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Leatt MTB AllMtn 4.0 review

Leatt’s flagship trail helmet prioritises protection over weight

Our rating 
3.5 out of 5 star rating 3.5
GBP £179.99 RRP
Leatt MTB AllMtn 4.0

Our review

A range of tech, hefty protection and coverage make this one of the most robust open-face helmets, just try before you buy for sizing
Pros: Good coverage over the back of the head and temples; well-integrated features such as glasses storage; impressive build quality
Cons: Sizes up large; those preferring lighter weight and less bulk should look elsewhere
Skip to view product specifications

The MTB AllMtn 4.0 is Leatt’s top-of-the-line open face helmet, featuring a raft of smart tech and design choices.


As you’d expect, there’s rotational brain injury protection, dual-impact foams and more considerations to keep your head safe and comfortable.

While the price is high, it feels warranted, although it’s not as light as some of the best mountain bike helmets on the market.

Leatt MTB AllMtn 4.0 helmet spec details

Leatt’s 360-degree Turbine Technology offers rotational impact protection with the benefit of added cushioning.
Steve Behr

Leatt uses a polymer shell to cover the helmet, in a bid to add durability and enhance structural strength. This shell wraps around the foam, not exposing the rim or edges to protect them from accidental damage.

The MTB AllMtn 4.0 benefits from a dual-foam construction using EPS and EPO foams. Leatt claims this provides better protection over a wide variety of impact speeds.

For rotational impact protection, Leatt employs its patented 360-degree Turbine Technology. This uses Armourgel discs, shaped like a turbine, which rotate and slide laterally in all directions to minimise rotational accelerations. The gel is claimed to offer added shock absorption.

The helmet features 18 strategically placed vents with internal air channels to keep things cool when the going gets sweaty.

For rider comfort, Leatt uses padding that’s sweat-wicking, breathable and odour resistant. It’s also removable, so it can be washed when it needs a freshen-up.

The three-position height-adjustable cradle uses a ratchet mechanism to tighten the helmet around your head. A Fidlock buckle keeps the straps secured.

Additional features include a breakaway peak to minimise injury risk. This is also adjustable, with three positions to choose from. There’s storage for your mountain bike glasses under the peak, with rubber grips to hold the arms securely. The helmet is also compatible with MTB goggles.

The Leatt MTB AllMtn 4.0 weighs in at 439g for a size small. There are three sizes to choose from: small (51-55cm), medium (55-59cm) and large (59-63cm). This helmet hasn’t been rated by Virginia Tech.

Leatt MTB AllMtn 4.0 helmet performance

The AllMtn 4.0 is a chunky helmet, but those looking for protection over weight will appreciate the design.
Steve Behr

The first thing you notice about the Leatt is its imposing size. With its size, weight and protection, it’s clear the MTB AllMtn 4.0 is focused more on gravity riding than marathon missions.

The Leatt offers impressive coverage, with plenty of protection over the temples and rear of the head. The helmet is comfortable while riding and venting is reasonable.

Its weight is balanced well and isn’t a noticeable hindrance while riding. The cradle tightens with no pinch points, which is great.

However, I have some concerns about the sizing. It’s rated for 51-55cm heads, but for my 55cm head, I had to tighten the ratchet fully to get the helmet to fit securely. If you’re at the smaller end of the size scale, I’ve got a feeling the Leatt would size up too big.

Once in place, I found the Leatt to be a good fit. The padding isn’t the plushest, but it’s up there with rival helmets and hugged my head with no harsh pressure points.

I set the three-position cradle to its middle setting, which gave good security while riding.

The Leatt is well ventilated for its size and keeps you cool while riding.
Steve Behr

I never noticed the Leatt slipping or moving around on the trails, even when charging into harsh compressions. The large peak creeps into your field of view when riding, but it didn’t obstruct my vision, and the peak is easy to push up a notch if you want to.

The Fidlock fastener is quick and easy to use, and the straps didn’t interfere with anything. The straps do sit off your face, so glasses slide underneath them. I didn’t notice the arms or earpieces of my glasses getting caught or sitting uncomfortably.

I tested this helmet in winter, meaning sweat wasn’t really an issue, but the forehead padding is thick, so should absorb some moisture. The two vents under the peak let in a reasonable amount of air flow, and ventilation was better than expected considering its size.

The glasses ports worked well, and I never lost my glasses during testing. If you tend to run hot on the climbs and want to avoid getting sweat on your lenses, this can be a useful feature.

How does the Leatt MTB AllMtn 4.0 helmet compare to the Specialized Ambush 2?

The Leatt feels as though it offers more protection due to its greater size and weight. It’s still well vented, although not as extensively as the Ambush 2. However, it hasn’t been tested by Virginia Tech.

Specialized’s helmet is more pedalling-friendly, and the sizing is good. The Leatt measured up a little larger than quoted, though.

Both helmets offer plush padding and good comfort, but the Ambush 2 is better priced.

Leatt MTB AllMtn 4.0 helmet bottom line

There’s secure storage for your glasses.
Steve Behr

If your riding has more of a gravity bias, but you still want an open-face helmet, the Leatt is worth investigating.

It’s surprisingly cool for its size, appears to offer plenty of protection, and is one of the more comfortable helmets around.


Its neat features are useful and it’s a reasonable price for a top-spec helmet. Just be careful with the sizing, though.

How we tested

These helmets make up our 2023 trail helmets group test.

We tested nine open-face lids from a range of brands, featuring different tech and takes on performance and comfort to see who came up with the goods.


Product Specifications


Price GBP £179.99
Weight 439g (Small)
What we tested Leatt MTB AllMtn 4.0
Year 2023
Brand Leatt


Features 360 Turbine Technology, adjustable retention cradle, adjustable peak
Helmet type Mountain bike open face