The CycleChat Helmet Debate Thread

[Mugshot]

Has there been a glitch in the matrix or did I imagine reading several pages of posts earlier?

 

[Fab Foodie]

Has there been a glitch in the matrix or did I imagine reading several pages of posts earlier?

Someone's been busy .....

 

[Rickshaw Phil]

Has there been a glitch in the matrix or did I imagine reading several pages of posts earlier?

You imagined it.

In reality, the thread was straying off topic and getting personal so a number of posts have been removed for those reasons or because they quoted posts that had been deleted. Sorry @Fab Foodie your cartoon got caught up in the widespread removals - I'm happy for the reposted version to stand.

Can I remind old and new contributors that there are special rules for this thread which can be found back on page 1. The 30 day ban will apply for those who continue to ignore them.

 

[Fab Foodie]

You imagined it.

In reality, the thread was straying off topic and getting personal so a number of posts have been removed for those reasons or because they quoted posts that had been deleted. Sorry @Fab Foodie your cartoon got caught up in the widespread removals - I'm happy for the reposted version to stand.

Can I remind old and new contributors that there are special rules for this thread which can be found back on page 1. The 30 day ban will apply for those who continue to ignore them.

Thanks :-)

 

[ufkacbln]

Like I said, people insure themselves against even more unlikely things than falling off a bike. Like I said these things happening to me may be rare (albeit not as rare as you're trying to kid yourself) - but them happening to someone is pretty much a guarantee.
.

... and non-cycling head injuries are far more common than cycling ones according to cohort studies of hospital attendances

If you are going to "pretty much guarantee" that someone is going to have a head injury that can be mitigated by the use of a helmet then it makes wearing them off the bike the better bet

 

[MartinQ]

I do generally wear a helmet, but I think I'll give it up just to stick two fingers up to JSP
http://www.bbc.co.uk/programmes/p03tm40m
http://www.bbc.co.uk/news/uk-politics-36247516
The debate here seems (almost) reasonable in comparison

 

[mjr]

I do generally wear a helmet, but I think I'll give it up just to stick two fingers up to JSP

You're not the first person to write that - I've seen similar on other forums. It seems that JSP's mistaken rant has woken a few people up to the non-wearing majority being our strongest defence against compulsion by the wrongheaded non-riders.

 

[glasgowcyclist]

You're not the first person to write that - I've seen similar on other forums. It seems that JSP's mistaken rant has woken a few people up to the non-wearing majority being our strongest defence against compulsion by the wrongheaded non-riders.

You know what? I really hope that this grows and becomes known as the Street-Porter effect; millions of helmetless cyclists across the UK.

GC

 

[philepo]

Sorry - you're playing statistical gobbledygook games with numbers. And they don't convince me.

By contrast (and I know it's been said before), this little exercise in real-life observation and measurement ---- "cyclists who wear protective helmets are more likely to be struck by passing vehicles".

I don't disagree with this. But he also said "“We know helmets are useful in low-speed falls, and so definitely good for children, but whether they offer any real protection to somebody struck by a car is very controversial."

Also, this 2007 research has been repeated (2014) with a control group by the same author and found that passing distances do not change with helmet wearing, so what do u think now? http://opus.bath.ac.uk/37890/

"A motive for this study was to test Walker’s (2007) hypothesis that the reduced passing proximities seen when a bicyclist wore a helmet might have been caused because, as Basford et al. (2002) suggested, drivers take helmeted riders to be more experienced or in control. However,.....did not lead to changes in mean driver overtaking proximities or in the proportion of very close passes. ... such that motorists no longer respond to perceived experience as they did when Walker (2007) collected data. At present, we cannot say for certain which of these explanations is likely to be correct and further research could usefully address this question."

Motorcycle helmets are tested and evidenced against real world scenarios. I believe that a cycling helmet makes no difference because there is nothing to show that it does. And given the price of some helmets, that is quite expensive snake oil being sold.

What real world scenarios ? They still hit them with lumps of weights.

The fact is, that any protective effect helmets have are not detectable in the data, so they clearly don't make a significant difference to outcomes.

Not detected is fine with me, but that is not evidence, just a lack of evidence.

I mostly read CycleChat on a Kindle. All text is black. You've put your words inside a box marked QUOTE="mjray... so it looks like I wrote it when I did not. Also, it's a PITA to reply because clicking "Reply" only quotes words that are marked as yours and omits what you put in QUOTE tags.

That defence of misquoting is about as ridiculous as the defence of abusing the injury statistics. Stop both now, please.

