Carbonfiberboy 

We have now blown 2 Conti 4000s tires off our rims. These are the ones with the reflective stripe. There was quite a discussion of that stripe on here a few months ago and we decided to buy four of them and give them a try ourselves. One tire succumbed to cuts in a few hundred miles. Its mounted mate blew off early in its life, but since the bead was destroyed I couldn't tell what the fault was. The second pair lasted long enough for us to wear about half the rubber off them. We always run 120 psi in these tires.

One rim was a Mavic CXP33, the other was a Velocity Aerohead. In both cases we were braking hard at the bottom of a terminal velocity descent. In both cases the rim was only warm to the touch. The first time was a front rim and the tire and rim were both destroyed. The second time, this past Sunday, it was the rear, which blew just as we came to a stop, so rim and tire were undamaged. We always carry a spare so we put that on and continued with no problem.

We have a friend who also blew a 4000 off her single this past May. She was sucking our wheel on a 30 mph easy descent and blew a rear tire off braking for the end of ride parking lot. Rim again only slightly warm. I don't know which model 4000 it was.

In all these cases, the tire had been mounted for several hundred miles, so it wasn't a mounting error, plus we are pretty good at mounting tires after changing few hundred flats.

Examining the tire, the bead shows frayed cloth on the surface in the bead groove and deteriorated rubber on the bead itself most of the way around the tire. I also removed the front tire and examined it. It also shows the beginnings of this same problem. The bead groove is mostly cloth and the bead itself is beginning to tear off.

I have four new regular 4000s 25c tires, purchased from PBK on that recently posted deal. I examined them and they seem to have a good layer of rubber over the cloth in the bead groove, though the weave of the cloth is visible through the rubber. On none of my other brands of tires is that cloth weave so close to the surface in the bead groove. I mounted a pair of these new tires and will keep a close eye on them.

My theory is that hard braking caused the tire to slip slightly on the rim because the metal of the rim bead was running on cloth rather than on rubber. This encouraged the bead to pull out of the rim.

I've emailed Conti about this and will post any response. Meanwhile, I'd encourage anyone running Conti 4000s tires to pull them off, examine the area of the bead, and post what they find.