【週刊一宮】NEWヘルメットサイズ選びの方法、今は周長はいらない？？

How to Choose a Helmet Size

The video updates earlier advice on helmet fitting. Its main message is that head circumference alone is not a reliable way to choose a helmet. Fit should be judged by head width, front-to-back length, height, and shape—and, most importantly, by trying the helmet on.

Key Points

• Circumference is only a rough reference. People with the same head circumference can have different head widths and lengths. The speaker notes that Japanese heads are often relatively wider, while European head shapes tend to be more elongated.
• A larger size can be misleading. Some helmets have narrow openings and may feel difficult to put on. Riders can mistake that initial resistance for a helmet that is too small, choose a larger size, and then find it loose.
• The ideal fit is snug and evenly supportive. The helmet should make good contact around the sides, forehead, and back of the head, without painful pressure or excessive movement. Check for gaps at the top, since head shape and height can create pressure in some areas and space in others.
• Fit varies by model, even within one brand. Interior shapes and padding thickness differ. The speaker says the SHOEI Z-8 fits him well in M, while another model might require L for someone with the same measurements. The SHOEI X-15 is described as running small, so someone who usually wears M may fit S.
• Measurements and size charts cannot guarantee a match. One example gives measurements of 195 mm front-to-back and 163 mm wide. A calculated circumference of about 57 cm could suggest a size that ultimately feels loose. The speaker advises against relying on circumference alone.
• Fitting and adjustment matter. Arai and SHOEI offer fitting services, where staff can adjust padding or help find a more comfortable size. The speaker gives examples of fitting one helmet in L, while another is too painful in L and requires XL.
• Fit matters more than the nominal size. Helmets are expensive, and although prices may rise slightly, choosing a helmet that fits properly is more important than choosing by the size printed on the label.

User Experience: Advantages and Challenges

Advantage: Professional measurement, trying on helmets, and padding adjustments can help achieve a safer, more comfortable fit.

Challenge: Fit depends on both the rider’s head shape and the specific helmet model. Even experienced staff may find some heads difficult to fit.

Practical recommendation: Visit knowledgeable staff, try on the helmet, and discuss pressure points or gaps rather than sizing by circumference alone. The shop says it can measure customers and suggest several options.

Views from the Speakers

• Ashida, the fitting specialist: Explains why circumference is no longer the primary sizing guide, how head shape affects fit, and why models can fit differently. He recommends professional fitting services.
• The host and shop staff: Encourage riders to consult trained staff and find a helmet that makes riding more enjoyable.

Verdict

Choose a helmet through a model-specific fitting and try-on—not by circumference or the size printed on another helmet. The video gives no product rating or numerical score.