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      03-31-2013, 04:58 PM   #1
ayao
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Drives: 1M
Join Date: Aug 2011
Location: CA

Posts: 591
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Tire pressures and temperatures at the track

Sorry to intrude here -- I'm a 1M guy over at 1addicts but follow some of the threads here as it seems there's a larger tracking population here. I wanted to run some of the numbers by forum folk here to see if I could glean any useful advice.

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 the idea of camber plates and whether I need them for the car.

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?)
4. Tire pressures seem more consistent with nitrogen

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.
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