Simplification to cut through the mis-perceptions?

This sub-forum all discussions about this "lively" subject. All topics that are substantially about helmets will be moved here, if not placed here correctly in the first place.
drossall
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Re: Simplification to cut through the mis-perceptions?

Postby drossall » 21 Feb 2017, 11:11pm

This discussion is losing sight of the basics. A (cycle) helmet is designed for the forces involving in toppling off sideways, vertically down onto the ground, from a standing start, with an impact velocity of about 10mph. Most of the relevant variables go more as the square of impact velocity. So, 30mph exceeds the design parameters of a helmet by nearer nine times than three.

In my view, it makes as much sense to argue that a helmet is really only needed by those likely to have collisions at 30mph as it does to argue that an infantryman really only needs a bulletproof vest when facing tank shells.

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Re: Simplification to cut through the mis-perceptions?

Postby Vorpal » 22 Feb 2017, 8:26am

Helmet discussions always lose sight of the basics. That's why the issue makes such good red herring.
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Re: Simplification to cut through the mis-perceptions?

Postby Steady rider » 22 Feb 2017, 8:47am

http://pure-oai.bham.ac.uk/ws/files/165 ... g_2014.pdf
http://ltces.dem.ist.utl.pt/lxlaser/lxl ... l_1586.pdf

Another bit of info.
http://www.sheldonbrown.com/rinard/aero ... namics.htm

perhaps joining the dots may be useful

The Bell Stratos, an ANSI approved helmet, increases the aero drag by approximately 1.3 % over a bald head. Short hair worsens it around 4.6%, long hair around 8.6%. The leather hairnet helmets which racers still often use - although completely insufficient according to ANSI - increase the aero drag by 6.3%. The common ANSI-approved Bell V1 Pro helmet increases drag by around 9.8% compared to a bald head.


The Birmingham Univ research reported on side wind forces;
The results showed that the wind induced force is a function of
the crosswind angle. The actual aerodynamic loads arising from such winds can be up to about 2.5 times the aerodynamic drag.


So, it appears that helmets can increase drag by up to 9.8% and the actual aerodynamic loads can be 2.5 higher.
When cycling with cross winds, head turning and helmets adding acceleration loads due to hitting say pot holes, the risk of falling off increases.

http://www.cyclehelmets.org/1261.html

Ruadh495
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Re: Simplification to cut through the mis-perceptions?

Postby Ruadh495 » 22 Feb 2017, 10:35am

drossall wrote:This discussion is losing sight of the basics. A (cycle) helmet is designed for the forces involving in toppling off sideways, vertically down onto the ground, from a standing start, with an impact velocity of about 10mph. Most of the relevant variables go more as the square of impact velocity. So, 30mph exceeds the design parameters of a helmet by nearer nine times than three.

In my view, it makes as much sense to argue that a helmet is really only needed by those likely to have collisions at 30mph as it does to argue that an infantryman really only needs a bulletproof vest when facing tank shells.


Isn't that the problem with cycle helmets though; they are designed for an impact type which is more likely for a pedestrian than a cyclist. I would say it's also an impact which is within the ability of the human skull to resist (usually it is) and so no helmet is required, however pedestrians do suffer serious head injuries. Very few people consider the risk great enough for pedestrians to wear helmets though. So why are cyclists expected to? "because motorcyclists", I think.

The enemy doesn't have any rifles bullets left, they are only firing tank shells, is there any point in our infantry wearing bulletproof vests?

That's not quite complete though, because I do believe that a helmet is likely to improve outcomes in certain types of impacts. I just don't believe the risk of an impact of that nature outweighs the negative aspects of wearing a helmet.

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Re: Simplification to cut through the mis-perceptions?

Postby mjr » 22 Feb 2017, 11:37am

A big +1 to the bit about 30mph speeds being basically irrelevant to the helmet debate while current helmets are only good to ~10mph.

Steady rider wrote:So, it appears that helmets can increase drag by up to 9.8% and the actual aerodynamic loads can be 2.5 higher.
When cycling with cross winds, head turning and helmets adding acceleration loads due to hitting say pot holes, the risk of falling off increases.

And all that extra load is going through the neck/shoulders, which basically evolved to support the human head, not the head with an extra load on top. It probably explains why I eventually developed a chronic neck injury when I used to ride using a helmet and no longer have.
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Re: Simplification to cut through the mis-perceptions?

