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Motorcycle Helmet Performance: Blowing the Lid Off Searching for the truth behind motorcycle helmet design, helmet standards and actual head protection By Dexter Ford Photography: Jim Brown How good is your helmet? These seem like easy questions, ones you probably think you can answer by reciting the lofty standards your helmet meets and the lofty price you might have paid for it. But the real answers, as you are about to see, a re anything but easy. There's a fundamental debate raging in the motorcycle helmet industry. In a fiberglass-reinforced, expanded-polystyrene nutshell, it's a debate a bout how strong and how stiff a helmet should be to provide the best pos sible protection. Because if a helmet is too stiff it can be less able to p revent brain injury in the kinds of crashes you're most likely to have. And if it's too soft, it might not protect you in a violent, high-energy crash. If you knew what your head was going to hit and how hard, you could choose the perfect helmet for that crash. To understand how a helmet protectsor doesn't protectyour brain, it hel ps to appreciate just how fragile that organ actually is. It's so gooey that when patholo gists remove a brain from a cadaver, they have to use a kind of cheesecl oth hammock to hold it together as it comes out of the skull. Your brain basically floats inside your skull, within a bath of cervical- spinal fluid and a protective cocoon called the dura. But when your skul l stops suddenlyas it does when it hits something hardthe brain keeps going, as Sir Isaac Newton predicted. Then it has its own collision with the inside of the skull. If that collision is too severe, the brain can sustain any number of injuries, from shearing of the brain tissue to bl eeding in the brain, or between the brain and the dura, or between the d ura and the skull. And after your brain is injured, even more damage can occur. When the brain is bashed or injured internally, bleeding and inf lammation make it swell. When your brain swells inside the skull, there' s no place for that extra volume to go. So it presses harder against the inside of the skull and tries to squeeze through any opening, bulging o ut of your eye sockets and oozing down the base of the skull. As it sque ezes, more damage is done to some very vital regions. Helmet designers have devised a number of different liner designs to meet the different standards. The Vemar VSR uses stiffer EPS than most, buthas channels molded in to soften the assembly (to ECE specs) and enhance cooling. To prevent all that ugly stuff from happening, we wear helmets. Modern, f ull-face helmets, if we have enough brains to protect, that is. A motorcycle helmet has two major parts: the outer shell and the energy-a bsorbing inner liner. The inner lining is made of expanded polystyrene o r EPS, the same stuff used in beer coolers, foam coffee cups, and packin g material. Outer shells come in two basic flavors: a resin/fiber compos ite, such as fiberglass, carbon fiber and Kevlar, or a molded thermoplas tic such as ABS or polycarbonate, the same basic stuff used in face shie lds and F-16 canopies. First, it's supposed to prote ct against pointy things trying to penetrate the EPSthough that almost never happens in a real accident. Second, the shell protects against abr asion, which is a good thing when you're sliding into the chicane at Day tona. Third, it gives Troy Lee a nice, smooth surface to paint dragons o n Ridersand helmet marketerspay a lot of attention to the outer shell and its material. But the part of the helmet that absorbs most of the e nergy in a crash is actually the inner liner. When the helmet hits the road or a curb, the outer shell stops instantly. Inside, your head keeps going until it collides with the liner. When th is happens, the liner's job is to bring the head to a gentle stopif you want your brain to keep working like it does now, that is. The great thing about EPS is that as it crushes, it absorbs lots of energ y at a predictable rate. It doesn't store energy and rebound like a spri ng, which would be a bad thing because your head would bounce back up, s haking your brain not just once, but twice. EPS actually absorbs the kin etic energy of your moving head, creating a very small amount of heat as the foam collapses. The Schuberth S1 uses five separate foam parts glued together to meet the ECE standard. The helmet's shell also absorbs energy as it flexes in the case of a poly carbonate helmet, or flexes, crushes and delaminates in the case of a fi berglass composite helmet. To minimize the G-forces on your soft, gushy brain as it stops, you want to slow your head down over as great a distance as possible. So the perf ect helmet would be huge, with 6 inches or mosre of soft, fluffy EPS cra dling your precious head like a mint on a pillow. Problem is, nobody wants a 2-foot-wide helmet, though it might come in ha ndly if you were auditioning for a Jack in the Box commercial. So helmet designers have pared down the thickness of the foam, using denser, stif fer EPS to make up the difference. This increases the G-loading on your brain in a crash, of course. And the fine points of how many Gs a helmet transmits to the head, for how long, and in what kind of a crash, are t he variables that make the helmet-standard debate so gosh darn fun. The helmets are mounted on a 5-kilo (11 pound) magnesium headform and then dropped from a controlled height onto a variety of test anvils to simulate crash impacts on various surfaces and shapes. In the real world, yo ur helmet actually hits flat pavement more than 85 percent of the time. Standardized Standards To make buying a helmet in the US as confusing as possible, there are at least four standards a street motorcycle helmet can meet. The price of entry is the DOT standard, called FMVSS 218, that every street helmet so ld here is legally required to pass. There is the European standard, cal led ECE 22-05, accepted by more than 50 countries. And lastly the Snell M2000/M2005 standard, a voluntary, private standard used primarily in the US So every helme t for street use here must meet the DOT standard, and might or might not meet one of the others. Just by looking at the published requirements f or each standard, you would guess a DOT-only helmet would be designed to be the softest, with an ECE helmet very close, then a BSI helmet, and t hen a Snell helmet. Because there are few human volunteers for high-impact helmet testingand because they would be a little confused after a hard day of 200-G impac tsit's done on a test rig. The helmets are dropped, using gravity to accelerate the helmet to a give n speed before it smashes onto a test anvil bolted to the floor. By vary ing the drop height and the weight of the magnesium headform inside the helmet, the energy level of the test can be easily varied and precisely repeated. As the helmet/headform falls it is guided by either a steel tr ack or a pair of steel cables. That guiding system adds friction to slow the fall slightly, so the test technician corrects for this by raising the initial drop height accordingly. The headform has an accelerometer inside that precisely records the force the headform receives, showing how many Gs the headform took as it stop ped and for how long. If you test a bunch of helmets under the same conditions, you can get a g ood idea of how well each one absorbs a particular hit. And it's importa nt to understand that as in lap times, golf scores and marriages, a lowe r number is always better when we're talking about your head receiving e xtreme G forces. All the Snell/DOT helmets we examined use a dual-density foam liner. Theupper cap of foam on this Scorpion liner is softer to compensate for the extra stiffness of the spherical upper shell area. Some manufacturers,including Arai and HJC, use a one-piece liner with two different densiti es molded together. On The Highway To Snell On the stiff, tough-guy side of this debate is the voluntary Snell M2000/ M2005 standard, which dictates each helmet be able to withstand some tou gh, very high-energy impacts. The Snell Memorial Foundation is a private, not-for-profit organizatio...
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