Just had my tire pressure warning go off on my road trip to Wisconsin.

It was showing "-7 psi!", and I'm thinking I just have a bad sensor. So I stop, look at the tire and it looks fine. (Haven't put an air gage In the glove compartment yet.)

Restart the car and the left rear is reading 30 psi with the others at 39. Ok, so its telling me Ive lost 7 psi - not good. I'm lucky enough to find a Porsche dealer and they show me a big bolt in the tire - too close to the sidewall to patch. Waiting on the new tire install.

Was counting on only using 4 Pirelli's before I switched to the Super Sports...

 

Tire pressure monitor is an excellent feature. Also tells you when to add air in the winter.