Abstract
Traditional motorcycle helmet performance standards provide a test for the strength and stiffness of the retention system. While such tests assure adequate strength, they do not assure that the helmet will be retained in place on a motorcyclist's head, even when securely fastened. The reason is that the geometry of the retention system can allow the helmet to roll off when contact or inertial forces are generated in a collision. This ejection of motorcycle helmets during accident events has been widely noted by various researchers.
Different types and styles of motorcycle helmets were tested to determine the susceptibility to roll off, i.e. “positional stability”. Tests were performed with two commonly used adult sizes of headforms corresponding to standards of the U.S. Department of Transportation (DOT) and the International Standards Organization (ISO). The laboratory test results were validated by comparable tests on one hundred human subjects. The results of the human subject tests show a meaningful relationship to the laboratory test that employs a 10kg mass dropped 60cm to jerk the helmet forward to cause it to roll off.
The results show that the geometry of the helmet retention system has a powerful effect on the ability of the helmet to resist forward roll off in both laboratory and human subject tests. Also, there is considerable difference in the retention characteristics between DOT and ISO headforms, with the DOT headform more closely corresponding to human subject data.
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