Helmet Wankers

[Martin Family]

On 7/2/04 9:36 pm, in article [email protected],
"David Kerber" <ns_dkerber@ns_ids.net> wrote:

> In article <[email protected]>, [email protected] says...
>> On Sat, 7 Feb 2004 13:15:06 -0500, David Kerber <ns_dkerber@ns_ids.net> wrote in message
>> <[email protected]>:
>>
>>> If you hit a rock or tree at 60mph, it's not going to matter one bit whether you have that
>>> helmet on or not. At 20 or 25, it probably would because the helmet will absorb a significant
>>> portion of the impact energy.
>>
>> Up to a point, Lord Copper. Actually a helmet will absorb the energy of a fall onto a flat
>> surface from a standing start at about 5'4" height.
>
> Exactly. And that leaves that much less energy to be transmitted to my skull. It won't absorb it
> all, but it will absorb whatever it can, reducing what hits my scull.

Do the math. E=1/2 mv^2 vs E= 1/2 m(v)^2 - (1/2 x 7 (12)^2)

(design spec for a helmet is to reduce an impact at 12mph of just the head to a just non-lethal for
50% estimated decelleration on a linear impact)

Using rather nasty non SI units (mph and kilograms)

I get the following equivalent speeds:

Speed just head full bodyweight 5 0 3.52 10 0 9.35 15 9 14.6 20 16 19.7 25 21.9 24.75 30 27.5 29.8

Let me explain these. The first column is the speed at impact. 5 and 10 are equivalent to falls from
a seated position on floor or chair, well below the height of a straight fall on a bike.

The second column is the equivalent speed of a head impact if the only momentum the helmet is
protecting against is the standard 7kg head.

The third column is the effective speed of an impact if the helmet is having to decelerate the whole
body (assuming an 80kg rigid body.) (bear in mind that the bodyweight has no effect on the
unhelmeted head)

These numbers are not terribly convincing for the utility of helmets.

Bear in mind that these assume certain things.
1. a rigid body
2. a linear impact. If there is a rotational component all bets are off. It takes 1/50th the force
to provide damage with rotational impacts than it does with linear impacts. Does the extra bulk
and nature of construction of a helmet contribute to rotational injuries? Given the lack of
effectiveness of helmets in preventing serious head injuries (including fatalities) the answer
may well be yes.

Personally I wear a helmet when there is a reasonable risk of falling off at slow speeds with linear
impacts, ie when I am riding off road (I am quite cautions so am not a downhill MTBer, just someone
who likes to get out for a pleasant ride.) or in the winter when there is ice on the ground. My
children wear helmets as they are still likely to fall off at slow speeds (7 and 5 years old) but I
will not force them to wear them when they are confident on two wheels and reasonably aware of the
risks of crashes.

I don't wear a helmet most of the time I ride the bike. I do not 'just fall off' on the road. If I
do have a collision it will be one where the speed will be relatively high and the energies involved
will make a bike helmet as useful as a teacup for bailing the titanic. Given my accident record and
riding style, I don't see that as a problem to be concerned with. I have bumped my head more times
just walking than cycling.

Might a helmet make a difference in the unlikely event of a serious accident? Possibly, but whether
it would be a positive or a negative difference is very hard to predict. I'll quite happily trade
off a few scrapes and bruises versus serious brain injury.

..d

 

[Tim Woodall]

On Sat, 7 Feb 2004 16:38:04 -0500,
David Kerber <ns_dkerber@ns_ids.net> wrote:
> In article <[email protected]>, [email protected] says...
>
> ...
>
>> God said, "div D = rho, div B = 0, curl E = - @B/@t, curl H = J + @D/@t," and there was light.
>
> So are you an EE or a Physicist?
>
Physicist.

Tim.

