure game.

As far as the lugs are concerned, the weird thing was that at the end of the first day, all the key lugs need just a little tiny bit of extra torque (117 lb-ft vs 118 lb-ft?). The other four per wheel lugs where fine at 118 lb-ft. Anyone ever see a difference in the keys vs normal lugs?

As for the tires, I was definitely going faster this time around and so the tires were hotter. Prior to getting on the track, I left them at their normal 28 psi. When I'd looked at my previous HPDE track pictures from the hairpin turn, the weight-bearing side looked perfect max tread coverage, where as the inside tires look slightly over inflated without weight on them. During a brief inspection the last day after going off the track at the hairpin, an experienced track member said he thought I might be slightly over inflated because there was little or no wear on the Pirelli indicator zeros on the edge of the tread pattern. He suggested I drop the pressure a pound next time. I plan to do this next time. The odd thing is, we had fairly cool weather overnight, and when I started out, the car indicated pressures of 26 psi, warming to 28 psi when I was on the highway driving to the track. I felt good about that but it sounds like I still need to drop a pound. Comments?

 

[DriveInHouston]

Did you check the pressure immediately after a hot lap (even from the TPMS readout). How much was it?

What was the target pressure?

 

[JazzCatGab]

Did you check the pressure immediately after a hot lap (even from the TPMS readout). How much was it?

What was the target pressure?

Thanks for taking a shot at this @DriveInHouston!

Of course, it would have taken a few seconds to look at the TPMS readout, and I have a nice pressure gauge sitting in the glove compartment. Unfortunately, I did neither. So I have no real comparative data, which probably makes my request somewhat moot. I'm a bit of a slow learner at this, or more to the point, over-cautious learner, so I'm too busy getting feedback from my instructor after the session to think of more practical data collection.

I guess what I'm looking to hear is if you more-experienced folks use strictly sensory indicators (like butt in the seat) and tire pressure data to gauge resulting needs as far as tire prep, or do you pair the pressure measurements to the built-in tire wear indicators, or if it is a combination of all these, or things I don't know about?

If I were to rephrase the question, most (all?) track rats check their tire pressures after they get off the track at some point. With some experience you use that data to create a target pressure for that track, those tires, and that ambient and pavement temperature combo. But you are using that data with your style of driving, which I suspect, becomes more stable with time. What should a rookie like me, as a moving target whose competence is slowly evolving, worry about and do regarding tire pressure? Do you make changes immediately or after the tire cools some? Is adding/subtracting X psi while at the track independent of current tire pressure? Should I, as suggested, simply drop a pound in the morning before going to the track and not really worry about it until I get to the "shaving seconds" stage of competence?

 

[DriveInHouston]

I am waaay behind you! I am trying to figure out at any given temperature (loosely speaking... like very cold, cold, ok, warm, Houston hot) what pressure should I fill the tires to.

Assuming ok being 20C (68 in Good Christian Units) I take the manual's recommendation to be 33 psi. That pressure stabilizes to 35 psi for normal driving at that ambient.

I've seen cold days (around 10C or 50F) and the tires show 30-31 measured with a hand gauge. That will get you to 33-35 once warmed up (remember there is no 34 in TPMS... )

So, it is a bit of a guessing game if you are using a gas station pump. It is 75 degrees outside and I was driving for 15 min. What should be the proper pressure so that they cool down to 33 psi?...

Thankfully we don't have different pressures for front and rear...

 

[JazzCatGab]

I hear you. Some folks keep pretty detailed logs of tire pressure vs temperature for whatever tire they are running, which makes sense if you are driving with consistent fervor. At my skill level, I think close is good enough. But so far, I’ve shown a tendency to fly off the track so I kind of want as much traction I can afford!

 

[RussellHodgson]

Thanks for taking a shot at this @DriveInHouston!
I guess what I'm looking to hear is if you more-experienced folks use strictly sensory indicators (like butt in the seat) and tire pressure data to gauge resulting needs as far as tire prep, or do you pair the pressure measurements to the built-in tire wear indicators, or if it is a combination of all these, or things I don't know about?

