Cycling UK Forum

pjclinch wrote:I wish I knew how to get realistic expectations across. We've tried giving people, you know, decent information but lots of them aren't having any of it

We know that logic and science won't change anyone's mind. Perhaps the cycle helmet's limits could be communicated best as a slogan or rhyming couplet.

For example: "A helmet might save you a bump on the head, but if you get squashed you'll still be quite dead"

Though that doesn't address the cases where the helmet may cause harm, or - more importantly - the small chance that the helmet will play any meaningful role in a cycle journey, for good or bad.

How about this slogan?

Helmets. Meh

Cunobelin wrote:You believe that there is only one element to the impact energy, and that it will always be less than 12 mph.I presume that this will also be on teh point of the helmet used in the tests as well?

I will continue to accept the reality that there are other components in the impact speed including a contribution from the forward speed. Feel free to be deny that element

Of course the "claim" that there is only a vertical element will also disprove rotational injuries, inquiries caused by the helmet sliding on the head )or being ejected and a multitude of other issues that should be considered in the effectiveness of cycle helmets

You're being disingenuous. The design spec is 12 mph because that is the speed that will come from gravity. That's it. I'm not claiming anything beyond that is why there's a 12 mph design. I'm certainly not in the business of believing that there is only ever one element in the impact energy. Where on earth did you get that idea from?

There may be all sorts of other elements, but then again there may not be, and the design spec is 12 mph for the good reason that that is something that will be fairly predictably present in lots of falls. What you say above is, as one of my old tutors would put it, "qualitative chit chat". There is nothing in there that tells us a helmet will fail in its design goal if the cyclist is travelling at overall speed greater than 12 mph.

There is no claim that there is only a vertical component, simply that that is a predictable element in just about any fall.

Again we return to the actual design coming from a better hairnet. The point of a hairnet was never to save lives, it was to give you a better chance to get back on and get on rather than rubbing the bump on your head saying "ow" while the stars in your eyes dissipated. That is a tangible and useful thing for a protective device to do. The problem is that we're on the order of gardening gloves, while widespread perception is we're talking about chainsaw-stalling Kevlar.

There will be many falls where mitigation of the gravity-powered component is genuinely useful to the wearer of a helmet, unless you think avoiding minor injuries isn't useful. If you want to say the instance of those falls is far lower than people seem to think then I'm right with you, but that doesn't take away that that is their design use and they can do that. That is what they are for, that is why their design is as limited as it is. That folk don't know that's the case is not an issue of what the specification actually is, and nor is it the case that they surely can't do that if you were travelling over 12 mph.

Pete.

bovlomov wrote:How about this slogan?

Helmets. Meh

Yup, I can buy right in to that!

I am not so scared of dying but I am scared of surviving seriously injured and crippled
Should I wear a h****t or not?

Cyril Haearn wrote:I am not so scared of dying but I am scared of surviving seriously injured and crippled
Should I wear a h****t or not?

The chances that a helmet will make any difference one way or another are miniscule. Do as you like.

Vorpal wrote:

Cyril Haearn wrote:I am not so scared of dying but I am scared of surviving seriously injured and crippled
Should I wear a h****t or not?

The chances that a helmet will make any difference one way or another are miniscule. Do as you like.

Spot on.

Do as you like.
That's what I do. I do as I like and not wear the thing.

I think that for many cyclists who wear helmets, it is not an entirely rational choice, i.e. based purely on rigorous evidenced based studies.

It can be much easier and less uncomfortable to believe that a helmet provides a high level of protection, than to accept that the risks we run are sometimes far higher than we would like, and to accept that our lives might be snuffed out due to a moment's carelessness (our own or another's) or just bad luck.

Thousands of years ago, people deified and prayed to the Sun, the sea, volcanoes etc., because it was more comforting to believe that natural cataclysms and disasters were caused by a supernatural force, who could be persuaded by ritual worship not to 'punish' people thus, rather than accept that these were just random unpredictible events.

Similarly many people wear a helmet more for its talismanic properties than the actual physical protection it provides, but will argue otherwise because the alternative is to confront an unpleasant reality about its actual effectiveness vs. the risks they run.

I think that effect can be even more pronounced for cyclists who have an accident where their helmet is damaged or destroyed. Having had a close call, they want to believe that the helmet made a decisive difference to the outcome, rather than believe that they were just lucky and that they could just as easily have been killed.

Cunobelin wrote:

pjclinch wrote:

Cunobelin wrote:
The question still remains, common sense says that if you are using "safety equipment" then it should be used within the proven design limits

The design limit is that the vertical component of your fall will be of the order of 12 mph. What percentage of falls do you feel this is unreasonable assumption, roughly?

There is the matter that helmets are pushed in a generic sense as lifesavers well beyond the above, but the actual design spec is the above, and is fair and reasonable, and the actual people making and selling the helmets aren't the ones claiming miraculous powers for them. Their legal folk are far too canny to let Marketing say they'll save your life, and why would they when so many cyclists are doing it for them in an unregulated and unactionable manner?

Once again, 12 mph design constraint is not an issue that relates to your forward speed on a bike, and banging on about it is unhelpful.

Pete.

You believe that there is only one element to the impact energy, and that it will always be less than 12 mph.I presume that this will also be on teh point of the helmet used in the tests as well?



I will continue to accept the reality that there are other components in the impact speed including a contribution from the forward speed. Feel free to be deny that element



Of course the "claim" that there is only a vertical element will also disprove rotational injuries, inquiries caused by the helmet sliding on the head )or being ejected and a multitude of other issues that should be considered in the effectiveness of cycle helmets

Unless you hit something sideways then the vertical speed is the only one that actually has any significance in the direct KE absorption... That's basic kinetics.