--
God said, "div D = rho, div B = 0, curl E = - @B/@t, curl H = J + @D/@t," and there was light.

http://tjw.hn.org/ http://www.locofungus.btinternet.co.uk/

 

[Frkrygow]

Rick Onanian wrote:

> <"frkrygow"@omitcc.ysu.edu> wrote:
>
>>Rick Onanian wrote:
>>
>>>They have never had any effect. There is no point. I spent way too much time trying to figure
>>>that out through participation last year.
>>
>>Then I'd say you didn't spend enough time reading and studying the factual data.
>>
>>It's like anything else. If you think you already know everything, you won't learn. If you don't
>>do the homework and studying, you won't learn.
>
>
> Frank, you are truly a low pressure vortex, trying to suck me into the tornado. I won't do it!
> What, rehash the same **** we already did? I read and studied, and made my decision for me; and
> stuck to me belief that my decision should only affect _me_. What more could you want from me,
> and _why_?

I'll type slowly, so you can follow. ;-)

1) You said these discussions have no effect.

2) First, many people responded, saying the discussions had, indeed had an effect - that the
discussions provided, or led to, information which changed their minds. (Always leading away from
helmet enthusiasm.)

3) You, however, claimed there was no point to this. Based on that, I assumed you didn't get very
far into the information others read.

What I'd want from you, I suppose, is to realize these discussions _have_ been educational for many
of us. They _have_ changed minds. Therefore, you shouldn't characterize them as a waste of time - at
least, not for everyone.

Sure, they can be a waste for people who don't care to learn. If that's you, then off to the (other)
tube with you.

> I refuse to watch tv. I went for a bike ride today, weather be damned!

Ah. Well, that's a point in your favor.

--
Frank Krygowski [To reply, omit what's between "at" and "cc"]

 

[David Kerber]

In article <[email protected]>, [email protected] says...

...

> I refuse to watch tv. I went for a bike ride today, weather be damned!
>
> Don't tell somebody on a bicycling newsfroup to go watch tv. Tell them to go for a bike ride, or
> go buy a trainer! If your

That's the only good use for a TV: eliminating the boredom of the trainer. I spend about 75 minutes
on mine today, doing intervals while watching the Millrose Games.

--
Dave Kerber Fight spam: remove the ns_ from the return address before replying!

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[David Kerber]

In article <[email protected]>, [email protected] says...

...

> >Exactly. And that leaves that much less energy to be transmitted to my skull. It won't absorb it
> >all, but it will absorb whatever it can, reducing what hits my scull.
>
> And at the same time aplifying the rotational component which is the most common cause of
> brain injury.

Do you have any cites for the claim that helmets "amplify the rotational component" of a head impact
to any significant degree? I don't need to see them for the fact that rotational acclerations are
more damaging to the brain; that is well-known, and has been for many years.

> >> Keyword: noticeably - i.e. you don't notice. Which is precisely the point. I ride much more
> >> cautiously without a helmet on my drop-bar bike, and am much more nervous at speed on my drop-
> >> bar bike than on my recumbent.
>
> >Not everybody is that way, though. It just sounds like I'm a more cautious rider than you are,
> >whether I have my helmet on or not.
>
> Or the difference is small in your case. It only needs to be small.

But because the difference in riding style is small for me, I think I personally gain in
_overall_ safety. I.E. the small increase (not noticeable by me) in risky behavior is more than
compensated for by the increased protection from the helmet. Obviously that will not be the case
for every cyclist.

--
Dave Kerber Fight spam: remove the ns_ from the return address before replying!

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[David Kerber]

