I had a shraeder valve stem ripped out, probably by tyre creep, on a fairly steep road section near Malham, instead of a normal puncture noise it sounded like a Catherine wheel. Don't know the speed and no harm done but now I always try and use talcum powder inside the tyre carcus and fit shraeder valves with a screw down valve rim ring, like they have on Presta valves. I think Schwalbe make them.