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Tire pressure and TPMS

  • 2007
  • Cayman S
Mileage: 
62 800
Wheels and Tires
Scottsdale, 
Arizona

Hi,

I have a couple of related question about tire pressure(s) in a 2007 (987.1) Cayman S.  To start with, there appears to be a discrepancy between the manual and the door placard.  On page 299 that manual suggests that correct pressures are 29 PSI in front and 36 PSI in back.  The door placard suggests 30 in front and 37 in back.  Which is correct?  TPMS appears to agree with the manual displaying cold pressure as 29/36 when initialized.  I have been following the door placard for quite some time now.

Second question, On page 122 describing the TPMS system, the manual says: "The Tire Pressure Monitoring continuously monitors tire pressure and tire temperature on all four wheels..."  On page 128 it goes on to say: "- The required pressures for cold tires at 68 F are indicated in the info pressure display in the Tire pressure menu."

I have always been under the impression that tire pressure should be set at ambient temperature.  But the manual suggests setting by the fill info display amd the local dealer tells me that temperature is considered in determining correct tire pressure (the manual doesn't explicitly state this as far as I can tell, but definitely implies it).  This leads to the follwoing scenario.  If I set the correct pressure using a calibrated gauage first thing in the morning in a 90F-100F garage (temps outside can be as high as 120+) and the car assumes correct pressure cold is at 68F, that will mean right from the start the TPMS system will think that my pressures are 2-4 PSI low (based on approx. 1 PSI per 10F.  So, do I set by fill info display (which will put my guage pressure between 31/38 and 32/39) or do I set pressure by gauge pressure?  I know that if I set pressure by gauge pressure the fill info reads that I am low, so I suspect that Porsche really does expect me to set pressure using the fill info rather than an external guage, especislly when temperatures are way out of the "normal" range (above or below).

Thanks!

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