I always start my track days with all 4 tires set to 30 psi. I'm using Michelin Pilot Sport 4S 19" tires. This usually works well. I can tell by the end of the session if the tires pressures are getting too high because the rear of the car starts to move around more, and the car feels like it wants to slide. This usually means the pressures are 37 psi or higher. When hot they feel really good at 36 psi - this is my target. So for me it is more seat of the pants feel. If I do start getting the car sliding around, then I'll check and lower the pressures as necessary. (I've never had them be too low once I got going.)

 

[DriveInHouston]

I always start my track days with all 4 tires set to 30 psi. I'm using Michelin Pilot Sport 4S 19" tires. This usually works well. I can tell by the end of the session if the tires pressures are getting too high because the rear of the car starts to move around more, and the car feels like it wants to slide. This usually means the pressures are 37 psi or higher. When hot they feel really good at 36 psi - this is my target. So for me it is more seat of the pants feel. If I do start getting the car sliding around, then I'll check and lower the pressures as necessary. (I've never had them be too low once I got going.)

This is the information most of us are after!...

I found 35-36 to be the right temperature in long, hot Texas trips.

Many thanks!

 

[antennahead]

I found 35-36 to be the right temperature in long, hot Texas trips.

Same here. It's pretty hot in Charleston as well. I have a nice gauge that I feel is very accurate and registers in .2 lb increments. After trial and error, I have set my cold temps at 30.6 psi fronts and 32.0 psi rears. Once warmed up I'm reading 33 front and 35 rear on the tpms screen. These temps seem to provide good performance and good steering feel/turn-in without being too harsh of a ride.

 

[Treemagnet]

Same here. It's pretty hot in Charleston as well. I have a nice gauge that I feel is very accurate and registers in .2 lb increments. After trial and error, I have set my cold temps at 30.6 psi fronts and 32.0 psi rears. Once warmed up I'm reading 33 front and 35 rear on the tpms screen. These temps seem to provide good performance and good steering feel/turn-in without being too harsh of a ride.

What tires and sizes are you running? Thank you!

 

[antennahead]

What tires and sizes are you running? Thank you!

19" Sport wheels. 235/40 and 265/40. I prefer the slightly higher psi settings versus the stock recommendation. Porsche actually has 2 recommendations for the 20" wheels, standard (33 psi all around) and comfort pressure (30 psi all around), but only the one recommendation for the 19s. The 33 psi recommendation for 20s is higher than my 19" settings. I'm kind of splitting the difference. I tried 33 psi all around but found it a little too harsh once the tires warmed up. I dropped the psi a few tenths at a time until I settled on my current psi. YMMV

 

[Treemagnet]

19" Sport wheels. 235/40 and 265/40. I prefer the slightly higher psi settings versus the stock recommendation. Porsche actually has 2 recommendations for the 20" wheels, standard (33 psi all around) and comfort pressure (30 psi all around), but only the one recommendation for the 19s. The 33 psi recommendation for 20s is higher than my 19" settings. I'm kind of splitting the difference. I tried 33 psi all around but found it a little too harsh once the tires warmed up. I dropped the psi a few tenths at a time until I settled on my current psi. YMMV

Thanks, this info will be quite useful as I begin my first track day on Saturday...since 1976 @ TWS-RIP.

 

[silvia718]

I have the 19" wheels and start my track days at the factory recommendation of 29 psi front and 30 psi rear. My target is 35psi all around. I got to this target based off the advice of an instructor who also drives a Cayman (granted his is a 981 GT4). I've found it works well for me. I usually start the day comparing the TPMS to an actual readout with a tire gauge. I've found my tire gauge is close enough to TPMS (within tenths due to rounding). The first thing I do after my sessions is check my tire pressure, esp if TPMS shows that they're getting hot and exceeding the 35 psi target. If you track in cold/wet weather at all definitely experiment with the pressures for those conditions as well.

