I was hurrying home from work today because of a little crisis. I have studded tires for winter, the kind with studs at the edges to aid in turns, but no studs down the middle for less rolling resistance. I was coming to a stop at a side street with some bare pavement and some packed snow, and BOOM, down I went. I landed on my side and felt the side of my helmet lightly tap the pavement.
I don't know what I ran into, but I would guess it was a little polished icy spot that I hit while going straight so no studs were in contact with the pavement. So one must not get overconfident with studs. As for the helmet, no damage, it was a very light tap, but it reminded me why I wear it.