There are two main cases where the 12 mph is the falling speed from upright is going to be exceeded.
- Any time you hit anything other than the ground (a vehicle, a wall, a tree, a rock, a lamppost)
- Any time you are thrown from the bike (high side, vehicle impact) and therefore start your fall from above 6'

The first of those is highly likely when doing downhill or mountain biking, and somewhat likely in an urban environment (there are just so many obstacles around).
The second is likely in any vehicular collision... the 12mph is based on a static fall...
Or is it?

A static fall from 6' would take (s=ut+1/2at^2) .37s, resulting in an 8mph collision
To fall at 12mph requires a starting height of 2.7m.

Of course the human body isn't a point mass, and so it's much more complex than that, with KE transfers as well as self protection being significant factors. In all the falls and collisions I've had I haven't hit my head, though I have seen it done.


The third issue is where horizontal velocity isn't retained by virtue of frictional forces. By definition those will be at the edge of your (now enlarged) head, and so will exert quite a significant torque to the neck, and induce a significant rotational acceleration in the skull. Both of those are known to cause very severe trauma, and for that reason motorcycle helmet specifications include (I am led to believe) elements designed to prevent such 'snagging'. Cycle helmets have no such design criterion, and the 'lightweight', 'vented' designs are pretty much designed to provide snagging points.
At least most helmets I see aren't worn properly, so they'll just rotate around the head or fall off...

Cyril Haearn wrote:I am not so scared of dying but I am scared of surviving seriously injured and crippled
Should I wear a h****t or not?

As above -your choice, but when you look at hospital admissions the greater incidence suggests that:
If you are a pedestrian -yes
I’ve you are male -yes
If you are over 60 -yes
If you are homeless -yes
If you are drinking alcohol-yes
If you are homeless, male, over 60 and drink alcohol- indisputably

slowster wrote:I think that for many cyclists who wear helmets, it is not an entirely rational choice, i.e. based purely on rigorous evidenced based studies.

<snip>

You're not the only one that thinks it has a lot more to do with things like psychology and culture.

This BMJ Editorial by Ben Goldacre (epidemiologist, popular science writer, campaigner for high quality evidence and scourge of bovine scatology merhants) and David Spiegelhalter (Winton Professor of Public Understanding of Risk) concludes:

The enduring popularity of helmets as a proposed major intervention for increased road safety may therefore lie not with their direct benefits—which seem too modest to capture compared with other strategies—but more with the cultural, psychological, and political aspects of popular debate around risk.

[XAP]Bob wrote:Unless you hit something sideways then the vertical speed is the only one that actually has any significance in the direct KE absorption... That's basic kinetics.

There are two main cases where the 12 mph is the falling speed from upright is going to be exceeded.
- Any time you hit anything other than the ground (a vehicle, a wall, a tree, a rock, a lamppost)
- Any time you are thrown from the bike (high side, vehicle impact)

I think you are missing the case where some part of the system which is you and/or the bike engages with the environment and converts forward energy into rotational energy, which could result in some part of you hitting the ground at substantially more than 12 mph.

To be more graphic, if I were to be traveling backward in a sitting position at 30mph, and my seat contacted the ground first (and didn't simply slide), the vertical component of my head catapulting into the road would substantially exceed 12mph.

Of course, that's somewhat contrived, but the point is that, depending on how you fall, a significant portion of your forward energy could be translated via rotational energy, into vertical.

Cunobelin wrote:

Cyril Haearn wrote:I am not so scared of dying but I am scared of surviving seriously injured and crippled
Should I wear a h****t or not?

As above -your choice, but when you look at hospital admissions the greater incidence suggests that:
If you are a pedestrian -yes
I’ve you are male -yes
If you are over 60 -yes
If you are homeless -yes
If you are drinking alcohol-yes
If you are homeless, male, over 60 and drink alcohol- indisputably

Only numbers 1+2 apply
Maybe I should wear half a h****t

Hi,
Back on OP's question.
"So my question is: in what way does your stance on helmets fit in with your other views on society and science?"

I believe they are one and the same, that is that if you simply rotate the key words the result will be the same difference.
Its quite possible for a brain surgeon to be a dinialist......on another subject.

Just because we may be a statistician does not mean we may not be prone to alcoholism or gambling etc.

You may work with sane or well thought of people .........but when they get behind a wheel of a car

Of course I would say that as I am a wearer

rfryer wrote:

[XAP]Bob wrote:Unless you hit something sideways then the vertical speed is the only one that actually has any significance in the direct KE absorption... That's basic kinetics.

There are two main cases where the 12 mph is the falling speed from upright is going to be exceeded.
- Any time you hit anything other than the ground (a vehicle, a wall, a tree, a rock, a lamppost)
- Any time you are thrown from the bike (high side, vehicle impact)

I think you are missing the case where some part of the system which is you and/or the bike engages with the environment and converts forward energy into rotational energy, which could result in some part of you hitting the ground at substantially more than 12 mph.

To be more graphic, if I were to be traveling backward in a sitting position at 30mph, and my seat contacted the ground first (and didn't simply slide), the vertical component of my head catapulting into the road would substantially exceed 12mph.

Of course, that's somewhat contrived, but the point is that, depending on how you fall, a significant portion of your forward energy could be translated via rotational energy, into vertical.

That list was for cyclists modelled as a point mass

[XAP]Bob wrote:That list was for cyclists modelled as a point mass