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I agree. I've raced on road, off road, been a bicycle messenger, and commuted on bike to work every working day since 1994. Accidents happen and helmets help. The most dangerous thing about a bike accident is generally the vertical distance. Try laying down on concrete, lift your head up an inch, and drop it. Keep in mind that when falling your acceleration is 9.8 m/sec/sec, so a 10 inch fall is worse than 10 times as bad as one inch.

The MIPS and Wavecell seem to assume that helmets grab the road with great traction and then snap your skull producing a large rotational acceleration so great that your brain falls behind. In my experience helmets (which are at first approximation spherical) hit in the center, easily skid, and induce approximately zero rotation in your skull.

I do recall in the 1990s or so that as brands switched from a heavier plastic shell (like the ancient bell helmets) to the then common nylon sleeve over the styrofoam that one manufacturer picked a particularly high friction material which did cause additional injuries. Once that was fixed everyone was happy again.

So absorbing energy from the fall is great. Playing games with additional layers with low internal friction or fancy ways to collapse is useless. I'm not completely against the idea, but seems laughable to pay 3-6X for something unlikely to help. Bike helmets that meet the toughest impact standards are available for $50 or so.

I personally have fallen many times, had my helmet skip many times (the longest was more than 10 feet) and never noticed my helmet gripping the ground and trying to torque my head.

> Keep in mind that when falling your acceleration is 9.8 m/sec/sec, so a 10 inch fall is worse than 10 times as bad as one inch.

Shouldn't that be sqrt(10) times as bad?

The distance fallen under constant acceleration g for t seconds is 1/2 g t^2, so it takes sqrt(10) times as long to fall 10 times as far. The velocity after falling t seconds is g t, so falling sqrt(10) times as long gives a velocity of sqrt(10) times as much.

It also depends on whether 'badness' is a property of energy or velocity. Velocity goes with sqrt(distance) as you've demonstrated, but energy is directly proportional to distance in this case.

You're right about the velocity, but the impact force really depends on the properties of the material one lands on.

First consider that our kinetic energy is

K = mv^2/2

Additionally is the material has a spring constant k, then the force that results when the material deforms by x amount is

F(x) = kx

If we let d be the max distance the material, then we can integrate over the force to get the energy absorbed, which is equal to the kinetic energy.

int_0^d F(x) dx = K

kd^2/2 = mv^2/2

Now there are two ways the impact could work. Imagine we have a really thick crash pad, then we consider it to deform without limit and have a constant k, giving

d = sqrt(mv^2/k)

F_max = F(d) = v sqrt(mk)

But what about a helmet? It can only over it's thickness, at which point your head is basically in contact with the concrete. Thus, we have a constant deformation distance d, and get

k = mv^2/d^2

F(d) = mv^2/d

As we can see, depending on how we consider it we get either a force of sqrt(10) or 10 times the original amount. I probably failed to take into account something that someone who knew more about materials could point out.

tl;dr it's complicated because impact force does not necessarily scale linearly with velocity.

update: so after some conversation with others. It seems that head on concrete is better modeled by a constant d. So a drop of 10 times the height results in 10 times the force.

The badness might be proportional to the energy being transferred through your head, which is simply proportional to the height you fell before stopping suddenly.

The square root in the velocity calculation goes away since

E_k = 1/2 MV^2

so the energy dispersed hitting the ground from a 10 inch fall is exactly 10x as bad as a 1 inch fall.

Of course the actual damage done by that energy transferred through your head will be some complex function due to bone breakage and cell tearing thresholds, etc. But as a first approximation of suck, I'd go with this simple linear model.

Ha, sorry, yes. I confused 10 times as long with 10 times as far... I should have double checked the math.

Still dropping your head an inch (painful) is a nice reminder of how much energy is involved from normal riding height.

Well, it's still worse than 10 times as bad because there are elasticity effects. You can see this on your nose. There is a force you can use to squeeze it that won't do anything but much more and you can break the blood vessels in it and give you a bruise. You could do that first thing many times but there's a threshold effect.

Or a balloon. It recovers from lots of pressing, even repeatedly. But there's a pressure from which it's never going to recover and crossing that threshold has binary outcome.

>>but seems laughable to pay 3-6X for something unlikely to help.