You're the one man in england who reads the interweb from a kindle in black and white. Sorry.

On the first point above - there is the word "if" - yet your head is quite a lot bigger so it's hard to argue you won't your head a lot more - nearly twice as often based on simple geometry quite apart from any risk-compensation effects by cyclist and passing motorists alike. Also the "making a difference" may also include extra leverage / rotation which may themselves cause more injury than they prevent.

This is why we should look at statistics from countries pre and post compulsion which should show if, in balance, they help or not. From Australia it appears they don't help on average.

On the motorcycle point the helmets are vastly stronger and better designed, and the whole set up is different. And unlike cycle helmets, to my knowledge there isn't a huge body of statistics suggesting the don't help. That said I haven't seen the stats for whether they actually do help, but it is at least more plausible.

1 It's not simple geometry. And if it was it would be about 28% based on radius increase of head with helmet. You'll hit your head more often, but you'd have to repeat an experiment of a cyclist falling off a bike 1000s of times and measuring his average distance of head from pavement to find out for sure. But point taken and agreed.
2 Australia is tricky as that is a blanket diktat which altered behaviour and is very sad. I don't want that here. I don't want to wear a helmet all the time.
3 More plausible is just opinion

Twice fark-all is still fark-all.

And the "2x" statistic actually means "somewhere between 0.8x and 2.5x", given the difficulty of measuring the mileage people walk and ride.

And the definition of "serious injury" is much looser than you think.

And most "serious injuries" are not head injuries.

As you say - nothing at all to think about or discuss.

2x sod all etc - agreed: based on simple numbers. But I would bet that within there the odds are much higher for a commuter in commuter traffic flow.
Yes, agreed, I'd like to know the head injury numbers...

 

[benb]

The fact is, that any protective effect helmets have are not detectable in the data, so they clearly don't make a significant difference to outcomes.

Not detected is fine with me, but that is not evidence, just a lack of evidence.

You are mistaken. If helmets were effective, we would be able to detect that protective effect in the data. That is, where helmet wearing has substantially increased we should be able to see a concurrent reduction in the proportion of head injuries. We do not.

Therefore, the evidence is quite clear: helmets are either so marginal that any protective effect is lost in the statistical noise, or other factors counteract the protection they offer. (ie cyclists taking more risks)

In either case, it is a fact that helmet wearing does not make any statistically significant difference to head injury rates, so any claims as to their effectiveness are utter speculation and/or exaggeration.

 

[philepo]

My reply is mixed up in the quotes, so if you are reading in B+W on a kindle like a 1950s time traveller, heads up my friend - my reply is in underlined text

How do you know?

Why do I get the feeling that you wouldn't have said a murmur had I said that the threshold of fatal injury was 300g's?
And to answer your question, I know because the Wayne State Tolerance Curve says so. In fact, for your hypothetical 100g example, impact duration is 6 ms [calculated, it is 3 ms @ 180g but i take your point] and the threshold of life threatening injury is 90-95g for this duration..And this assumes that the helmet not merely performs perfectly (does not fail under load by brittle fracture as opposed to crushing) but compresses to a density significantly higher than that of bulk polystyrene. This simply is not possible. [not sure what u meaning here?] And I'm neglecting the (incompressible) polycarbonate shell! [tiny effect from thin shell designed to spread load and decrease pressure - it's designed that way] Under the most favourable conditions, with the most benign of assumptions, helmet wearing fails to prevent fatal injury. [1] [the WSTC is very interesting, thanks]

actually average radius is most important factor and that helmet increases it by about 28% - implying that the probability of a fatal impact load is increased by helmet wearing.Agreed, but the probability increase will be tiny

Incorrect. Collisions take place at surfaces, not radii. [I was answering another poster who used diameter. I said that increase in radius was the important factor, meaning that the torque produced is a function of radius - I am not trying to trip anyone up on science, torque is force times radius thats all - i was making an 'anti helmet' case but also describing that case as minimal] Which is why physicists talk about "collision cross sections", measured in units of area. It is not the length of the barn door, nor its height - or even its volume, but its frontal area which determines your chances of hitting it at 6 paces. Your 28% increase in radius (assuming circular geometry, because I CBA to work out a more complex model) means a collision cross section increase of over 60%. And how do you know that the probability increase will "be tiny"? Kindly show your workings. [No, becasue I agree with you! - my point was about torque, not probability. I am happy with your theory]

That is 12 mph head on, like a bash to a car. I calculated it from a fall from a height to pavement, ie like being knocked off the bike and free falling to ground

