Accident this morning

[OneWayTraffic]

The biggest advantages of a motorbike helmet over a bicycle helmet is the full face option, visor and stronger build. The bicycle helmet is lighter weight, well ventilated and looks 'right' on a bicycle.

Neither will save you from a 30mph-0 impact over a distance of their 2-3cm thickness.

Helmets are usually designed with a impact speed in mind where they provide maximum protection. And that is usually about the speed of an object falling from a 2m height for bicycle helmets, and more for motorbike helmets. At higher speeds, they provide less protection, and even at lower speeds too (the helmet is too rigid to deform properly at lower speeds.) A perfect helmet would deform completely during an impact in a manner that smoothly decelerates your skull from impact velocity to zero within the distance of its thickness. Using velocity^2=2* acceleration*distance, and a value of 3cm for the helmet's thickness we get the following acceleration values:

At 5m/s (18km/h) 416 m/s ( 42g)
At 10m/s (36km/h) 1,667 m/s ( 170g)
At 20m/s (72km/h) 6,667 m/s ( 680g)

The human head can actually withstand the first two over very short periods. Of course real world impacts have lots of complicating factors, and helmets are never perfect. Still not even a perfect 3cm thick helmet would save you from a 30mph right angle impact with a solid object. So why do they work?

Usually the head hits an object obliquely in an impact. Say your motorbike is going 100km/h (60mph) and you come off and hit the ground head first. The vector of motion relative to the ground is mostly in a forward direction and you don't actually hit the ground at 100km/h, you hit it at about 20km/h and slide across it at 100km/h. The helmet saves you twice, once from the falling impact, and again from the sliding friction.

In another common accident, you hit the side of a car or SUV. In that case the panel would deform considerably as you hit, and there is more room to decelerate, allowing the helmet more chance to moderate the forces. Hitting a solid, rigid object such as a tree trunk is pretty much the worst case possible.

In my sole motorbike accident I lost control at 70km/h due to a sidewind pushing me into the unsealed road verge. The motorcycle started to serve from side to side and I lacked the experience to retain control. Finally it slide into a ditch full of blackberry brambles. The blackberry saved me and my bike from serious harm, and my helmet and leather jacket saved me from the blackberry.

 

[OneWayTraffic]

Let me just say: I wear a "bicycle helmet." If bicycle helmets were only good to 20mph, road bikers wouldn't wear them. I realize the danger of a frontal crash caving in my whole face. I envision myself turning my head before collision to avoid this disaster. I try to keep my straps snug. Also, a guy on a motorcycle died around the corner from me from hitting a tree. He was only doing around 30. He was wearing a full helmet. Still didnt' work. Lots of blood came out of his ears.

Bicycle helmets are designed with the reality that without proper ventilation and lightweight construction no one would be able to wear them. This may or may not apply to ebikes, according to how you ride it.

Don't turn your head, tuck it in to your chest. Rotational impact is a biggie. Imagine the helmet being used as a wrench's lever arm with your brain as the nut. This is a reason why helmets are never going to be too thick. Too much leverage would pull your head right out.

In a bicycle crash you want to roll. Tuck your head in and down and Put your arms out. This is usually instinctive. Then if you can drop a shoulder and pull that hand closer in to you, you will roll over that shoulder and take the impact over your shoulder, back and side. I've done this once or twice, and I don't even remember doing so, but I got up and walked away.

In a motorbike crash you want to slide. Higher speeds make rolling very dangerous. Of course you have gear to save your skin. Sliding also removes the possibility of rotational injury causing internal brain damage.

Anyone have anything to add, or correct?

 

[SamSpeed]

I wear a helmet all the time now although I've never really used one. Yet.

I remember way back they would sell you these bicycle "helmets" that were nothing but strips of leather. Always thought that was a joke. Never had one until about 10 years ago I was riding through these woods down a hill around a bend when right in front of me, right in the middle of a clearing was this beautiful 5 foot jump and I went for it and spent some time in the air singing, "What kind of fool am i?"

Anyway, no harm but took a detour on the way home to the bike shop gotta helmet and have not been quite so foolish since.

I am thinking that a full face shield might be a good thing to have. Bugs and gravel tossed up at 25mph+ can be pretty painful. Does anyone ever really use one on a bike?