Factors Affecting Motorcycle Helmet Use: Size Selection, Stability, and Position

<p><b>Objectives:</b> One of the main requirements of a protective helmet is to provide and maintain appropriate and adequate coverage to the head. A helmet that is poorly fitted or fastened may become displaced during normal use or even ejected during a crash.</p> <p><b>Methods:</b> Observations and measurements of head dimensions, helmet position, adjustment, and stability were made on 216 motorcyclists. Helmet details were recorded. Participants completed a questionnaire on helmet usability and their riding history. Helmet stability was assessed quasistatically.</p> <p><b>Results:</b> Differences between the dimensions of ISO headforms and equivalent sized motorcyclists’ heads were observed, especially head width. Almost all (94%) of the helmets were labeled to be compliant with AS/NZS 1698 (2006). The majority of riders were satisfied with the comfort, fit, and usability aspects of their helmets. The majority of helmets were deemed to have been worn correctly. Using quasistatic pull tests, it was found that helmet type (open-face or full-face) and the wearing correctness were among factors that affected the loads at which helmets became displaced. The forces required to displace the helmet were low, around 25 N.</p> <p><b>Conclusions:</b> The size of the in-use motorcycle helmets did not correspond well to the predicted size based on head dimensions, although motorcyclists were generally satisfied with comfort and fit. The in vivo stability tests appear to overpredict that helmets will come off in a crash, based on the measured forces, tangential forces measured in the oblique impact tests, and the actual rate of helmet ejection.</p>