Slashdot Mirror
Science and Bicycling Meet In a New Helmet Design (arstechnica.com)
John Timmer from Ars Technica got a chance to take a look at Trek's new bicycle helmet that they claim offers "the first major change in helmet technology in years," and is backed up with peer-reviewed science. Here's an excerpt from Timmer's report: WaveCel is the product of orthopedic surgeon Steve Madey and a biomedical engineer named Michael Bottlang. The two had been working on a variety of ideas related to medical issues and protective gear, funded in part by federal grant money. When considering the idea of a lightweight material that could evenly distribute forces, Bottlang told Ars that they first focused on a honeycomb pattern. But they found that it was actually too robust -- the honeycomb wouldn't collapse until a lot of force had been applied, and then it would fail suddenly.
The design they eventually developed has a shape that allows flexing almost immediately when force is applied. "It starts to glide right away," Bottlang said. The manufacturing technique creates a clear point of failure that allows more extensive flexing once a certain level of force is exceeded -- part of the structure will fold over rather than experiencing a complete failure. Then, once folded, the polymer it's made of will allow neighboring cells to glide over each other. This provides some resistance even after the structure has collapsed. For the helmet, a patch of this material is attached to the inside of a more traditional EPS helmet, which provides impact resistance. But the WaveCel mesh is allowed to float within the helmet and can absorb much of the force of off-axis impacts. The thin strips of soft material that cushion the helmet where it rests on the head (also found in more traditional helmets) are attached directly to the WaveCel mesh.
It looks more uncomfortable than it is. Madey, the orthopedic surgeon, said they've done tests that show that, even if placed directly on the skin, the WaveCel mesh wouldn't break the skin under most impact forces. How does their new helmet work? According to a paper authored by Bottlang and Madey, helmets including the material reduced rotational acceleration from impacts by 73 percent compared to a normal helmet. A slip pad within a normal helmet (MIPS) only dropped acceleration by 22 percent, which seems like a substantial difference.
The design they eventually developed has a shape that allows flexing almost immediately when force is applied. "It starts to glide right away," Bottlang said. The manufacturing technique creates a clear point of failure that allows more extensive flexing once a certain level of force is exceeded -- part of the structure will fold over rather than experiencing a complete failure. Then, once folded, the polymer it's made of will allow neighboring cells to glide over each other. This provides some resistance even after the structure has collapsed. For the helmet, a patch of this material is attached to the inside of a more traditional EPS helmet, which provides impact resistance. But the WaveCel mesh is allowed to float within the helmet and can absorb much of the force of off-axis impacts. The thin strips of soft material that cushion the helmet where it rests on the head (also found in more traditional helmets) are attached directly to the WaveCel mesh.
It looks more uncomfortable than it is. Madey, the orthopedic surgeon, said they've done tests that show that, even if placed directly on the skin, the WaveCel mesh wouldn't break the skin under most impact forces. How does their new helmet work? According to a paper authored by Bottlang and Madey, helmets including the material reduced rotational acceleration from impacts by 73 percent compared to a normal helmet. A slip pad within a normal helmet (MIPS) only dropped acceleration by 22 percent, which seems like a substantial difference.
This helmet is worth a close look.
For the last 40+ years, bike helmets have been designed to protect the contents of the head from a single direct impact, They are the best protection for the occasional crash when the cyclist is thrown over the handlebars such that he drops head first onto the pavement from a height of 5 to 6 feet, or less. That kind of crash doesn't happen very often.
Most crashes involve significant shear forces as well as direct impacts. Also most crashes involving other vehicles are a very fast sequence of bounces where each bounce is a complex of impact and shear forces. Foam helmets offer no protection with shearing and often no protection after the first impact.
This helmet's design offers more protection against multiple direct impacts and shear forces.
Shouldn't there be helmets for car drivers and passengers? Brain injuries are the most serious car crash injuries. And those brains are more valuable too, because you know, unlike cyclists, these people can afford cars. I say we make helmets mandatory in cars. All professional racers wear helmets already.
Well, there are a few standards. Here's a link
Note that in most crashes, the cyclist, if they strike their head on the ground, will have an impact consistent with a drop of 5 to 6 feet. The cyclist may be going 20 mph, but their head is still likely to receive the same force as just dropping at 0 mph (since there's horizontal velocity (their speed)) and vertical velocity (force of gravity).
Now motorcycle helmets have a similar standard for an impact test (DOT, Snell, and ECE). Again, because despite your velocity in the horizontal plane, it's the same force of gravity. Motorcycle helmet standards tend to have a few other tests as well (such as making sure the visor doesn't crack if a rock hits it at 55 mph), but there's only so much that can be prevented by a helmet.
Now there are tradeoffs - you can make a helmet that's stiffer, or that survives multiple impacts better, but that tends to come at the cost of how much energy it can absorb in one impact. Snell faced accusations of this in one of their previous motorcycle helmet standards (either M2005 or M2010) - the helmet was more durable, but at the potential cost of more G-forces transmitted to the brain.
Nothing in the above should be interpreted as me being anti-helmet - I always wear bicycle helmets, as well as full face, either Snell or ECE rated, motorcycle helmets.