07-01-2013, 11:50 AM
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#1
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Registered User
Join Date: Mar 2013
Location: New York
Posts: 347
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Autocross tire pressures
Any autocrossers out there with a recommendation on tire pressures to run? I have a base Boxster with 16 inch wheels.
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07-01-2013, 12:33 PM
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#2
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Certified Boxster Addict
Join Date: Nov 2010
Location: Los Angeles
Posts: 7,669
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What tires are you using?
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1999 996 C2 - sold - bought back - sold for more
1997 Spec Boxster BSR #254
1979 911 SC
POC Licensed DE/TT Instructor
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07-01-2013, 01:00 PM
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#3
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Registered User
Join Date: Mar 2013
Location: New York
Posts: 347
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Formoza f-1 on the front. Rears are a different make, I'll check when I get home tonight...can't recall the name!
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07-01-2013, 01:55 PM
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#4
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Registered User
Join Date: Jul 2009
Location: Arlington Heights, IL
Posts: 1,561
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Quote:
Originally Posted by Blackcloud
Formoza f-1 on the front. Rears are a different make, I'll check when I get home tonight...can't recall the name!
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You need 4 matching tires. Then worry about proper pressures.
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07-01-2013, 04:46 PM
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#5
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Registered User
Join Date: Apr 2012
Location: Riverside, CA
Posts: 1,666
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With different tire makes and supposedly different stickiness of the rubber it will probably be a bit difficult to predict how the pressure needs to be adjusted.
I'll give it a shot at explaining and then the experienced racers can correct and fill in the gaps. (I'm still very new to AX, under 10 racing days)
It may be a case of trial an error, but from what I recall was told to me at an AX you start with the tires recommended pressure and then + or - a pound or two of pressure at a time depending on what the tires/car do when cornering hard.
The goal is max tire contact with the pavement and equalizing the front and back adhesion so that you have the best grip possible and equal break away of the front and back under higher G's. To reduce under and over steer.
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"It broke because it wants to be Upgraded  "
2012 Porsche Performance Driving School - SanDiego region
2001 Boxster S, Top Speed muffler, (Fred's) Mini Morimotto Projectors, Tarret UDP,
Short Shifter, Touch Screen Dual Din Radio, 03 4 Bow glass Top (DD & Auto-X since May 17,2012)
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07-01-2013, 05:21 PM
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#6
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Registered User
Join Date: Apr 2010
Location: Canada
Posts: 3,151
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36 front / 38 rear work for me.
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07-24-2013, 02:41 PM
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#7
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Registered User
Join Date: May 2011
Location: weehawken nj
Posts: 240
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I liked 34/38 on street tires.
On slicks I like 35/38
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07-01-2013, 01:03 PM
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#8
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Track rat
Join Date: Nov 2006
Location: Southern ID
Posts: 3,701
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Yes exact tire sizes and model please for best response. Also your skill level: How many years have you been AXing? Any suspension changes or stock?
I was not aware you could still get 16" wheels on a 2004 Boxster. Hmmmm.
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2009 Cayman 2.9L PDK (with a few tweaks)
PCA-GPX Chief Driving Instructor-Ret.
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07-25-2013, 11:36 PM
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#9
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Registered User
Join Date: Aug 2004
Location: Alta Loma, CA
Posts: 1,334
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I run our Hoosiers at 24 cold.. lol for 30hot (on most SoCal days) Maybe 32 if we are playing with chassis tuning.
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07-30-2013, 07:29 AM
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#10
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Registered User
Join Date: May 2011
Location: weehawken nj
Posts: 240
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24 seems really low. I tried running kunmho v710s at 30 psi and ended up losing pressure through the sidewall after a run...
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07-31-2013, 07:21 AM
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#11
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Registered User
Join Date: Aug 2004
Location: Alta Loma, CA
Posts: 1,334
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Big,
it depends on the tire size and whether it is an A6 or an R6  It also depends on surface and surface temp.
cant say that I've lost pressure through the sidewall on ANY tire, but I *guess* it's possible??
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Engine Builds, Transmission Builds, Engine Conversions, Suspension Installs, Suspension Tuning, Driver Coaching, Data Acquisition, Video, SCCA/PCA/POC/NASA/GRAND AM/ALMS.
We have worked with amateur and professional drivers for over 26 years. In house machinist, In house fabrication. Our cars, our parts, our engines, our transmission's run nationwide at events every weekend. We work side by side with industry names developing parts.
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07-31-2013, 08:31 AM
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#12
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Rennzenn
Join Date: Feb 2005
Location: Virginia
Posts: 1,369
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A bit off the OP's specs, but on my car I run 32front/34 rear. Hoosier A6, 2700# car, -3.4 camber front, -3.2 camber rear.
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07-31-2013, 08:53 AM
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#13
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Registered User
Join Date: Aug 2004
Location: Alta Loma, CA
Posts: 1,334
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Whats size tire?? 
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Engine Builds, Transmission Builds, Engine Conversions, Suspension Installs, Suspension Tuning, Driver Coaching, Data Acquisition, Video, SCCA/PCA/POC/NASA/GRAND AM/ALMS.
We have worked with amateur and professional drivers for over 26 years. In house machinist, In house fabrication. Our cars, our parts, our engines, our transmission's run nationwide at events every weekend. We work side by side with industry names developing parts.
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07-31-2013, 08:54 AM
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#14
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Registered User
Join Date: Aug 2004
Location: Alta Loma, CA
Posts: 1,334
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When people say *run* "J.Fro" is that cold or hot?
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Engine Builds, Transmission Builds, Engine Conversions, Suspension Installs, Suspension Tuning, Driver Coaching, Data Acquisition, Video, SCCA/PCA/POC/NASA/GRAND AM/ALMS.
We have worked with amateur and professional drivers for over 26 years. In house machinist, In house fabrication. Our cars, our parts, our engines, our transmission's run nationwide at events every weekend. We work side by side with industry names developing parts.
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07-31-2013, 04:51 PM
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#15
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Rennzenn
Join Date: Feb 2005
Location: Virginia
Posts: 1,369
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Ahhhh...
I start 1st run at those pressures, reset to those after first sand second runs, then possibly adjust in later runs. On a typical 90 degree day, I gain 2 psi all around on he first run, about the same on the second, 1 psi for the third. Then it's usually time to break out the sprayer to cool the tires, and things stabilize.
Brad, just to give a bit of info, Kenny Schreeves and I set the alignment two years ago. Last year I took a PCA regional AX championship, NASA Mid-Atlantic class and overall champs, and SCCA regional F-Prepared champs. The setup seems to be working really well!
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07-31-2013, 05:59 PM
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#16
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Registered User
Join Date: Aug 2004
Location: Alta Loma, CA
Posts: 1,334
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I forgot your name, but I recall the conversation!!
You see me pointing people in your area to him
I support and send customers to shop owners nationwide.
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Engine Builds, Transmission Builds, Engine Conversions, Suspension Installs, Suspension Tuning, Driver Coaching, Data Acquisition, Video, SCCA/PCA/POC/NASA/GRAND AM/ALMS.
We have worked with amateur and professional drivers for over 26 years. In house machinist, In house fabrication. Our cars, our parts, our engines, our transmission's run nationwide at events every weekend. We work side by side with industry names developing parts.
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07-31-2013, 07:35 PM
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#17
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Registered User
Join Date: Nov 2008
Location: Champaign, IL
Posts: 355
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I have 18's and the RE11s. I run 34 in the rear and 32 in the front.
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Lov'n my boxster!
2013 Lexus IS350awd
2007 Toyota FJ Cruiser
2004 Porsche Boxster S
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Lil Red
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