I just bought a new helmet and the one with MIPS was among the cheapest options at the bike store I went to. There were many many other helmets without it that were vastly more expensive. I paid £50 for a Scott helmet that had MIPS, most other helmets were in the £80-150 range and most of them didn't have it. So I don't exactly feel like I paid extra for this technology, it just happened to be included with the helmet that was 1) within my budget 2) fit comfortably.

Sorry, I should have made that comment specific to WaveCel, the article mentioned helmets available in the $150 to $300 range.

I recall an American football study looking for concussion symptoms and impairment.

They found people with a history of repeated concussions, and then as what they thought might be a group to compare to some American football linemen with no history of concussions to compare with.

They found linemen with the same issues despite no concussion history.

This raised the possibility that worrying about severe hits that result in a concussion was possibly missing a larger issue.

It seems our understanding of brain injury and even how it comes about may be inaccurate.

American football involves constant collisions. That type of research suggests that even without a “concussion” the same type of damage can occur from repeated, more mild collisions.

Cycling seems like a different order entirely, it’s extremely unusual for a cyclist’s head to hit anything and only happens during an accident or mishap.

Soccer is a good example. You are rarely concussed from heading a soccer ball, but there is some evidence that players may suffer brain damage from from repeatedly heading the ball.

https://www.sciencedaily.com/releases/2018/04/180424112923.h...

45 headers in two weeks were enough. Holy Jesus! Thank you for bringing this to my attention. I probably won't heal but maybe I'll protect from damage.

> They found linemen with the same issues despite no concussion history.

With no reported concussion history.

Reported can mean many things. If I was asked in such a study I would bring up the 7 our situations I know of where I even suspected I might have had a concussion, mostly snowboarding related actually (with helmet), odd given I also played 9 years of football and 9 of Aussie rules. None of them with concussion effects other than maybe I'm done for the day (you tend to take bigger falls when you are tired).

Also seen enough concussions and evaluations to be able to identify those exhibiting obvious symptoms tho I'm not trained in it.

I would let the people running the study decide how to classify them.

Its also not like there is a standard "reporting" form for concussions. Especially further back and esp if you had a team doctor.

I think the parent is implying that all experienced american football linemen have had many concussion situations, so the whole idea of splitting them in to "concussion history" and "no concussion history" can only reflect how the events are reported, and not whether their heads have been smashed repeatedly.

It depends on the definition of concussion used. If you go broad enough everyone likely has had multiple minor ones if they were ever on a playground or ambulatory (walk into wall, accidentally hit in head, fell, etc).

Maybe also of interest in that regard is the movie "Concussion" with Will Smith about the story of Dr. Bennet Omalu.

https://en.wikipedia.org/wiki/Concussion_(2015_film)

> They can get away with it because it’s such an easy marketing sell- most people think their life is worth more than $250, so any helmet tech is a bet on the order of Pascal’s wager.

I think this is basically accurate. Even if you have zero expectation that either this or MIPS or whatever works, I don't see how anyone who has seen Crash Reel or any of the football-related concussion documentaries could possibly not spring the extra few bucks.

Someone should put together a list of the cheapest or highest expected-value Pascal's wagers. Even things like flossing your teeth are a good example, where it's clearly good for your gum health even though the Cochrane research is equivocal. (Although using a WaterPik is probably better, especially if you do so in addition to flossing.)

Anyway if you haven't seen it, this movie will change the way you think about sports: https://www.youtube.com/watch?v=c1hxtjlbTHI

If you have long hair, MIPS will eat it and not let it go. I don't get how MIPS is different from just wearing a cycling cap

MIPS (you seem to know this, but many might not) is an internal layer in the helmet, usually a very thin rigid plastic layer, that has some elastic nubbins/supports between it and the outer helmet styrofoam shell. This means that the inner shell is free to stay put while the outer styrofoam shell rotates.

This would be different than a cap in that the elastic nubbins should dissipate some of the energy. All this is a bit speculative, but that's what I'd go with.

Interesting take-away from having watched football-related concussion documentaries.

For a long period of time football players were told that if they wore helmets they were protecting their head. So they were lured into dangerous behaviors. If cycling is a dangerous as playing football (it's not) then bicycle helmets would fulfill the same misleading role as football helmets. As it is cycling is relatively safe and helmets are observed to make no measurable difference in outcomes[1]

1. https://www.badscience.net/2013/12/bicycle-helmets-and-the-l...

Wearing a helmet is always better than no helmet. Any helmet.

