I want to buy a helmet but my head size seems to be one that none are made for. My size is between 54 and 55 and checking the sizes available for helmets shows that I should go for M. But helmets are not designed in all head sizes. For example Giro has a range from 54 to 59, if I were to buy that helmet, it would wobble when placed on my head. Does anyone have any experience on whether wearing a loose helmet held in place only by the straps provides the same protection as a perfectly fitting helmet.

Any suggestions on what I should do if I bought this 54-59 helmet. Thanks a lot.

Have you tried any of them on?

I always buy the universal fit helmets and just adjust the ratcheting mechanism.

But what about the space between your head and the helmet. On the web, they all say, buy a helmet so that if you shake your head up and down and sideways without the straps it doesn't fall off. Wouldn't that happen with the new Universal adult fit that are being sold.

The Giro Reverb uses an elastic band along with the chin straps, so it fits pretty snug.

I'm using a medium. It's tight when I add my fleece cap (it was 32F this morning).
I can't speak for the other models.

I don't know about "universal fit", but my Specialized helmet has both the quick strap adjustment dial and foam pads that affix with velcro. Those pads came in different thickness, IIRC.

That is what the ratchet mechanism does. It tightens the helmet to your head.

There will always be space between your head and the helmet.

Go to a store and try some on. Play with the adjustments.

Ooookay, I've recovered from the dizziness of shaking my head up and down and sideways. My Bell Impulse (with Bell's superlative universal True Fit system) stayed right where I put it, without fastening the straps the way I certainly would when wearing it on a ride.

Remove your hands from the keyboard, step away from the computer, and go try on some helmets.

Assuming you buy one within the ratchet's adjustment range, it will be tight enough... Also, having some extra room is good so you can wear a cap or headband or beanie.

Seemed Bell oval was a bit rounder, Giro narrower-longer..

Anyhow, .. Bell Sports owns both brands, now..

Kind of like buying shoes...go to the store and try on. Buy one that fits. I always have either a headband, lycra cap or balaclava under my helmet, so if you plan on the same, don't get one that is too small. The ratchet is an absolute essential if you plan to ride with helmet lights in order to snug up sufficiently to hold in place with the extra weight. Forget the MTB visor, which is totally uncool.

This.

Yeah, except maybe I shoulda put a smiley at the end.

This. It's not like buying a motorcycle helmet where you either fit in a Shoei or an Arai. Adjust the adjusters until it feels right and then go ride.

Nutcase helmets are sold in three sizes (kids, small, large) and in addition to the ratchet include three different thicknesses of pads. I wound up mixing thicknesses to get the right fit.

The pads do come in different thicknesses, and I have a bunch of thin ones left over from the bike helmet giveaways I've done. PM me if anyone wants any.

... and I've heard that Catlike (might be out of your price range) tend to be deep.

Just like all other forms of apparel, different manufacturers have their own take on a particular size.