Tire pressures and temperatures at the track

[ayao]

My first HDPE of the year was with HOD at Thunderhill in the intermediate run group (for the first time.)

Big O Tires was out there with a crew of people offering free nitrogen flushes in addition to tire pressure measurements/adjustments and pyrometer readings. I stopped by immediately after each track session primarily because I've been recently obsessed with camber plates.

I wanted to run some of the numbers by forum folk to see if I could glean any useful advice.

Relevant info is as follows:
-staggered 245/40/18 - 265/40/18 on OEM M3 18" wheels on factory PS2s
-35 psi cold all around
-tires have maybe 7,500 miles and 3 HPDEs on them
-stock suspension
-starting ambient temps were 60F warming up to 80F as the day progressed
-20-25 minute sessions, counterclockwise direction
-MDM mode
-RBF600 fluid and PFC08 pads

Session #1
LF temp (outer/middle/inner) - 98/102/101; 40 psi
RF temp (inner/middle/outer) - 103/102/104; 41 psi
LR temp (out/mid/inn) - 97/95/96; 40 psi
RR temp (inn/mid/out) - 96/97/100; 40 psi
-tires were purged with nitrogen and pressures adjusted to 34 psi front / 30 psi rear

Session #2
LF (out/mid/inn) - 130/128/125; 36 psi
RF (inn/mid/out) - 128/132/134; 37 psi
LR (out/mid/inn) - 122/126/129; 33 psi
RR (inn/mid/out) - 128/128/125; 33 psi

Session #3
LF (out/mid/inn) - 128/130/128; 37 psi
RF (inn/mid/out) - 134/143/142; 37 psi
LR (out/mid/inn) - 125/129/132; 33 psi
RR (inn/mid/out) - 134/133/133; 33 psi
-front tire pressures reduced to 35 psi

Session #4
LF (out/mid/inn) - 149/152/152; 37 psi
RF (inn/mid/out) - 155/162/157; 36 psi
LR (out/mid/inn) - 142/150/152; 34 psi
RR (inn/mid/out) - 152/151/149; 34 psi
-front tires pressures reduced to 35 psi

I didn't bother getting measurements after the 5th session. Session #1, the tires felt great. With each subsequent session the tires felt progressively greasy and slippery. Session #4 just felt like a disaster. (Session #5 was salvaged by dialing back the pace and paying more attention to smoothness and consistency.)

I'm trying to reason through the data and don't have enough experience to draw even broad-brushstroke conclusions about car setup or driving deficiencies.

My analysis of the data:
1. right-sided temperatures are higher than the left, since we were driving the track in a counter-clockwise direction
2. no problems with RR camber given relatively even temperature distribution
3. LR inner temps are higher than outer temps given the direction the track was driven -- (is a 10 degree temp difference significant or acceptable given the track configuration?)

My conclusions are that I need to burn through these PS2s. (Incidentally, tire pressures the following morning were about 28 psi cold.) They're great on the street but no good for the track. After that I'm hoping that AD08s in the same stock sizes will be a reasonable next step. My impression is that camber plates won't offer very much at this point.

I'd greatly appreciate any insight the track warriors on the forum have to offer.

[MDORPHN]

I've had good experience with PS2s on the track.

I'd generally start around 28.0-28.5 cold and shoot for 37-38 hot -- at all four corners -- on track (measured immediately after coming in after a hot lap).

Don't have much experience with nitrogen. I believe the theory is that since it contains less water vapor, they don't experience as much as a pressure increase on track.

Neil

[3liter1]

looks like the decrease in tire pressure caused an increase in temperature. The tire guys who gave you nitrogen did you no favors. Rule of thumb is to run 5psi higher for track than street. I sometimes wondered why, but your data seems to provide the explanation

[ayao]

That is one way to interpret the data but I'm not convinced that it's the root cause. I think rising ambient/surface temps may have played a larger role than the nitrogen. In fact at the time I interpreted the data to mean that the nitrogen was more consistent and required less pressure adjustment.

And ultimately based on what I've gleaned over at the M3 forum, these temps may be relatively meaningless because they weren't taken -immediately- after a series of hot laps. I generally ran at least 1/2 a cooldown lap and typically had to wait 5-10 minute before getting the temps actually measured.

[vantagesc]

Originally Posted by AudiS4

looks like the decrease in tire pressure caused an increase in temperature. The tire guys who gave you nitrogen did you no favors. Rule of thumb is to run 5psi higher for track than street. I sometimes wondered why, but your data seems to provide the explanation

Sometimes that's a bandaid to avoid tires rolling over for heavy cars or cars without enough camber. Too high of a pressure will over work the tire, cause it to overhear, and then chunk. Have seen this many times from track newbies who forget to lower their "cold" tire pressure from street levels.

[vantagesc]

Originally Posted by ayao

That is one way to interpret the data but I'm not convinced that it's the root cause. I think rising ambient/surface temps may have played a larger role than the nitrogen. In fact at the time I interpreted the data to mean that the nitrogen was more consistent and required less pressure adjustment.

And ultimately based on what I've gleaned over at the M3 forum, these temps may be relatively meaningless because they weren't taken -immediately- after a series of hot laps. I generally ran at least 1/2 a cooldown lap and typically had to wait 5-10 minute before getting the temps actually measured.

Yes, five to ten minutes is way too long. Ideally you have someone take te temps in the hot pit without a cool down. Since I don't have a pit crew the first thing I do when returning to the paddock is check the tire pressure.

[MDORPHN]

Originally Posted by vantagesc

Yes, five to ten minutes is way too long. Ideally you have someone take te temps in the hot pit without a cool down. Since I don't have a pit crew the first thing I do when returning to the paddock is check the tire pressure.

+1

Neil