In article <BC4B178C.C551%[email protected]>, martin- [email protected] says...
> On 7/2/04 9:36 pm, in article [email protected], "David Kerber"
> <ns_dkerber@ns_ids.net> wrote:
>
> > In article <[email protected]>, [email protected] says...
> >> On Sat, 7 Feb 2004 13:15:06 -0500, David Kerber <ns_dkerber@ns_ids.net> wrote in message
> >> <[email protected]>:
> >>
> >>> If you hit a rock or tree at 60mph, it's not going to matter one bit whether you have that
> >>> helmet on or not. At 20 or 25, it probably would because the helmet will absorb a significant
> >>> portion of the impact energy.
> >>
> >> Up to a point, Lord Copper. Actually a helmet will absorb the energy of a fall onto a flat
> >> surface from a standing start at about 5'4" height.
> >
> > Exactly. And that leaves that much less energy to be transmitted to my skull. It won't absorb it
> > all, but it will absorb whatever it can, reducing what hits my scull.
>
> Do the math. E=1/2 mv^2 vs E= 1/2 m(v)^2 - (1/2 x 7 (12)^2)
>
> (design spec for a helmet is to reduce an impact at 12mph of just the head to a just non-lethal
> for 50% estimated decelleration on a linear impact)
>
> Using rather nasty non SI units (mph and kilograms)
>
> I get the following equivalent speeds:
>
> Speed just head full bodyweight 5 0 3.52 10 0 9.35 15 9 14.6 20 16 19.7 25 21.9 24.75 30 27.5 29.8
>
> Let me explain these. The first column is the speed at impact. 5 and 10 are equivalent to falls
> from a seated position on floor or chair, well below the height of a straight fall on a bike.
>
> The second column is the equivalent speed of a head impact if the only momentum the helmet is
> protecting against is the standard 7kg head.
>
> The third column is the effective speed of an impact if the helmet is having to decelerate the
> whole body (assuming an 80kg rigid body.) (bear in mind that the bodyweight has no effect on the
> unhelmeted head)

An extreme, and unwarranted assumption for most crashes, IMO; usually your body is also going to hit
the ground at roughly the same time. For a counter-example, reason from a different angle and assume
that the helmet only has to absorb the kinetic energy of the head, which is probably closer to the
truth than having it take the entire body's energy (I am aware that a real crash is going to be
somewhere between those two extremes).

Without actually doing the math to derive actual joules, assume a helmet can absorb 100 units of
energy, which we will say corresponds to your 12mph impact of just the head. If I'm then going 24
mph and have a direct impact in the direction of my motion (such as the side of a car, or a tree),
the kinetic energy of the head is obviously 4x what it was at 12mph. The helmet will absorb 25% of
the impact energy in deforming, leaving only 75% of it transmitted to my skull. To me, 25% is a
pretty significant reduction in potential damage. Of course, if you don't hit an obstruction, but
instead fall off the bike at speed and just land and slide in the road, then the only *impact* your
head will take is the vertical (falling) component of your fall, and does not have to absorb the
energy of your forward motion. That will be dissipated in tearing your clothes and skin.

Obviously as you go faster and faster, the percentage reduction is smaller and smaller, so a helmet
gives you less and less relative protection. So it seems to me that a helmet will give relatively
better protection to slower riders, and less to faster riders.

> These numbers are not terribly convincing for the utility of helmets.
>
> Bear in mind that these assume certain things.
> 1. a rigid body

And IMO, this is a very poor assumption for most real-world crashes and falls.

> 2. a linear impact. If there is a rotational component all bets are off. It takes 1/50th the force
> to provide damage with rotational impacts than it does with linear impacts. Does the extra bulk
> and nature of construction of a helmet contribute to rotational injuries? Given the lack of
> effectiveness of helmets in preventing serious head injuries (including fatalities) the answer
> may well be yes.

Maybe, but I doubt the overall effect will be negative.

> Personally I wear a helmet when there is a reasonable risk of falling off at slow speeds with
> linear impacts, ie when I am riding off road (I am quite cautions so am not a downhill MTBer, just
> someone who likes to get out for a pleasant ride.) or in the winter when there is ice on the
> ground. My children wear helmets as they are still likely to fall off at slow speeds (7 and 5
> years old) but I will not force them to wear them when they are confident on two wheels and
> reasonably aware of the risks of crashes.
>
> I don't wear a helmet most of the time I ride the bike. I do not 'just fall off' on the road. If I
> do have a collision it will be one where the speed will be relatively high and the energies
> involved will make a bike helmet as useful as a teacup for bailing the titanic. Given my accident
> record and riding style, I don't see that as a problem to be concerned with. I have bumped my head
> more times just walking than cycling.

