Originally Posted by Brian Ratliff

The mechanical engineer in me says that a fall, regardless of horizontal speed, onto a horizontal surface (IOW, not a curb, lamppost, garbage bin, car bumper, etc), is a fall from 5-6 vertical feet.

In any case, I won't tell you to wear a helmet. You are convinced by population statistics. I don't trust them in determining the best course of action for me. Population statistics pertain to populations. Not individuals. I ride in pack situations. I know for a fact that the type of crashes that happen in pack situations are not controllable. When your front wheel gets swept out, there is no time for the body to react in the normal way to protect your head. I've fallen a fair amount in the course of the last 15 years or so I've been riding road bikes; it wasn't until I started racing three years ago that I started getting into situations where I couldn't protect my head in a fall.

Thus, for me, I wear a helmet (most of the time) because 1) I know the type of risks I expose myself to involve crashes where I cannot control my body position, and 2) my falls typically happen onto horizontal pavement, meaning a fall from 5-6 vertical feet, which is the type of crash the helmet is optimized to absorb. A helmet makes sense for me. If most of my riding were short, 5 mile, low exposure, non-pack riding, commuting, then I probably wouldn't wear a helmet . If my riding was solo training in low car traffic areas, I might not wear a helmet (I do, though it's just out of habit, not because I believe I actually need it). And I don't wear a helmet on my rollers (too hot) even though the risk of falling is similar to that of riding solo on a country road. But in a race or group training ride, a helmet is an essential piece of equipment for injury prevention.