totalnewbie

as a curious observer, what I have seen in general, is that the more expensive models of any particular brand tend to be lighter than the less expensive ones in their lineup. I understand that weight reduction in any bicycle component usually warrant a price premium and I understand all these helmets pass the base safety tests. Granted, the expensive helmets may have additional features like kevlar that holds the polystyrene better after impact.

However, considering the polystyrene is the main component that absorb the impact force, wouldn't the lighter (and more expensive) model (say, eg. 250g) offers less protection than the heavier (and cheaper one) model (eg. 350g)? isn't it simple physics that determines the more polystyrene, the more material there is to absorb the impact?

Or do manufacturers use a better grade of polystyrene on their top-of-the-line models that really offer better protection than the run-of-the-mill polystyrene?

What I want to know is, disregarding the benefit of having a lighter object on my head and fashion, am I better off with a heavier helmet if head protection is my one and only one concern? (Ok, won't go as far as a motorbike helmet)

dpeters11

In the US, all helmets have to meet safety standards. But it does seem in Taiwan, it has been an issue.

https://www.taipeitimes.com/News/taiw.../26/2003384763

I'd certainly go with a name brand, but I don't know if there is a big problem with counterfeit products of that sort in Taiwan.

Generally though, the more expensive helmets are just as safe, just lighter with more vents. Of course any helmet can only do so much, and from the things I've read, most aren't good at preventing concussions

https://www.bicycling.com/sites/defau...-13-Helmet.pdf

DX-MAN

Some of the more expensive helmets (such as Garneau) had other materials incorporated into the poly, such as carbon 'skeletons'; whether it was a marketing gimmick or a real benefit, only users could tell you. I won't throw $100-150 at a product that can A.) serve the purpose as well at $40; and B.)require replacement after serving its purpose ONCE.

License2Ill

There isn't as much variation in materials in bicycling helmets as heavier crash helmets like motorcycling helmets where a more expensive fiberglass or reinforced fiber composite shell will be used rather than the cheaper plastic to save a couple ounces. If it's done, it's done for the same reasons, but makes no difference to the performance standards passed. There is the CPSC standard in the US but there is also a better performance standard in the Snell B90 certification. Specialized is the only mainstream brand to carry the B90 certification, and all of their price points from least expensive up have been approved. I have never noticed a difference in weight in bicycling helmets I've worn, it's a non-issue. Some differences may be seen in the amount of ventilation offered and/or the overall size, but it's barely perceptible imo. I had a $5 Pro-Rider Snell-approved lid that was basically an older style, thicker and less vents, and may ultimately be more protective, but again still only approved to the same standard. The bottom line is that it was the wrong shape for my head, which could lead to less protection due to pressure points and looseness over areas of the head. Shape is critical in terms of fit, and the much more of a priority in terms of what to look for in a helmet.

Looigi

It's simple physics, but not quite that simple. The polystyrene in this case is foam, and the fact that the foam crushes it what makes it spread out the impact over time/distance and lessen acceleration. More, harder and stiffer may provide less protection. If it were solid, there would be more polystyrene and it would weigh a lot more, but it would do nothing to lessen impact acceleration. The thickness, density, and area of the foam (considering vents, etc.) are chosen to optimize appearance and ventilation and minimize weight while still being able to pass the specific safety tests.

In addition to the the foam's ability to absorb impacts, there are other considerations and test criteria. If the foam breaks apart, it can't do it's job so a tough skin or framework can help prevent the foam from breaking and reduce the area of foam needed. There are retention standards that determine the layout and strength of the straps and other elements used to position and hold the helmet on the head.

One thing that's been a current topic of concern is that the current specification for helmets is intended to reduce the incidence of skull fracture, but short of that it is less effective at minimizing concussions. For example, a softer foam might make a helmet somewhat less effective in preventing fractures but make it better at mitigate the severity of concussions.

FrenchFit 

My Prolights are probably 200g or less and my sense it they are not as protective, profile wise, as some of the bigger, heavier helmets I've owned. But, I wear them...and I didn't wear the others. It seems Giro has discontinued the Prolight, perhaps they have some concerns they didn't offer enough side, rear or front protection...but only access to Giro's super secret internal memos would tell that story.

The Prolights are about $100 off everywhere right now, ...and now you know.

License2Ill

You want it as hard as possible for as long as possible up to the amount of g-force the brain can withstand. The original specification for any standards were based on skull fracture data and those understandings, but that has long since been replaced by g-force limits decades ago. The shell adds to bending strength of the skull, but the EPS foam is really just their for the crush space. That acceptable depth of the crush space should apply the maximum braking force the brain can withstand for as long as possible in order to be effective over the largest range of impact energy. Once the crush space is used up, you've got both a spike in g-force applied to the brain and more possibility of skull fracture as well.

There have been questions about g-force over longer periods of time at lower levels being harmful as well, and that was taken into consideration with the motorcyclist DOT helmet standard, but much of that was not based on good evidence. As it stands, it's not an issue in any modern examples of any helmets that meet any of the other standards. They all will pass DOT as well in any size.

