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How to Choose a Mountain Bike Helmet

How to Choose a Mountain Bike Helmet
Thursday February 25, 2021
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Types of Cycling Helmets

Looking for a mountain bike helmet, but not sure which is right for your riding style? In the same way that there are different bikes designed for specific disciplines of cycling, there are a variety of helmets to meet the needs of the cyclists who wear them.

Helmets are made to meet the demands of each sub-discipline of cycling: mountain biking, road biking, bmx, bike commuting, time trialing, you name it. Within the sport of mountain biking alone, there are helmets designed for enduro, all-mountain, cross-country, dirt jumping, and downhill. The type of helmet you need will depend on the type of riding you do, in some cases you may even need or want to have several different helmets for your road, trail, or downhill rides.

mountain bike helmet - half-shell mountain bike helmets are the best option for most...
Half-shell mountain bike helmets are the best option for most mountain bikers. These versatile helmets are lightweight, have good coverage, ventilation, and useful features.
Credit: Jeremy Benson

First, consider your riding style. Do you spend your days pounding pavement on a road bike? Check out our road bike helmets review. Are you an adrenaline-fueled gravity mountain biker who spends the majority of your time riding chairlifts or shuttling laps to bomb the downhills? Then you should check out our Full Face Downhill Helmet Review.

If you're an all-around rider looking for something that can do it all, then you'll probably want to check out our Mountain Bike Helmet Review aimed at trail and all mountain-riding and includes a few lids which will meet the needs of weight-conscious cross-country riders.

mountain bike helmet - half-shell mountain bike helmets are designed to meet the demands of...
Half-shell mountain bike helmets are designed to meet the demands of trail riders, with more coverage than road bike helmets, and visors to shield your eyes from the sun.
Credit: Jeremy Benson

Mountain Bike Helmets

You can divide mountain biking helmets into two basic categories — full-face and half-shell. The differences are exactly what the names imply. Full-face helmet models provide full coverage of the head, including a chin and face guard, which wraps around the front of the helmet for additional protection. Half-shell helmets offer less protection and coverage than full-face models, covering the top of the head, down on the sides above the ears, and the back of the head.

Cross-country, trail, all-mountain, and some enduro riders will generally wear half-shell mountain bike helmets. In contrast, more aggressive downhill, enduro, and some bmx riders will typically opt for a full-face model. Of course, you can wear any mountain bike helmet for any type of mountain biking. Some are just better suited to specific disciplines than others. This article focuses primarily on half-shell mountain bike helmets, but we will touch briefly on the other types of cycling helmets for comparison.

mountain bike helmet - three distinct types of bicycle helmets. from left to right: full...
Three distinct types of bicycle helmets. From left to right: Full Face Mountain, Half Shell Mountain and Road Bike.
Credit: Luke Lydiard

Half-Shell Mountain Bike Helmets

Half-shell mountain bike helmets are appropriate for the vast majority of mountain bike riders. It's one of the most versatile styles of helmets and works for road biking, commuting, lapping the pump track, and trail riding. Half-shell mountain bike helmets are similar in many ways to road bike helmets, although modern models typically have a visor and more coverage than their road-oriented counterparts. The best half-shells these days have extended coverage for the sides and back of the head, a versatile range of fit, a rotational impact protection system, and an adjustable visor. We evaluate the helmets in our review based on several criteria, including protection, comfort, adjustments, ventilation, weight, and features.

mountain bike helmet - notice the difference in coverage between a road bike helmet (left)...
Notice the difference in coverage between a Road Bike Helmet (left), a Half Shell Mountain Bike Helmet (center) and a Full Face Downhill Helmet (right).
Credit: Jeff Fox


A Helmet's most important function is to keep your head safe in the event of an impact, so protection should be a huge consideration when searching for your next lid. In general, helmets designed for mountain biking have more coverage and offer more in the way of head protection than a road bike helmet. In recent years, the coverage of half-shell mountain bike helmets has been increasing with shells that extend lower on the sides and the back of the head, covering more of the temporal and occipital lobes. A prime example of this are the new full-coverage, open-face models—like the Giro Tyrant Spherical and Fox Dropframe—that have been popping up recently. These helmets are designed as a middle ground between full faces and half-shells to allow the best of both worlds.

mountain bike helmet - more coverage = better protection. it's simple science, but it's...
More coverage = better protection. It's simple science, but it's still science.
Credit: Jeremy Benson

Rotational impact protection systems have also been growing in popularity in all types of mountain bike helmets. MIPS (Multi-directional Impact Protection System) was the first on the scene, and this system features a slip-plane liner integrated into the helmet design between the foam and the pads of the helmet. The idea behind it is that the MIPS liner shifts in the event of an impact to reduce the rotational forces on the brain. MIPS is currently the most common type of rotational impact protection system, but some manufacturers have developed their own proprietary to achieve similar protection.