That doesn't mean the technology can't be improved, and there's actual science being done. Brains are being imaged. There are peer reviewed articles published every year that details the challenges of how to model brain damages. It's not fair to brush them off as just an invention in marketing.

So far it does seem that measuring impacts at an angle matches real world brain damages better than the older standards of measuring dead-on impacts. That's what "rotational acceleration" means. Acceleration is just another word for impact. It doesn't mean your skull should rotate freely.

There are enough indications that this translates to helmet improvements that most consumer organizations have started to recommend them should you buy a new one. That doesn't mean you should throw away your old helmet but it should be enough to disqualify it as "snake oil".

This new Wavecel system hasn't been reproduced yet, two testing institutes has so far failed, but it is similar enough to existing cell and slip systems that performance is not likely to be worse.

> Wearing a helmet is always better than no helmet. Any helmet.

This isn't true when wearing a helmet alters behaviour of the user or other road users. In the UK it has been found that motorists leave less space for cyclists who are wearing a helmet, and that helmets increase risk-taking behaviour.

As I recall it, that was one academic cycling round one city for a month or so wasn't it? I'd be interested in a citation.

Pointing out that words like 'always' and 'any helmet' are overly broad.

It was one study on car driver behaviour. It was on roads I use.

Most experiments on helmet use shows increase in risk behaviour of the wearer. Observational studies are less important for decision making.

I hope you wear a helmet in the shower and when you drive a car.

How often do you hit your head at 30mph in the shower?

Doesn't your car have seatbelts and airbags?

Bicycle helmets are not designed for "30mph" "hits". They are designed for exactly the same sort of situation that you experience when falling in the shower or falling downstairs or off a step-ladder:

2 meter drops that achieve about 14 miles per hour (22.5 kph) on the flat anvil. In Europe the drop height is only 1.5 meters. Why so low, when bicyclists frequently exceed 14 mph in forward speed?

The typical road or trail bike crash involves a drop to pavement. The important energy in that crash is supplied by gravity, not by forward speed. Although forward speed can contribute some additional energy, the main force is the attraction of gravity, and the impact severity is determined by the height of your head above the pavement when the fall begins. It is gravity that determines how fast your helmet closes with the pavement. Some of the crash energy is often "scrubbed off" by hitting first with other body parts. The typical bicycle crash impact occurs at a force level equating to about 1 meter (3 feet) of drop, or a falling speed of 10 MPH. The rider's forward speed before the crash may be considerably higher than that, but the speed of the head closing with the ground, plus a component of the forward speed, less any energy "scrubbed off" in other ways, normally average out at about 10 MPH.

So bike helmets are tested with a 2 meter (6.56 feet) drop. Motorcycle helmets are tested at 3 meters, about 17 mph. A really good bicycle helmet can handle

https://helmets.org/limits.htm

The (now foolishly down-voted) comment that you are replying to is exactly right that a bicycle helmet would mitigate the shower scenario injuries.

If you're doing 30mph on your bike you're doing a different type of biking than me and most commuters.

I use the same helmet when commuting and on longer/faster rides.

>The dirty secret is that literally nobody has ever seen a brain rotate inside a skull and result in concussion.

Are you sure?. We have a thing called tomography with things like xrays, magnetic resonance that let's us look inside bodies.

Experiments were done in the past with animals that have a similar brain to us, specially aviation military, that were extremely interested on concussions.

At least they have x-rays photography of impacts. By the way all this research led to car's seatbelts.

Thousands of brain surgical procedures are done each year, there are experts in the anatomical features of the brain, and we have detailed maps of sliced brains and complete heads.

Tens of thousands of people die in car accidents and hundred of thousands are injured. Insurance companies have extensive documentation on those.

We know the physical properties of those things and we have things called computers that let us do very complex models about the brain with finite elements or just analog 3d printed models with gelatin and plastics.

To say that nobody can imagine a brain in motion, so everything is a hypothetical mechanism is quite unfortunate.

We know a lot about what happens more or less. Things have improved dramatically for people like motorbike racers because we actually know a lot and lots of lives had been saved because of that.

