Tire pressure starting point for R6?

[Flying Toaster]

I have an autox event coming up in 2 weeks and will be running R6's for the first time. Those with experience with this tire (or A6's), what is a good starting point for tire pressure? I realize the R6 will be hard to heat up for an autox, but I got them from a friend, couldn't refuse. My plan is to go for a 5 minute ride down the street & back to try pre-heating them. Here is my setup:

-73 911 weighing in roughly 2400lbs?
-21mm/30mm front/rear t-bars
-stock front & rear sways
-2.5 degrees negative in the rear
-1.5 negative in the front
-(I forget my front & rear toe settings, written down somewhere)
-225/45/15 hoosier r6's in the front on 15x7's
-275/35/15 r6's in the rear on 15x9.5's
-The event is in upstate, NY, so morning temp may very well be in the high 40's, low 50's

Thanks in advance. With a good starting point range, I can tweak after each run.

[JohnJL]

Mine like about 32 psi front 38 rear when warm. I am guessing you may need to start around 4 psi below before your warm up? you are going to really give them a good working out, like some figure 8 donuts off in the corner of the lot, Top Gear style.

[962porsche]

with dot-R's the rule is one LB of air to every 100 LBS of the cars weight for a starting point .
so if your car is 2400 LBS your starting point is 24 LBS of air pressure .

driving around the streets will not do a dam thing to build the heat needed in your tires to work as they should and build the heat needed to get them up to temp .
the R'6 like to be about 200 degrees F.
even after your run at a auto-X your not going to get the tires that hot to get them to grip .

[paradisenb]

Well, it is track and track temp specific. Best to build a log book and keep it up to date. My experience is on a racing circuit. Going to be difficult to get operating temp heat into R6's in 1 minute runs.
I have a 2700 lb 911 and generally like to run 36 psi square hot. I start around 30-32 and check temps after session and note grip. Move up or down in small increments until the car feels hooked up by your standards. Record in log book.

[kandhmfg]

My best experiences on R6s, with a 2300 lb car on track are 28-30H front and 30-32H rear. 245/275 on 16s. I usually start them cold (as 962porsche stated) around 23F and 24R. They will usually pick up about 6lbs +/-, but track and temp dependent. When I run higher pressures, the car is much looser. But that may be a benefit in the autocross. I like a looser car in Autox vs. track.

[SCOTITUDE]

from hoosier website.

VEhICLE SIzE hOT PRESSuRE COLd PRESSuRE
1800-2200 LBS. 30-33+ 22-27
2200-2600 LBS. 31-34+ 23-28
2600-3000 LBS. 33-37+ 23-28
OVER 3000 LBS. 34-39+ 23-29

[Flying Toaster]

Thank you all for your feedback, all very helpful info. I will report back my log from the day, hoping for good weather...

[campbellcj]

I have been running them at 36psi hot (square). My car is very light but this seems to work. Stuff I heard and read over the years indicated that the R6 likes higher pressures than other DOT-R tires and also more than most slicks.

[kandhmfg]

I will throw in that you be sure you have calibrated your air pressure gauge. I have had problems myself with bad readings on my own gauges. For a about 3 yrs, I was using one that gave a reading 4lbs lower than what the actual pressure was. Nobody could believe that I ran such low pressures with RA1s...30 hot...for years. That's because the pressure was actually 4-5lbs more than the gauge read, which in the end made sense. Because RA1s like 35hot...Figured it out when I borrowed air from a buddies tank that had a gauge on it, which varied greatly from my own.

This weekend racing, I forgot my gauge, borrowed a friends, what do you know started at my normal pressure. However his gauge read 4lbs lower than the actual pressure. Car was loose from the get go. I thought the tires were shot. Then I used another guys gauge, tires were fine, pressures were too high. We compared his to a few others, same thing, his gauge was bad. Tires were fine.

[Walt Fricke]

Most of us accumulate quite a number of gauges, not to mention what are on compressors or air tanks, over the years. Frightening to see all the variation.

[Flying Toaster]

I agree. I have two gauges. One is definitely off by 5-10psi. Its the one I use for my RV tires which are G rated and need to be at 110psi. I figured that out when I purchased a TPMS system & it always was off by several psi.

So far the weather looks ok for this sunday. 50 degrees in the morning, warming up to 60. My combined vehicle & driver weight is 2530 with 1/2 tank of fuel, so I will start the tire pressures at 24F / 27R and go from there. I will pre-drive as much as possible to try to get some temp in the tires, hopefully. (With 400ft/lbs of torque, at least the rears will heat up quick )

Thanks again. -John

[Flying Toaster]

So it ended up being cold (45 degrees) all day with on/off showers and the parking lot was in mediocre condition at best. A good portion of the surface was wet for 6 out of my 8 runs during the day and on a 40 second course, 20 seconds of it was on pavement that was in poor condition and deteriorated throughout the day. (You could not only see the loose asphalt on the surface, but could hear it in the wheel wells of every car that went by). The cars that did well at the event were all wheel drive...
962Porsche was dead on, even after driving / weaving on the R6's for 10 minutes on area roads trying to heat them up, the air & road temps kept them stone cold. I started the day at 24/27psi and ended up lowering them to 21/24 by my last run.
On my 6th run, the course had dried and it was my best run of the day as the tires were really starting to grip. Unfortunately a quick shower rolled through before my 7th run...
So in short, I am anxiously awaiting next year for a hot summer day to really test these tires out. (I understand the R6 is not meant for autox, but again, its what fit my budget).
I appreciate everyones feedback, thanks again.