Spoke wrote a review of Continental Grand Prix 4000 S Tire - Clincher on September 27, 2011
After 3 pinch flats in the first month I came to the conclusion that the sidewall strenght and tire shape required a higher pressure be maintained at least in the rear tire. I incresed the pressure from 125 to 135psi and had no more pinch flats.
The tires are smooth and wear well and were a replacement for my GP 4's.
My belief is many people are running this tire at 110psi and are having issues. I believe these tires are rated 145psi so pump them up.