The CycleChat Helmet Debate Thread

[mjr]

I offer the following from the "freshers cycling" information sheet put out by a certain university:

"Get the right equipment- the absolute minimums are a mechanically safe bike that fits you, front and rear lights, rear reflector and a good quality lock. Most experienced [name of town] cyclists also decide, after a few near misses, to wear a helmet (if you do decide to wear one make sure it is fitted correctly) and something high-visibility and reflective, particularly at night."

Thank you Oxford. I also like "Never cycle after drinking alcohol as the same rules and limits apply for people in charge of bikes and cars" which is incorrect on several levels. Don't overdo it but then we're meant to be against binge-drinking in general now, aren't we?

Anyone want to go challenge them?

 

[swansonj]

Thank you Oxford. I also like "Never cycle after drinking alcohol as the same rules and limits apply for people in charge of bikes and cars" which is incorrect on several levels. Don't overdo it but then we're meant to be against binge-drinking in general now, aren't we?

Anyone want to go challenge them?

Err... I did. The "same rules and limits" bit was last year's letter from the university cycling officer which I challenged. This year's letter does not say that particular falsehood anymore. The college site you link must still be quoting a previous year's version; feel free to challenge that college but other colleges are using this year's better-but-still-not-ideal version.

 

[hatless]

It is the right metric. Collisions occur at surfaces. This is why you get physicsts talking about "colliosn cross sections" and when I go off to do my neutron scattering experiments, I have to consider coherent and non-coherent scattering cross sections [1]. When aiming your pistol at the barn door, it does not matter how wide or how high it is, merely its area.

[1] Well, actually, a macroscopic analogue which simplifies the maths somewhat.

I think radius is the right measure. It's not the chance of a particle striking your head, it's the chance of your head impacting a plane surface, the road or the Audi windscreen, as against merely your shoulder impacting it. That depends on the stiffness of your neck, the momentum of your head, and the radius of you'd head. If your helmet was 1 metre thick, you would hit your head, hard, every time you fell over. If your head was 1 cm in diameter, you would almost never hit it.

 

[srw]

The helmet section is (probably - I haven't been to the city for a while) factually accurate. It doesn't advise helmet wearing. It simply says that most people decide to. As my college bike (knackered beyond my repair abilities after an altercation with a kerb) would testify, some advice about cycling after drinking is probably sensible.

If you want to have a go at someone, have a go at OUSU - the (not terribly influential, unless things have changed a lot) student union.
https://ousu.org/advice/transport/bike-safety/

The (much more influential) Daily Info's advice, on the other hand, is good, and straightforward - fit lights and be careful of buses.
http://www.dailyinfo.co.uk/oxford/guide/bikes#safety

 

[mjr]

The helmet section is (probably - I haven't been to the city for a while) factually accurate. It doesn't advise helmet wearing. It simply says that most people decide to.

Does Oxford really buck the national trend and have most people wearing helmets?

Guess it's time I switched my allegiance to the light blues, then. They aren't as irrational!

 

[swansonj]

.... As my college bike (knackered beyond my repair abilities after an altercation with a kerb) would testify, some advice about cycling after drinking is probably sensible.
...

I think (and told Mr Ed when I wrote to him) that cycling home after a pint with mates or a glass of wine with dinner is perfectly sensible and responsible, and that advice aimed at discouraging drunk cycling would be better than the absolutist "don't cycle after any drink". I am a great believer in honesty rather than exaggeration, both on principle and also because I think it is usually more effective.

 

[Wobblers]

I think radius is the right measure. It's not the chance of a particle striking your head, it's the chance of your head impacting a plane surface, the road or the Audi windscreen, as against merely your shoulder impacting it. That depends on the stiffness of your neck, the momentum of your head, and the radius of you'd head. If your helmet was 1 metre thick, you would hit your head, hard, every time you fell over. If your head was 1 cm in diameter, you would almost never hit it.

No. You need to take account of the fact that you can fall in any direction. So you need to consider the full 360 degrees. That describes a circle, so radius squared is correct. Your suggestion implies that a helmet that is one metre long but 1 cm wide has the same probability of hitting the ground as one which is a 1 metre hemisphere, which cannot be true simply from geometric arguments.