Literally all those things you mentioned happen in static environments. Note that I said we can’t image a brain in motion, all we have for that are computer models. Sure, they’re plausible, but we can’t even agree on what crashing forces applied to the cranium look like, let alone the resultant brain movement and pressures induced. You can’t CT a brain as the head is falling. Nobody has ever drilled holes in someone’s skull and mounted pressure transducers inside the skull to truly validate the pressures during impact. All the “validation” has happened in lower fidelity domains (particularly the time domain), this is a bit like claiming that you know calculus because you can do addition really good. Every mechanical engineering student will tell you that dynamics is a different beast than statics. Fancy computer images does not the truth make.

Note that I’m not saying that a MIPS or WaveCel helmet is worse than the previous generation, I’m just pointing out that the timing in which these features appeared on the market is suspect, which causes me to suspect the “science” behind it. It is most likely that these antirotation features don’t make the helmets worse but also not any better.

> I bought a Giro Atmos over a decade ago and never needed to upgrade...

I’m sure you’ve heard this but they say to replace a helmet every two-three years even if it hasn’t been in a crash.

It’s up to you whether you think that makes sense, but I’d sooner believe it than not.

It'd be hard to miss the potential for that to be marketing-speak for "buy more helmets more often", especially given the context of the comment you replied to.

I've had old helmets develop cracks spontaneously so this is marketing that I tend to believe.

By old do you mean two years or twenty?

I think that helmet was less than four years old. And it wasn't a cheap one either.

That's a warranty issue more than a reason to buy another one of the same brand.

And your mattress doubles in weight every eight years....

That is just a way to sell more product by shaming people into "being safe".

Uncrashed styrofoam doesn't stop being effective and turn into a pumpkin after two years. But you can double revenue if you can halve the replacement cycle.

"And your mattress doubles in weight every eight years"

I'd never heard that one before.

https://www.snopes.com/fact-check/mattresses-double-weight-e...

As the plasticizer leaves plastics, it becomes embrittled.

You want the EPS to crush smoothly -- if it cracks and displaces, it will not be in place to absorb energy and cushion the impact further.

We replace our bike helmets every ~6 yr.

Source: Have listened to the crackle of decade-old plastic kayaking helmets under tensile/compressive stress and watched them shatter like glass after impact with a concrete floor. New helmets from the same manufacturer did neither.

> That is just a way to sell more product by shaming people into "being safe".

The cynic part of me agrees, but is it though?

Some plastics seem to get "stressed" over time, especially if under sunlight (not sure if it's the temperature or UV that's the issue) - I wonder if that's part of the concern here?

Guy in a motorbike shop told me it's UV that makes styrofoam lose its useful properties, a quick Google seemed to confirm that.

The guy in the shop wants to move helmets. The internet is littered with factoids that "everybody knows". It's on the internet you know.

I've never seen any motorcycle helmet with exposed styrofoam though.

I've raced for about 6 years now and have not replaced my tri helmet, but have replaced the one I use when I'm on my road bike (only because it broke in a crash), where did you hear that you should replace the helmet that frequently?

Any safety equipment made from plastic needs to be replaced every 3 - 5 years because it's weakened by light and air. Same for rock climbing ropes, life jackets, children's car seats, etc.

The official guidance for life jackets is 10 years.

https://www.secumar.com/en/servicing/

For bike helmets, independent safety labs have actually done the science and found no measurable deterioration in impact testing nor material properties with helmets as much as 26 years old. (Link to journal paper at end of summary linked below.)

https://helmets.org/up1505a.htm

Rock climbing ropes have very clear performance metrics. "Hard hat" style helmets are similar, they are made to protect from falling projectiles like tools or rocks and must not break.

Bicycle helmets just add a few mm of valuable deceleration distance in the best case, that's all they do apart from protecting from purely cosmetical abrasions. The maximum amount of extra deceleration distance is provided at one very specific kind of impact. When the material properties change, the maximum will be achieved at a different impact. But you cannot predict which one you will have that one time when you actually use the helmet. The old one might be better or worse, nobody knows.

If manufacturers knew exactly what would eventually hit you, lots of engineering could be applied to precisely tune the helmet to that impact, but they don't know so they cannot do that. So all the engineering goes into achieving comfort while hitting regulation targets and into marketing features that only need to appeal to "common sense". There is no engineering at all going into the main purpose. Even aerodynamics, a clearly defined performance metric orthogonal to protection, is just barely starting to move on from hand-wavey "fast looks" to actual engineering.

For motorcycle helmets the replacement interval is 5 years for most manufacturers. Why are bicycle helmets supposed to replaced more often?

