It's a shame so many motorcyclists die young, before they get a chance to "grow into" some safety sense. I distinctly remember talking with my friends age 12 about how (apologies) "gay" helmets were on our bicycles. We'd speedbomb hills too, it was fun. I remember feeling no fear back then. I remember my parents telling me "you're an idiot for thinking you're invulnerable."

Why do we think that way when we're young, that we're immune to damage? What changes? We experience more death firsthand? If I hadn't had to clean up car accidents and watch a friend lose her intelligence to a helmetless bicycle accident, would I still feel invulnerable?

I wonder about this woman - did she do this because she lacked the fear? Or did she feel it, and all the positives of doing it overruled her fear? Maybe she was just confident enough in her safety measures to do it anyway?

It is all about the angular momentum of the cyclist wrt to the road.

I'm used to motor cyclists wearing leathers. Bare skin in an accident looks terrifyingly abrasive.

Nobody's ever managed to make it more that a second.

http://i.imgur.com/gRqg50J.png

at about 22mph. ;)

That's pretty much what happened to me. I was going walking speed on a bike, popped a wheelie, handle bars came off, I tumbled forward and landed collar bone first onto a curb. Hairline fracture at about age 14.

I pulled the brake lever on my road bike once, and it FELL OFF. Went right into the front spokes and launched me over the handlebars like a cannonball. It was like putting a metal rod right into the front spokes.

That sounds very concerning. I didn't know that could even happen...

I don't know too much about bikes, but the one I had used some type of bolt to connect the handlebars to the main frame.

I was adjusting the height of the handlebars and I guess I didn't tighten it enough in the end. User error in all its glory.

1: spherical cow/fermi estimate

You can probably produce more power approximated by the volume of the muscle though.

This never made any sense to me. Muscles are made up of groups of fibers, which are made up of chains of sarcomeres. How could strength be proportional to cross sectional area rather than volume of the muscle?

The same reason that's true of strength of passive members; the limiting factor is the force that will cause shearing, which is basically the strength of one bond in the lengthwise direction times the number of them supporting in parallel in the cross section. So, given the same material, cross sectional area determines strength.

The entire line of reasoning seems to rest on the idea that the smallest unit we consider runs from one end all the way to the other.

It doesn't really matter, except the not being homogenous end-to-end means it's the weakest point that matters. But, irrespective of the structural details, there is some force in the direction of contraction that will cause failure, and that force is proportional to, basically, the number of linkages it is distributed across in parallel (not connections in series, such as along the chain) which is proportional to cross-sectional area.

> The entire line of reasoning seems to rest on the idea that the smallest unit we consider runs from one end all the way to the other.

It is not (in fact, the entire reason it is true of any material is because even structures which seem to be end to end are composed of smaller structures with fallible linkages; if there were indivisible end-to-end structures, this would cease to be a concern.)

Although I was basing that on force exerted by gravity (which is proportional to mass), whereas deceleration might be spread out proportional to length, so it might work out to L² anyway. It's too late to edit though.

Or is this a myth?

I looked up the stats going back a few decades - in the sixties, an average hundred kids died in traffic each year here in Norway. Now? Two or three. Yet we drive more and the population is significantly larger, too.

Drowning (the other biggie) is down by a similar factor.

Generic accidents? Also down by at least an order of magnitude.

We may sigh all we want that kids today are glued to their playstations while we were out building tree huts, conducting -ahem- applied pyrotechnics experiments and similar - but the fact of the matter is that kids today survive childhood. We didn't. :/

The main difference is being supervised by a reasonable adult or not and how streets near homes have changed.

Kids can only be left to free roam in a very safe environment - and even that is not entirely without risks. Alternatively only kids who are shown to be reasonable can do that - it takes parental sensitivity.

