The Met Trenta 3K Carbon helmet is lightweight, it feels cool in use and, if you accept Met's claims, it offers an aero advantage over a traditional lid, but you're going to have to dig deep for this one.
Pros: Lightweight, cool, comfortable, aerodynamically efficient
Cons: It ain't cheap
Our medium sized Met Trenta 3K Carbon helmet was 220g on our scales, 5g heavier than Met's claimed figure but still very lightweight. The weight saving over most other helmets will have a negligible effect on your speed, obviously, but you might find it more comfortable than one that's even 50g heavier. I barely noticed it in use
Met has managed to keep the weight down by using EPS (expanded polystyrene) foam that's 20% less dense than normal, it says, without affecting the helmet's capacity to absorb energy in the case of impact. How come? It's down to the elastic modulus of the carbon cage that's embedded into it, says Met. You can see the black woven carbon beneath the white in-moulded polycarbonate shell. Met insists that this carbon is structural rather than cosmetic. It's the addition of the carbon, which you don't get on the standard Trenta (£220), that allows the use of the lighter EPS.
Met says that the drag of the Trenta 3K Carbon (and the non-carbon Trenta – they're exactly the same profile) is equal to that of a traditional aero helmet when sprinting on the drops at 60km/h and 7% lower than that of a traditional road helmet when riding at 45km/h with your hands on the handlebar tops. Met doesn't say what those 'traditional' helmets are.
One point to bear in mind is that 45km/h is, you know, pretty damn quick, especially if your hands are on the tops rather than the drops. It's about 28mph, so even if you get that 7% advantage sometimes – riding in a big group, say – you're not going to enjoy it constantly. At the speeds you'll typically ride at, your potential gains will be much lower. Still, a win's a win and if you find yourself in a sprint to the line, when you might well be moving at 28mph+, you'll be glad of any advantage you can get.
The Trenta 3K Carbon's cooling is linked closely to its aero performance. They're both based on airflow, after all. The design features large vents at the front, deep internal channelling and what's called a NACA Vent towards the top – the one that runs horizontally and looks like a coin slot. It's something that Met uses in other helmets like the Strale and the Rivale.
The idea is that the NACA Vent results in the Venturi effect (if you think back to your physics GCSE or O Level, it's the increase in speed and decrease in pressure that occurs when a fluid, or in this case air, is forced through a constricted area), pushing warm air through the large exhaust ports at the rear while fast-moving air cools your head.
Essentially, it ensures constant airflow through the helmet without catching the wind and creating drag – or that's the story. Whatever factors are at play, the Trenta 3K Carbon feels cool in use. I've done most of my riding in this helmet in UK spring conditions where staying cool hasn't been much of a challenge, but I've also taken it on some hot and hilly rides in Mallorca and I've never given a second thought to overheating.
The Trenta 3K Carbon uses Met's Safe-T Orbital fit system, which I really like. As the name suggests, it surrounds the full circumference of your head. We'd suggest that you always try a helmet on before you buy but a quick test in the office found that the fit system allows the Trenta 3K Carbon to conform to a wide variety of different head shapes comfortably via the clicky wheel at the back. The rear section is four-position height adjustable (you can control how far it reaches down the back of your head) and you get independent occipital adjustment (the parts that touch your head back there can be moved inwards and outwards).
One thing that was mentioned by pretty much everyone we got to try the Trenta 3K Carbon is that it feels as if your head sits fully inside it rather than that it perches on top of your head, if you get the distinction. I find that this distributes the pressure and adds comfort although I know other people who aren't so keen on this type of fit.
Stowage for your eyewear is very good. I've not found any glasses whose arms don't fit into the vents at the front of the helmet – some the right way up and some upside down – and most fit in comfortably into the ports at the back too.
The Trenta 3K Carbon comes with its own soft bag for safe storage and is compatible with Met's USB LED (£34.99) that clips to the back of the Safe-T Orbital fit system without affecting adjustability
Naturally, the helmet conforms to CE safety standards although there's no MIPS http://mipsprotection.com/ version, which is a bit of a surprise these days (Met does offer other MIPS helmets).
Overall, I've got loads of good things to say about the Met Trenta 3K carbon. It's lightweight and comfortable and we've found that most people get on with the fit (there are always exceptions so try before you buy). Plus, if you accept Met's figures, it offers an aero advantage. The only real sticking point is the price.
Lightweight and comfortable helmet with aero claims, but it doesn't come cheap
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road.cc test report
Make and model: MET Trenta 3K Carbon Helmet
Size tested: Medium 56/58
Tell us what the product is for
Met describes the Trenta as "a performance road helmet". It is designed to be lightweight and more aerodynamically efficient than a standard road helmet.
Tell us some more about the technical aspects of the product?
According to Met, "Our R&D team discovered that the carbon's elastic modulus allows us to reduce the density of the EPS foam by 20%, without affecting its capacity to absorb energy.
"The parallel 'ribs' are linked from the centre of the helmet by a carbon cage embedded into the liner, making it dramatically lighter compared to a traditional construction.
"The result is a lightweight, yet better-performing shell that sets a new standard in terms of ventilated helmet manufacture."
Ours medium sized helmet hit the scales at 220g, just a little higher than Met's claimed weight of 215g. That's certainly lightweight.
The Trenta 3K Carbon sits a long way down on your head rather than sitting high, perched on top, if you know what I mean. The Safe-T Orbital fit system surrounds the full circumference of your head (it doesn't join the EPS liner at the temples, like most) so it can accommodate various different head shapes in comfort.
£265 is clearly a lot to spend on a bike helmet when you can buy one that offers a similar level of protection for a fraction of the price, but this is a pro-level option and they never come cheap.
Tell us how the product performed overall when used for its designed purpose
It's a really comfortable helmet that's lightweight, it feels cool in use and, Met claims, it's aerodynamically efficient.
Tell us what you particularly liked about the product
The low profile, the level of ventilation and the fit.
Tell us what you particularly disliked about the product
The price is a tricky one.
Did you enjoy using the product? Yes
Would you consider buying the product? I'd certainly consider it
Would you recommend the product to a friend? Yes
Use this box to explain your overall score
You already know that £265 is a lot to pay for a helmet. You might argue that the price should drag the score down but everything else about the Met Trenta 3K Carbon is exceptionally good so I think it warrants a 9 overall.
About the tester
I usually ride: My best bike is:
I've been riding for: Over 20 years I ride: Most days I would class myself as: Expert
I regularly do the following types of riding: commuting, club rides, sportives, general fitness riding,
Mat has worked for loads of bike magazines over 20+ years, and been editor of 220 Triathlon and Cycling Plus. He's been road.cc technical editor for eight years, testing bikes, fettling the latest kit, and trying out the most up-to-the-minute clothing. We send him off around the world to get all the news from launches and shows too. He has won his category in Ironman UK 70.3 and finished on the podium in both marathons he has run. Mat is a Cambridge graduate who did a post-grad in magazine journalism, and he is a past winner of the Cycling Media Award for Specialist Online Writer.