I do. I've read papers and articles by professional helmet engineers. The chances are that if a helmet fails that it provided about zero meaningful protection.

Why?

Helmets absorb energy when the foam liner compresses. But to compress properly the liner must have a shell to brace against - think of it as being like a fluid. If it is confined, then compressing it takes a lot of energy. If it isn't, the liquid flow freely at hardly any energy cost.

When helmets split they do so because the shell has failed. This takes place BEFORE compression. So meaningful energy absorption hasn't taken place - the helmet might have absorbed something 1/10 to 1/100 the energy it is designed to. To put this in perspective, that's take the 1/10 figure and call that amount of energy absorbed a "splat" and consider a 24mph crash:

- Helmet absorbs 1 splat

- Would have absorbed 12 splats in 12mph (design limit) hit

- Actual crash energy 48 splats (kinetic energy is a square law)

Important note: impact speed is the component of speed at right angles to the impact surface. If you hit a road and you were cycling at 30mph, then hopefully your impact speed will be vertical only. In theory. (In practice, some helmet shells may shatter from the "belt sander" effect of the 30mph collision - this isn't part of the helmet cert test, and in the real world helmets have an extremely high failure rate.)

I doubt that any helmet company will go on the written record with that claim: the legal consequences would be disastrous.

In the UK the case law accepts that helmets have no possible benefit at over 12-14mph - repeated attempts to argue that cyclists deserve reduced damages for not wearing a helmet have been rejected for this reason.

The problem with this "experiment" is that it is stupid. It isn't enough for a helmet to do a tiny, pointless amount of energy absorption - that's like trying to justify sunscreen as a defense against nuclear weapons, a small parasol as a replacement for an effective parachute. To be worthwhile a helmet has to have some chance of reducing a dangerous head impact to a less dangerous one. Changing a 48 splat to a 47er (see above) isn't doing that.

To discuss the stupidity of the above further: even failed helmets increase the total head size (making head impact more likely) and rotational damage. These are significant dangers - so you can't even assume that negligible safety benefit of a helmet isn't outweighed by the negatives if you crash outside its design limits.

so um... do helmets really make your head cooler?

Yeah. Been answered. Nope. Even the ones with big vents that break easier.

great. i guess thats about it then.

This is something that could be studied empirically without too much difficulty -- I already gave a general outline of how it could be done.

But if there's no studies, papers and articles by professional helmet engineers that actually discuss the issue rather than just assume the status quo might do. Have any links?

Yeah. Been answered. Yup -- IF their design doesn't suck.

Unlike some here, I've had... let's see... five notably different helmets. Some of them work a lot better than others.

Chief, I'd rather risk breaking some vents than for sure grinding my scalp across the road. You'd pick the scalping?

it seems like if the helmet is designed to cool the rider by directing air towards the skull, that means it's less aerodynamic than a helmet which keeps the air moving around the helmet..

but i don't have a wind tunnel handy to prove it..

Unfortunately, the helmet is only required to take away the energy of a straight drop of no more than 2 meters (this does not include the speed of the bike or the spped of the car which may have caused the fall) on a flat surface and, get this, 1.2 meters on a curb! https://www.bhsi.org/testing.htm

Also, see this overly confident article from the same PRO-HELMET site: https://www.bhsi.org/limits.htm

In other words, yes, I agree they absorb some small part of a direct fall down from a stop, but much beyond that they are basically useless. They would not work for what I would need them for (car/bike incidents) so I will still not wear one...and yes, they may be cooler than a bare head if they have more vents and therefore less protection, but are not as cool as a wet cycling cap.

I was admittedly being tongue-in-cheek. It was merely an attempt to point out that the main attitude of helmet pushers (you should never sacrifice safety) can be blown up on their own terms; basically,they are doing the same thing within the realm of helmet effectiveness. I agree that we always make compromises and make our own assessments of whether something is reasonable or not.

I'd rather risk scraping my scalp across the road than risk one of those big vents grabbing asphalt. One is painful, but the other could make you a vegetable.