Each of these new rotational impact systems is aimed at reducing the g-forces applied to your head in an impact, but they all approach it in a slightly different way. MIPS uses a plastic shell on the interior of the EPS foam that can slip and rotate within the helmet on impact. Other systems like 100%'s Smartshock, Kali's LDL, Leatt's 360 Turbine, POC's Spin, and 6D's ODS use shock-absorbing inserts in the helmet that tout both impact absorption and leeway for rotation on indirect impacts. Even among these systems, however, there are varied approaches. 6D's system is quite unique in that the shock-absorbing inserts sit between two separate EPS shells while all the others feature inserts between the EPS shell and the helmet's interior padding. Beyond these systems, Bontrager's WaveCel is a layer of a porous, cellular structure that they claim works like a crumple zone to absorb forces from direct impacts and work like a slip-plane in an oblique or rotational impact.

mountain bike helmet - here we show the yellow mips (left) in the troy lee a1 and the blue...
Here we show the yellow MIPS (left) in the Troy Lee A1 and the blue SPIN in the POC Tectal Race SPIN. The MIPS is a shinny plastic surface. POC bakes the SPIN tech into the blue pads.
Credit: Chris McNamara

Proper Fit

For a mountain bike helmet to function properly, you have to get the right size. Mountain bike helmets come in several sizes measured in centimeters. To figure out your head size, measure the circumference of your head using a flexible measuring tape. Go completely around your head on a level plane, beginning and ending just above your eyebrows. Don't have a flexible tape? Just use a piece of non-stretchy string and then compare it with a rigid measuring device. In general, each helmet size is intended to fit a range of head sizes. For example, a size medium Smith helmet fits 55-59cm head sizes. Make sure your head measurement falls within the size range of the helmet you order.

It's also important to keep in mind that not all EPS shells work well with all head shapes. While we didn't find any that were downright uncomfortable, we noticed that some brands work best with long, oval-shaped heads, while others fit rounder heads a little bit better. We also discovered some brands like Giro, Specialized, and Bell had refined EPS shapes that work well with a wider variety of heads.

The fit of a helmet is also dictated by its adjustments. Adjustable features like the straps and the fit adjustment on the back of the head allow the user to dial in the fit to their exact preferences. Straps are typically adjustable under the chin and also where they split below the ears. Adjusting the straps allows the user to set them up perfectly for their head shape and size and to achieve proper tension so that the helmet stays on your head in the event of a crash. Most modern helmets also have a size or fit adjustment on the back of the helmet to tighten or loosen the fit within a specific range. Since the helmet shell doesn't have a perfect fit for each person's head, the fit adjustment allows the user to dial in the appropriate snugness for their cranium. These days, the fit adjustment is usually in the form of a dial that pulls tension evenly from both sides and cradles the head at the bottom of the occipital lobe.

mountain bike helmet - the vaporfit dial on the smith session is easy to use even with...
The Vaporfit dial on the Smith Session is easy to use even with gloves on.
Credit: Jeremy Benson

In addition to proper fit, a helmet must also be worn properly to function as intended. This means the helmet is level on your head from front to back, and the front pads/sweatband should sit just above the eyebrows around the middle of the forehead. The rear fit adjustment should be tightened so that it is snug (hopefully, you started with it fully loosened) by turning the wheel or sliding the sliders until the helmet feels secure on your head. You also must adjust the strap harness so that the helmet will stay put on your head even in the event of an impact. We've found there is a fine line between a properly tightened chinstrap and one that is uncomfortable.


In cycling everything is subject to weight scrutiny, and helmets are no exception. The differences in weight between half-shell helmets aren't that extreme, but all other things being equal, lighter is better. The half-shell mountain bike helmets we tested weigh between 350 and 515 grams. Cross-country racers or especially weight-conscious riders may be more inclined to find a super lightweight helmet, and sometimes they will trade coverage for weight savings and opt for a road bike style helmet or XC race-specific model.

mountain bike helmet - not the lightest helmet around, but the session is far from heavy.
Not the lightest helmet around, but the Session is far from heavy.
Credit: Jeremy Benson


Half-shell helmets are all designed with ventilation in mind. The vents of a mountain bike helmet are typically in the form of large ports in the outer shell and foam liner that allow air to flow directly to the head. Many helmets also incorporate air channels that allow the air to flow over the head from front to back to further enhance the ventilating properties of the helmet.

