I had my 10 AX event in the last two years. North Country PCA puts on some awesome events. 8 runs on a course utilizing the entire airfield (best times were in 75seconds range). Four cars on the track at the same time, so you barely had time to regroup in your mind, since you had to queue up right after your run.

On my last run in the afternoon (4 in the afternoon part) it felt like I was driving on butter. Tires weren't gripping at all.
My fronts got up to about 39 in pressure and backs were 43.
Was my tire pressure the culprit?

1st and 2nd runs were nice. 3rd was getting mushier. 4th was no fun.

I was running stock Michellin PS2s.

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'07 Porsche Cayman S: de-snorked, "free sound mod". '05 Dodge Magnum RT: catback, high-flow cats, custom intake, projector headlights, SC FlashPaq.

I am no expert on this and my track days are long ago, but it just sounds like the track got hot and greasy as the day wore on. I can remember spinning in turn one at Watkins Glen late in the afternoon and it felt just like you described.

While the track probably has something to do with it, those pressures are very high for PS2s. As they heat up, and the pressure goes higher, you need to bleed-off the air pressure and get them down into the neighborhood of 32-44 front/36-37 in the rear.

brad

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21-year PCA Member
PCA DE Instructor

Beez,

The predominant opinions on this board afor PS2's for Track/DE's seems to be running the tires @ 38-40 Hot. As aspinkus commented above AX seems to be a diferent animal. THe pressures you cited (F32-34; R 36-37) is where I usually run my PS2's on the street (34F-36R on 19"). For AX I have been running a little higher pressures but one of my instructors (non - Porsche) thinks the pressures should be running more in the range you cited "hot". I haven't felt the grip go away but it's only getting warm in Reno now. For AX is the F34 - R37 a good HOT target?

Craig

I would not attribute it to the conditions of the surface. Devens AFB is probably one of the best surfaces I had a pleasure AXing on. Plus the time between the last four runs was not more than 5 minutes. So all eyes are on tires. The other Cayman at the event has R-comps on, so I had nothing to compare to.

I just know that the firs 2 runs the car felt like on rails. The fourth run was a disaster. I think the pressure in the backs went up maybe 2 points, but the pressure in the fronts went up by at least 5 points between first and last run in the afternoon.

I would have dismissed it as just bad driving, but the difference in grip was just too drastic.

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'07 Porsche Cayman S: de-snorked, "free sound mod". '05 Dodge Magnum RT: catback, high-flow cats, custom intake, projector headlights, SC FlashPaq.

I was "Apollo's" instructor yesterday, and also the "other Cayman" out there (a non-S), on Kuhmo 710s. It was a hot and dry day, mid '80s. Tires were heating up a LOT. I typically bled off 2-4 lbs per run. The really serious guys broke out the spray bottles by the end of the morning sessions and used them extensively in the afternoon sessions.

The "greasy" feeling the SC was experiencing was almost certainly due to overinflated tires and excessive overheating of the compound itself. Too bad I didn't know about it at the time, we only took a few runs together in the morning...he didn't ask for any coaching in the afternoon. I would also advise Cayman autocrossers to seek the advise of Boxster drivers (there were about 10), some with a decade of experience in these cars.

This was my first real test of the "new set up", which is a hybrid between PCA's "production" class, SCCA's AS, and COM's Time Trial Stock Class. PCA's rules allow almost unlimited suspension upgrades except camber plates, whereas the other two just allow non-adjustable shocks, and all allow R compounds (which is all I've done to be legal in all 3). I finished a respectable 3rd, behind an early Boxster, the class champ, and we were both beaten in a late and very hard charge by another extremely experienced autocrosser, also a Boxster. While they both drove very well (and clearly outdrove me!) and have tons of events in these cars under their belt, I think this particular circuit (a couple of very tight pivots which required digging out from a dead stop) rewarded their lower gearing more than some layouts.

Perhaps the clearest lesson I learned was that unlike a 911 the top guys were running almost dead even tire pressures front and rear. I finally tried it and it worked very well, knocking off nearly a full second. In fact, the class champ (2 yrs running no less) says he typically has 2 lbs more in the front. Hmmm. Would this also hold for a 300 hp CS? I'd try it because the f/r wt balance isn't all that different.

So, looking forward to seeing you at the next event, Apollo, and good luck with your new home!

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2007 Cayman, midnight/tan
2004 Mercedes Benz E500
2003 BMW 330i (RWD), ski car and wifey-mobile
1993 BMW 325is Spec E36 race car

Take a big sprayer filled with water to wet the treads down between runs. It will make a huge difference as the pavement gets hot and slippery. It sounds like your tire pressures are about right - I always put a little extra in mine and it feels better. I tried the water after watching some of the regulars at my last AX and my times dropped almost 2 seconds. Try it - it works. Have fun!

I've been running AX's with 45 front and 40 rear hot. I have OEM Continental Sportcontact 2's (I think that's close to the right name - they were on the car when I bought it new off the dealer lot). This was suggested to me by Alan Jung, who is a VERY FAST and VERY EXPERIENCED AX driver, also running a CS on stock tires.

I am not experienced enough to comment as to whether or not Alan's suggestion is a good one, but he's a lot faster than me. I have been having good results my last couple of PCA AX's - usually the fastest or 2nd fastest overall on street tires. The guys who beat me are all on R's.

How can I resist chiming in after such a nice compliment from Fort?

I vote for hot tires being the culprit. Street tire compounds vary in their ability to maintain grip as the temps rise (Falken Azenis are notorious for losing grip as they get warmer). If you were running lots of laps on a hot suface with little cool-down time between runs, it is likely that your tires got too hot. The previously mentioned water sprayer is a good solution in these cases.

As for tire pressures, it really depends on a lot of factors (car alignment, driving style, suspension mods, etc). With max neg camber on a stock CS (-1.0 degrees) and on Bridgestone RE050s, I run 46 front and 41 rear. I should qualify this by saying that I am really, really hard on tires and therefore tend to run higher pressures than most. Other excellent drivers (insert Beez's name here) might do equally well on lower pressures given their own particular driving style.

OMG thats a bad deja vu! I once went off track sideways and flipped my bimmer cos of that. It was my 5th consecutive lap on an F1 international race circuit that I had lapped on literally hundreds of times in the past. It was a hot hot day, and leading up to that memorable slide, I was not going any faster through that turn (a fast sweeper)from the previous lap (in fact I was probably putting down less speed). Expensive lesson that one ...but a story to tell the kids when I get old :-)

oh btw the bimmer flipped back on all fours and while it was not in condition to track, it was drivable :-)