Helmet Cams and the integrity of cycle helmets

[Mick F]

..........the bit of my head that took it was my chin...

I have the scars on my chin to prove it.

[TonyR]

Though unless you hit a horizontal constraint (like a wall) you won't actually scrub off all of that speed in the thickness of a helmet. It's not how much KE you have when you hit, it's the rate at which you lose it.
Come off directly square on to a wall at 57 kph and that will do far, far more damage than hitting a flattish road with space to slide at the same speed, because in the latter you'll scrub off speed more slowly. You'll scrub off more skin in the process, but that's not as bad as skull to wall well above what it's evolved to take.
And a helmet might reduce the peak deceleration, but quite probably not enough: they're not designed for that sort of hit.

Pete.

In most slides your head/helmet does not really impact anything anyway. But if it does then there is a risk of rotational brain injuries which are the worst - the sort Schumacher had. At the point of impact the vertical velocity from falling off the bike will result in the helmet being pushed into the tarmac with a force equivalent to about a tonne for a brief period. At that force it not going to slide much but grab the tarmac resulting in a sharp angular impulse on the head from the forward velocity. So not as benign as you are suggesting.

[Cunobelin]

UCI think it's a problem... http://www.pinkbike.com/news/uci-amend- ... -2015.html

There is an optimistic and pessimistic approach

They have NOT stated they think there is a problem, simply taken the pessimistic approach.

[Cunobelin]

Though unless you hit a horizontal constraint (like a wall) you won't actually scrub off all of that speed in the thickness of a helmet. It's not how much KE you have when you hit, it's the rate at which you lose it.
Come off directly square on to a wall at 57 kph and that will do far, far more damage than hitting a flattish road with space to slide at the same speed, because in the latter you'll scrub off speed more slowly. You'll scrub off more skin in the process, but that's not as bad as skull to wall well above what it's evolved to take.
And a helmet might reduce the peak deceleration, but quite probably not enough: they're not designed for that sort of hit.

Pete.

In most slides your head/helmet does not really impact anything anyway. But if it does then there is a risk of rotational brain injuries which are the worst - the sort Schumacher had. At the point of impact the vertical velocity from falling off the bike will result in the helmet being pushed into the tarmac with a force equivalent to about a tonne for a brief period. At that force it not going to slide much but grab the tarmac resulting in a sharp angular impulse on the head from the forward velocity. So not as benign as you are suggesting.

Ironically these are the same dangers that are introduced by the venting and aerodynamic design of modern helmets

Many have sharp angles and "Snag points" that interact in exactly the same, yet no-one seems to be concerned about the dangerous design

[pjclinch]

Though unless you hit a horizontal constraint (like a wall) you won't actually scrub off all of that speed in the thickness of a helmet. It's not how much KE you have when you hit, it's the rate at which you lose it.
Come off directly square on to a wall at 57 kph and that will do far, far more damage than hitting a flattish road with space to slide at the same speed, because in the latter you'll scrub off speed more slowly. You'll scrub off more skin in the process, but that's not as bad as skull to wall well above what it's evolved to take.
And a helmet might reduce the peak deceleration, but quite probably not enough: they're not designed for that sort of hit.

In most slides your head/helmet does not really impact anything anyway. But if it does then there is a risk of rotational brain injuries which are the worst - the sort Schumacher had. At the point of impact the vertical velocity from falling off the bike will result in the helmet being pushed into the tarmac with a force equivalent to about a tonne for a brief period. At that force it not going to slide much but grab the tarmac resulting in a sharp angular impulse on the head from the forward velocity. So not as benign as you are suggesting.

It's something of a straw-clutching exercise to predict exactly what will happen, especially when the general flight-path of an over-the-bars will typically have something of a rotational element encouraging the rider to roll at high speeds rather than pancake.
In other words, it's pretty much up to fate how you come out of it, rather than if you're wearing a helmet or not.

Pete.

