Horsepower and Torque
Why wear a helmet?
Headlight Modulator Law
Riding in Europe
25kW (34HP) Motorcycles
|Timberwoof's Motorcycle FAQ
In August of 2004 some friends and I took a ride from San Francisco up to Sacramento to visit Snell Labs where they test helmets.
Snell Laboratories test helmets for motorcyclists, car racers, skiers, and bicyclists. Compliance with the program is voluntary. Manufacturers agree that once the initial tests are complete and certification is issued, Snell Labs will randomly buy helmets at retail, test them, and bill the manufacturer. If any helmet fails the test, that model will lose its Snell certification.
The tests are all done the same way on test jigs built for those specific tests. Thus they are objective and repeatable.
The first step in the testing process is to measure the helmet's face
opening to show that it does not interfere with peripheral vision. A headform
is inserted in the helmet and rulers formed to the minimum view angles
are held to its "eyes". As long as the edges of the opening
don't interfere with the angle-forms, it passes.
Then the helmet is marked according to the locations of the official
testing area. Manufacturers and Snell Labs agree that it is difficult
or impossible to provide the necessary impact protection at the very edge
of the helmet, so the minimum area of protection is marked. Anything within
that area is fair game. The engineers at Snell Labs are experienced in
what will typically fail, so they aim for those parts.
First they test the helmet's chin bar. Basically a weight is dropped
from a specific height and the deflection of the chinbar is measured.
It is not permitted to bend inwards more than 60 mm (2 3/8"). This
particular helmet, in for initial certification, failed the test. Snell
will notify the manufacturers of their findings and let them submit another
one when they've redesigned it.
The next set of physical tests are the chin-strap tests. They make sure
that the helmet will not roll off and that the chin strap has the correct
strength. For the pull-off tests the helmet is attached to a headform
and a calibrated weight, attached to a strap, is dropped in a way that
tries to pull the helmet off the headform. The helmet is tested twice,
for a forward and a backward pull-off. If the helmet comes off the headform,
it fails the test.
A guide is hung from the chin strap to make sure that it does not tear
off its mounts or stretch too much or too little.
Then the helmet is placed on another headform, this one weighing 5.5
kg, and dropped onto two different targets from a specified height. The
headform contains an accelerometer which measures the impact. The Snell
standard is that the maximum deceleration from impact must be less than
300G. The headform with the attached helmet is attached to a frame which
is lifted up into a hole in the ceiling. The guide wires ensure that the
helmet drops in a predictable way. The speed at impact is measured by
an optical sensor, the red thing at the right side of the second picture
The helmet made quite a loud noise when it hit the anvilwe all cringed. This particular helmet got dropped about four or five times onto the same spot, just to see what would happen. Surprisingly, even though it was visibly damaged after the third drop, it still met the test requirement. (Nevertheless, it had reduced protection after the first drop.) The tester told us that when a helmet fails the test, you can feel it through the floor of the building.
A motorcycle helmet works by crushing the expanded polystyrene (EPS,
or Styrofoam) layer, absorbing and slowing down the impact. If a helmet
doesn't slow down the impact, the energy gets transmitted to the skull
and brain inside and to whatever it hits.
Unfortunately at this point I ran out of film. The second roll is still in my camera. When I get those developed, I will add the photos here. Do come back and check ... the second roll justifies me using my old Canon. There are pictures of the drop-test instrumentation, the dimples in the paint on this helmet, and the visor-test rig.
After the tour of the laboratory, we asked some questions.
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