4 ms·

> The guy sounds insane. Simple physics indicates that the longer the collision the less force applied will be. The problem is that helmets are only designed (

> The guy sounds insane. Simple physics indicates that the longer the collision the less force applied will be. The problem is that helmets are only designed (and tested!) to cover one very specific type of crash. The head smashing into the ground directly and at high speed one. And all it does is turn a potentially very severe injury into a less severe one. It shifts the risk-profile from maybe dying, maybe breaking bones in your head and definitely having a concussion to less risk of dying, less risk of breaking bones and definitely having a concussion. It doesn't do anything when you get in a low speed crash because the compressive strength of the foam inside helmets is actually very high. Expanded Polystyrene (EPS) is the crushable material inside bicycle helmets. Here you can see that 10psi is a very reasonable number and that 25psi plus isn't unreasonable. http://www.epsindustry.org/building-construction/compressive-strength http://www.epsindustry.org/building-construction/compressive... Let's suppose that 10psi is the number and that you manage to crush a substantial portion of the helmet. Maybe that's 20 square inches. That means it took 200lbs ( 10psi * 20sqin ) of force to do that. If the average head weighs 11lbs it must have experienced something like 18 Gs to make that happen. Sure 18 G is better than 60 G (or whatever if you didn't have a helmet) but it's not as though wearing a helmet turns any crash into something very survivable and with very little consequence. Anecdotally I went over the handlebars once at 22mph. Another cyclist popped out of stopped traffic (not at a crosswalk) and I had about 10 feet to react. I hit her back tire and knocker her over, but I went over the bars and pivoted around my front wheel right into the ground. Headfirst. I was wearing a helmet and very glad to have been but my helmet only had about a 3" diameter flat spot on the top. Personally I would have preferred that the foam had only been 5psi (instead of 10psi) and that the crush zone had been larger and it would have slowed things down more. But helmets have to pass a CSPC test and it's a 6 foot drop, which means that it doesn't do much unless it's a very, very bad fall. Personally I thought my fall was pretty horrible and that the helmet should have used up the majority of the crush zone, but while the flat spot was 3" in diameter it was only about 1/4" deep out of the 1" or so of total foam depth. http://gearfinder.bicycling.com/senseless/index.html http://gearfinder.bicycling.com/senseless/index.html I get that you understand the simple physics, but as it turns out, real life is substantially more complicated than JUST simple physics most of the time.

monksy 11y ago
So you're upset that the material will not protect against lower impact collisions and still protect you against high impact collisions? (yet still be wearable)
- msandford 11y ago
  I wouldn't say "upset" is the correct word, but perhaps "disappointed" is accurate. It is disappointing that helmets only seem to protect against very severe events. Because these very severe events also happen to be fairly rare. So basically a bike helmet is not like buying health insurance, but more like buying life insurance that only pays out if you're eaten by a wild animal. And you live in the First World. But you pay for it just the same, because you have to put on and wear that helmet EVERY SINGLE RIDE because you never know when your ticket might get punched. The point is that it seems like if you want to make people safer, the helmet should protect them against lower energy collisions and higher energy collisions both. But the CSPC test is a one-size-fits-all test that ALL helmets have to pass and as a result, there's absolutely no differentiation whatsoever. So all bike helmets have to protect you against truly horrific crashes, crashes that people riding around at 5-15mph will never experience. It'd be nice if the CSPC would make a few categories of protection that you can buy helmets for. Casual cycling, BMX, mountain and road say. And then let the manufacturers tailor the helmets towards the risk that people ACTUALLY face when they bicycle. The way it's done right now would be like requiring formula 1 cars to have airbags because they're cars too and all cars have to have airbags. > So you're upset that the material will not protect against lower impact collisions and still protect you against high impact collisions I don't think it would be impossibly difficult to get a helmet that had 1/2" of 3psi foam and 1/2" of 15psi foam. Then you could get some protection against the common concussion injury and still retain most (if not all) of your death mitigation as well. But so long as the CSPC has a one-size-fits-all test it's very unlikely that things will change.
maxerickson 11y ago
The helmet buys you t. Lower density foam buys you less t. Pondering it briefly, I think it is difficult to arbitrarily change the size of the compressed zone of the helmet, as that depends on the contact patches (helmet head and helmet ground) and so the shape of the helmet more than the density of the foam. It can be optimized for a given foam thickness, and then you're done.

monksy 11y ago

So you're upset that the material will not protect against lower impact collisions and still protect you against high impact collisions? (yet still be wearable)

msandford 11y ago
I wouldn't say "upset" is the correct word, but perhaps "disappointed" is accurate. It is disappointing that helmets only seem to protect against very severe events. Because these very severe events also happen to be fairly rare. So basically a bike helmet is not like buying health insurance, but more like buying life insurance that only pays out if you're eaten by a wild animal. And you live in the First World. But you pay for it just the same, because you have to put on and wear that helmet EVERY SINGLE RIDE because you never know when your ticket might get punched. The point is that it seems like if you want to make people safer, the helmet should protect them against lower energy collisions and higher energy collisions both. But the CSPC test is a one-size-fits-all test that ALL helmets have to pass and as a result, there's absolutely no differentiation whatsoever. So all bike helmets have to protect you against truly horrific crashes, crashes that people riding around at 5-15mph will never experience. It'd be nice if the CSPC would make a few categories of protection that you can buy helmets for. Casual cycling, BMX, mountain and road say. And then let the manufacturers tailor the helmets towards the risk that people ACTUALLY face when they bicycle. The way it's done right now would be like requiring formula 1 cars to have airbags because they're cars too and all cars have to have airbags. > So you're upset that the material will not protect against lower impact collisions and still protect you against high impact collisions I don't think it would be impossibly difficult to get a helmet that had 1/2" of 3psi foam and 1/2" of 15psi foam. Then you could get some protection against the common concussion injury and still retain most (if not all) of your death mitigation as well. But so long as the CSPC has a one-size-fits-all test it's very unlikely that things will change.

maxerickson 11y ago

The helmet buys you t. Lower density foam buys you less t. Pondering it briefly, I think it is difficult to arbitrarily change the size of the compressed zone of the helmet, as that depends on the contact patches (helmet head and helmet ground) and so the shape of the helmet more than the density of the foam. It can be optimized for a given foam thickness, and then you're done.