I was running the original Michelin Pilot HX tires on my 2002 Z3 2.5. I had about 30K miles on them, and thought I'd better look into new tires. The tires weren't quite down to the wear bars, but I was concerned about their age. After some research, I bought four Michelin Pilot Exalto PE2 tires from Tire Rack and had them installed by a local BMW independent which specializes in track preparation. What a difference. I don't know how much of the improvement is due to the age of the OEM tires, but there is mech better steering response and general road feel. The tires were $159 and there is currently a $70 rebate when four tires are purchased. These are "N" rated tires, which meet Porsche specs, by the way. I just wanted to throw out one data point to the board.