[exelius]

A common misconception is that bicycle helmets protect you in a serious crash. They don't: if you get hit going 30 mph, anything less than a motorcycle helmet isn't going to help you much. But most bike crashes aren't serious; they're minor, low-speed crashes where the rider is knocked from the bicycle or bumped just hard enough to lose balance. Because the center of gravity on a bicycle is high, it's easy to hit your head in these types of crashes -- hard.

Those are the crashes that bike helmets are designed for. Let's say you were waiting at a light, and the light just changed. A car mirror clips you just as you're pushing off and getting your balance, you fall over and hit your head on a curb. If you have a helmet on, you walk away with a headache and maybe a skinned elbow. Without a helmet on, you crack your head open and potentially die.