It’s assumed that head shapes very roughly follow a standard distribution and, when plotted, probably follow a “bell” shaped curve.
Of course, this is only a supposition, but it’s based on a detailed study of motorcycle helmet fit, evaluating over 120 helmets and discussing the topic with hundreds of motorcycle riders over the past 10 years.
Frequent webBikeWorld visitors know that we sometimes use this analogy to describe helmet fit, and our 7 helmet fitment types were derived from the Gaussian function:
This is not an exact science.
Sizes and shapes are not consistent between brands or even helmets of the same brand.
Shapes can vary between different sizes of the same helmet.
Fit is different as helmet sizes change.
Manufacturers may change the internal shapes over time.
Human head shapes vary considerably and individual features make helmet fit difficult.
From “L.L.” (April 2015): “Not sure I trust your analysis of the helmet shapes. I have a Shark Evoline (first gen) an HJC Sy-max (first gen) and both are either round or lean heavily in that direction. Both fit perfect (size small).
I recently tried on an HJC Sy-Max III in a small and could not hardly force it on my head. I then ordered a medium and it was way too tight also (head size 56 cm falls into the sizing guide of small). I wore it for an hour and had terrible pressure points and had to return it.
I called RevZilla and they said the new Sy-Max III is definitely oval shaped but the old Sy-Max was round. The are obviously correct. You list all three (I, II, and III) in the same category, leaning toward round, which they aren’t and you list the Shark Evoline leaning more toward the oval by one category, which it isn’t…it’s just as “round” as my old Sy-Max.
That sure makes it hard to buy a helmet online as it seems more run toward oval now than toward round. I’m going to try a G-Max G54 next, then the Speed and Strength SS1700 last (as that was recommended as a round helmet) but you don’t list either of those.”
Editor’s Reply: You bring up an interesting topic. There are several issues here; first, each head shape is different and the listed internal shapes are general guidelines. Slight differences in actual head shapes can and do change the way a helmet fits.
There just is no absolute guideline when it comes to finding the correct fit. This is why we always tell people to try as many helmets as possible and in different sizes. That’s the only way you’ll really get a good “feel” — and that’s what it is — for which helmets fit.
Another thing, the manufacturers definitely change internal shapes over time and sometimes even during a production run. We have reported recently that many of the manufacturers — like Arai — have moved towards a more “neutral” internal shape. So the helmet shapes may have changed since the webBikeWorld review was published.
And head size matters when it comes to evaluating the internal shape. The shapes are much more noticeable when you try one size larger than normal, because the padding isn’t as tight and it lets you feel the inside of the helmet.
And one manufacturer’s idea of a size “M” may be different from another manufacturer’s. Some manufacturers use different sizes for S, M, L, XL, etc. Example: SCHUBERTH uses a non-standard jump between their size L and XL. All of this means that the head size also matters when you’re evaluating the internal shape.
The internal shape can feel quite different, depending on which size helmet you’ve tried, which brand and even which model. Each helmet has particular quirks and sometimes you have to move up or down in a size range, which will either mask or amplify those quirks and pressure points.
You say you have a Shark Evoline and HJC Sy-Max and “both are either round or lean heavily in that direction”. We listed those as neutral to round, so we’re in agreement there. The Sy-Max II and III we listed as “slightly round”.
But the shell stiffness and construction were changed as the Sy-Max evolved, thus a more modern Sy-Max feels different than the previous versions, because the shell may not flex as much or in the same way. This can mean that a head size that is borderline or that has some slightly non-standard shape will suddenly feel tighter, as you report.
I don’t know about the RevZilla folks, but I’d bet for sure that a phone rep hasn’t worn and studied the 325+ helmets we have over 15+ years.
Bottom line? As you can see, this is a very complex issue with many variables. If we knew exactly how to match a helmet to each rider’s individual head shape, that would be fantastic…and it would also be called a miracle!
I can also sympathize completely. I apparently have a unique head shape and it has always been very difficult to find a helmet that fits perfectly.
From “H.S.” (December 2014): “Read every test for round heads. From Quantum II (discontinued, fragile visor) through the Vemar Geo (no spare parts in US, Motonation ceased support). What is your editor’s round head wearing or recommend for a street bike helmet? Didn’t know if your chart is up to date. Modular or full face with internal visor preferred. There is an eBay seller offering a new Vemar Geo for $150 shipped, but the lack of cheek pads, liners, visors, etc. is a big issue for me.
Editor’s Reply: The chart is always kept up to date, the problem is there have been almost no “Round” helmets released in quite some time. Most of the manufacturers, including Arai, have gone to a “Neutral” shape.
I always have problems because my head is wide at the temples. I’ve been wearing a SCHUBERTH SR1 (review) lately, which (surprisingly) fits pretty nicely, although it’s ridiculously expensive.
I’ve heard that the helmets sold in Japan for the Japanese market tend to fit “Round” heads, but not sure if that helps. You might be able to custom fit an Arai RX-Q by changing out cheek pads and/or liner.
If you find anything, let me know!
From “T.R.” (April 2013): “Man I can’t thank you guys enough, your helmet shapes article and information is awesome for a “long and narrow” who has struggled through the years to find a helmet that fits. I’ve been hanging on to dear life to my 2001 Arai Quantum F thinking I would never find another helmet that fit by silly oblong head! Now you’ve given me some options that I’m really excited about!”
From “D.A.” (April 2013): “Many thanks for your head shape information in your helmet reviews. I have sought out and purchased X-Lite X901, Shark RSI, and SCHUBERTH R1 and S1-Pro helmets based on this information. In the cases of the Schuberths, I have had these shipped over from Europe, sight unseen, and they fit my head shape perfectly. Thanks again, keep it up!”