The Kevlar-reinforced internal skeleton inside every Specialized S-Works Prevail helmet helped the company's designers get away with massive vents that wouldn't be possible with pure foam. The added structural support allowed them to shave away external foam to create massive ports and channels, which have a double benefit: They allow more cooling air to flow over the wearer's head and also, according to Specialized, improve aerodynamics.
I don't have easy access to a low-speed wind tunnel, so I can't speak to aerodynamics, but all of Wired's testers who've been wearing the Prevail over the past several weeks agree it's possibly the most well-vented helmet they've worn. It's markedly cooler than my 2009 S-Works helmet.
Our testers were also unanimous, though, in dinging the Prevail for its large profile. The vents may let a massive volume of air through, but there's no getting around the fact that, straight on, this lid looks larger than other high-end bike helmets. That doesn't come with a weight penalty, though. The sub-8-ounce Prevail is right in line with the competition, but delivers the best venting I've ever encountered in a helmet. So if that was Specialized's target, the company has nailed it.
There are some other technological wins inside, too. The simple one-handed adjustment system lets the wearer dial in the fit on the go, and the rear part of the fit mechanism ratchets up or down to snug up against the back of your skull. It locks down without feeling oppressive.
Unlike with most helmets, though, there's no fore-aft adjustment on the straps. The Prevail straps join at fixed points to create an "ear box" that prevents them from slipping over your ears. This is great, but we all missed the ability to take the slack out of the rear straps. The only adjustment here is tightening or loosening the main chin strap.
So, if you ride in hot places, there may be no better helmet for you. My quibbles with the size and strap system aside, this is my new favorite helmet.
In the end though, its girth grew on me. The advantages in aerodynamics and heat relief go a long way to make this a great lid, and I recommend you give one a go.
WIRED More air flow than a jet intake. Micro-adjustable fit system for fine-tuned snugness.
TIRED Fixed strap system may not be for everyone. If you are already self-conscious about the size of your melon, beware.