Then you get older and experience aches and pains where there were none before, when you get hurt instead of shaking it off you either take longer to heal and/or need a trip to the doctor, maybe you deal with a nasty illness/injury or two, see people you know dealing with and/or taken out by nastier things. Throughout all this you start becoming your parents saying things like 'stop running around with that... you could put an eye out' (hell, by this time you probably met someone who did just that)

I figure in a few more years I'll be driving 20mph in the fast lane with my blinkers on... after all, what's the rush? Hey kids, get off my lawn! ;-)

My young cousins were playing tug of war with a bungie cord. One let go and the other ended up with a damaged eyeball.

I'm not saying that all of the "life experiences" answers are wrong, but I think there's more to it. For an organism to be successful it has to survive (to a point), but it also has to be efficient at doing physical tasks. I think we're naturally inclined to push our limits at a young age so that we know where those limits are, and we can more safely straddle them when we're older. Evolution could have made children cautious, and it did, to an extent. But there is a balance. A child who is too cautious never learns how to run safely, and an adult who doesn't know how to run safely can't chase a gazelle very well.

I see you've received a lot of answers already, but not an explanation (worthy by my standards). Here's my stab on it:

1. Remember how everyone got to ride a bike in the first place. It looked dangerous, yet we had to get over our fear AND try to suppress it consistently long after the point of riding and not falling any more. And that kind of fear suppression exercise was necessary again and again all over our childhood. It's no wonder that with so much repetition it grew to become part of our character, at least for a while, at least until the voices that once encouraged us to overcome our fears went silent.

2. The level of responsibility we bear and the awareness of it, including the responsibility for ourselves, especially enough to feel it in our choices, grows only with time. As younglings, we care less about "serious and boring" (i.e. "act responsible") and more about "fun and exciting" and weight our decisions accordingly.

An adults perspective is they young think they will never get hurt. A youths perspective never thinks about getting hurt in the first place.

The answer to this question is simple: Ignorance

It is the same ignorance that causes a toddler to put its hand in the fire without any fear.

>>What changes?

The experience of being burned is what changes. You are no longer ignorant.

>>Maybe she was just confident enough in her safety measures to do it anyway?

Or maybe she's just an adrenaline junkie. Also, doing something dangerous plenty of times with no consequences will reduce your fear.

Probably overprotection by parents. When I was a kid I was left alone with my friends with no parents supervision a lot.

We did very risky things and risked our lives several times, but in controlled and normal environments like climbing trees and going to the mountain. When something went wrong you will get painful feedback like bruises. But you knew what your limits were.

Quite interesting, those children that had their parents forbidding them to go with us actually had traumatic experiences later in life, once they were free from their parents. They will buy a motorcycle or car, take risks and die or almost die.

It was like they lacked the experience we had and replicated it, but with machines in non humane environments. Instead of bruises they will crash a very expensive car.

Of course, e-scooters and bike shares provide a counter-trend as they don't make it convenient to have a helmet.

Yea this one surprised me recently. I learned to downhill ski as a kid in the 80s, and never once saw anyone with a helmet. I obviously gave it up when I moved to Florida, but now, decades later I’m living somewhere I can go skiing again and was shocked to see so many people (even adults!) wearing them. The group from work I was with was equally shocked that I wasn’t wearing one. They were also shocked that I was wearing jeans and not one of those hundreds-of-dollars skiing outfits, but whatever. I mean I guess helmets make sense but it just feels unnatural, as unnatural as bicycle helmets (which we also did not wear back in the 80s) feel to me. I’ll never get used to wearing one of them either.

What, seriously?

What kind of skiing are you talking about? I've never once seen anyone wear a helmet for cross-country skiing, and I wouldn't think it's necessary anyway. For one thing it's usually walking pace, but also snow is soft.

I think the change was due to some high profile deaths from tree collisions in the late 90s.

ADDED: I also wonder if the rise of snowboarding played a role because backward falls where it's easy to hit your head on ice is probably more common than with skis.

