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  • MattHurst

    Interesting, are these helmets available in Australia?

    • Dave

      The Overtake and Forefront are both on the Smith Optics website if you select AU.

      The bike helmets aren’t on any of the linked online dealers, and none of the dealers in the search results within a 100km radius of either Sydney or Melbourne appear to be bike shops.

  • Bex

    i found the video very interesting, particularly the comparison to results achieved in a car. How does Australia compare to these numbers they’re bandying about? I haven’t seen any marketing for helmets about the impact absorption and safety (apart from some articles about MIPS). It’s got me thinking about waiting before i get another helmet to see if anyone else will produce something comparable.

  • ridein

    Are the MIPS / Koroyd helmets considered disposable trash after one impact?

    • James Huang

      Sadly, yes. All bicycle helmets that I know of dissipate energy through self-destruction. In other words, they absorb the force of the impact so that your head does not.

      Even if the Koroyd panels were made available separately, there would still most likely be irreparable damage to the surrounding EPS support structure.

  • jules

    interesting article James. I’ve had a bit to do with crash testing and HIC scores etc. the honeycomb system is definitely interesting and may well be superior to EPS. but…

    there’s not enough info in this article for me to make a judgment (not that anyone asked). I know (think) you’re an engineer, so I don’t mean to be preachy, but in general – the ‘science’ of crumple zones is frequently misrepresented. the basic concept is to ‘ride down’ the energy of a collision, by increasing the duration of the collision event, the force (and acceleration) experienced by the human occupant is reduced. pretty much analogous to selecting a smaller gear on your bike and using more pedal strokes with lower effort/force.

    that’s all very nice, but you can have too much crumple zone. if there is too much ‘give’ in the material/structure designed to crumple, it eventually (as in, within microseconds) crushes (bottoms out) and the crash force/pulse increases dramatically. so in reality, a structure (helmet, or car body) has two jobs:
    1. crumple in a way that modulates the forces transferred to the human occupant.
    2. but don’t crumple too much that it bottoms out and the full force is directly transferred to the human occupant.

    the problem is, those 2 criteria are in conflict. the more your protective structure (car or helmet) crumples, the more likely it is to bottom out – for a given crash energy (impact speed, or change of speed). this is where I struggle with the concept a bit – if the developers are talking greater impact absorption, then to me, there are broadly 2 ways to achieve that:
    1. more absorption – i.e. more material, or thicker padding in the helmet, or
    2. less capacity to ride down severe impacts, before bottoming out – and reduced protection when it does.

    the 3rd option is potentially where the benefit is – a more controlled management of crash energy. if you can get a more consistent rate of deceleration, that’s also going to reduce the peak force/acceleration experienced by the occupant (head).

    but the talk in the article of “we should go to automotive testing standards” seems like bunkum to me. helmet testing standards already use the standard HIC threshold criterion. what do they mean here? it smells a bit like marketing speak to me.

    • James Huang

      One of the keys to Koroyd’s claims – and I’ve tried to be careful to portray them as such – is that Koroyd supposedly uses a greater percentage of its liner thickness than EPS to dissipate impact energy. I don’t recall the exact numbers off the top of my head, but I think it was somewhere in the neighborhood of 65 vs 80% or so. According to Koroyd, impact events are also spread out over a longer duration.

      So, at least according to Koroyd, the fancy plastic honeycomb stuff seems to satisfy all three of your criteria.

      As for the HIC criterion, I’m most certainly not an expert in helmet testing standards. Koroyd isn’t saying that current helmet testing standards for bikes and motorcycles don’t use HIC at all; just that the acceptable limits are much higher than they are in automotive crash testing. If that isn’t correct, I’m all ears!

      Either way, I definitely was not trying to bill Koroyd as the be-all-end-all when it comes to helmets; I’m obviously in no position to make that call. But I do think it’s an interesting material, and I do think they deserve a little credit for at least saying that we could – and should – do better.

      • jules

        thanks James. I understand your perspective. I can see how it might work in the way as claimed – particularly if there is a greater depth of impact material available to spread the crash pulse over.

        but I’m stumped on the automotive claim. the test used in automotive standards is to crash a car into a barrier and measure the HIC score from the sensors wired up to the dummy’s head.

        for bike helmets, they just drop the helmet on a test rig – I think different standards may use different rigs – i.e. flat surface, sharp surface. but you can’t just take the automotive test – the objective is to see what happens to the dummy strapped into a car seat. that’s got no relation to a bike helmet test.

        you also can’t directly compare the HIC limits. I think it’s 1000 HIC for a pass in automotive standards – which is a score associated with good odds of escaping permanent brain injury. that sounds logical, until you remember that the HIC score is broadly reflective of 2 criteria:
        1. the occupant protection on offer (vehicle crashworthiness, or helmet protection level for cyclists), and
        2. the impact severity

        basically you can make any car or helmet pass that HIC test by reducing the impact severity (speed), or fail by increasing it enough. the car test speeds are too low. consumer crash tests are done at higher speeds, to reflect the gains made in vehicle engineering and give more useful info to car buyers on which cars really offer decent protection. the regulatory tests can and are passed by cars that score poorly on the consumer tests. both tests may yield a ‘result’ of 1000 HIC, say. meaningless to compare.

