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Bike Helmet Shell Thickness

Old 08-17-21, 07:10 PM
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Bike Helmet Shell Thickness

I've been searching and can't find what I'm looking for. Most my helmets have a pretty thick shell that holds it's shape quite well. I just picked up a helmet with MIPS that looks very nice, but the shell is really thin. Like you can press it and it will move. It's the Bell Revolution MIPS helmet. Is a really thin shell fine? Really cheap helmet obviously, but I got a different MIPS helmet at Costco that seems much more quality for less. So I thought I'd check this one out since it's similar price. Looks good, has the MIPs inside, but the outer shell is weirding me out. Is a thicker outer shell important, or is it all about the foam? I think briefly they made helmets that didn't even have a shell.
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Old 08-18-21, 07:22 AM
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https://helmets.org/howmade.htm
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Old 08-18-21, 08:45 AM
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Are you talking about the plastic which covers the styrofoam? Its only real purpose, from what I understand, is to allow the helmet to slide on the pavement instead of having the strofoam catch on the ground and twist your neck, causing an injury. The plastic isn't really there to absorb impact, that's the job of the styrofoam.
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Old 08-18-21, 06:50 PM
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Actually if I could have any helmet, I would love to have back a helmet like my late 80s Bell Tourlite. It had a fairly thick lexan shell. It would have taken a really hard pointed hit to penetrate that shell. And yet I didnt find it all that heavy at all.
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Old 08-19-21, 04:35 AM
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I would be interested to know how strong & how much less weight/bulky a carbon fiber helmet would be compared to the average helmet?

It could be a good use for carbon fiber material.
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Old 08-19-21, 07:27 AM
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Originally Posted by Troul View Post
I would be interested to know how strong & how much less weight/bulky a carbon fiber helmet would be compared to the average helmet?

It could be a good use for carbon fiber material.
If you had a carbon fiber helmet it might make your head asplode in a crash.
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Old 08-19-21, 08:37 AM
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Originally Posted by Troul View Post
I would be interested to know how strong & how much less weight/bulky a carbon fiber helmet would be compared to the average helmet?

It could be a good use for carbon fiber material.

Sounds like a $1700 solution to save how much weight? Also, is there a carbon fiber foam? The helmet's function isn't to be strong, it's to deflect the impact effects away from the brain.
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Old 08-19-21, 08:56 AM
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If all helmets were made the same, there'd only be one helmet to be made.

Don't worry so much about one being a flimsy shell. It likely is designed to work with all the other components of the helmet to provide you the safety required.

Do you even know that the thicker material of one shell is the same material as the thinner material? Do you even know if the foam is exactly the same? Even if it is, the design of the entire helmet structure that will make a difference.

So just get what you trust.
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Old 08-20-21, 07:10 PM
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Carbon she'll with a tubeless inflatable liner? Make it have a presta valve too!
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Old 08-20-21, 10:04 PM
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The hardshell helmets came back into vogue a couple of years ago. Perhaps they have some benefits for MTB riding and hitting branches.

But, for most riding, the thin plastic may even be preferable. They are designed as a one-hit helmet, and to take and dissipate the force of impact.
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Old 08-24-21, 04:30 PM
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It seems to me the duty of the shell is also to somewhat protect the foam upon impact, so I'd be asking questions, too. I'll stick with my (2009) Bell Array and (1996) Image Pro. Did you write to Bell to get their explanation?
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Old 08-25-21, 05:17 AM
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Originally Posted by Troul View Post
Carbon she'll with a tubeless inflatable liner? Make it have a presta valve too!
And then a thread (with a poll) asking whether you use valve stem covers with your helmet.
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Old 08-25-21, 02:47 PM
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Originally Posted by 1989Pre View Post
It seems to me the duty of the shell is also to somewhat protect the foam upon impact, so I'd be asking questions, too. I'll stick with my (2009) Bell Array and (1996) Image Pro. Did you write to Bell to get their explanation?

No, the function of the foam is to compress upon impact. The foam itself is not expected to survive the impact as a functioning helmet and thus there is no reason to protect it in an impact.
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Old 08-27-21, 07:24 AM
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Originally Posted by 1989Pre View Post
It seems to me the duty of the shell is also to somewhat protect the foam upon impact, so I'd be asking questions, too. I'll stick with my (2009) Bell Array and (1996) Image Pro. Did you write to Bell to get their explanation?
See my comment above. Back in the 80's and into the early 90's, at least, bicycle helmets were all styrofoam with maybe a spandex cover over them. The problem with these helmets is that, even though the styrofoam protects the head in a crash, the friction between it and the ground is enough to twist someone's neck in a crash and cause injuries. Adding a thin plastic shell over the styrofoam allows the helmet to slide on the pavement so that doesn't happen. The styrofoam still compresses and absorbs impact, but the pavement doesn't dig into it and cause that kind of friction. There really is no protecting of the foam, since bicycle helmets are considered a one crash use item.
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Old 08-27-21, 09:26 AM
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Milton Keynes,

I am un-convinced that the shell of the helmet plays no important role in impact-protection of either the foam or the rider's head. (Think football shoulder pads or hockey knee pads).
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Old 08-27-21, 10:56 AM
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Originally Posted by 1989Pre View Post
Milton Keynes,

I am un-convinced that the shell of the helmet plays no important role in impact-protection of either the foam or the rider's head. (Think football shoulder pads or hockey knee pads).
Yeah, but I'm not convinced that the thickness of the shell makes a difference since all these helmets at least meet the minimum requirements of the CPSC.

And your statement supposes that Milton Keynes was stating the shell was only for the purpose of protecting the foam. I don't see that he was saying that at all.

