Last month, while completing a forty mile ride, I was cruising down a one mile 5% hill going about 25mph, when I hit a baseball size rock. I was launched over the bars and landed on my left side and back. My head hit the ground so hard that one of my front tooth fillings was knocked out. The back of my helmet was shredded and split almost exactly in the center rear. Lots of road rash but thats it. I am "certain" that had I not been wearing a helmet, I would have cracked my head open on the asphalt. I have that helmet sitting in my office here at home. It didn't seem like much when I was wearing it, but it is my friend for life now.