Motorcycle helmets generally have a thicker, smooth exterior shell that better protects the foamed plastic under it from UV and O2 degradation. With cheaper bike helmets, they often have more ventilation holes, and you can usually see the formed EPS.

That said, you could just put zinc oxide sunblock on your helmet and then protect the UV-blocking layer with a spray urethane top-coat, and thereby extend the useful lifespan of your helmet by years.

Can't really do much about O2 damage or migration of plasticizers, though, unless you want to freeze your helmet any time you're not wearing it. Keeping it in an air-conditioned interior room rather than a hot garage or bike locker might help.

EPS can last quite a while when buried, where it is protected from UV, excessive O2, or heat extremes, but I wouldn't entirely trust an EPS helmet beyond 10 years. It's not so much that EPS can't last that long, but that you can't guarantee that it hasn't encountered environmental conditions that would result in degradation over longer time spans. Better a 10-year-old helmet than no helmet, though. There's no excuse for doing that when municipalities sometimes just give away free (to the recipient) bicycle helmets, maybe with sponsorship by an insurer or National Safety Council or similar organization.

> That said, you could just put zinc oxide sunblock on your helmet and then protect the UV-blocking layer with a spray urethane top-coat, and thereby extend the useful lifespan of your helmet by years.

Please don't fuck about with safety critical equipment.

I do not accept as axiomatic that bike helmets are "safety critical". They may be safety-improving, but I have no evidence available as to how much.

While following up, I discovered that what I suggested is patented. US 6884501.

Anyway, please don't ask people not to hack on a site with "Hacker" in the title. You are free to replace your own expanded-polystyrene bike helmets on a schedule set by helmet manufacturers and cyclist-targeting publications, if you choose. I believe that if a helmet shows no outward signs of degradation or damage, and no known incidences of impacts, there is no particular need to replace it. Just use it until it's dirty, damaged, or unfashionable, and replace it then.

There aren't a lot of studies on the real-world effectiveness of factory-new bike helmets, and as far as I know, none that actually support any particular expiration date for them. Even Snell admits that their 5-year guideline is based on "consensus" and "prudence", and not any actual evidence [0]. And one of the arguments is literally that "we will probably have better helmets available five years from now". Having been around longer than that, it just isn't true (at the price point where I buy helmets). The bike helmet I have now is largely the same as the one I had as a kid. More holes. More fashionable. More comfortable. Functionally the same. Wrap skull in 2" shell of expanded polystyrene, and put a cover over it.

Keep your helmet cool, clean, and out of direct sunlight, and it will last longer than five years. Prophylactically treating one of the well-known causes of failure in expanded polystyrene, immediately after purchase, will help.

Anyone who cycles frequently will likely replace more often based on acquired grime or stink, anyway.

[0] https://www.smf.org/helmetfaq#aWhyReplace

It might be five years, I’m just saying I think there is a recommendation and I think it’s less than 10.

>>I’m sure you’ve heard this but they say to replace a helmet every two-three years even if it hasn’t been in a crash.

Just like the sofa store tells me that ideally you need to flip all cushions on my sofa every day? It's a load of marketing nonsense.

> The manufacturers noticed that helmet sales were declining, and all of a sudden “new science” appeared with a theory about concussions being caused by brain rotation and MIPS technology helps prevent that.

> There isn’t an ethical test for blunt force trauma in real life conditions, and bike crashes are very rarely reported if they don’t send the rider to the hospital.

There's one ethical source of data - televised bike races. Surely there are enough crashes recorded in publicly accessible videos to provide a fairly representative sample of how a human head moves when the helmet it's wearing hits the road.

> They can get away with it because it’s such an easy marketing sell- most people think their life is worth more than $250, so any helmet tech is a bet on the order of Pascal’s wager.

It's exactly the same with motorcycle helmets. You can get a DOT approved helmet for $150, but the general perception in the community is "if you have a $150 head, wear a $150 helmet". Then everyone pays $800 for helmets designed to European standards which are meant for racing, and give dubious benefit if any at normal road-going speeds (eg. see https://www.nytimes.com/2009/09/27/automobiles/27SNELL.html).

> You can get a DOT approved helmet for $150, but the general perception in the community is "if you have a $150 head, wear a $150 helmet".

This is absolutely not the modern perception. The modern perception is that DOT is a joke and that a $120 SNELL or ECE helmet is better than a $500 DOT helmet.

