987 Boxster 18" Wheel Questions

[vincesf]

I went back to my 2008 owner's manual and found that the recommended cold tire pressure for 18" tires is 29 psi front and 36 psi rear. Those owners that have a sticker that references 18" tires and loading information on the inside of the driver's door jam tell me that the recommended cold tire pressure is 30 psi front and 37 psi rear, no problem as 1 psi is not a big deal, and there is also a reference to: "See Owner's Manual For Additional Information". What is confusing to me is that when my car was cold (not driven overnight), I manually checked the tire pressure with a tire pressure gauge, the tire pressure is 29 front 36 rear, and the Tire Pressure Monitor System read 26 front 33 rear or an alternative reading of -0- on each wheel, indicating perfect pressure. Driving the car about 5 minutes, the TPMS read 29 front 36 rear and again indicating perfect pressure -0- to be added at each wheel. Makes me believe that the TPMS is not completely accurate when the car has been sitting and cold, that the truer reading can be obtained after driving the car for 5 minutes to provide a "cold-operating" psi of 29 and 36.
vincesf