There are mishaps that no rider, regardless of how skilled, could avoid. But if that rider knew exactly what kind of accident it was going to be, an engineer could build the ideal helmet to withstand it.
That's impossible, of course, and it's a major design challenge. Conventional motorcycle helmets, which absorb collision energy by deforming a crushable portion in a predictable manner, can be engineered to mitigate injuries resulting from only a certain range of impact forces.
There's a problem when an impact is not strong enough for the absorption -- typically at the helmet shell liner made of expanded polystyrene foam -- to take place and the shock is passed to the skull. Although less likely to be fatal, those shocks can still cause serious concussions.
Early this year, 6D Helmets of Brea, Calif., began offering helmets for off-road riders that it engineered to provide protection in hard and soft collisions. It does this by suspending a liner designed for low-energy impacts inside a helmet built for hard impacts. The helmets, which the company says are certified by the Transportation Department and legal for on-road use, may soon share their technology with helmets for all motor sports, and perhaps contact sports.
The 6D design suspends a foam layer inside the one covered by the helmet's hard outer shell. Between the two foam layers are rubbery elastomers, which look like ear plugs and act like shock absorbers; an impact too low to crush the foam is still enough to move the shock absorbers.
There is another advantage to using this elastomer suspension. It lets the inner liner twist, reducing how hard a rider's head will rotate in a crash. That matters because even low-speed rotational blows can be damaging.
Christopher Giza, a neurologist with the University of California Los Angeles, Medical Center, explains the principle to his students this way: "The brain floats inside the skull like a pickle in a pickle jar."
Nearly all falls result in some twisting force to the head, which is "more likely to bend and twist the brain on top of the brainstem, as well stretch and damage the 'spaghetti' strands connecting different parts of the brain," Dr. Giza said.
Act Lab, a testing company headquartered in El Segundo, Calif., found 6D helmets among the top performing helmets in linear crash tests, the sort required for certification, in a study financed by 6D.
Bob Weber, chief executive and founder of 6D (an allusion to the design's accounting for six directions of movement), said the company began with off-road helmets because that was where the need was greatest. The company is at work on a design for road bikes due out in about a year, he said.
While logic dictates that the 6D helmets, which retail for $750 and are about the same size as today's typical helmets, are a step in the right direction, it is not known how much difference they will make.
"They say it dampens forces, but does it dampen them enough to reduce the chances of concussion?" Dr. Giza asked. Because the level of force it takes to cause a concussion differs from person to person, a long-term study comparing concussion rates would be needed.
This article originally appeared in The New York Times. First Published October 12, 2013 2:01 PM