What is the difference between "Porsche Certified" and "non-Porsche Certified"?

Haven't heard about this. Perhaps they don't meet load or speed rating requirements and the dealer or shop won't put them on because of this. I thought Porsche put Pirelli Scorpions on some of the Cayennes though and most of those are all weather tires. I'm not sure to be honest.

Porsche Certified means that Porsche would put recommend that you put them on your car. Non-certified means like they recommend that the performance of the tires won't be as good if you purchase the so called "certified" ones.

Porsche certified tires can be recognized by a N-code on the tire, this is the letter N followed by a number (N0, N1, N2 and so on). The N-codes are specifically for Porsche. It is not merely a certification, N-coded tires are truly different from the stock version of a particular tire. When a tires manufacturer comes out with a new tire that could be suitable for a Porsche, Porsche may incorporate it in its comprehensive tires testing program. During testing Porsche will work closely with the tire manufacturer to adjust the tires to Porsche specifications. These tweaks and modifications can include softer or harder rubber compounds, different side wall characteristics, and may even include slight deviations in circumference to match the front and rear tire diameters, this is especially important on the Carrera 4 models. Of course the deviations differ from tire to tire, so it is very hard to say what the exact difference is between a standard Michelin and the N-code Michelin in a specific size. A Porsche should be fitted with 4 tires of the same brand and type, with matching N-codes. It is not recommended to use N1 front tires and N2 rear tires. I have experienced that a Porsche feels entirely different when not fitted with correct or mismatched tires. We've also had customers complain about the handling of their Porsche only to find that the car had the wrong or mismatched tires on it. More on this: http://www.karrera.net/tires/N-Specification2006.pdf