Never happened on a bike, but the wife and I had it happen in her Blazer on an interstate last summer. A tractor-trailer was losing his cap from one of his trailer's tires and there were big chunks flying everywhere. I pulled up along side him and tried to gesture to him but he was totally oblivious. Those caps can come right through a windshield and kill you in a car!, on a bike, it would be instant crash and burn....
