About helmets

A helmet is a passive safety equipment that can mitigate some consequences of a crash, but doesn't prevent the crash itself. It would be a mistake to think that all you need to be safe is to put a helmet on your head. Of course, it does provide some benefits in case of a headfirst fall:

It provides a layer of material between your head and sharp objects, reducing the chance of skull puncture.
It provides sort of crumple zone. Styrofoam is not very crumplable, but better than nothing.
Smooth plastic surface slides well on asphalt, so the passing-by road surface shouldn't catch your head and break your neck.
If you don't plan to crash, a helmet can double as a platform to mount reflectors, blinkies or mirrors.
Nobody shouts "Where's your helmet?" at you.

There are also downsides:

It's yet another bulky item you have to lug around, it mangles haircuts, interferes with hats etc.
You can also die of many other injuries than just a head blow, and a helmet can't prevent those. It can't even prevent all of the head injuries.
A helmet can get caught by something that wouldn't catch on a bare head or that would miss it by a narrow margin.
Cyclist with a helmet may feel less vulnerable and ride more riskily. But that's his own problem, not his helmet's.
Other drivers may perceive a helmeted cyclist as less vulnerable and behave less carefully. So you have a greater chance of survival if you get hit, but also a greater chance of getting hit.

What do I mean by the last line? There's a study which found that drivers pass helmeted cyclists somewhat closer. I wondered how big a difference it can be, so I did a similar research myself. I bought a helmet, alternately wore it or not, and recorded every commute and every uncomfortable situation for almost a year. I expected if there would be any difference at all, it would be pretty small, almost negligible. The actual result was quite surprising. Boring technical details are at the end of the page, here is a brief summary:

Purple - extremes. Near misses by only a few centimetres.
Red - dangerous. Overtaking with less than a metre of distance at high speed or under half metre at lower speeds, with no space for emergency evasive maneuvers.
Yellow - uncomfortable. Overtaking that also scared me a little, but was not outright dangerous and if I swerved, nothing would probably have happened.
Green - days when no dangerous or uncomfortable situation happened.

It reminds me of LARP battles: look, an armoured guy, we can bash him harder! The takeaway for me is: I will only wear a helmet at races where it is mandatory or where there's a real risk of hitting branches, skidding or falling. Not on the road.

What is the takeaway for you? If you are less than 18 years old, you have no choice, helmets are required by the Czech law. If you are older, do whatever you like. In my opinion, it's best if helmets are neither banned nor mandatory. All countries which made them mandatory experienced 30 to 50 percent drop in number of people cycling and no significant drop in number of serious head injuries (source), so all in all the net impact on population health was negative (less physical activity and more engines on the roads). Statistically, riding a bike on a road, paying attention to traffic and not racing, is not much more dangerous than for example walking. And much less dangerous than riding a car, where strangely no one expects you to wear a helmet.

Technical details

I recorded 195 rides without a helmet and 20 with it. Yes, very unequal, but there was no choice: I need a warm hat in winter, air cooling in the middle of summer, and as little luggage as possible when shopping. So I was only wearing the helmet when it was no trouble, from spring to autumn, roughly once a week. Anyway, I care about percents, not absolute numbers. One ride means a commute to work in the morning (Prague, from Břevnov over Ladronka park, through Motol valley by Kukulova and Bucharova streets to Nové Butovice) and back again in the evening by the same route, about 14 km total. Rides via different route, on different time or different bike were not recorded.

The scoring system is subjective, I don't have a proximity radar. It works like this: whenever I get scared so that I want to shout "Are you trying to kill me, you ****?!", it's a red. If I hesitate whether it was bad enough to be worth recording at all, it's a green. Yellow is somewhere in between.

The only point in the extreme category was an overtaking maneuver before the descent near Vypich with a safety margin of about three centimetres. The statistics became a bit biased that day because I started to mercilessly take the lane there to prevent such situations completely - survival over science. Similarly, I also eliminated overtaking on the following descent (yes, there are morons willing to overtake in the middle of a blind turn with double line between lanes, with buses and ambulances in the opposite direction and with me doing 40 km/h) and right hooks before the bridge on the other side of the valley (yes, there are morons who almost overtake a cyclist coasting at 55 km/h and then turn right over a solid line, into a steeply descending exit lane with 50 km/h limit and a stoplight at the end), both before first helmeted ride.

My helmet weighs 330 g and it took about three rides to get used to it and forget it's there. I only notice it after getting off the bike - if the head is not craned up a little, chin strap pushes on the neck. So it should have no subconscious influence on my riding style. I can also confirm the extra weight doesn't cause neck pain.

The helmet is fluorescent yellow, so it is improbable the overtaking drivers wouldn't notice it. In theory, they should even see me better and there should be fewer dangerous situations. In practice - see the graph above.