Not all ventilation systems are created equal, and some helmets keep your head much cooler than others. Interestingly, we've found that a helmet's ventilation is not directly related to the number of vents that it has; instead the effectiveness is more related to the placement of the vents and overall design of the system. If you live and ride in an especially hot area, you'll probably be happier and more comfortable with a helmet that has better ventilation. If you live in a cooler climate, then ventilation may be less of a concern, but even in the cold, it can get a little bit steamy on a long climb, and you'll still appreciate good ventilation.

mountain bike helmet - the tectal race mips's 16 vents do a great job of keeping the air...
The Tectal Race MIPS's 16 vents do a great job of keeping the air flowing and your head cool.
Credit: Jeremy Benson


Half-shell helmets are being designed with more features to enhance your riding experience or improve their protection. Examples of these features are adjustable visors, rotational impact protection systems, goggle clips, ventilation, GoPro and light mounts, crash detection sensors, and ways to hold your sunglasses when not in use. Features are great, but only as long as they are actually functional and useful while out on the trail. Overall, we believe that a rotational impact protection system is a great feature to have that may enhance your protection. The price of these systems has come down over the years, and nowadays it only costs a few dollars more to get a helmet with MIPS or a similar system. We feel it is worth the extra money.

Visors are a feature on virtually all-mountain bike helmets. Visors are designed primarily to block the sun from your eyes, although many are adjustable for goggle compatibility. If you like to ride with goggles, you'll want to be sure to get a helmet with an adjustable visor that flips up and out of the way far enough so that you can rest your goggles on the front of the helmet when not in use. If you never ride with goggles, then a fixed visor may work just fine for you.

The features offered by each helmet varies from model to model, and each helmet's features are described in greater detail in their individual reviews. Some helmets pour on the features while others stick to the basics and execute the traditional design as well as they can. We found that there's a fine line between well-executed features and ones that feel like pure marketing gimmicks.

mountain bike helmet - the bell transfer 9 is a full face downhill helmet. downhill helmets...
The Bell Transfer 9 is a Full Face Downhill helmet. Downhill helmets are typically worn with goggles and can be combined with a neck brace for very aggressive riding.
Credit: Jeff Fox

Full-Face Downhill Mountain Bike Helmets

Full-face bicycle helmets are appropriate for downhill, BMX, and aggressive enduro riding. They encompass the entire head and have the most coverage of all types of bicycle helmets. They are designed for very aggressive riding and higher speeds where violent crashes are more likely. In addition to full head coverage, full face helmets also feature a chin guard that protects your face in the event of a crash. Full face helmet models are generally worn with goggles and are typically much heavier and far less ventilated. But they offer significantly more protection than their half-shell counterparts. If you're in the market for a full-face helmet, then check out our Full-Face Downhill Mountain Bike Helmet Review.

mountain bike helmet - the kask vertigo is an example of helmet designed specifically for...
The Kask Vertigo is an example of helmet designed specifically for road cycling.
Credit: Jeff Fox

Road Bike Helmets

Bicycle helmets designed for road bike use are typically designed with two things in mind — low weight and excellent ventilation. Since road riders tend to crash a less than dirt riders, helmets designed for the road sacrifice coverage for added ventilation and lighter weight. This type of helmet typically has the least amount of coverage and does not have a visor because one would interfere with the field of view in the forward position on a road bike. Normally, on road helmets, in place of an attached plastic visor, road bikers often combine a non-visored helmet with a short-brimmed cycling cap to shield the eyes from sun or rain. Another design priority in road helmets is aerodynamics, which is another reason road helmets forego the visor that would catch too much air while you crank past cars on the downhill. If you're looking for a dedicated road cycling helmet, we urge you to check out our road bike helmet review to find the model that best suits your needs.

Certifying Agencies and Certifications

In the United States, the certifying agency for bicycle helmet safety is the Consumer Product Safety Commission. For a bicycle helmet to be sold in the US, it must pass the CPSC test and bear the CPSC label. All of the helmets in our test have this label. All of our test helmets also carry the CE EN 1078 label, which is a similar European standard. None of the bicycle helmets we have tried meet the DOT standard, and shouldn't be used for the motorized riding of any kind.

If you want to dive really deep, read a history of bicycle helmet standards in the US.


The bottom line is that, just like everything else that's fun, riding a bike can be dangerous, and a helmet is the most important piece of protective gear you can wear. No matter what helmet you decide to go with, wearing one is always a good idea. Hopefully this guide helped point you in the right direction for your next helmet purchase.

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