GROUP TEST TRAIL HELMETS
Helmets are firmly ingrained in mountain bike life. We all have one, and they’re far more than just a fashion statement, a rain cover or somewhere to stow your glasses. In the event of a big stack, they could literally mean the difference between life and death.
They do this firstly by spreading the force over a larger area – especially important if you hit a sharp rock, for example – and then by slowing it down, causing it to take milliseconds longer to reach your head. This smooths out and reduces the peak impact spike (or ‘impulse’) that’s the cause of brain damage. The fractional delay may not seem like much of a difference, but it works.
To extend this impact time, expanded-foam liners, commonly made from polystyrene, are designed to crumple to destruction. Helmet brands are now fine-tuning use of different densities of foam to make this even more effective. (Lighter-density foams help with smaller knocks but ‘bottom out’ with larger ones, so denser foams are needed in combination.) Koroyd ‘straws’ are another recent development – thin plastic cylinders designed to deform on impact, spread the load and reduce that peak ‘impulse’. Rotational forces can be dangerous, too, though, which is where systems such as MIPS (Multi-directional Impact Protection System) come in. To combat your head being forcibly twisted, MIPS allows for some rotation between the foam liner and a polycarbonate layer attached to the helmet pads (among other methods). Not all lids have it; look out for the yellow circle if you like the sound of it.
To protect the easily-damaged foam, the liner is wrapped in a hard-plastic microshell. This adds a little extra protection from knocks and should extend the life of the helmet. Make sure you replace your lid after any impact, and every two
