Giro Manifest MTB helmet review

Giro's Manifest brings Giro's Spherical rotational force system to mountain bike helmets in this light, airy, and streamlined trail/enduro lid.

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Review Rating


Giro’s unique MIPS Spherical system; Fidlock magnetic buckle; goggle compatible


Looks great; fits exceptionally well; ventilation is top-notch


No convenient place to stash sunglasses when you’re not wearing them; sky-high price tag

Size Reviewed



396 grams





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While much of the heated debate in helmet technology land has been focused on Wavecel, Koroyd, and MIPS, Giro has quietly taken a different path to address rotational forces. The Aether launched about two years ago, using a new design dubbed MIPS Spherical — essentially, a ball-and-socket design that places one EPS shell within another EPS shell, allowing the two to rotate independently. It took a while, but now MIPS Spherical has come to the mountain bike side in Giro’s Manifest.


EPS ball and socket
Photo: Dan Cavallari |

But now it’s just called Spherical, ditching the MIPS moniker — not because it isn’t a MIPS design, but instead because consumers were getting confused by the lack of a traditional MIPS liner inside the helmet. Giro fielded enough phone calls and emails that it seemed logical to drop the MIPS from the Spherical name, though the technology remains the same.

Naming conventions aside, the Manifest is a very cool helmet. I’ve long been a fan of Giro’s Montaro MIPS mountain bike helmet, but it was time for an update. Giro delivered with the Manifest. It features the same ball-and-socket Spherical design as the Aether, but with a host of other features specifically tailored to trail riders.

Manifest’s trail touches

The Spherical system was actually intended to start its life in mountain bike helmets. Giro’s first implementation on the dirt side came in the Tyrant helmet, but it was a much simpler system. The Manifest works identically to the Aether’s system, and it caters more toward the trail and enduro crowd.

For starters, the Manifest shaves a lot of weight when compared to the popular Giro Montaro. The Manifest weighs 346 grams (size medium), which is, according to Giro, 35 grams lighter than the Montaro. (NOTE: By my Feedback Sports scale, my size large Montaro MIPS is actually 431 grams — 85 grams heavier than the Manifest.)

This may just be a cosmetic cue, but the Manifest’s visor also appears to be shorter than the Montaro’s. Notably, the visor adjusts 15 degrees to accommodate goggles, but it doesn’t click with detents, which is a common feature on many mountain bike helmets these days. I’m not sure this matters a whole lot, but it bears mentioning. To me, as long as the visor stays in place where I adjust it, that’s just fine.

Giro Manifest
Photo: Dan Cavallari |

The Roc Loc Trail Air fit system works a lot like Giro’s Roc Loc Air system on the road-side, but with some adjustments for mountain bikers. It’s a bit beefier than the Roc Lock, and the Roc Loc Trail Air system provides a 3mm gap between your forehead and the front of the helmet to help increase ventilation.

If you’re an enduro shredder, you’ll appreciate the gripper at the rear of the helmet to help keep your goggle straps in place. The Manifest is full of small touches like this that cater to a wide swath of dirt riders.

The Fidlock magnetic buckle is another one of those small touches. It’s a quick and easy buckle system that you can secure and release with one hand. I’ve used such systems on other helmets and it’s nifty, something I would expect from a high-end helmet like the Manifest.

Photo: Dan Cavallari |

Giro says the Manifest is 7 percent cooler than the Montaro MIPS. That’s a nice number. In testing, I can’t tell you whether it was 7 percent cooler or not, but I can tell you that I was never bothered by the helmet, even on the hottest days. Air flows well through the helmet, and Giro has created generous vents and ports at the front and rear of the Manifest to keep air moving over your head. On grind-it-out climbs in 95-degree heat, the Manifest felt cool compared to other MTB lids I’ve tested recently.

The Manifest’s shell extends low over your temples. That’s great for safety, but other helmets have experimented with such designs and largely failed because the shell interferes with your sunglasses. Giro addresses this concern by notching the EPS to make room for your sunglasses. It works well, though it does actually make it slightly difficult to take your sunglasses off with one hand, as the arms of your sunglasses can get caught on the EPS lip. That said, I do like that the helmet doesn’t interfere with my sunglasses while I’m riding, so to me this is a minor complaint.

