Hey, guys. I stumbled upon the site and the discussion while on one of my bi-annual googling sessions for helmets one can comfortably wear with dreadlocks. It's probably redundant now because of the intro, but my conclusion remains the same as it has been for the past 8 years: there is no decent option. There are some half-decent ones and a couple of utterly appaling, however no motorcycle helmet is designed to be worn over dreads or anything that changes the shape of your skull or neckline.
For example: myself, I found it impossible to wear full-face helmets, for two main reasons. The first is that I have rather thick dreads and, since they mainly sit on the sides and back of neck, this pushes the helmet up and to the back and leaves you with two choices, equally unacceptable: either let it push against your forehead and lower jaw and be in atrocious pain for most of your ride, or go several sizes up (not just one, mind you) and end up with something that feels more like a bucket in terms of fit and noise reduction - also defeating its own purpose. The second is that the same thick, long dreads, if worn loose underneath a full-face, will itch like crazy if you're wearing anything less than a full suit with balaclava.
Instead, I chose to wear a half-helmet, which, while admittedly not nearly as effective as a full face one, at least is something I feel comfortable riding with. Of course, it still needed to be two sizes up and looks a bit weird - but at least on halfs you get much more options in terms of fashion (I'm guessing few fellow dreadheads would enjoy the typical racing look of most full face helmets) . Mine has denim on top (true denim, not paint - over the years it got to look like a well-worn pair of jeans:)
The other option (a good compromise between the first two) is what we call here a "flip-up" (dunno if it's the same in the States), which is nice if you need the wind protection (not the impact, though) of a full face for highway or short trips, but would rather have an open face in the city or otherwise (mostly that, since the squeezing issue still applies). So it's nice, if you don't mind looking like a cop back here:)
There's also a unique helmet from Schuberth, called the J1. which is essentially a half helmet with a steel chin bar to offer protection against chin impacts. Never tried it, am willing to bet that it's extremely effective (like all Schuberths), wouldn't wear it in a million years.
That's about it. I guess another downside is that if you ride a lot (I get about 15k a year), you will end up getting flattened dreads on the temples (if they're thick). Upside is that you will still be about the nicest looking thing on the road:)) helmet or not (preferably the former).
Oh, and one more thing: as I said, I've looked long and hard for a solution for this, and it's still half-assed. If you look closely at the issue, you realize that potentially every dread-wearing biker in this world will encounter the same problem and end up more or less giving up. I'm not much of a business person, but it seems to me that this is a wonderful niche market and somebody might wanna look into making products for this exact type of customer. It's not a huge market, but it's constant, and it's better to have the whole small pie than to fight for a tiny slice of the big one.
So go ahead, kiddies. Make your millions. You're welcome. Spread the love:)