Also, your statement about "european standards meant for racing" is nonsense. ECE is a standard for street use, and SNELL is an American standard.

I'm pretty sure that I read somewhere the argument that because Snell standards involve a higher speed impact, that there might be a tradeoff and they would be less cushiony for a lower speed one. So maybe more stringent standards are not necessarily better; it depends on what standard is the most realistic wrt the average crash.

Both are better than DOT which is an absolutely useless standard.

https://youtu.be/0BUyp3HX8cY

Most of the crashes I've seen in televised pro races were shot from only a single angle some distance away, and often with obstructed sight lines. So I'm skeptical that those videos will give us useful data on head movement.

Also, pros crash differently than your typical bike commuter or recreational cyclist. For one, there's a large difference in speed (45+ kph for pros, half of that or less for your typical commuter - somewhat negated by the e-bike boom). Next, pros in televised races don't have to deal with oncoming traffic, so head-on collisions are a non-factor. And lastly, pros know how to crash (tuck in, roll over, dissipate energy over a distance), while non-pros tend to tense up in a crash situation.

There's probably other ways in which pros crash differently, making them a less than ideal sample of the overall cycling population.

True, but it'd at least help to verify what sort of helmet would best protect pros and semi-pros. I'm sure there are plenty of keen amateur cyclists who often ride in similar conditions.

And, on the other hand, cyclists who are casual enough to crash very differently to the pros probably wouldn't be looking up in-depth analyses of bike crashes when choosing a helmet either. They'll just buy the second cheapest one.

It's the other way around. ECE standards are meant for lower speed crashes than the American standards. SNELL is the racing standard. Nevertheless, then comes along someone like (SHARP)[https://sharp.dft.gov.uk/] and performs helmet tests with objective ratings and you see that all helmets vary, regardless of standards.

Because there's no one way to crash, there's hardly one way to test. Buy the most expensive helmet you can afford, more likely than not that it's a better product.

And then you have companies like Arai that have internal standards that arguably exceed SNELL but score low on SHARP due to differences in design criteria.

https://www.revzilla.com/common-tread/shoei-vs-arai-helmets

DOT certification is the biggest joke in safety there is. To start, companies self-certify. To continue, watch this: https://youtu.be/0BUyp3HX8cY

> most people think their life is worth more than $250

FYI, I just bought the Bontrager wavecell last weekend for $150 at REI. It was a no-brainer, so to speak.

[I just had the worst crash of my life 2 weeks ago. I incurred nothing worse than scrapes and bruises, mostly because the helmet did its job, but needed to replace it after the crash.]

Congratulations! Any bike accident that you walk away from was a good one. I had one that I definitely did not walk away from and it's been a real joy to this day, every day.

Can you describe what happened? Always interested in learning from other cyclists what to watch out for.

If the helmet wasn't damaged in the crash it meant the energy was harmlessly transferred into your head. You want the helmet to be damaged/destroyed.

It's often not clear whether the energy went into the helmet. It could have cracked something internally or substantially weakened the EPS under the plastic shell without it being super visible.

Better to not risk it: serious crash, replace helmet.

> If the helmet wasn't damaged in the crash it meant the energy was harmlessly transferred into your head.

Foam can and does distribute and absorb shock without being significantly damaged or destroyed in less severe collisions, crashes that can still put you in the hospital without a helmet.

I would maybe describe how helmets work as having a shock-absorbing cushion that slows deceleration of it’s contents. Talking about “energy” is bound to be misleading or confusing, since from a given speed, you always transfer the same amount of energy no matter how you stop, whether it’s a sudden strike against concrete or a slow gentle braking, or even waiting several minutes for air and tire friction to wear out all your kinetic energy.

I don’t want the helmet to be damaged or destroyed only because that means the crash is bad or severe.

There's much in this thread about the helmet absorbing the energy of the impact, but that's far from the whole benefit of wearing one.

The helmet, by conforming to the shape of your head, distributes the energy from the point of impact to a much larger area. So instead of having your head cracked open at the point it hits the tarmac, or pierced by a pointy rock, the force will be evenly distributed across your head.

The helmet also has a low-friction shell that will slide across a surface, which helps avoid head rotation, snapping your neck or getting whiplash, and will protect you from cuts and abrasions.

I've been saved by my helmet many times.

If you didn't know better, it looked like someone hit the helmet with a hammer a couple of times.