Giro Manifest
Photo: Dan Cavallari |

The Manifest’s $260 price tag certainly places it in the high-end range. That’s a lot of money for a helmet for sure, so Giro’s execution here has to be near-perfect to justify it.

Why Spherical matters

The Manifest’s Spherical system is essentially a slip plane design: One layer of material slips past another to help disperse rotational forces. The outer EPS shell is a different density than the inner shell, again to more effectively disperse forces as they get closer to your head. Different EPS densities address high-speed crashes and low-speed crashes.

Giro Manifest
Photo: Dan Cavallari |

We have heard in the past that slip plane systems can bind up, thereby making them less effective than other systems. But Rob Wesson, Giro’s vice president and general manager, disagrees.

“Certainly you can design a bad slip plane,” he says, “but everything we do here, we work closely with MIPS, and every helmet has to go through MIPS testing. They have to sign off and say it passes our testing for rotational energy management. Can you develop a bad one? For sure. But we respect and look to MIPS to help guide us to make the right choices.”

The Spherical system in the Manifest is a unique take on a problem all helmet manufacturers are now trying to address. Rotational forces can do incredible amounts of damage to your brain during the first milliseconds of a crash, and these systems all aim to reduce those forces and the impacts on your head. Unlike other systems, which generally incorporate a distinct layer of material within an existing EPS shell, the Spherical system is the helmet’s EPS itself. This in theory should help reduce weight, improve fit, and allow more flexibility for venting.

On top of that, the Aura reinforcing arch (that clear piece between the vents) increases strength throughout the helmet while allowing ventilation to remain largely unobstructed.

Photo: Dan Cavallari |

Does all that check out? It’s hard to say. The need for independent testing of spherical systems still leaves a bit of a void for testing one system against another. Giro’s data says this is one impressive helmet when it comes for force dissipation, and cooling is unparalleled. I would love to see more independent data on the safety factor.

Riding the Manifest

Since I didn’t intend to hurl myself over the bars to see how well the Manifest’s Spherical system works, I focused on grading the Manifest on its other features — ventilation, comfort, weight, and ease of use.

Giro has positioned the Manifest as a trail/enduro helmet, so in a sense, it seems as though it should replace the Montaro MIPS — one of my favorite MTB helmets. So my comparisons are largely based off my experience with the Montaro, which incorporates a more traditional MIPS liner inside the EPS shell.

Giro Manifest
Photo: Dan Cavallari |

For starters, the Manifest feels lighter and smaller than the Montaro. It feels far less balky on my head and I don’t really notice it often while I’m riding. As I mentioned, the Manifest is 85 grams lighter than the Montaro by my scale, which is significant. So that’s a solid win for Giro.

The Roc Loc Trail Air fit system is also wonderful. It’s a burlier version of Giro’s Roc Loc Air, a system I’ve praised on the company’s road helmets. It hugs the head comfortably and doesn’t pinch anywhere, and it feels positively locked to my dome regardless of how much trail chunder I encounter.

My only nitpick with the system is the same nitpick I have with other helmets in this category: The dial tucks far enough up underneath the rear EPS coverage of the helmet that it’s a bit hard to get my fingers on it to turn it on the fly. I would love a bit more finger access here.

goggle texture
Photo: Dan Cavallari |

Everything about the Manifest, from its appearance to its fit, and its refined bonus features, all feels well-executed, except for one. The eyewear pads inside the helmet, which are supposed to keep your sunglasses in place when you’re not wearing them, are a nice touch that go largely unused because I just couldn’t find a good place to stow my glasses. They don’t slot in cleanly from the back of the helmet or the front, so I found myself getting frustrated and simply hanging my glasses off the back of my jersey.

Manifest verdict

I mentioned that, for the price, this helmet needs to be perfect. It isn’t quite, but it’s darn close. The Manifest looks great, fits great, ventilates exceptionally well, and features a nifty MIPS system you can’t get anywhere else. It’s currently my favorite mountain bike lid, but I’m not a big fan of the price tag, or the execution of the sunglasses retention when I’m not wearing my glasses. I’m willing to look past the latter, but the former definitely puts this beauty of a helmet out of reach for most riders, which is unfortunate. If you’ve got the coin for it, you won’t regret your purchase, though.

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