The Smith Mainline helmet falls squarely into the enduro camp, the idea being you use this for enduro racing, bike park laps and possibly even trail riding on freezing cold days.

What has enduro ever done for us? Nothing, that’s what. Well, apart from the development of better bikes, more racing, new trails, a slew of global events and a million vlog channels. And not forgetting a whole new category of helmet – the lightweight mountain bike full face helmets, or enduro lid, represented here by the Smith Mainline. Offering much of the protection a traditional DH lid brings, but with more ventilation and less weight, these helmets are easier to live with if you have to pedal your bike up the hill as well as down it. There are two distinct approaches to the enduro lid, some brands like Bell have gone down the convertible solution that lets you whip the chinbar off and transform the helmet into an open face. Others like Tory Lee and Fox have stuck with the full-face design and fixed chinbar, paring back materials and enlarging the vents to give all over protection with greater airflow. 

Inside the box is a helmet bag, three sizes of cheek pads, two crown liners and two neck rolls, all made from a hybrid blend of X-STATIC and XT2 fabric. I opted for a size medium for size 55-59cm heads, which puts me right on the upper limit, but by putting the thinnest neck roll and crown liner inside it felt snug without being restrictive. It sounds crazy, but by trial and error I settled on a medium cheek pad on one side, and a small one on the other. The upshot is a rock solid fit without pressure points… and no noticeable wonk to my jaw.

The Smith Mainline uses Koroyd technology to protect against impacts, improving the helmet’s airflow in the process

The Mainline is DH certified and brings a ton of high end features to the party, starting with a MIPS liner that sits between the pads and the rest of the helmet. It’s silent when you’re riding, and adds slip plane protection to the Mainline. Next is a layer of Koroyd that takes up much of the space EPS foam would usually fill in a traditional helmet – its honeycomb structure is purported to absorb more energy from an impact, and is therefore a better and safer use of the available space. Next is a layer of traditional EPS and EPP foam, and the whole thing is wrapped in a nylon shell.

Chinbar is reinforced with EPS and EPP, adding weight but also protection

When you’re standing in the lift line or waiting for a friend to sort out their social media life the Mainline feels like a pretty warm place to be. Get moving though, and the huge vents (21 in all) suck in air and push it out the back like a jet engine. I’ve not tried the Stage helmet, but compared to Leatt’s DBX 4.0 it’s cooler, probably because – unlike EPS – Koroyd can provide impact protection without stifling the air flow. 

Rounding out the Mainline is a traditional D-ring secured chinstrap, which is more of a faff than the new fangled magnetic buckles but is easy enough when you learn the knack, and a moveable peak that goes high enough to park a set of goggles under. Smith says the Mainline works best with its own goggles, but rest assured it’ll work fine with pretty much any brand.

Multiple sizes and padding options makes the Mainline a great fit for most head sizes

Lightweight full face helmets are supposed to be just that, lightweight, and the Smith Mainline helmet does a reasonable job at 812g. It’s 100g heavier though than the similarly priced TLD Stage, and 50g more than the superlative Fox Proframe though. That said, it doesn’t feel cumbersome even after a day’s summer riding, and it’s certainly less of a burden than a traditional full face.