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This question was posted on the excellent BikeHacks website:

I don't have a hack, but a question. My head measures 66cm. I can't find a helmet that fits. Even ones that go to 66cm are too small. I've considered looking into motorcycle helmets. Any advice?

big helmet

I'll post a link to this question under the blogpost.

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Note for the future: if you use the "link" under the question that has 2 numbers in the URL, you get credit for people following the link that can earn you a badge (and this week helps you in the contest). – freiheit Nov 30 '11 at 18:01
My upvote is purely for the question and not at all for the photo of Lord Dark Helmet. Nope, nope, not at all. – Neil Fein Dec 1 '11 at 7:44
@freiheit I just got that badge :) – Hugo May 11 '15 at 6:56
up vote 4 down vote accepted

Try multiple shops. Try multiple brands and models.

Head shapes vary, so it's possible that one "66cm" (26in) model will be too small and another "66cm" model will fit. It's worth trying multiple shops since most shops will only stock one or two brands of helmet and only carry one model intended for larger heads. Having an idea whether your head is long or wide might help. It's hard to measure your head properly with a measuring tape, however.

The Bicycle Helmet Safety Institute website has a page about helmets for large heads that gets updated when new models come out. It seems that 66cm is the largest size for bicycle helmets.

If you can find any sort of multiple options, a helmet that fits lower on your head and wraps more around the sides and back is better than one that perches on the top of your head.

If you can find a motorcycle helmet that fits, that should provide as much or more protection as a bicycle helmet. I believe motorcycle helmets are measured against a higher standard. The problem with motorcycle helmets is that they're heavy and tend not to have as much ventilation as a bicycle helmet, so it might be uncomfortable.

Note on sizes: 66cm = 26inches = XXXL = 8 1/8 UK = 8 1/4 US = 9 1/2 FR. Those last few are hat sizes, but many helmets seem to have the hat size type sizing info easier to find. Look for helmets with those sizes or larger.

I have big head issues, but luckily most of the big-head helmets do fit. I've had good luck with the "Specialized Max" line even though the official sizing printed on it is smaller than my hat size. I think they're a more rounded rather than circular shape on the inside and that makes all the difference. I'm not recommending this model for you, however, I'm recommending you check out the big helmet options at multiple shops.

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Check out this post from Bicycle Helmet Safety Institute. Helmets for Large Heads

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Welcome to Bicycles! This may theoretically answer the question, but it would be preferable to include the essential parts of the answer here, and provide the link for reference. – freiheit Dec 1 '11 at 21:20

I'd look for a ski helmet at your own risk (or roller skating, or horse riding, before a motorcycle helmet).

Then again, I quit wearing a helmet altogether in the height of summer.

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I have a large head and Fox XLs are nice.

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Welcome to Bicycles.SE! Whilst your post answers the question, the second chatty, forum style comment has been deleted. – Gary.Ray Dec 1 '11 at 5:44

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