The tales of fitting a helmet to my oddsized head.

Discussion in 'Equipment' started by SoCalledFreeman, Feb 12, 2020.

  1. SoCalledFreeman

    SoCalledFreeman n00b Supporter

    Nov 20, 2016
    Hey Adventurers!

    Finally wanting to upgrade my aging Shoei TZ-X (Qwest) street helmet to something more dual sport. Had a Shoei Vmoto dirt lid before, both extremely comfy, size L.

    59cm noggin, from above - bit like an egg as per my partner, wider at the back

    Purchased an Arai XD4 was fine initially on short commutes, first proper ride had awful pressure points in between my ears and temple, splitting headache, very uncomfortable ride. Found it much more uncomfortable with my SENA speakers installed, not really a place to put them.

    Tried a Shoei Hornet ADV today, loved the design and features and that there is more of a space for intercom speakers, comfy in the shop but felt a small pressure point above each ear, not sure I want to risk it after the Arai... :(

    Tried Shoei GT air and NXR street helmets, both extremely comfortable, no pressure points.

    Tried a Bell MX-9 Adv sz L, minimal pressure points, fit ok, not super comfy. Not impressed by the visor mech, single layer EPS or plastic construction.

    Has anyone had similar experiences?

    Want to try an Airoh, Nexx, and maybe a BMW GS helmet. Any suggestions?

  2. Guoseph

    Guoseph Been here awhile

    Sep 8, 2011
    Alameda, California
    It sounds like you have more of a round head if you are having pain above the ears. I have the same pain. Most helmet makers for the US market have shifted toward an "intermediate oval" shape that is more of a "one size fits all" rather than the old round vs long shapes that are more defined.

    Arai XD 4 has 2 pieces of removable foam one on each side in the comfort liner that should help if you take them out.

    For me the most comfortable helmet is a Japanese market Arai Tour Cross 3, it is essentially the same as an XD 4 but is a bit rounder on the inside. Must order from Japan and no DOT (yes Snell) if you are concerned about that.

    Good luck on you search, hopefully you will find something that fits your head.
  3. Guoseph

    Guoseph Been here awhile

    Sep 8, 2011
    Alameda, California
    Also I put my Sena headphones inside the cheek pads on the XD 4 and they seem to fit fine without causing additional pain.
  4. SoCalledFreeman

    SoCalledFreeman n00b Supporter

    Nov 20, 2016
    Thanks so much, didn’t even notice those pieces of foam in the liner - tried it today on a short ride, much better! Funny how small things make a difference. Will await the SENA 50S before I make speakers fit into the cheekpad. Cheers!!!
  5. JTerryM

    JTerryM -/\~

    Sep 11, 2014
    Santa Cruz, CA
    Also, you can buy thinner liners and cheek pads for Arai helmets from the usual vendors. If your helmet is a large (shell size III) it would come standard with a 7mm thick liner, and 5mm thick liners are available, which also have the removable foam pieces making them even thinner. Likewise with cheek pads.

    Screen Shot 2020-02-13 at 11.32.34 AM.png
  6. Guoseph

    Guoseph Been here awhile

    Sep 8, 2011
    Alameda, California
    Glad that helped a little bit. I feel your pain. My head is almost square and lately it's been harder and harder to find proper fitting helmets. When I take long rides I make sure to get my hair cut short above my ears for the extra mm of potential comfort.
  7. S/W

    S/W Long timer

    Oct 21, 2003
    Maybe some company will do what Bell helmets was doing. Scan your head and make the helmet for you. I got one of those custom helmets and it fit perfectly. Unfortunately Bell stopped making them. They cost around 1000 bucks, and few people will spend that much. With my long oval head, it was the first helmet I had in fifty years of riding that fit properly and is very comfortable. In a couple of years my "Custom Fit" helmet will be due for replacement, I hope the technology doesn't sit dormant. PLEASE, someone make affordable custom helmets!!!!!!!

    S21FOLGORE Been here awhile

    Jul 17, 2011
    San Rafael, CA
    If you tend to have painful hot spot on the side of the head, I'd recommend to measure your head CI.

    Here's a part of the stuff I wrote a while ago.


