From "Just Ride: A Radically Practical Guide to Riding Your Bike" by Grant Petersen Helmets aren’t all they’re cracked up to be If you ride often enough without a helmet, eventually you’ll be scolded by a stranger. Everyone has an opinion, and they love to share them. Helmets are the most complex and divisive issue in the bike world today, but it’s a division that’s far from right down the middle. The safety arguments for helmets are obvious and even boringly well known, but let’s go over the mechanics of how a helmet works. When you smack your helmeted head on a curb or car or tree or rock, the Styrofoam in the helmet compresses, slowing down your brain so it doesn’t bang as hard against the inside of your skull. The Styrofoam is too fragile by itself, so helmets have a hard shell to distribute the force. A strap holds it on your head. We could wrap it up right there if that were the end of the story, but maddeningly, it isn’t. Helmets increase risk compensation. Any protective gear you wear or use — a hazmat suit, a bulletproof vest, a parachute, snake-proof boots, or a bike helmet — increases the likelihood of you taking a risk. That is the point: protection, so you can do the thing that would be dumb to do without it. You could argue that it’s just sensible to wear knee-high boots in snake country, but you could also argue that it’s safer not go tromping around the snakes in the first place than to do it with snake-proof boots. A snake sunning itself on a hip-high rock could strike you in the crotch, for instance. Wearing a bike helmet and then riding a bike in traffic or at high speed or down a rocky trail — as opposed to riding more slowly or even walking your bike down it — is a bike rider’s form of risk compensation. Risk compensation makes the most sense when the protection is a sure thing when the protection is overkill, but a bike helmet is far from absolute protection. Unlike motorcycle helmets, bike helmets have to be light and ventilated enough to be comfortable, and there’s only so much protection possible within the marketable weight and ventilation requirements of a bike helmet. Helmet tests are valiant attempts by well-meaning private, corporate, and governmental organizations to duplicate real-world crashes in the test lab, but real-world conditions are hard to duplicate with the consistency that standardized tests require. Over the years, the tests and passing scores end up being close to the same. The glory test is impact absorption, measured in g-forces. A typical test places an eleven-pound fake head inside the helmet and drops it on various metal shapes (called “anvils” in the test literature) from a height that generates predetermined impact speeds. The shape determines the height from which the helmet falls and the speed at contact. If the striking surface is flat, the helmet drops from higher up and hits it at a faster speed-up to about 13.5 miles per hour. If curved, which localizes the impact more, the helmet drops from a lower height, and hits it more slowly. The shapes are supposed to simulate things you might hit with your head if you crashed a bike. That sounds conscientious, but how realistic are the tests? Your head may weigh about eleven pounds, but I’m guessing there’s a 120- to 300-pound body attached to it. In the lab test, there’s no body — just the eleven-pound fake head. The lab’s maximum speed of 13.5 miles per hour (varies with the test, but this is typical) seems unrealistic, too. When you consider how fast you ride and how fast cars go, impact speeds of 20 to 40 miles per hour don’t seem unrealistic. Yet no bike helmet made would pass those tests. And in the curved-surface test, the helmet falls from a lower height and hits at a slower speed. Why? Are you more likely to be going slower when you hit the corner of a curb or a fire hydrant? The question remains: Are you safer wearing a helmet and overestimating its protection, or going helmetless and riding more carefully? Maybe the answer is to wear the helmet and forget you have it on, but that’s easier said than done. Most people are keenly aware when something’s on their head."