        • James Huang

          Sorry, I should have been more clear. Koroyd’s “Safety Initiative” aims to maintain how bicycle helmet tests are conducted currently, but lower the acceptable G/HIC limits as compared to where they are now. They’re not advocating using an automotive test for bike helmets.

          • jules

            fair enough. one thing I’d like to see is published results of helmet standards tests. currently helmets receive type approval if they pass and get a sticker. but you don’t know if they passed with flying colours, or scraped it in under the max. HIC limit.

            that would provide better info to understand the implications of lowering the regulated HIC limit.

            a good case study in the automotive world is a well-known Saxon brand with 3 pointed sky-bound emblem. it traded off safety marketing for years until the Euros started consumer crash testing. the results were a tad embarrassing, to say the least. not anymore – they’re top shelf now.

            • James Huang

              Absolutely agreed. Unfortunately, companies (at least the ones operating within the US) are legally forbidden from publicly stating that their helmets even exceed testing standards. They’re only allowed to say if the helmets pass, or don’t pass. It’s frustrating, to say the least.

        • Bas

          Hi Jules,

          Thank you for your interest in the Koroyd Helmet Safety Initiative, especially with your background in car crash evaluations.

          At Koroyd we wanted to know how effective helmets are at reducing the risk of severe head injuries, we therefore intensively researched the topic and discussed it with various biomechanics specialists.

          Though car crashes are very different from helmet impacts, high acceleration levels of the skull and brain can cause severe injuries in both types of impacts. Acceptance criteria in several crash standards of new car assessment programs are based on head injury risk curves, that link maximum deceleration of the head and HIC values to the correlated risk of suffering respectively skull fractures and traumatic brain injuries. In the car industry they work towards low risks, for instance towards a < 5% risk of suffering a severe traumatic brain injury.

          We were shocked to see that the one helmet standard that incorporates HIC is accepting a limit of HIC 2400, which correlates with very high risks of suffering traumatic brain injuries according to the Prasad/Mertz risk curves. This limit for HIC was set based on what was achievable to manufacture decades ago, rather than what was necessary to protect riders from specific severe injuries in typical impacts.

          With technologies that progress, it would be logical to update these standards with stricter limits over time, just like the car industry has done, but sadly this is not happening for helmets. That's why we present our safety initiative, where we ask manufacturers to voluntarily adopt lower limits for maximum deceleration and HIC, regardless of the underlying technology.

          There are two reasons why in general the Koroyd core can absorb more energy in the same thickness, volume or weight compared with EPS. First of all, the Koroyd core has very linear impact absorption properties throughout an impact, just like other honeycomb structures and unlike foams. The second reason is that the Koroyd core buckles further, reaching more displacement within the core before bottoming out, which also helps to absorb more energy.

          And you are right, you can't protect from any and all impact velocities. With cars, the current limits for acceleration and HIC will protect the rider from severe head injuries in for instance frontal impacts at the tested impact velocity. And as you say, great if consumer tests increase the impact velocity so that manufacturers also optimize the performance in more severe impacts.

          Helmets have a pass/fail criterion on 250/275/300 g or HIC 2400 and many manufacturers will optimize their helmets for these limits. But if a person is exposed to these acceleration levels, the correlated risk of suffering a skull fracture is between 40 and 79%, while the correlated risk of a fatal traumatic brain injury is 77% according to the risk curves.

          We believe it is bad practice to optimize a safety product for the type of impact where the user still has a very high risk on these severe head injuries.

          Instead, it would make much more sense to bring these limits down, so we can effectively reduce the risks of these severe head injuries at the tested impact velocity. We know that these stricter limits are already achievable today, without the need to increase the size of helmets.

          And even though the tested impact velocity of cycle helmets is not really criticized at the moment, it is good practice to also test helmets at higher and lower impact velocities, to make sure a helmet is not just optimized for one test condition.

          In the end, with stricter, lower limits for maximum deceleration and HIC, helmets will offer more protection to the rider and will reduce the risk of severe head injuries significantly at the reference impact velocities. And that's what we strive for.

          With kind regards,

          Bas Jongsma


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