Absolutely not. You cannot simply discount lateral velocity: momentum does not disappear! Hint: conservation of momentum. One of the more fundamental postulates in physics. Lateral velocity simply cannot be ignored as you claim. [I did not claim it can.. i'm thinking grandmothers and eggs here! Momentum, however, can be split into orthogonal components so you can ignore rotational effects that the horizontal 12 mph would have on the helmet (as I said I would) and then only consider vertical velocity (hence vertical momentum change) and the deceleration. The horizontal deceleration from the 12 mph velocity component would be a much lower (less g) one and so I ignored it - but yes, that rotational torque from the force of friction should be considered ideally]


[1] For any innocent bystander - if there's anyone left after all this time! - this actually is the perfect example of why common sense breaks down in situations like this. The human body is surprisingly resilient to extremely high accelerations - for 2-3 ms duration a acceleration of 200g's or more can be tolerated without fatal injury. But it's time dependent! The longer the duration of the acceleration load, the less can be endured. A 75g load will induce a life threatening injury if it lasts for more than 10 ms. [this is very interesting, thank you. But, the WSTC graph does not tell you about the damage high g does in other ways like bleeding and crushing fractures - the data is for brain tests, not impacts as far as I can tell... you know otherwise?]

In other words, it is not sufficient merely to reduce impact loads, as common sense suggests. This does not reduce impulse (that pesky conservation of momentum again) [correct, except that you are forgetting about conservation of energy, and this is why crushing a helmet will always result reduced energy of impact going into the brain - the helmet is also a damper in this system] any decrease in the collision forces must necessarily be accompanied with a increase in impact duration [see conservation of energy above]. Since acceleration tolerance falls substantially as duration increases, this means any protective headgear must act to reduce the experienced force by a greater magnitude than is commonly realised. In fact, given the shape of the Wayne State Tolerance Curve (negative exponential) [you mean hyperbolic I think] , it is perfectly possible for an inadequate helmet to simply increase the impact duration such that a very short duration but high force impulse which will not cause potentially fatal injuries is extended such that the duration enters the lethal zone simply because it cannot reduce the impact acceleration sufficiently. This worse outcome due to protective head gear is not one that "common sense" would ever predict...

[Well we agree on that! But the point of spreading the impact load over a larger area to reduce chance of impact injury is still valid and so is reduced energy into the brain . Out of curiosity, do you accept that motorcycle helmets are worthwhile???]

Mod note: In future, please use the quote function like everyone else, rather than inserting text into other people's posts. You are not only making things difficult for people who choose to read on a Kindle or other B&W device, but also anyone who does not have full colour vision.

 

[philepo]

You are mistaken. If helmets were effective, we would be able to detect that protective effect in the data. That is, where helmet wearing has substantially increased we should be able to see a concurrent reduction in the proportion of head injuries. We do not.

Link to data / evidence / journal paper?
Lack of evidence or the fact that someone hasn't sieved through the data to find it is not contrary evidence, it is just lack of and that's fine. I am not arguing about it.

 

[benb]

Link to data / evidence / journal paper?
Lack of evidence or the fact that someone hasn't sieved through the data to find it is not contrary evidence, it is just lack of and that's fine. I am not arguing about it.

If you'd bothered to do any actual research rather than just regurgitating prejudices and anecdotes, you'd already know this.

From https://www.ncbi.nlm.nih.gov/pubmed/11491251

 

[mjr]

If you'd bothered to do any actual research rather than just regurgitating prejudices and anecdotes, you'd already know this.

From https://www.ncbi.nlm.nih.gov/pubmed/11491251

And that's a very helmet-friendly rendition of it! Another is:

 

[Profpointy]

On bigger head point...
1 It's not simple geometry. And if it was it would be about 28% based on radius increase of head with helmet. You'll hit your head more often, but you'd have to repeat an experiment of a cyclist falling off a bike 1000s of times and measuring his average distance of head from pavement to find out for sure. But point taken and agreed.
.

I think you've made a geometry error in your 28% - surely propensity to hit is going to be be area related not radius after all. So something like 65% to 70% if I take your 28% as being the "true" radius difference. That's actually quite a lot. Helmets would have to do quite a bit of good to compensate for the misses becoming hits.

At the risk of being naughty with a thought-experiment - the oft quoted by the "pro-" lobby example of "hit your head with a hammer with and without helmet" could be replaced by "miss your head entirely with a hammer versus hit your helmeted head with the hammer"