So yes, some amount of kinetic energy was dissipated in deformation of the plastic rather than my skull. I was more than a little grateful.

When I was a kid, I put an egg in a container of honey and dropped it from a 2nd-story balcony onto a hard surface. The egg remained unbroken. The honey was undamaged.

The kinetic energy represented by the difference in height was still added to the egg, but the honey slowed the transfer down, and spread it out to the whole object, in the same way that walking the egg down the stairs, instead of dropping it off the balcony, would have slowed it down.

You don't always want the helmet to be damaged. I wouldn't want my helmet to be constantly denting, cracking, spalling, and ablating every time it touched something. You really want it to be damaged only when the kinetic energy is coming in too quickly to safely (slowly, widely) transfer it all to the protected head, and permanent deformation is the fastest way to bleed off that excess. In theory, the helmet could also heat up when it gets hit, but that's more expensive than just wrapping EPS around whatever you want to protect.

My understanding of MIPS was that it was meant to redirect linear force against the head, such as banging your head against a car in a relatively straight line, into a rotational force that would let the helmet slip off the head and that would reduce the amount of trauma to the skull. I never heard of anything about "brain rotation"

This explanation of MIPS goes pretty much all-in on it being about rotation: https://www.torpedo7.co.nz/community/help-and-advice/bike/ge...

Edit if you prefer it directly from the marketing horse’s mouth: https://mipsprotection.com/

  When you have suffered a concussion or an even more serious damage to the brain, rotational motion to the brain is the most likely cause.

from the mips protection website, you are correct and i understood it upon first reading as something else

Wow, given that they're talking about something that invariably has a significant linear acceleration factor, that's a pretty... confident... way to put it.

I believe all the current Giro helmets are MIPS now, even the cheap ones. In fact I was contemplating of getting one myself, not necessarily because of MIPS but if it's safer and also looks good, cool.

Just a quick tip, bike helmets actually have expiration dates and should be replaced every 3-8 years depending on the helmet.

why not use an animal model?

Because diagnosing an animal concussion is harder than diagnosing a human concussion. Animals can’t tell you if they have a headache, light sensitivity, nausea, etc. You would only be able to diagnose the worst class 3 concussions where the animal can’t even walk straight. It’s probably not ethical to subject animals to that much pain if you can’t even confirm half of the injuries.

Aren't concussions visible in MRI?

How cruel.

Cancers are regularly induced in mice and rats. Almost every single medicine has been tested on animals before they're used on humans. Modern medicine is built on animal models. It's unfortunate, but a sufficient tradeoff a vast majority of people are willing to make.

I’m not entirely sure what you are saying. Is it not cruel, or that the cruelty is OK?

They're saying it's cruel, but some cruelty is sometimes needed if the benefits for humanity are worth it.

Blah blah blah. While I appreciate the skepticism, this is BS only for the sake of it (as so many HN comments are).

You instantly lose credibility with this line: "I bought a Giro Atmos over a decade ago and never needed to upgrade because the top of the line helmets were only a couple grams lighter, after a decade of “improvement.”

I hope you've since replaced it. General guidelines are to replace a helmet every three years due to material degradation and UV damage.

Yes, you are correct that there is a marketing element. Likewise, you are correct that people value their lives over $250 price tag.

As a bit of antidotal evidence, I had a fall this weekend on Evolution trail on Galbraith MTN in Bellingham, WA. I fell from about 6-7 feet up on a feature called the Stinger, a long, super fun north shore style bridge (watch some youtube videos if you want to see it). My face and head were impacted in the fall and I suffered, what I think is, a very mild concussion. I replaced my helmet afterwards as per the recommendations. I also have a history of TBI caused by a cycling accident where wearing a helmet saved my life. I am absolutely going to buy something that even vaguely suggests an advantage for injury prevention. Mountain Biking is, after all, and inherently dangerous sport.

As you suggest, any progress is good progress when it comes to saving lives. But I absolutely disagree that it "is a bet on the order of Pascals wager," especially when it seems I myself have made that wager and come out ahead. So, with the utmost respect, unless you are a leading researcher in this field, STFU.

This reply doesn't seem to be in line with HN guidelines. "Be kind. Don't be snarky." and "When disagreeing, please reply to the argument instead of calling names. 'That is idiotic; 1 + 1 is 2, not 3' can be shortened to '1 + 1 is 2, not 3.'" https://news.ycombinator.com/newsguidelines.html