[nez]

Oh this has gone very gloomy

[Mick F]

Yes,
I'm not wearing one any more.
I'm wearing a cap now. A nice warm one.

[[XAP]Bob]

Though unless you hit a horizontal constraint (like a wall) you won't actually scrub off all of that speed in the thickness of a helmet. It's not how much KE you have when you hit, it's the rate at which you lose it.
Come off directly square on to a wall at 57 kph and that will do far, far more damage than hitting a flattish road with space to slide at the same speed, because in the latter you'll scrub off speed more slowly. You'll scrub off more skin in the process, but that's not as bad as skull to wall well above what it's evolved to take.
And a helmet might reduce the peak deceleration, but quite probably not enough: they're not designed for that sort of hit.

Pete.

In most slides your head/helmet does not really impact anything anyway. But if it does then there is a risk of rotational brain injuries which are the worst - the sort Schumacher had. At the point of impact the vertical velocity from falling off the bike will result in the helmet being pushed into the tarmac with a force equivalent to about a tonne for a brief period. At that force it not going to slide much but grab the tarmac resulting in a sharp angular impulse on the head from the forward velocity. So not as benign as you are suggesting.

Ironically these are the same dangers that are introduced by the venting and aerodynamic design of modern helmets

Many have sharp angles and "Snag points" that interact in exactly the same, yet no-one seems to be concerned about the dangerous design

Some of us are... But anything questioning the "safety" aspects of a device marketed as a fashion accessory, promoted as a safety requirement is poorly taken...

[TonyR]

It's something of a straw-clutching exercise to predict exactly what will happen, especially when the general flight-path of an over-the-bars will typically have something of a rotational element encouraging the rider to roll at high speeds rather than pancake.
In other words, it's pretty much up to fate how you come out of it, rather than if you're wearing a helmet or not.

On an individual level yes. But the cases where the helmet/head never touches the ground are not going to be affected one way or the other by wearing a helmet. What matters is what happens in the cases where it is impacted hard enough such that it should theoretically have made a difference to the linear impact. You are saying they only matter where there is a vertical obstruction that gets in the way of the forward component of the helmet velocity. I am saying that even if there is no such obstruction you are not in the clear because the vertical impact will produce a sharp rotational impulse from the forward velocity that can be very neurologically damaging.

[[XAP]Bob]

And those cases where wearing a helmet causes the collision due to the larger diameter of the helmet than a bare head - I frequently smack my head on walls/doors when wearing a magic hat, but almost never without one...

[pjclinch]

On an individual level yes. But the cases where the helmet/head never touches the ground are not going to be affected one way or the other by wearing a helmet. What matters is what happens in the cases where it is impacted hard enough such that it should theoretically have made a difference to the linear impact. You are saying they only matter where there is a vertical obstruction that gets in the way of the forward component of the helmet velocity.

No I'm not. I'm bringing that up as a limiting case, not suggesting it's the only time it matters.

I am saying that even if there is no such obstruction you are not in the clear because the vertical impact will produce a sharp rotational impulse from the forward velocity that can be very neurologically damaging.

It might, but again if the head hits and the rider rolls over thanks to the inertia of their lower body (much as Quintana did in his "unplanned dismount" in the 2014 Vuelta TT) there's far less chance of a significant jerk and the basic vertical impact absorption may be beneficial.

Lots of ifs and mights in there. Like I said, as far as we have data to tell it's really about how God's dice are rolling that day, rather than being able to say they're more likely to come down one way or another on the basis of whether our unfortunate example is wearing a lid or not. Just as we don't have information to sensibly speculate helmets are a Clear Win in an accident, we're similarly at an impasse about declaring them a Clear Fail.

Pete.