I see that we do agree that at higher relative impact speeds, a helmet provides relatively less
protection. We just disagree on whether you will derive "significant" benefit from whatever energy
dissipation the helmet can give you, even if it will not provide full protection.

Thanks for making a reasoned, logical argument rather than emotional one!

....

--
Dave Kerber Fight spam: remove the ns_ from the return address before replying!

REAL programmers write self-modifying code.

 

[David Kerber]

In article <[email protected]>, [email protected] says...
> On Sat, 7 Feb 2004 16:38:04 -0500, David Kerber <ns_dkerber@ns_ids.net> wrote:
> > In article <[email protected]>, [email protected] says...
> >
> > ...
> >
> >> God said, "div D = rho, div B = 0, curl E = - @B/@t, curl H = J + @D/@t," and there was light.
> >
> > So are you an EE or a Physicist?
> >
> Physicist.
>
> Tim.

That was my guess; most EE's of my acquaintance (including me) aren't that big into theory to
remember the basic equations years later, even though they certainly learned them at one time.

--
Dave Kerber Fight spam: remove the ns_ from the return address before replying!

REAL programmers write self-modifying code.

 

[Peter Keller]

On Sat, 07 Feb 2004 16:36:22 -0500, David Kerber wrote:

> In article <[email protected]>, [email protected] says...
>> On Sat, 7 Feb 2004 13:15:06 -0500, David Kerber <ns_dkerber@ns_ids.net> wrote in message
>> <[email protected]>:
>>
>> >If you hit a rock or tree at 60mph, it's not going to matter one bit whether you have that
>> >helmet on or not. At 20 or 25, it probably would because the helmet will absorb a significant
>> >portion of the impact energy.
>>
>> Up to a point, Lord Copper. Actually a helmet will absorb the energy of a fall onto a flat
>> surface from a standing start at about 5'4" height.
>
> Exactly. And that leaves that much less energy to be transmitted to my skull. It won't absorb it
> all, but it will absorb whatever it can, reducing what hits my scull.
>

Not necessarily. The destructive energy of the impact increases as the square of the closing
velocity. Bicycle helmets are designed to absorb safely impact energy from 20kph ca 12mph. At 20mph
there is already nearly three times the destructive energy produced by the impact then the helmet
was designed to absorb, and the energy continues rising steeply as the velocity rises slowly. Peter

This transmission is certified free of viruses as no Microsoft products were used in its preparation
or propagation.

 

[Graeme]

David Kerber <ns_dkerber@ns_ids.net> wrote in
news:[email protected]:

> That was my guess; most EE's of my acquaintance (including me) aren't that big into theory to
> remember the basic equations years later, even though they certainly learned them at one time.

EE = electrical engineer? That's me (well, at least if what your degree was defines you). V=IR is
about all I can remember instantly, most other stuff takes a bit of thinking or a book :-/ Mind you,
I fell into the computer side of things soon after graduating and even Ohm's law became irrelevant
:-/

Graeme

 

[bikinchris]

I think that trying persuade someone who thinks helmets are stupid that they should use one is a waste of time. However for those who believe that protecting the brain should be a priority and that most other damage can be overcome, here is a link for you:
http://starbulletin.com/2004/02/02/news/index3.html

 

[Benjamin Lewis]

Rick Onanian wrote:

> Don't tell somebody on a bicycling newsfroup
^^^^^^^^^ Okay, you have to do something about this habit of
yours... Or maybe not -- I get a giggle out of it ever time I
see it. Ah, simple pleasures.

--
Benjamin Lewis

"Love is a snowmobile racing across the tundra and then suddenly it flips over, pinning you
underneath. At night, the ice weasels come." --Matt Groening

 

[Benjamin Lewis]

David Kerber wrote:

>>>> God said, "div D = rho, div B = 0, curl E = - @B/@t, curl H = J + @D/@t," and there was light.
>>>
>>> So are you an EE or a Physicist?
>>>
>> Physicist.
>>
>> Tim.
>
> That was my guess; most EE's of my acquaintance (including me) aren't that big into theory to
> remember the basic equations years later, even though they certainly learned them at one time.