 

[Big Andy]

I think radius is the right measure. It's not the chance of a particle striking your head, it's the chance of your head impacting a plane surface, the road or the Audi windscreen, as against merely your shoulder impacting it. That depends on the stiffness of your neck, the momentum of your head, and the radius of you'd head. If your helmet was 1 metre thick, you would hit your head, hard, every time you fell over. If your head was 1 cm in diameter, you would almost never hit it.

That was my way of thinking. Although having thought about it some more I can see an argument for both radius and cross sectional area being valid depending on the type of impact.

 

[hatler]

And, of course, we know precisely what the type of impact will be, in all instances.

 

[srw]

That was my way of thinking. Although having thought about it some more I can see an argument for both radius and cross sectional area being valid depending on the type of impact.

It's not the (single) type of impact that counts. As @McWobble implies, it's the universe of possible impacts.

This is a constant theme in this discussion* - people focus on small details rather than the big picture.



*OK - and in life in general.

 

[Tin Pot]

Bicycle helmets reduce risk of serious head injury by nearly 70%, study finds - the guardian
https://apple.news/AucO_w6tKRgKTfCBk4mM2Pw

major study of bike helmet use around the world from more than 64,000 cyclists has found helmets reduce the risks of a serious head injury by nearly 70%.
The study also found neck injuries are not associated with helmet use and cyclists who wear helmets reduce their chance of a fatal head injury by 65%.

The NSW government has recently reviewed cycling laws and introduced harsh new penalties for a range of offences. The fine for not wearing a helmet has risen from $71 to $319

 

[hatless]

No. You need to take account of the fact that you can fall in any direction. So you need to consider the full 360 degrees. That describes a circle, so radius squared is correct. Your suggestion implies that a helmet that is one metre long but 1 cm wide has the same probability of hitting the ground as one which is a 1 metre hemisphere, which cannot be true simply from geometric arguments.

Radius does take account of this, because a round thing, like a head in a helmet, doesn't have just one radius in one direction. It's the thickness of the helmet, and therefore the direction the head has to travel to make impact in whichever direction you happen to be falling today which makes the difference.

If it was the chance of a raindrop landing on your helmet, then it would be horizontal cross section. If it was the chance of a low flying bird hitting it as it flew past, then it's the height of the helmet that matters. I think falling and hitting your head is more like the second example.

 

[srw]

Bicycle helmets reduce risk of serious head injury by nearly 70%, study finds - the guardian
https://apple.news/AucO_w6tKRgKTfCBk4mM2Pw

Click on the abstract and, unless I've seriously misunderstood something, that's not what the research actually says. In other words, the press release on which the article is based is lying.

It talks about an odds reduction in any kind of head injury of about 50%, of a serious head injury somewhere between 25% and 40%, of a face injury of about 70% (actually between 56% and 80%) and of a fatal head injury of somewhere between 15% and 90%.

http://ije.oxfordjournals.org/content/early/2016/09/06/ije.dyw153.abstract

Someone with access to the article itself can, I'm sure, point out more flaws.

 

[Big Andy]

It's not the (single) type of impact that counts. As @McWobble implies, it's the universe of possible impacts.

This is a constant theme in this discussion* - people focus on small details rather than the big picture.



*OK - and in life in general.

Small details are however still quite important.

 

[srw]

Click on the abstract and, unless I've seriously misunderstood something, that's not what the research actually says. In other words, the press release on which the article is based is lying.

It talks about an odds reduction in any kind of head injury of about 50%, of a serious head injury somewhere between 25% and 40%, of a face injury of about 70% (actually between 56% and 80%) and of a fatal head injury of somewhere between 15% and 90%.

http://ije.oxfordjournals.org/content/early/2016/09/06/ije.dyw153.abstract

Someone with access to the article itself can, I'm sure, point out more flaws.

No. I think I've got that wrong. The paper does seem to claim a 70% reduction in "risk". Which is mathematically odd, because the number of papers claiming that size of reduction, and in which this meta-analysis is based, us tiny. Possibly as small as one.