There's also questions of concussion, but crash helmets have never been designed as concussion protection or for consistent crashing, but just to protect against the big one.

ro-monster

Well, if you consider that the most protective bicycle helmets are full-face downhill MTB helmets, which weigh considerably more than the usual skullcap style, then the answer is yes, lighter helmets offer less protection.

totalnewbie

i am not sure i follow what you said. let's say one helmet has a uniform foam thickness of 1 inch (lighter) and another one with 2 inch (heavier). at point of impact, don't you think the 2-incher will always fail/crush after the 1-incher does? a metaphor will be a honda civic vs a mercedes s-series. both pass the crash test, but i would think the mercedes driver will have a better chance of surviving a crash given the bulk of the car.

gsa103

Having more mass only helps when you're impacting an object of similar mass. In this case of car vs car, the lighter car sees a higher velocity change for the same momentum transfer.

In bike accidents, the mass of the rider is negligible compared to the other object (car, wall, tree, etc). This is much closer to the case of car vs immovable object (ie solid wall). Having a higher mass car doesn't help at all, and frequently has a negative impact since the crash structure has to dissipate more energy. Many of the smallest cars actually do better in car vs wall tests that larger heavier SUVs.

Looigi

That's the crux of the problem. Studies have shown that there is no hard threshold. Brain damage occurs at much lower accelerations and is cumulative. A "softer" liner would reduce acceleration of the brain over what a "harder" liner would until the impact was severe enough to exceed the crush limit. Resulting brain injury is less with the softer helmet until the crush is exceeded. No?

And yes, the standard is an acceleration limit with test mass. But AFAIK, that limit was based on what the skull fracture.

Seems to me, it'd be a tradeoff of having less brain injury over most impacts against the risk of more injury in the rare case of the most extreme impact.

License2Ill

Minor traumatic brain damage may be cumulative, but crashes and damage from a single impact event are not. From my understanding, and beared-out through all of the crash helmet standards, the g-force levels are conservative.

There is never any reason to use a softer liner. You want as much crush space as possible within known limits of g-force. There is really no such thing of less brain injury, there's vegetable/dead or alive. The g-force threshold was not set to measure skull fracture. The original studies and limits first used in any standard were based on fracture, but later changed when it became apparent that the brain was being injured against the skull.

The understanding of minor injuries and cumulative minor injuries is being studied more, but the levels of those hits are not even close to what the brain can withstand in one a single impact event, and they don't correlate to death or profound injury prevention levels at all.

totalnewbie

i see your point. a 2x weight car hitting a wall may not be safer because while it has 2x mass, it also carries 2x energy in momentum. so it's a wash.

but in a bike accident, the helmet weight is negligible compared to the cyclist's weight and therefore, unlike the car case, the overall mass/energy that need to dissipate remains unchanged for both the 2-in helmet and the 1-in helmet. but in this case the protective element is doubled, which still leads me to believe the 2-in helmet is safer.

maybe i need to change the metaphor - two honda civics, one with a regular airbag, the other one with a half-sized airbag. wouldn't it be reasonable to assume the regular airbag has a better chance to cushion most impact force?

Null66

Unlikely that twice as thick would have the same crush resistance per inch... It maybe softer, or even multimodal.

It is reasonable to presume the manufacturers would consider layering the poly such that some yield at lower thresholds and some yield at higher. This would allow protection in both severe and lower energy events. It would also allow some slip to avoid the spin that can be induced which greatly increases the brain trauma. Look up the physics of a knock out ion boxing. The lowest g knock outs are through inducing rotational force.

Looigi

Of course, cumulative, by definition, needs more than a single impact no? In various activities I've experience a fair number of head strikes over a fairy wide range of severity, up to including unconsciousness and amnesia, but not skull fractures. And no, the G force ratings for bicycle helmets are not conservative and brain injury occurs at much lower accelerations.

FBinNY 

By that logic, solid polystyrene being heaviest would offer the most protection. Of course that's not what you meant, but I just wanted to show that there's not a reliable linkage between weight and protection. There are various ways of making EPS which can affect the crush rate.

Probably the best predictor of potection is thickness, (assuming the crush rate is similar) since that offers the most braking distance (lowest g-force) but even that isn't totally reliable.

It would be nice if the helmet makers or independent reviewers offered a standard basis of comparison such as internal G-force vs. impact speed, maybe for both direct and angular strikes. Until then, folks are asked to assume that all helmets with a given sticker, ANSI, Snell or other are equal, or to make judgements based on factors that may or may not make a difference.

achoo

Seems as if there's a trade off between protecting better against relatively low-energy impacts that would cause a concussion vs. protecting better against high-energy impacts that cause skull fractures.

Since concussion damage is cumulative, though, and cyclists as a whole don't crash all that often, I think I'd rather have a helmet that leans towards protecting against higher-energy impacts. I hopefully won't crash enough that cumulative effects of multiple potential concussions are worth worrying about anyway.