No, you didn't. You think you did but your method is junk. It relies on magic "sensors" (WHAT are they sensing?) And uses full body crash test dummies (helmets are only designed to take the mass of the head.)

There's stuff at www.cyclehelmets.org/ about how helmets work that explains the failure mode. And no, there are no articles by helmet engineers that " just assume the status quo might do" - i.e. back up your silly opinion that split helmets have absorbed energy. This is something you made up for yourself. No professional would make such a claim - it isn't true and the legal fallout would be enormous. (And I would have seen the paper, believe me.)

This wins a prize for its level of intellectual malfunction. IT IS THE HELMET THAT BREAKS, BECOMING WORTHLESS, NOT THE VENT! It doesn't matter if a vent breaks - a helmet has to be thrown away after a crash anyway.

This would depend on the exact conditions. Helmets reduce airflow but block sunlight. So the benefit/cost will depend on the strength of direct sunlight and on humidity. On a hot but overcast day with low humidity a helmet will just be a nuisance; on a day of direct sunlight and high humidity it may be much more effective.

As far as scalp-grinding goes, it is (a) likely to be a protective mechanism which will reduce rotational injury, and (b) can be easily ameliorated, to some degree, by baseball cap, cycling cap, or do-rag. No need for bulky, hot, styrofoam.

My favorite hot-weather headgear is a do-rag. Dip it in a stream, slap it on, air-conditioned brain cells for the next hour.

This is a good point: the scalp is designed to slide and then to tear. A helmet grips the road and holds the held firmly by a retention system (if worn properly.) It also increases the moment arm of impact. Given that most serious brain damage is rotational, these are not good things.

Accelerations, of course. Linear, rotational (I imagine some do, anyways), etc. They record the readings of each sensor many times a second over the entire test for analysis later. It's not magic. Read more about them.

Also, we'd want a rig or something that could repeat a collision over and over, exactly the same every time. Throw a dummy onto the ground. Throw it into a wall. Into a car. Put it on a bicycle and crash it into a fast moving car, etc. Repeat each variation with and without helmets, perhaps with different types of helmets, at various speeds, etc.

I would expect that the test runs where the helmet does not fail (mostly the minor impacts) would show the helmet providing significant improvements over the same impact without a helmet. (But of course we'd measure that too.) But what would happen in the more serious impacts? That's what the purpose of the whole thing would be.

It's not perfect, of course. A better study would involve live humans, of course, but volunteers might be hard to find.

We would want to approximate a human body as closely as possible. A cyclist's head who has a collision with something usually has a body attached (if it doesn't, we probably don't care much about how bad that collision is) so we would do better to model that rather than just throwing separated heads around.

Yes, helmets are designed to take the mass of the head. But the purpose of this experiment would be to actually test helmets past what they're designed to take, to failure and beyond, to see just how much benefit they provide, and we'd want to try and model the real world as closely as practical. Full body crash dummies would be ideal.

Yes, they say that when the helmet splits, it fails -- true -- but then they assume that no protection was offered when that happens. At most, they'll say that the liner wasn't compressed and so very little energy was absorbed (but I've seen no empirical data about the liner not being compressed either, just assertions like this.)

Actually, if you'd read my post, that's not quite my position.

Still, it's stupid to say that they absorbed *no* energy, because if that was true, they wouldn't have split. Obviously they have absorbed some energy -- helmets don't spontaneously split. The question is how much.

All I did was make an obviously true assertion (the helmet must absorb some energy, or it would not split) and then come up with a question (did it absorb enough energy to provide more than a minuscule amount protection for the head inside?) and devised a fairly good (IMHO) experiment to study the issue. I don't have the equipment or budget (done properly, we'd smash a lot of helmets and more than a few bikes and cars) to do it myself, however.

Why are you replying to other people's conversations in such a tone? You need to relax and put a helmet on before you smash your head on the keyboard. Wearing that helmet will probably help to keep your head cooler also. Try it out, it's not the big deal you're childishly making it out to be.

pretty simple....no. None that I've ever used, your mileage may vary...