    Anatomy Lesson

    Head shape classification

    Anatomical terms for the three types of the head shapes (that we know as, Long oval, intermediate, and round)

    Dolichocephalic (long head : what we call “long oval” head)

    Brachycephalic (short head : what we call “ round head”)

    Mesocephalic (intermediate)

    The head shapes are classified by

    Cephalic Index = x/y × 100
    (CI = (bipareital diameter or BPD, side to side measurement) / (occipitofrontal diameter or OFD, front to back measurement) ) × 100

    click on the picture to see larger image
    [​IMG][/url]Hot spot 18, on Flickr

    CI < 75 (female) 75.9 (male) is Dolichocephalic
    CI 75 to 83 (female) , 76 to 81 (male) is Mesocephalic
    CI > 83 (female), 81.1 (male) is Brachycephalic

    Note : There’s a difference between male and female skull. That's why the numbers are different for male and female.

    What matters for helmet fitment are

    Smooth, more vertical frontal bone (forehead) on female skull

    Male skull has more angled (tilted back) forehead

    Rounded chin (female skull) vs Square chin (Male skull)

    The more blocky and massive cranial mass on male skull vs rounder and tapering at the top female skull

    Male skull have a deeper cranial structure

    (I should probably explain the difference between caucasoid vs mongoloid skull shape , but let me keep on explaining about round head hot spot problem (pain on temple area) for now.)

    (There’s also CRANIAL INDEX, which is essentially the same thing except for the fact that it uses the measurement taken from the skull.
    For the people who deal with live human’s head (such as helmet manufacturers), Cephalic Index (which takes flesh and skin in account) is the one that matters.
    For the people who deal with the skull (such as forensic artist), Cranial Index (which takes shrinkage of the dried bone in account) is the one to use.)

    Now, this Cephalic Index would have been really useful if the helmet manufacturers had used this, to indicate the internal shape of their helmets.

    Helmet for the round head

    For example, Arai Quantum-X, supposed to be the most “round head friendly” helmet in U.S. market, would only work on the head with CI around 80 to 85.
    I can tell, because my own head’s CI is 89, which is almost extreme end of Brachycephalic head, and Quantum-X is nowhere near as round head friendly as RX-7 -X (which is the JDM version of Corsair -X.)
    If your head’s CI is greater than 85, even with Quantum-X (which Arai calls “round oval” helmet), you need to go one size up.

    Instead of just saying “round-oval”, if Arai had said “Quantum-X ; round-oval shape, fits Cephalic Index 80 to 85”, it would have been much clearer. (Of course, they need to educate their potential customers, by explaining what Ci is. But, this will greatly reduce the hassle of buying a new helmet.)

    AGV AX-8 Evo has egg shaped internal, and runs a little bit on the large side. But they have a lot thicker, plush crown pad in there.
    The result is the helmet that works for the wide range of the head shape. (AGV GP-Tech was such a helmet also.)
    I would say it (AX-8 Evo) works on the head with CI 75 to 85, even up to 90 so long as your forehead isn’t really wide.
    (If you have wide, flat forehead and the CI is around 88 or over, it wouldn’t work.)

    But, the hard, cold fact remains.
    The true round head helmet is virtually non existent in today’s North American market.
    NON of the helmet that are officially sold in US are designed for the head with CI greater than 85.

    So, .... is there any option, other than going one size up, for the people who’s head CI more than 85?

    Yes, there is.
    Well, .... sort of.

    ... to be continued.

    Firs, let me show you this rather interesting data.

    Brand∙∙∙∙∙Model∙∙∙∙∙∙∙∙∙Market∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙internal width / internal length × 100

    Arai ∙∙∙∙∙Rapide SR ∙∙∙∙∙∙Japan ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙86

    SHOEI ∙∙∙X-14 ∙∙∙∙∙∙∙∙∙∙ Japan ∙∙∙∙∙∙∙∙∙∙∙∙∙∙stock 86 / with thinner side pads, thicker back pad 93

    AGV ∙∙∙∙GP Tech ∙∙∙∙∙∙∙∙∙US∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙96

    Schuberth∙∙C3 Pro ∙∙∙∙∙∙∙∙∙US∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 80

    Arai∙∙∙∙∙∙RX-7-X ∙∙∙∙∙∙∙∙Japan∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙86

