I have michelin pilot sports on my 986... they say 51psi max... when i got the car from the dealer there was a sticker saying my tires had been filled with nitrogen.... now i'm wondering would this affect how a tire gauge reads it? They're showing about 35psi now which seems very low... is that normal for a nitrogen fill? can i go ahead and just add regular air to them to the desired psi?

 

Anytime i have ever filled my tires with N, i never mix with with anything else.
I think its best that you call your dealer and ask them yourself. best of luck

 

Max pressure is not the same as recommended. You should probably be at about 29/36 front/rear.

 

Don't just add regular air if you had a choice. 29/36 is cold PSI for 18" tire set up.

 

The max pressure on the side of the tire is not the recommended pressure from Porsche. Your owner's manual will have the recommended pressures. I personally run 32 front/34 rear. I think recommended front is 29.

Pressure is pressure, it will read the same on your gauge with nitrogen or air.

If you plan on continuing to only use nitrogen and have someplace where you can do this, then only use nitrogen. If you don't care, then fill it with air. It won't hurt to mix them as air is mostly nitrogen anyway.