When riding on streets you cannot avoid the occasional sharp object that will destroy a race tire. I have been pretty lucky so far with the ProRace and ProRace2. One day I rode over a metal hook that I saw too late. That was the fatest and noisiest flat I ever experienced. To top it, it was on the front tire. Luckily it was on a flat road and I could stop without crashing. But the tire had a 1/2" cut. I replaced the tube and still used the tires for many more miles. I eventually had to replace it because the tube was starting to pop out through the tire. My other ProRace were retired because of worn thread, most of them with small but external cuts as well.