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Topic ClosedMore hair, less speed
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fards View Drop Down
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Points: 2543 		Direct Link To This Post Posted: 05 November 2006 at 10:28pm
The new EN 1028 is a laughable farce..

A helmet that meets it's requirements will only absorb 1/3 the energy of those designed to meet the snell b96..

So sod all in fact..

Table at the end of this sums it up..
http://www.cyclehelmets.org/papers/c2023.pdf (reprinted from CTC mag).

 To tie in with any standards, gNick, Hadden, I can't see why someone like the guys that do this testing couldn't test yours to see if it was conformant. Other than the cost obviously.








Edited by fards - 05 November 2006 at 10:54pm
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KeithD View Drop Down
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Points: 625 		Direct Link To This Post Posted: 06 November 2006 at 7:18pm
Does anyone ride with an aero helmet? I was surprised not to see any at Reading in September.
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Neil F View Drop Down
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Points: 449 		Direct Link To This Post Posted: 06 November 2006 at 7:29pm
Yes, Big Ian and I ride with them. I don't use it at every race, it depends on the temperature (poor cooling) or twisting tracks.
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Points: 471 		Direct Link To This Post Posted: 13 December 2006 at 1:05pm
Why does it depend upon "or twisting tracks"?!!
Never believe an atom they make up everything.
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Points: 1079 		Direct Link To This Post Posted: 13 December 2006 at 2:14pm
Originally posted by Haddon Haddon wrote:


It should be possible to make a much tougher and better shock absorbant helmet as mass produced ones use quite low performance materials.

Though I am not sure how whether it will really be able to improve to a massive extent.
Trawling around the internet it seems that the brains tolerance is less than 50g before damage. So if you assume that the helmet has got to stop you then hitting a solid object. Let's assume the material is perfect. So it slows your head in an even acceleration until it stops. So we have the bike velocity V at brain damage level, a deceleration a. then V^2 = 2aS where S is the thickness of the padding. Lets assume a is 50g (the max) i.e. approx 500m/s^2
S will be about 3 cm - 0.03 m
Then V^2 < 2*500*0.03 = 30
==> V = 5.5 m/s is that about 12.5MPH
That seems worryingly low to me so I have probably made a mistake. Anyone know where?
Kevin Jenkins

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kit wolf View Drop Down
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Points: 220 		Direct Link To This Post Posted: 13 December 2006 at 3:51pm
==> V = 5.5 m/s is that about 12.5MPH
That seems worryingly low to me so I have probably made a mistake. Anyone know where?

I don't think you made a mistake - but that's also about the speed your head would hit the ground if you were to fall off an upright sideways.

Opponents of cycle helmets say this design speed is so low as to make helmets next to useless as most collisions (esp. those involving motor vehicles) involve higher impact velocities. There's an oft-repeated claim that bike helmets aren't designed to protect you in crashes faster than 12mph - which is nonsense on any bike save a lowracer, because you have to work out the vector of the forward and downward motion of the head - which would be 1.412x12 ~= 17mph. By their reasoning, helmets actually wouldn't protect you in any accident when you were moving and also fell to the ground.

Although it's possible to cycle into a brick wall, or to fall straight towards the kerb, these are worst-case scenarios and I imagine most accidents involve considerably lower forces. For example you might hit a windscreen glancingly, or fall to the ground and slide a bit. Even windscreens have quite a bit of give in them (I passed the aftermaths of two bus/pedestrian accidents in the past few weeks, and the depressions in them were several inches deep - both accidents occurred in 20mph zones and I suspect at least one was fatal). How useful that little bit of protection actually is, I have no idea.

It was discussed in depth on uk.rec.cycling a few years back:
http://groups.google.co.uk/group/uk.rec.cycling/browse_thread/thread/9dcadcea1df34a89/13aabfc9b0398c97?lnk=st&q=helmet+12mph+anonymous+coward&rnum=1#13aabfc9b0398c97
(warning - heat as well as light).

I think there are links to the Snellen testing specs on the parent thread.

Kit
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Points: 8036 		Direct Link To This Post Posted: 13 December 2006 at 4:37pm
For what it's worth, I worked for BSI from 1980 to 1996 testing (among other things) cycle helmets. I was involved with the development of the PAS (Product Approval Specification) that we used to Kitemark them before the British Standard was finalised.

The PAS and the BS were pretty much just written around what was available at the time, and a lot of those products were er.. Poo!

I'm sure things have improved over the past 10 years, but I still see one of the main problems as being the retention systems. I've never had a helmet I feel confident would stay in place in the event of an impact.

I very rarely wear a helmet other than for racing.

Alan.

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Neil F View Drop Down
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Points: 449 		Direct Link To This Post Posted: 13 December 2006 at 7:16pm
Twisting Tracks.
well you need to move your head round to see into the corners and I find that the tail doesn't help head modility - especially as I only had 2 inchs cleararance to the rear wheel on the NoCom.
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Points: 163 		Direct Link To This Post Posted: 16 December 2006 at 11:05pm
What worries me about helmets is the lack evidence that they are useful.  In places where they are compulsory they don't seen to reduce the rate of serious injuries - they just reduce the number of peole cycling!  Most serious head injuries to cyclists are caused not by a straight blow, but by a blow that causes rapid rotation.  I wonder whether the helmet, being considerably bigger than the head, increases that risk.  So I only wear one when racing - or to keep the hood of my anorak in place in the rain, which it does rather well!Smile
Andrew Horne
One Challenge Wizard - so far
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AlanGoodman View Drop Down
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Points: 8036 		Direct Link To This Post Posted: 17 December 2006 at 8:00am
Originally posted by Andrew Andrew wrote:

I wonder whether the helmet, being considerably bigger than the head, increases that risk. 

    
Not just the size... The shape of the helmet shell and position/shape/size of ventilation features also have a big effect on rotational forces in the event of an impact.

A lot of work was done on this for motorcycle helmets, and those tests (with tri-axial accelerometers/load cells) resulted in a big change to the mechanisms used for attaching visors as well as to ventilation features and overall helmet design...
    

Edited by AlanGoodman - 17 December 2006 at 8:00am

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