If you limit the shell to a specified thickness, then you are essentially saying it has to be made from one type of material and maybe a specific formula for their plastic.

So again, use the helmet you trust.
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Old 08-28-21, 02:07 AM
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Most current "hard" shells in bicycle helmets are of the "in-mold" variety. This used to be a feature only in the most expensive helmets. But it's now on almost all of them. These shells serve two main functions: as mentioned to reduce "grabbing," but also to "contain" the foam. When the foam fails, you want it to stay together. The in-molded shells help with this, as does internal "re-bar."

MIPS is another attempt at reducing rotational forces upon impact.

To the OP: as long as the helmet you're looking for meets all required safety standards and FITS YOU WELL, that helmet should provide excellent protection. (ASTM, CPSC, among others, depending on country {ANSI & SNELL years ago}). But it can't be 10 years old either! Helmets have a shelf life of about five years. Debatable, but if you're concerned about safety, replace any time it's gotten an impact, or abused, or is at the end of its designed life. Don't buy used or accept "free" helmets unless you're DARN sure it's still pristine. And spend time getting the fit right and the straps properly adjusted. I'm amazed to see people with helmet straps hanging 3" below their necks and the ear clasps completely wrong. Get it as tight as you can handle.

Also, please note that no bicycle helmet is designed to address concussions! They're designed to reduce incidence of skull fracture and "traumatic brain injury," whatever that is. But not concussion.

Anyone concerned about concussion should consider having "concussion baseline testing" done. Talk to your doctor; it will help diagnose a suspected brain injury and its severity. Especially your kids if you have them, especially if they're playing sports where concussion is a possibility.

Good luck.
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Old 08-28-21, 06:44 AM
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Originally Posted by 1989Pre View Post
Milton Keynes,

I am un-convinced that the shell of the helmet plays no important role in impact-protection of either the foam or the rider's head. (Think football shoulder pads or hockey knee pads).
Again, the plastic shell is not there to protect the foam. It's to allow the foam to slide on the pavement. It's expected that in a crash the foam will be compressed and it's only a one-time use object. There's no use in protecting the foam, since it's expected to be destroyed as it protects the head. The plastic just prevents neck injuries by allowing the foam helmet to slide and not catch on the pavement, so it doesn't need to be very thick. I don't know how to explain this any clearer.
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Old 08-28-21, 04:08 PM
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Milton Keynes: You've explained your opinion well. I just disagree with it.
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Old 08-28-21, 07:36 PM
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Originally Posted by 1989Pre View Post
Milton Keynes: You've explained your opinion well. I just disagree with it.
Based on what? Are you denying that helmets are a one-time use product? This has nothing to do with knee pads.

MK isn't expressing an opinion, that's well-known fact.
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Old 08-28-21, 08:10 PM
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Hypothesis- With a good whack, the styrofoam can break apart.
Methods-I've cut and peeled the outer plastic off an old helmet and whacked it with a bat. Styro broke apart. Whacked another with the plastic intact, helmet stayed together. Both cases 10+ year old helmets were wrecked.
Conclusion- outer plastic good.
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Old 08-28-21, 08:44 PM
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Originally Posted by 1989Pre View Post
Milton Keynes: You've explained your opinion well. I just disagree with it.
Disagree all you want, but the information is widely available.

https://pediatriceducation.org/2018/...head-injuries/'

Plastic shell this is designed to allow the head to slide or skid on the ground. Remember there are items on the ground which can catch on the helmet and cause rotational or torque to the head and neck. The shell also helps to keep the foam intact.
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Old 08-29-21, 04:43 AM
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The fact that a bicycle helmet shell is "designed to slide on the ground", does not suggest nor imply that this is it's sole, or even primary purpose.
A bicycle helmet will not slide on many surfaces such as grass, and at an acute angle of impact, will not "slide" on tarmac, either.
Construction helmets are not designed in anticipation of any colliding object "sliding off". They are made of impact-resistant materials.
It is counter-intuitive to suggest that the shell plays no role in impact resistance/dissipation.
https://www.explainthatstuff.com/how...mets-work.html
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Old 08-29-21, 05:10 AM
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Originally Posted by 1989Pre View Post
The fact that a bicycle helmet shell is "designed to slide on the ground", does not suggest nor imply that this is it's sole, or even primary purpose.
A bicycle helmet will not slide on many surfaces such as grass, and at an acute angle of impact, will not "slide" on tarmac, either.
Construction helmets are not designed in anticipation of any colliding object "sliding off". They are made of impact-resistant materials.
It is counter-intuitive to suggest that the shell plays no role in impact resistance/dissipation.
https://www.explainthatstuff.com/how...mets-work.html
Why do you keep talking about other kinds of helmets and knee pads? Bike helmets are designed differently from other types of helmets, and the single use aspect is almost unique to bike helmets.

Intuition has nothing to do with this, there's plenty of literature where this primary function is stated explicitly. Good luck finding anything similar indicating protection of foam or force dissipation.

It's true that plastic can be used to support the foam structure so that holes can be made larger and the helmet less bulky, but that is not "protecting the foam" or dissipating forces.

Your linked source says nothing of relevance to the protective role of plastic.
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Old 08-29-21, 06:49 AM
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Iride01, I did not mean to infer that that was one of Milton Keynes' points. That the shell protects (both from impact and abrasion) both the foam and the rider's head was a point I was trying to make.

"Yeah, but I'm not convinced that the thickness of the shell makes a difference since all these helmets at least meet the minimum requirements of the CPSC."

Let's hope you're right.
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