Also, I was under the impression that EEs usually express these in a different format.

--
Benjamin Lewis

"Love is a snowmobile racing across the tundra and then suddenly it flips over, pinning you
underneath. At night, the ice weasels come." --Matt Groening

 

[Benjamin Lewis]

[email protected] wrote:

> I think that trying persuade someone who thinks helmets are stupid that they should use one is a
> waste of time.

I agree. Many or most of these people have actually done research into the matter, unlike the bulk
of the helmet proponents.

--
Benjamin Lewis

"Love is a snowmobile racing across the tundra and then suddenly it flips over, pinning you
underneath. At night, the ice weasels come." --Matt Groening

 

[Dave]

> Nearly right. In fact the motorcycle crashes tended to be more seriously injurious of the riders.
> The interesting point is that somehow this greater risk of injury in crashes balanced out the
> lesser incidence of crashes to produce the *same* risk of injury per mile.
>
> Was this just an extraordinary co-incidence?
>
> The suggestion of the author was that *if* risk compensation occurs, we should expect it to be
> most clearly demonstrated in the most experienced and capable people, because those are the people
> whose appreciation of the risks and of their own capabilities would be the most realistic.
>
> That's why he chose specially trained police drivers and riders, those who've graduated from the
> special advanced training courses.
>
> His suggestion was that these experienced capable drivers and riders had a certain level of injury
> risk which they felt comfortable with, and adjusted their behaviour on motorcycles or cars in such
> a way as to compensate for the very different characteristics and vulnerabilities of these
> different vehicles, so that they ended up, realistically, taking the same level of risk. Risk
> compensation.
>
> Of course that study didn't *prove* risk compensation, it simply either exemplified it well or was
> a remarkable coincidence. You need to pile up some more, and fail to find counter-examples, to
> strengthen the case.

And this intuitively feels right.

Someone is going to howl me down about this but it just seems obvious to me that there is a
perceived risk level I am ok with and one I am not. And that the more experience one has the more
likely the percieved risk is to be close to the real risk.

Incidently my ex, a **** driver if anyone was went on to fail the police pursuit course... twice

Dave

 

[Eric S. Sande]

>And this intuitively feels right.

>Someone is going to howl me down about this but it just seems obvious to me that there is a
>perceived risk level I am ok with and one I am not. And that the more experience one has the more
>likely the percieved risk is to be close to the real risk.

That seems rational to me. I was definiteley afraid of city traffic before riding in it and gaining
some experiece.

A small amount of training and some years of practice makes the risk component seem insignificant to
me, in comparison to the rewards.

There is always, I suppose, a base level of risk. But training and experience smooth this out
remarkably.

--

_______________________ALL AMIGA IN MY MIND_______________________ ------------------"Buddy Holly,
the Texas Elvis"------------------
__________306.350.357.38>>[email protected]__________

 

[Bernie]

David Kerber wrote:

>In article <[email protected]>, [email protected] says...
>
>>On Sat, 7 Feb 2004 13:15:06 -0500, David Kerber <ns_dkerber@ns_ids.net> wrote in message
>><[email protected]>:
>>
>>>If you hit a rock or tree at 60mph, it's not going to matter one bit whether you have that helmet
>>>on or not. At 20 or 25, it probably would because the helmet will absorb a significant portion of
>>>the impact energy.
>>>
>>Up to a point, Lord Copper. Actually a helmet will absorb the energy of a fall onto a flat surface
>>from a standing start at about 5'4" height.
>>
>
>Exactly. And that leaves that much less energy to be transmitted to my skull. It won't absorb it
>all, but it will absorb whatever it can, reducing what hits my scull.
>
>>>I've found that I don't ride noticeably different with a helmet than without.
>>>
>>Keyword: noticeably - i.e. you don't notice. Which is precisely the point. I ride much more
>>cautiously without a helmet on my drop-bar bike, and am much more nervous at speed on my drop-bar
>>bike than on my recumbent.
>>
>
>Not everybody is that way, though. It just sounds like I'm a more cautious rider than you are,
>whether I have my helmet on or not.
>
If I can put my 2 cents worth in here.. In the last 41/2 years of mostly daily commuting I've gone
down four times. Once because I was unfamiliar with harder skinnier tires, twice on black ice, once
because I tried an impossible move around a car that could not actually stop at a stop sign. They
just slowed down and very gently rolled in front of me... (I'll try not to be bitter} My point is:
and remember this is a helmet ****: In 4 instances I went down. twice my helmet protected me, no
question. One time I slid downhill , even crossed a set of railway tracks (under the skytrain at
Canfor Industrial Park in New Westminster, BC if ya wanna know) and I do believe, was protected from
concussion and abrasions by my helmet. The other serious crash happened last summer when that little
Honda just couldn't quite stop and I tried to skew around her and not be messed up by the rr tracks
i was crossing at the same time. Lost it big time, slid for home, no concussive fall, but the helmet
definitely saved the side of my face from a major scrape, protected my glasses. For this I am
thankful. Do I support helmet wearing? Yes! Should it be mandatory? Leave me out of it! Best
regards, Bernie

 

[Just Zis Guy]

On Sat, 7 Feb 2004 20:14:07 -0500, David Kerber
<ns_dkerber@ns_ids.net> wrote in message
<[email protected]>:

>most EE's of my acquaintance (including me) aren't that big into theory to remember the basic
>equations years later, even though they certainly learned them at one time.

Always assuming that their lecturers, call them for the sake of argument Professor Hammond, made the
bloody things comprehensiuble in the first place.

Guy
===
May contain traces of irony. Contents liable to settle after posting.
http://chapmancentral.demon.co.uk

 

[Just Zis Guy]

On Sun, 08 Feb 2004 01:45:01 GMT, Graeme
<[email protected]> wrote in message
<[email protected]>:

>EE = electrical engineer? That's me (well, at least if what your degree was defines you). V=IR is
>about all I can remember instantly, most other stuff takes a bit of thinking or a book

Scarily true. I can't remember most calculus any more.

(B.Eng Hons, Electrical Engineering)

Guy
===
May contain traces of irony. Contents liable to settle after posting.
http://chapmancentral.demon.co.uk

 

[Just Zis Guy]

On Sat, 7 Feb 2004 20:03:46 -0500, David Kerber
<ns_dkerber@ns_ids.net> wrote in message
<[email protected]>:

>Do you have any cites for the claim that helmets "amplify the rotational component" of a head
>impact to any significant degree?

Cites? No, the jury is still out. But it is a concern whihc has been raised by a number of doctors,
and the proposed mechanism is credible
- it is also one possible explanation for the rise in seriousness of injuries since 1985, as helmets
have become more common. Other factors could also account for this.

>But because the difference in riding style is small for me, I think I personally gain in
>_overall_ safety. I.E. the small increase (not noticeable by me) in risky behavior is more than
>compensated for by the increased protection from the helmet. Obviously that will not be the case
>for every cyclist.

That's your choice. I don't see from the data anything which makes a good case for even
strong encouragement of helmet use, let alone the current emphasis on helmet use to the
exclusion of all else.

Guy
===
May contain traces of irony. Contents liable to settle after posting.
http://chapmancentral.demon.co.uk

 

[Graeme]

"Just zis Guy, you know?" <[email protected]> wrote in
news:[email protected]:
> Scarily true. I can't remember most calculus any more.
>
> (B.Eng Hons, Electrical Engineering)

Snap! This is getting scary Guy, I find myself agreeing with your posts more and more, and now I
find we both have the same degree. I live in fear of waking up some day with a dodgy moustache (but
I'll live with it if it comes with the associated recumbent bike).

;-)

Graeme