I have about 19.5K miles on the original set of Pilot Sports on my '09 Carrera S. They're all highway miles; no track days. Lately I have noticed an increase in what I attribute as tire noise coming from the rear. The rear tires look good with even wear and no cords showing. They would pass state inspection right now but maybe not in November when the next inspection is due. The weather has been on the cool side lately with the highs in the middle 40's to low 50's and I'm guessing that summer tires can be stiff and a little noisier in the colder weather.

With the tires pushing 4 years in age along with a couple of hot patch fixes by my dealer for minor punctures, think it is time for new tires??

 

You answered your question yourself!

But here is my 2 cents, we all are frequently guilty of delaying paying $$ for tires, as it is an expensive item. However we should all keep in mind that the only "link" between us and the pavement is those 15-20 square inches of rubber hitting the road.
I too have bought new Michelins, awaiting to put them on the backs within the next couple of weeks.
27k, and am on my second set.

 

Do a search: "tire wear bars"

 

4 years and plugs/patches are not cause for replacement unless they are worn or doing a track day.

 

+1, wear indicators built into the tire


Also check tread depth. Local shops by me will not mount anything with less than 6/32nds of tread left for public roads. You can get a tread gauge at any auto parts store or even the automotive section of any big-box store for a couple of dollars.


And finally check for even tread wear, especially in the inside edges on the rears. Negative camber and/or aggressive cornering with off ramps will cause uneven wear on the inside edges.


Drive your pcar like its meant to be driven and replace the tires as you wear them down!

 

Here is what they are talking about
tread wear bars

 

I recently upgraded to a 2009. During the test drive I noticed a howl around 65-68 mph and was concerned enough the Porsche dealer let one of their mechanics take a ride with me. He immediately identified it as the sound of worn Michelin Pilots.

The dealer put new tires on at as part of the deal and the howl disappeared. I went with their recommendation of the Bridgestone Potenzas... I had good luck with them on my 2006 and had never heard a howl even though they were similarly worn.