Postby pjclinch » 22 Feb 2017, 2:20pm

Wanlock Dod wrote:I believe in risk compensation/homeostasis, so I don't find it hard to believe that wearing a helmet might well lead to people being more open to taking risks which they otherwise wouldn't (it isn't safe enough to ride on the road without a helmet, thus the helmet makes the road sufficiently safe, provided it is worn in the appropriate manner).


It's not really something "to believe in", it's pretty much established fact. Your problem with it is that it isn't something that affects everyone equally or in a measurable way. Some people are quite open about their use of PPE as risk management, others are using it "just in case" due to active risk aversion, and though both are aspects of risk compensation the ultimate chances of each group crashing will be quite different. This ultimately amounts to just further unhelpful cloudiness in our data.

Wanlock Dod wrote:Personally I am inclined to think that it is a lack of acceptance of unconscious risk compensation that is the biggest factor in failing to understand just how protective helmets really are.


It may be a factor, but I think the biggest problem by a country mile has been decades of people going on and on (and on some more, and then some more again) about how helmets are "essential" and are lifesavers, coupled with an expectation that you're on borrowed time to ride without one. This bigs up the danger of an accident in the first place, coupled with an assumption that accident is almost inevitably involving one's head, and for an encore bigs up the protective effect of bike helmets while suggesting human skulls are remarkably weak if you've just fallen off a bike.

We've largely bought in to bike helmets being a Good Thing. Unsticking that is a problem because it needs people to reset their default assumption. The Dutch have, by way of alternative, largely bought in to utility bike riding being a benign activity.

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pjclinch
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Re: Simplification to cut through the mis-perceptions?

Postby pjclinch » 22 Feb 2017, 2:57pm

Ruadh495 wrote:Isn't that the problem with cycle helmets though; they are designed for an impact type which is more likely for a pedestrian than a cyclist.


Not as big an issue as is often made out, because they're typically pretty similar in terms of the amount of energy soaked up in the initial impact, which is a gravity-powered fall on to a (usually hard) hard, constrained surface. I might be going at 30 when I have an "unplanned dismount", but if I don't hit a wall or other horizontal constraint I'm going to scrub off that speed relatively slowly. I might scrub off quite a bit of skin in the process, but while that's unpleasant it's not usually life threatening. The thing that will knock me (at least temporarily) senseless is the whack in the vertical that stops very, very quickly indeed, and that will be about the same for a cyclist as a pedestrian.

Ruadh495 wrote:I would say it's also an impact which is within the ability of the human skull to resist (usually it is) and so no helmet is required, however pedestrians do suffer serious head injuries. Very few people consider the risk great enough for pedestrians to wear helmets though. So why are cyclists expected to? "because motorcyclists", I think.


We didn't need them for years after m/cycle helmets were not only legal but accepted by most m/cyclists as something they should use, so I don't think that explains it entirely. But the continual pressure from many sources, including the cycling community, has made them perceived to be "essential".

You're quite right that the human skull is quite up to the sort of fall a cycle helmet is designed for, so why bother at all? That's because they were originally developed as a "better hairnet". A hairnet was only used in a sports context and I doubt many people ever thought they'd save a life. What they might reasonably be expected to do was help someone who'd just taken a spill in a race get back on and not lose much time, as opposed to stopping for a few minutes seeing stars and putting themselves right out of contention.
That people can take the sort of falls is easily illustrated by a typical primary school, where on any given day the lunch hour is quite likely to see someone helped to the school office by their pals after they've fallen and hit their head. It was common enough in the 200 roll school my children attended that the school had form letters to send home and a sheet of "I've banged my head!" stickers to supplement the usual "I've been brave!" stickers for that great paediatric trauma intervention of stickers and sympathy.
Had the falling child been wearing a helmet they might well have able to get straight up and carry on their game of chase or whatever: that's the design goal, and it is relevant to at least some sports cycling, and when you look at the number of folk on televised cycle racing riding despite post-fall "interesting" track burns or gravel rash, it's clear that exceeding 12 mph in the horizontal doesn't really affect that.

Ruadh495 wrote:That's not quite complete though, because I do believe that a helmet is likely to improve outcomes in certain types of impacts. I just don't believe the risk of an impact of that nature outweighs the negative aspects of wearing a helmet.


Yup.
This sort of thing...



Difficult to be sure whether his forward roll involved much impact on the head/helmet, but it would happen sometimes in this sort of crash and it might make the difference between getting back on (as Quintana did on this occasion) and finishing in a race that has very big financial implications for teams and rider. Or you might get a head-whack off a tree branch miles from anywhere on your MTB and wearing a helmet would make it easier to limp back to civilization, and so on.

But these cases are not relevant for nearly as many people as those that wear helmets in the UK.

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