 

[antennahead]

Thanks, this info will be quite useful as I begin my first track day on Saturday...since 1976 @ TWS-RIP.

Just to make sure I was clear here, my settled on pressures are for street use. I'm not tracking the car. The pressures I'm using "might" put you a little too high once the tires warm up. Of course you can always check them after a run and see if you need to drop them a little to reach 35 psi, assuming that is your target.

 

[JazzCatGab]

I always start my track days with all 4 tires set to 30 psi. I'm using Michelin Pilot Sport 4S 19" tires. This usually works well. I can tell by the end of the session if the tires pressures are getting too high because the rear of the car starts to move around more, and the car feels like it wants to slide. This usually means the pressures are 37 psi or higher. When hot they feel really good at 36 psi - this is my target. So for me it is more seat of the pants feel. If I do start getting the car sliding around, then I'll check and lower the pressures as necessary. (I've never had them be too low once I got going.)

This is the information most of us are after!...

I found 35-36 to be the right temperature in long, hot Texas trips.

Many thanks!

Thanks @RussellHodgson, and I echo @DriveInHouston kudos for hitting the nail on the head! So it sounds like you are running what the manual says, except a little high for the fronts. That makes me feel like I wasn't too far off just leaving my tires set to 28 psi for all four 18" Pirellies, as per the manual. I'm thinking for my next track adventure (probably next June) I will take a pound off and see if I can tell a difference in stability when I get the tires to track temperature. Then, if I ever get consistent, I'll try to fine tune based on ambient temperatures. I did have a 1 minute 35 second run on a 1.88 mile course last time, but that was like one lap out of about 50 laps for the weekend.

 

[vhs]

Here's a pretty good write up on tire pressure management for the track, two scenarios and approaches. There's also a good tip about torquing your wheels between sessions. I'm taking my car to them before my Laguna Seca weekend, and will ask if it's best to break the nuts individually before torquing or break them all, and then go around and torque.

How To Manage Your Car During A Track Day

 

[CaymanMatt]

I'm more interested in the keyed wheel bolts loosening up. Has anyone else had this happen?

 

[jimmuller]

I'm more interested in the keyed wheel bolts loosening up. Has anyone else had this happen?

The OP mentioned 117 vs 118 ft-lbs. That isn't much by conventional mechanic'ing standards and is within the tolerance of any normal, typically uncalibrated torque wrench. The more interesting question is why the locking nuts were consistently different from the others. Given that they were likely made by a different manufacturer with different steel on different tools and to different tolerances so that their thread surfaces were different, the subtly different behavior isn't surprising. If they had loosened by 5 ft-lbs or more, I'd be concerned.

 

[CaymanMatt]

The OP mentioned 117 vs 118 ft-lbs. That isn't much by conventional mechanic'ing standards and is within the tolerance of any normal, typically uncalibrated torque wrench. The more interesting question is why the locking nuts were consistently different from the others. Given that they were likely made by a different manufacturer with different steel on different tools and to different tolerances so that their thread surfaces were different, the subtly different behavior isn't surprising. If they had loosened by 5 ft-lbs or more, I'd be concerned.

Good point. I forgot that the change was in the noise.
Thanks!

 

[nineball]

things have been pretty hectic for me over the past few months so i am late to the party but i'll chime in my $0.02....

i run nitto nt01, 245/40 and 275/40, in 18. for a typical track day i start out around 28 and by the end of a session i gain anywhere from 6 to 10 pounds depending on the weather. i typically shoot for around 35 hot but i also use the seat of my pants. if after a few laps i am still squealing around corners i know i am low. as russell said if i start to slide a bit (and still have tread left!) i know i am too high.

i prefer a good tire gauge over the tpms readout.

i check them, and the lugs, after every session. ambient temps play a large role.