Troy Lee Designs' D4 helmet has a pedigree that can be traced all the way back to 1996, when the original Daytona debuted. That was the era of Nico Vouilloz and Shaun Palmer, a time of rapid progression by mountain bike riders and manufacturers alike. In the years since, Troy Lee Designs' helmets have evolved – the D2 came next, followed by the D3, and then, you guessed it, the D4, which first started showing up in the fall of 2019.
The D4 builds on the foundation left by the three previous versions, and it's the lightest carbon-shelled DH race helmet that TLD has ever produced.
TLD D4 Carbon Details
• Weight: 971 grams (large)
• TeXtreme carbon shell
• MIPS C2 liner
• 24 vents
• 6 color options
• Sizes: XS, S, M, L, XL, 2X
• 3-year warranty
• CPSC 1203, CE EN1078, ASTM F1952-DH certified
• MSRP: $575 USD
I wear a size medium for Troy Lee's half shell helmets, but I'm a size large for the D4. As with any sort of apparel or protective gear, it's best to try before you buy. For me, the fit was spot on right out of the box – I have more of an oval-shaped head, and the fit was snug without being too tight, and free of any unwanted pressure points. Compared to a Bell Full-9, the D4's padding isn't quite as thick and plush, but it was still very comfortable even during big days of shuttling or lift-served laps. I used the D4 with several different brands of goggles and didn't run into any compatibility issues.VENTILATION
The D4 has a total of 24 vents, which includes six positioned over the top of the head, and seven rear exhaust ports to give that hot air somewhere to escape.
Its ventilation system works well, and while it's not at the same level of the Troy Lee's extra-airy, enduro-oriented Stage helmet, there's plenty of airflow to keep it from becoming stifling on warm days. It's a little bit cooler than the Bell Full-9.
Vents at the front and top of the D4 help keep the air flowing.WEIGHT
My size large test helmet weighed in at 971 grams, right in line with TLD's claimed weight of 1,000 grams, give or take a bit. For comparison, a Fox Rampage Pro Carbon weighs 1,230 grams, and a Bell Full 9 weighs 1,122 grams.
That light weight is made possible in part by the use of TexTreme Spread Tow, a very thin carbon tape that saves weight and bulk compared to conventional carbon fabrics. TeXtreme is used in the shell of the D4, where it covers the EPS foam that provides the bulk of the helmet's impact absorption. A MIPS liner is attached to that foam by elastomers, where it's designed to allow the helmet to move on a rider's head during an impact, potentially reducing the rotational forces that reach the brain.
The low weight is a benefit too, especially during long days in the bike park or shuttling. If you're still wearing a big, bulky DOT-certified bowling ball on your head, you should at least try on a D4 – that 971-gram weight is impressively low for how solid and secure the helmet feels. SAFETY
As with most helmet reviews, I was lucky enough to not put the safety technology to the test during the review. That said, the D4 has modern safety features like a MIPS C2 liner and quick release cheek pads.
On the topic of reducing impact forces, TLD use expanded polypropylene (EPP) foam for the helmet's chin-bar and on the lower portion of the helmet that sits above a rider's collarbone. That foam is softer and more flexible than the EPS foam used around the skull; the idea is that this "suspension system" should reduce the impact forces that can occur between the helmet and a rider's shoulder or collarbone, potentially preventing further injury during a crash.
Despite its light weight, the helmet still feels quite robust, and it achieves the CPSC 1203, CE EN1078, ASTM F1952-DH, and ASTM 2032-BMX safety certifications.PRICE
The D4 comes in at $575 for the carbon version and $399 for the composite variant that weighs 50g more. In comparison, a Fox Rampage Pro Carbon is $500, a POC Coron Air Carbon Spin is $450, a Bell Full-9 Carbon is $445, and a 100% Aircraft Carbon is $400. While the top-of-the-line carbon D4 is significantly more expensive than its competition, the cheaper composite version retains all of the features and comes in lighter than most of the competition's more expensive carbon versions.ADDITIONAL FEATURES
Other nice touches include titanium D-ring fasteners and an adjustable, replaceable visor. The D4 comes with its own carrying bag that's a step above the basic cloth sacks that accompany many full-face helmets – the bag has a separate zippered pocket for goggles and gloves, and there's enough room to toss in a few extra accessories as well. ISSUES
The only real gripe that I have has to do with the noise that the MIPS liner makes. It's not particularly noticeable if you're bombing down a wide-open track, but at slower speeds on quieter sections of trail it makes a sort of creaking noise when it rubs against the foam on the inside of the helmet. That's obviously not a massive issue, but still, given the D4's price, I'd like it to be completely silent when it's sitting on my head.
I did have a strange incident where a big ol' fly flew into one of the larger vents above my forehead and got trapped inside. The noise was downright frightening, and I had to stop and immediately pull off my helmet since I was sure a swarm of bees was trying to get me. That only happened once, so I'm going to chalk that up as a random event, but a little piece of mesh over the biggest vents might not be a bad idea.
Light & well ventilated+
Very comfortable fit
MIPS liner can be noisy-
One of the more expensive options in this category