[[XAP]Bob]

Though unless you hit a horizontal constraint (like a wall) you won't actually scrub off all of that speed in the thickness of a helmet. It's not how much KE you have when you hit, it's the rate at which you lose it.
Come off directly square on to a wall at 57 kph and that will do far, far more damage than hitting a flattish road with space to slide at the same speed, because in the latter you'll scrub off speed more slowly. You'll scrub off more skin in the process, but that's not as bad as skull to wall well above what it's evolved to take.
And a helmet might reduce the peak deceleration, but quite probably not enough: they're not designed for that sort of hit.

Pete.

Apologies for diving so far back - I missed commenting on this...
The other factor is that the body isn't rigid (which I mentioned in my calculations) - the question is how beneficial those extra couple of cm are in comparison with the 18" or more the arms can provide, and the several feet over which the legs will decelerate (as they fold and come up past the torso)

Lots of ifs and mights in there. Like I said, as far as we have data to tell it's really about how God's dice are rolling that day, rather than being able to say they're more likely to come down one way or another on the basis of whether our unfortunate example is wearing a lid or not. Just as we don't have information to sensibly speculate helmets are a Clear Win in an accident, we're similarly at an impasse about declaring them a Clear Fail.

^ this ^
There are two cases in which a helmet is a clear fail:
- Discouraging cycling (by implying that it is a dangerous activity).
- Cost to the cyclist (helmets cost more than not helmets).

There are no cases where there is a clear win for the cyclist, only the manufacturer.

[AlaninWales]

There are two cases in which a helmet is a clear fail:
- Discouraging cycling (by implying that it is a dangerous activity).
- Cost to the cyclist (helmets cost more than not helmets).

There are no cases where there is a clear win for the cyclist, only the manufacturer.

Agreed
Agreed
Disagree: They make a nice stable mount if you choose to wear a camera on your head.

[pjclinch]

Lots of ifs and mights in there. Like I said, as far as we have data to tell it's really about how God's dice are rolling that day, rather than being able to say they're more likely to come down one way or another on the basis of whether our unfortunate example is wearing a lid or not. Just as we don't have information to sensibly speculate helmets are a Clear Win in an accident, we're similarly at an impasse about declaring them a Clear Fail.

^ this ^
There are two cases in which a helmet is a clear fail:
- Discouraging cycling (by implying that it is a dangerous activity).
- Cost to the cyclist (helmets cost more than not helmets).

This is, however, in a different context to the one I'm talking about there.
While on the one hand what you say is entirely correct in the Big Picture scope, above I'm talking about the far more limited scope of the cyclist being in an accident and heading towards something that'll probably hurt when they hit it. They haven't hit yet, and we're not sure of how they will hit, can we say whether they'll likely be better or worse off reliably based only on the presence of a helmet? No, we can't.

There are no cases where there is a clear win for the cyclist, only the manufacturer.

What I was getting at above is that as the cyclist flies towards their impact you cannot say for sure, based on whether or not they're wearing a helmet at the time, that they will be better or worse off. That's not the same thing at all as saying there can be no benefit from wearing a helmet. The modern cycle helmet is a development of the old hairnet, intended to make the difference between a minor scrape making stopping the rider getting straight back on and losing a minimum of time and holding their head for a wee while going "ow" as the butterflies circle. The former is a clear win for the cyclist, because they hurt less and lose less time. Neither of these are much to do with gross safety in terms of serious accidents, of course, and in most cycling contexts aren't especially likely.

Pete,

[TonyR]

What I was getting at above is that as the cyclist flies towards their impact you cannot say for sure, based on whether or not they're wearing a helmet at the time, that they will be better or worse off. That's not the same thing at all as saying there can be no benefit from wearing a helmet. The modern cycle helmet is a development of the old hairnet, intended to make the difference between a minor scrape making stopping the rider getting straight back on and losing a minimum of time and holding their head for a wee while going "ow" as the butterflies circle. The former is a clear win for the cyclist, because they hurt less and lose less time.

Its not a clear win. Its a speculative win as the ability of the helmet to do that is anecdotal and unproven. It could be that they are walking around saying "ow" because their helmet smacked the pavement hard when their unhelmeted head may not have hit anything,