I don't downhill ski much these days but I did ski at Squaw Valley a couple times recently because of an event there. And I was definitely an outlier in not wearing a helmet. (In my partial defense, I do wear a hat with impact resistant material sewn in (D3O) and I'm not exactly banging down moguls through the trees these days.)

There's a theory that, from an evolutionary standpoint, young men are wired to fearlessly fight and die to protect the rest of the community. If they survive long enough, they calm down and take on other roles, letting the new generation of kids take over as cannon fodder.

Take with a grain of salt, obviously, because we're all a lot more complex than our evolutionary history, but it seems plausible.

Exposure -- As kids, we aren't exposed to consequences of accidents, blood, etc. So because we have 'seen' less of it, we believe it cannot happen to us.

Responsibilities -- I believe the 'responsibility' factor kicks in as we age. When we are kids, we are for ourselves so we end up taking more risks. As we get older, get married, have kids, watch our parents getting older, we start caring more for security as life seems to be important because of our dependents.

We are adults for majority part of our lifetime so as we grow older we only become habituated to remain careful about our life.

We've evolved this way — not just humans, but mammals in general, and probably other species too. Risk-taking when young is adaptive for the community, if not always for the individual. If no one ever hunts in the place where a tiger was once seen, how will the tribe ever find out that the tiger has moved on?

> The most reliable estimates indicate that at speeds of up to 20 km/h helmets reduce the risk of head injury by 42%, the risk of brain injury by 53%, and the risk of facial injury by 17%, whereas they increase the risk of neck injury by 32%. These estimates are partly based on research carried out in countries like the United States and Australia, where standards for bicycle helmets are stricter than they are in Europe and can offer protection at higher impact speeds.

In wikipedia [2] I find this quote: "This effect is statistically significant in older studies. New studies, summarised by a random-effects model of analysis, indicate only a statistically non-significant protective effect"

And to the parents around here, make sure your kids know when to not wear a helmet (choking accidents [3])

[1] https://www.helmets.org/stats.htm#effectiveness

[2] https://en.wikipedia.org/wiki/Bicycle_helmet#Effectiveness

[3] https://en.wikipedia.org/wiki/Bicycle_helmet#Accidental_hang...

In the only serious bike accident I have been involved in, the victim would have walked home on their own feet had they worn a helmet. Instead, a fall from the bike on low speed and hitting their head on tarmac ended up in serious head injury and 6 months in the hospital.

Had they walked home, it would have not ended in the stats.

The helmet literally saved my life.

Typical fall has the first contact either direct front or direct back based on kinematics which means they're subject to most force. Falling on side of head is somewhat more rare. Falling on top of the head is rare.

At least we usually figure it out. "More injuries because less deaths" is simple enough, I guess.

I don't think this phrasing makes sense. A particular study may find a positive effect but with p>0.05, but that depends as much on the size of the study as on the effect itself.

TL;DR: Human brains are fully formed after 25 years. This means that you make decisions differently before 25 and after 25.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2396593/

That's the longest tldr I've ever seen.

Long winded way of saying... yes, riding bicycle even at 30-40mph is no joke...

Land yachting, where you are about 10cm off the ground is like this. Big wide beach on a windy day with no one about and it’s amazing.

That said the thing from the linked article is obviously on the more dangerous side, since the lane is super narrow and the margin for errors low.

I have a 53x12 setup and top out at just above 120 cadence. It really is interesting to be going 70kph, passing mopeds!

When I'm drafting behind these random cars, vans, and box trucks, I stay right at the edge of being in the slip stream. If the vehicle ahead does something dodgy, I have an escape route or at least a bit more distance to brake.

Getting dropped out of the slipstream is really a drag! Easily lose 20kph+ of speed.

Exactly, even if you have a kevlar one, your organs, brain, spine, neck etc will not be happy once you from 50mph to zero once you hit a car or wall.

On a motorcycle I wore full armor.

Then I realized I would cycle at similar speeds wearing lycra. I don't anymore.

I can’t imagine getting to 80, must’ve been terrifying.