    Arai ∙∙∙∙∙Quantum-X ∙∙∙∙∙∙∙US ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙84

    Suomy ∙∙∙SR Sport ∙∙∙∙∙∙∙∙∙US∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙78

    Arai ∙∙∙∙∙RX-Q ∙∙∙∙∙∙∙∙∙∙∙∙US∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙77

    AGV ∙∙∙∙AX-8 Evo ∙∙∙∙∙∙∙∙∙∙US ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙94

    Some of them are now getting pretty old.
    However, you can see, Arai & SHOEI ‘s JDM helmets are designed and built for the CI 85+ type of head, and it hasn’t changed over time.

    IF you know your CI, and it happens to be greater than 85, you will get a better, a lot better fit from JDM helmet.
    (Most probably, you have been wearing one size bigger helmet, or suffering the painful hot spot. For example, I can wear helmet with width / length ratio 78 helmet, but it will hurt after an hour or so.)

    Some interesting stuff you can learn from this info

    RX-Q wasn’t really that “round” as some people believed.

    C3Pro, while it is definitely not a long-oval helmet, it isn’t really round helmet at all, as some people believe.
    (It’s just that they tend to run small, which means they are too short front - back for the size.)

    Arai’s JDM full face has consistent width / length ratio over the decade (always around 85, 86).
    With their center pad (crown pad) design, which has two layers of removable foam on the side,
    You can change it close to 90. (around 88, 89. If you still need more room at the side of the head after removing these peel-away sponge, you can use “leather punch” technique I described earlier. )

    You can also change the center pad to thicker or thinner one.

    SHOEI X-14 has the best liner system as far as the adjustability (for the different head shape types) is concerned.
    You can adjust it (JDM X-14) from 80 to 96. AND it’s very easy to do.

    Very interestingly, AGV occasionally produce the helmet that works for the round head.
    (But, the majority of their line up is not for the round head.)

    So, the decision is up to you.

    Anything you can try locally, it WON’T fit if your CI is more than 85. (Unless you go one size up.)
    Anything you can buy from Revzilla / STG (so that you can return them easily) WON’T fit, either.

    You know the helmets for the CI>85 head is available, but it has to come from the other side of pacific ocean.
    There’s no way you can try them on before purchasing,
    Even though you can return the item , exchange for different size / model, you want to avoid that.

    What to do?

    Sending a detailed e-mail to the customer service of online vendor in Japan, telling them your CI and asking if this ZZZ helmet you’re interested would fit your head will not help.
    You only get reply that says to look at the manufacturer’s sizing chart.

    ... to be continued...


    To OP,
    Some models, helmets fit differently depending on the labeled size.
    (Just because size M fits in certain way doesn't mean size L also fits in the same way.)

    The untold story of fitment, shell size and liner thickness.

    (I’m going to use round heads (CI ≧ 85) as an example here. But, what I’ll explain applies to all type of head / helmet internal shape.)

    Example story


    So, you are in between the sizes, S and M.
    You have been advised by people on the internet forums and by people at the local shop.
    “Go for a smaller size, because the helmet (internal) will break in / stretch / mold onto your head.”

    You believed that advice and purchased size Small instead of Medium.

    You go for a ride happily with a brand new helmet ...


    ... and an hour later, you get unbearable pain on the side of your head ...


    Sounds familiar?

    If you have been riding many years already, tried more than a few different helmets and still get the hot spot on the same area, then you are either ...

    wearing the wrong shaped helmet

    wearing the wrong sized helmet

    ... or, could be doing both ...

    You came across this thread, and measured your head’s front-back, side to side, and it turned out that you have CI 88 head.

    So, now you know you have two problems.

    The first problem is CI.
    The helmets that you can buy locally, or from Revzilla, STG, etc, are all designed for the CI<85 head.

    Knowing that JDM Arai / SHOEI are CI 85-86 helmet as a standard (can be tuned for higher CI), you decided to give it a shot.

    But now, you are facing the second problem.

    You are in between S and M size.

    Which one should you order?

    For obvious reason, you don’t want to end up ordering the wrong size and shipping it back to Japan, reordering the different size.

    How do you decide the size when actually trying it on is not an option?

