On 8/6/2019 10:52 AM, Joerg wrote:
On 2019-08-05 21:55, Andre Jute wrote:
On Tuesday, August 6, 2019 at 2:10:34 AM UTC+1, Sir Ridesalot wrote:
On Monday, August 5, 2019 at 8:41:29 PM UTC-4, Andre Jute wrote:
On Monday, August 5, 2019 at 9:29:26 PM UTC+1, Tom Kunich wrote:
On Monday, August 5, 2019 at 1:33:00 AM UTC-7, Andre Jute
wrote:

Somebody on my ride was saying only the other day that
crashes at our age are so much more consequential. Though
they were talking about breaking a hip, I thought of that
when a couple of days later I fell while dismounting from my
bike (I hooked the mixte bar between my foot and its heel)
and landed so heavily that the deep dent in my helmet looks
like the most dangerous accident I've had in 30 years of
cycling -- from a standstill! The helmet saved me from a gash
on the head, painful stitches, and perhaps even a concussion.
That's definitely worth its price.

Andre Jute Not an old crock

Modern safety helmets reduce concussions not by softening the
blow via cushioning with the Styrofoam but by fracturing and
breaking via the "vent" holes in the helmet. I have a Bontrager
Wavecell helmet and it has a lot less vents for two reasons -
1. Unlike Styrofoam air passes rather freely though the open
core material and 2. you have to have the Wavecell material
covering most of your head to have the expected effect.

So my helmet isn't wrecked by the impact-dent?

Separate question. That helmet is actually pretty old, being on
its third bike. Is there a natural raging process (embrittling?)
of helmet materials that requires helmets to be replaced after x
time?

Andre Jute

I think that aging of the foam in a helmet depends on t he foam
material itself plus incidentals such as exposure to sunlight
(UVA/UVB rays)bumps it has suffered and even exposure to sweat. I
have an old hard-shell Vetta helmet here that appears to be in mint
condition. I guess it'd take a microscopic examination of the
underlying foam section to tell if the foam has deteriorated.

Manufacturers like to sell helmets and also protect themselves from
litigation and thus many helmet manufacturers tell customers to
replace the helmet every five years or some other number of years
and also to replace the helmet if it has suffered a hard knock or
fall.

Cheers

Thanks, Ridealot. I'll inspectÂ* the outside shell under a strong
light and magnification for cracks. None are visible with the naked
eye.


In the UK that may not be such a big deal but here in sunny California I
had to retire a helmet because the UV content of the sun light started
to embrittle the shell. It was only about three years old.

Helmet manufacturers used to routinely say every helmet should be
replaced every three years. Why? Because supposedly the magic foam could
be degraded by sunlight, or maybe fumes, or maybe heat, or maybe by
dropping them on the floor, or maybe just age.

It was a nice marketing trick, dutifully parroted by many "safety"
organizations. (And I heard that sledge hammer manufacturers briefly
thought about mimicking it. "Hey! More sales!" But the hammer
manufacturers had more honesty.)

Then some lab tested old helmets. From the world's most rabid helmet
promotion website: "In 2015 MEA Forensic reported on their extensive
testing of used (but not crashed) bicycle helmets shows that the foam
liners retain their performance over many years. Some of the helmets
were as old as 26 years. They crash tested 675 helmets in their lab.
Their analysis showed that there was no significant impact performance
change with age. Their data including all 675 helmets tested produced
only a 0.7g per year increase in impact readings at the higher drop
height. After crash testing the helmets on a standard test rig, MEA took
core samples from an uncrashed area of 63 helmets and tested them. This
generated data based solely on the foam performance. Again, the findings
indicate that helmet liner foam does not deteriorate with age."

So last time I looked, Bell Sports changed its tune. They still said you
should replace your helmet every three years (of course!) but not
because it won't work. Instead, to "take advantage of improvements in
technology and styling" or some such nonsense.

Back in the 1960s, I think it was General Motors who advertised
"Wouldn't you rather have _this_ year's model?" It really meant "We
really want you to buy another car. We need the money."


--
- Frank Krygowski