On Sep 9, 8:37*pm, "MikeWhy" wrote:
Phil W Lee wrote:

Utter bull****.
If cycle helmets met the same standards, don't you think some
motorcyclists would be wearing them?

Not bull****. Look it up if you can figure out Google. Motorcycle helmets
have additional criteria not specified for bicycle helmets, including
coverage area and involving the chin bar when present. Retention criteria
are also more stringent. Impact loads and survivability, however, are
essentially the same.

A funny thing happens when one actually looks up what MikeWhy claims.
Specifically, they find that MikeWhy is either mistaken or lying.

Here's an article that discusses motorcycle helmet testing standards
in detail. (I've got it bookmarked.)
http://www.motorcyclistonline.com/ge...iew/index.html
or http://tinyurl.com/zglbq

What it says? "The killer—the hardest Snell test for a motorcycle
helmet to meet—is a two-strike test onto a hemispherical chunk of
stainless steel about the size of an orange. The first hit is at an
energy of 150 joules, which translates to dropping a 5-kilo weight
about 10 feet—an extremely high-energy impact. The next hit, on the
same spot, is set at 110 joules, or about an 8-foot drop. To pass, the
helmet is not allowed to transmit more than 300 Gs to the headform in
either hit."

Later, it says: "Where the Snell standard limits peak linear
acceleration to 300 G, the DOT effectively limits peak Gs to 250.
Softer impacts, lower G tolerance. In short, a kinder, gentler
standard."

I'm not sure about that "effectively." According to
http://www.smf.org/articles/mcomp2.html
DOT limits acceleration to 400 gs, but from a drop height (for a large
helmet) of about 7.35 feet, or 2.25 meters, which corresponds to 110
Joules for a 5 kg headform mass.

By contrast, the CPSC bicycle helmet standard calls for just a two
meter drop. It allows 300 gs acceleration of the same headform. The
standards are NOT the same.

Furthermore, the motorcycle helmet standard has much more rigid
penetration tests. This is what drives the design of their heavy,
hard shells. And this is pertinent, because a heavy, hard shell is
less likely to get traction with the road during a tangential impact,
and is more likely to have significant rotational inertia, to aid in
reducing the brain's rotational acceleration. This might be
considered an accidental benefit, because penetration of any helmet is
rare, but rotational brain accelerations are now commonly recognized
as being more likely than linear ones to cause serious brain injury.
(Still, NO helmet standard tests for them!)

What's even more enlightening is that article's discussion of the
effect of various acclerations: "Newman is quoted in the COST study
on the impact levels likely to cause certain levels of injury. Back in
the '80s he stated that, as a rough guideline, a peak linear impact—
the kind we're measuring here&151of 200 to 250 Gs generally
corresponds to a head injury of AIS 4, or severe; that a 250 G to 300
G impact corresponds to AIS 5, or critical; and that anything over 300
Gs corresponds to AIS 6. That is, unsurvivable."

Bike helmets are designed to attenuate the acceleration of a
decapitated human head - no body attached - to 300 gs in a 14 mph
impact. 300 gs is the borderline between critical and unsurvivable,
according to that estimate. And that doesn't take into account
rotational acceleration, which is worse in its effect, and which
helmets may exacerbate (by their larger diameter and higher friction
compared to a bare head).

So leave the cyclist's head attached to his body, subject him to a
head impact greater than 14 mph, include a slight tangential component
to the impact, and you've blown away the "protection" of a bike
helmet.

Is it any wonder they haven't been shown to reduce serious head
injuries?

- Frank Krygowski