    4-shell size vs 2-shell size helmet

    Would you be surprised if I tell you that, with some helmet, the fitting is quite different from size to size?


    Let’s take a look at two examples.

    SHOEI X-14 VS OGK Kabuto RT-33

    X-14 4-shell size


    RT-33 2-shell size


    First, let’s take a look at X-14.
    They come in 4 different shell sizes, 5 different EPS liner.
    S(S and XS use the same shell), M, L, and XL (XL and XXL use the same shell).



    The relationship between the shell, EPS liner, comfort liner, and the available inner space of the helmet is the same all across the sizes, except for XXL.

    Except for XXL, all the helmet comes with 9mm thickness comfort liner as a standard, and you have options to go either thicker (+4mm) to make the fit tighter, or thinner (-4mm) to make the fit looser.

    Each size of the helmet (except for XXL) has the same amount of tolerance / limitation for irregular bumps and slightly oversized head.

    To put it simple, M is the scaled down copy of L, and S is the scaled down copy of M, they all have the same amount of space for fine tuning.

    Now, RT-33, which comes in 2-shell size.

    It uses the same shell for XS, S, and M. And L, XL, XXL share the same, bigger sized shell.

    Now, look at the picture below, pay particular attention to the liner thickness and the helmet labeled size.



    Yes, you guessed it right.

    Size XS, S, and M are THE SAME HELMET with different thickness comfort liner installed.
    And size L, XL, XXL are the same helmet, the difference is just the comfort liner thickness.

    With this type of helmet, it is a little bit tricky to choose the size.

    If you happen to be between the S and M size, you should order S, NOT M.

    You have 15mm thick foam surrounding your head, that’s a lot of cushioning, and that will tolerate the slightly oversized head (56.5 cm) without problem, even if your head has some irregular bumps, bulges, etc.

    BUT, if you are in between M and L, then, you’d better get L.

    Why? I don’t want a bigger shell size ! You just said “L” size helmet use the same shell as XL an XXL, that would make me looking like a bobble-head figure!!

    Well, I (sort of) understand the feeling, but take a look at the fig. 20 again.

    RT-33 in size M comes with the 2nd thinnest (9mm) comfort liner. (thinnest being 5mm on XXL).

    Size M comes with the least amount of tolerance(extra space), besides XXL, for irregular shapes and oversized head.

    If your CI is 88 for example, and circumference is 58.5 cm, I can almost guarantee you that you are going to get painful hot spot on the side of your head with size M.

    IF your head shape is slightly off (eg: CI 87, 88) BUT the correct size (between 57 and 58 cm), then M will work.

    Or, if the head shape is correct (CI 85, 86) but circumference is slightly greater (58.5 cm), them M will work also.

    However, when both the shape and the size are off at the same time, you can’t go for smaller size.

    So, I hope you now understand the “multiple shell size” is NOT for the looks, but for function.

    Also, I hope you understand now, that why some helmets cost more than the others.
    (Just making 4 different sized molds for shell, and 5 different mold for EPS liner would easily make X-14’s production cost more than twice the production cost of RT-33.)

    Oh, by the way, the same rule applies for multiple shell sized helmet, when it comes to sizing.

    If you happen to be in between the sizes, you can go for a smaller one
    ONLY IF your CI is close enough(±1) to the helmet’s target CI.

    Otherwise, you’d better order the larger size.

    One method that works (for only Arai and SHOEI) for size checking is to use genuine issue boonie hat.
    Go to the military surplus store and try them on.


    The brand doesn’t matter, as long as it’s made to proper specification which is MIL-H-44105B.

    For example, the size 7 is 55.9 cm. If the size 7 feels too tight, but next size which is 7-1/4 (57.8 cm) fits alright, you should get M, instead of S.
    If 7-1/2 is too tight, you should get XL, not L.

    You know, boonie hat does not stretch, so you should be able to tell clearly if it’s too tight.

    Full thread is here

    I wrote in the original thread, if your head CI is greater than 86, you will NOT find a helmet that fits your head properly.
    Because NONE of the helmets that are officially sold in US has internal shape made for CI>85.
  9. flei

    flei cycletherapist

    Apr 1, 2013
    Western Mass.