Cunobelin wrote:I don't think that is a very good analogy.
If we accept for the sake of argument that helmets have some capability to absorb energy, and reduce an injury, then they will absorb energy, up to their maximum capability whether the impact speed is 12 mph or 20 mph. It's just that a a 20 mph impact is more likely to exceed the energy absorption capability. That doesn't make it pointless to wear.
It also ignores that people might have other reasons to wear a helmet. The principle reason in my case is that I sometimes enter events that require them. If I want to do an event, I typically protest (once) helmet rules, just to make my point, then take my helmet along, and ride the event anyway. Why? Because I want to participate, and my not doing so out of protest will not be noticed by anyone, or contribute to any cultural changes.
It is because it is simple and factual.
If you were to use a set of brakes limited to 20 mph to stop from 60 mph then there would be a real danger and in reality an explanation that they may not function
If the brakes failed and you had an accident because you failed to stop, you would be seen as negligent or reckless in your actions.
Yet none of this simple visit to reality doesn't apply to helmets?
It may be simple and factual, but in physics/engineering terms it is not very realistic.
Even with the brakes example, depending on the system, it is likely that they would slow the vehicle you were trying to stop, even if they were not capable of stopping it (before anyone starts in with examples, yes I know that there are brake systems that would effectively not be able to do anything).
With helmets, I can imagine that some designs are likely to fail without absorbing much energy. However, they are basically designed to absorb energy. And in most circumstances that's what they will do, even when the test parameters (which aren't necessarily the design parameters) are exceeded.
It is probaly the case that if a cyclist hits their head in a crash with a car at an effective speed of 60 mph, there is little point in the helmet being there, because the design parameters have been exceeded by so much that it's miniscule by comparison. Using the brakes analogy, it would be like trying to stop a car with bicycle rim brakes.
But a fall or crash at 20 mph? There is plenty of evidence that (the majority) of helmets have some capability to absorb energy that would otherwise cause or contribute to a head injury.