Troy Lee Designs D4 Carbon helmet review

First Look: The D4 is the latest in Troy Lee Designs' best-selling helmet line. Here are our first impressions of the latest carbon version

What is a hands on review?
Troy Lee Designs D4 Carbon Helmet
(Image: © Sean Fishpool)

Early Verdict

If money is no object, you’re not going to be disappointed by the D4 Carbon. It's noticeably lightweight, premium looks and feel, and sophisticated construction makes this a classy all-day option for downhillers


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    Very light

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    All-day comfort

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    Sophisticated safety features

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    Awesome looks


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    Not cheap

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If you watch pro downhill mountain biking, freeride or BMX racing, you’ll be familiar with the Daytona series full-face helmet, which has been winning races since the late 1990s. The D4 is the latest in the best-selling family line and one of Troy Lee Designs' best full-face mountain bike helmets and is available as its lightest-ever carbon-shell model at below 1,000g or as a cheaper composite option. We take a look at Troy Lee Designs top of the range D4 Carbon full-face helmet.

Design and aesthetics

The D4 is more angular and aggressive than the D3. Its silhouette is classic Troy Lee, and if you want their signature stunning paint options, you have a number to choose from, as well as plainer colorways.

Increased airflow was a design priority, and there are more external vents than before, now with open steel mesh covers. Inside, the washable liner has been redesigned, with more channels for airflow and rear vents with no mesh to allow heat to escape easily.

The pads and chin strap are soft and comfortable with a really premium smoothness, and the titanium D-rings are secure and easy to use


The D4 Carbon isn’t just designed to be lightweight, but it packs a number of sophisticated safety features. 

The ultra-thin ‘spread tow’ carbon layup in the outer shell ticks both boxes - higher strength and lower weight (and great looks). 

The EPS inner is protected across the whole helmet, including the edges, to protect against abrasion. There’s also kevlar reinforcement. The inner is also protected within the vents, for added durability and a sleek look.

The only place the inner foam is not covered on the outside is in a slender wedge shape above the bottom edge near the side of the jaw. This is a deliberate ‘suspension system’, designed to crumple more easily if the helmet smashes against the collarbone in a crash, potentially reducing the risk of a collarbone break.  Also, this part of the inner, along with the chin bar, is made of expanded polypropylene (EPP) which is softer than the rest of the inner layer.

Between the inner foam and the pads is a familiar MIPS system, designed to reduce rotational forces to the brain in a crash. And significantly, there are quick-release cheekbone pads, which allow first-aiders to remove the helmet more gently.

On the outside, the height-adjustable visor is designed to break off in a crash, rather than risk twisting the head, and the shear screws are easily replaceable. 

Troy Lee Designs D4 Carbon Helmet

The D4 is comfortable enough to wear all day (Image credit: Sean Fishpool)

Early verdict

The light weight of the D4 Carbon is noticeable, and the improved airflow over the D3 should make it a comfortable all-day lid in most UK conditions, even if there are better-vented options on the market.

If the $550 / £500 RRP is outside your budget, consider the $395 / £375 Composite version, which lacks the technical sophistication of the carbon shell, and comes with a less classy bag, but otherwise is identical and weighs in at only 50g more.

Tech Specs: Troy Lee Designs D4 Carbon Helmet

  • Price: $550 / £500
  • Weight: 997g (size M)
  • Sizes:  XS-XXL, via three shell sizes and different thickness pads
  • Vents: 24
  • Rotational protection: MIPS C2 liner
  • Colors: 5
Graham Cottingham
Senior reviews writer, Bike Perfect

Graham is all about riding bikes off-road, based in Edinburgh he has some of the best mountain biking and gravel riding in the UK on his doorstep. With almost 20 years of riding experience, he has dabbled in downhill, enduro, and gravel racing. Not afraid of a challenge, Graham has embraced bikepacking over the last few years and likes nothing more than strapping some bags to his bike and covering big miles to explore Scotland's wildernesses. When he isn’t shredding the gnar in the Tweed Valley, sleeping in bushes, or tinkering with bikes, he is writing tech reviews for Bike Perfect.

Rides: Cotic SolarisMax, Stooge MK4, 24 Bicycles Le Toy 3, Surly Steamroller

Height: 177cm

Weight: 71kg

What is a hands on review?

'Hands on reviews' are a journalist's first impressions of a piece of kit based on spending some time with it. It may be just a few moments, or a few hours. The important thing is we have been able to play with it ourselves and can give you some sense of what it's like to use, even if it's only an embryonic view.