A week without a helmet.

[Racing roadkill]

No. A material can only absorb energy by deforming, which is what the metal in a car's crumple zone is designed to do, or by cracking. If your CF shell deforms, then it'll be deforming into your skull, which I suspect isn't a desirable outcome. Except of course CF doesn't deform, it's brittle so cracks. But not in the way that expanded polystyrene foams do, by forming any thousands of microcracks which create the new surface area that absorbs energy. No, it'll shatter into large, sharp shards. Which absorb very little energy, but will gain considerable kinetic energy of their own. Not the sort of thing you really want to have spinning around your head and eyes...

Of course, it's also possible that they don't want to test it against a tougher standard because they know it won't pass. After all, the amount of energy any structure is capable of absorbing can be calculated by anyone who can use an engineering finite element model analysis package.

20 years ago,pre preg Carbon Fibre behaved like that, not these days it doesnt. It disintegrates in a very controlled and confined manner. You won't see shards flying off, unless it really is a catastrophic super high energy event (think explosion, or Formula 1 car body work Kinetic energy levels). These materials are designed to act more like the deformable nose cone structure of an F1 car / aircraft. as long as the manufacturing process has worked (lay up, cut and form, autoclave, and finish) you won't see the armageddon-esque disintegration and flying shards of CF.

 

[Racing roadkill]

I fail to see how the carbon fibre can be designed to stop penetration and absorb impact. Surely if it is stopping penetration it would be a very stiff material and not have any give in it, which is what you would need for it to spread the force around the shell? I would have thought Kevlar would be a better material for this?
One in 3 accidents happen within a mile of your home. If a helmet has been in an accident and it absorbed any force (which is a contentious issue with all cycle helmets), then it will not be any good if you get hit in the same place again. If you are not worried about the helmet not actually working in the "short" journeys, why wear a helmet at all? Your thinking seems to be the helmet is not good enough to sustain any impact (otherwise you would have no qualms wearing it all the time) so only wear it on short trips (where you are pretty likely to have an accident according to statistics) At the end of the day it is your head and how you choose to protect it is up to you, but I really dont get the idea of using a helmet that has been in an accident for any journey.

It's got Kevlar inside the shell and in the central zone, only the sides are CF and even they are lined with Kevlar. Hence the name Carbon-Kevlar.

 

[Wobblers]

20 years ago,pre preg Carbon Fibre behaved like that, not these days it doesnt. It disintegrates in a very controlled and confined manner. You won't see shards flying off, unless it really is a catastrophic super high energy event (think explosion, or Formula 1 car body work Kinetic energy levels). These materials are designed to act more like the deformable nose cone structure of an F1 car / aircraft. as long as the manufacturing process has worked (lay up, cut and form, autoclave, and finish) you won't see the armageddon-esque disintegration and flying shards of CF.

Sorry, what, a brittle material fails in a predictable manner??? Really? Let me be the first to congratulate you on achieving the holy grail of engineering - and your prospective Nobel Prize. You deserve it!

PS: Kevlar won't absorb the impact energy either, not without deforming (which is how a bullet proof vest works).

 

[Pumpkin the robot]

It's got Kevlar inside the shell and in the central zone, only the sides are CF and even they are lined with Kevlar. Hence the name Carbon-Kevlar.

I understand carbon Kevlar, but you said it was CF not CK in the original quote. I did not look at the helmet specs, I just went by your post, my mistake.

 

[MarkF]

It's got Kevlar inside the shell and in the central zone, only the sides are CF and even they are lined with Kevlar. Hence the name Carbon-Kevlar.

That helmet is extreme, why not just wear a motorcycle full face one? What do you use to protect your limbs?

 

[totallyfixed]

This threD is turning out to be quite a classic.... Not had the like since the glory days of simoncc, nickm and Linf .....

I think Rr deserves some praise, without his contribution, and in spite of the fact that he can now only be arguing with himself, the whetstones would have remained untouched.

 

[Racing roadkill]

That helmet is extreme, why not just wear a motorcycle full face one? What do you use to protect your limbs?

The weight. it's feather light, it weighs about as much as a bag of crisps. A motorcycle lid is a bulky pain in the backside. I just wear normal cycle clothing, I might lose some skin, or break some bones, but they grow back, as long as I don't lose too much skin, or break too many bones, I'll get over it.

 

[Jon George]

Many thanks to all who posted a link to http://www.cyclehelmets.org/0.html - I have begun reading some of the material and absorbing the information in much the same way as (most?) helmets apparently don't absorb impact in most accidents. I had regretted starting this threat because of the reaction from the likes of Rr (Now ignored. Ahh, it's as if I've walked to the other side of the bar.), but that link has made it wroth while. Whilst I had always been in the anti-compulsion camp, it's now nice to be armed with good arguments, other than gut feeling.

Oh, I'm still noticing a general change in other road users when in my vicinity - I'm getting more wider passes (even from White Van Man) and more hesitation (presumably to ensure a safe gap) before overtaking. Sure, there's still numpties having a go because of bad road craft, but their numbers have thinned out.

 

[Brandane]

Oh, I'm still noticing a general change in other road users when in my vicinity - I'm getting more wider passes (even from White Van Man) and more hesitation (presumably to ensure a safe gap) before overtaking. Sure, there's still numpties having a go because of bad road craft, but their numbers have thinned out.

That's good news; it should reduce your chances of getting whacked on the head by car/van mirrors. Twice.

 

[Mugshot]

As I'm on the Kevlar Kids ignore list (well most of us are lets face it) so am unlikely to get an answer from him and I'm incredibly nosey, does anybody know if he rides a recumbant? I'm not sure how you get hit on the head by a Berlingo wing mirror otherwise.

 

[Mugshot]

Because @Mugshot has asked the question before, and because he's been very patient, the answer (Welcome Mat) apparently is no.

Thank you

 

[Mugshot]

I'm not sure that will work, I though you'd have been #1

 

[Mugshot]

Because @Mugshot has asked the question before, and because he's been very patient, the answer (Welcome Mat) apparently is no.

Just realised what you meant by Welcome Mat , a good place to look, I'd checked the recumbant area, I hadn't found anything there.

 

[srw]

I just wear normal cycle clothing.

Me too. I find a suit works really well for commuting.

 

[david k]

indeed my friend. I don't mind a lively debate, and I don't mind people disagreeing with me. In my mind just because they hold a different view doesn't mean I like them any less as people.

What I do object to is the legion of internet bullies who reside on here, who resort to foul language and abuse. I'm pretty sure they don't go round doing that in real life, but they suddenly become very brave in the isolation and anonymity of the internet.

They're small men with inadequacy issues, who resort to bullying to fill the void left by the lack of self esteem. I ignore arses like that in real life and do the same on here.

Well said that man