Q. I have fallen off my bike!
Not injured or anything, and the bike wasn’t damaged, but there were some scratches on my helmet and I’ve read somewhere that it should be replaced . Is this just the shops trying to sell more helmets or is it real?
A . I’m sorry to hear you fell off, but we all do it at least once on a lifetime, Like tripping over the cat at home, and it’s good that it was trivial. It usually is unless you are racing.
Now, the helmet.
You really should replace it, but first let me explain why.
The outside of the helmet, the shiny bit, is just a thin plastic shell and all the real work is done by the thick foam padding inside. This is created by mixing chemicals together so that they froth up like bottle of fizz when you shake it, but these chemicals then set into a lightweight mass. It is, of course, made of lots of tiny bubbles, and the idea is that in the event of an impact they will absorb the force by using the energy of the impact to break down the walls of the bubbles, and so to protect your head.
A human head weighs 10 to 11 pounds, about 5 kilograms, and if it has fallen from your height onto the solid ground it’s comparable to a big builder’s hammer being brought down onto your head. Ugh!
If an adult trips over, they usually put their hands out to check the fall, or curl up a bit so that the fall is absorbed. The last little bit of about a foot or so is not such a severe impact, but when we are on a bike we very often are unable to move our feet off the pedals , and our hands from the bars quick enough and we fall on our hips and shoulders. Our poor heads are left flopping at the end of our neck and can hit the ground quite hard.
If we are wearing a helmet, as I explained, most of this force is absorbed by the little bubbles being crushed, and we get away with being a bit dazed for a second or two while we check our bottom for bruises.
Now, the helmet may look OK on the outside but if half the bubbles have burst inside they won’t be there to absorb the blow next time. We just can’t see that, and even with a microscope you’d have to cut the foam in half to see which ones were damaged.
So, you need to replace the helmet, and a new one needn’t be expensive. I’ve seen perfectly good ones for £10.00 or so and the more expensive ones are often a matter of fashion, or novelty changes designed for the more challenging rides.
Finally, if I have to replace a helmet I always saw the old one in half because it would be dangerous for anyone to use it.