Editors Note: This article was written by Art’s Cyclery web content editor Brett Murphy, who uses his mechanical engineering background to explain the latest industry advances and breakdown component design. The original post can be found here.
With cycling helmets ranging wildly in price, you might be wondering what the heck’s the difference between the Giro Saga ($65) and the Giro Synthe ($270). Both helmets have to pass the same impact testing standards, and are even constructed from similar materials. So how do you decide which is best for you?
The first thing to focus on is shape, and how the helmet fits your head, which varies depending on the manufacturer. Art’s Cyclery uses a comparison system for classifying helmet shape, or ovality, across brands. Each helmet is categorized as having an oval, intermediate or round fit, expressing the ratio of the width of the helmet to the length. While two helmets can both be sized for the same head circumference, one could be much wider and shorter than another.
Road cyclists will be far more concerned with the aerodynamics of a helmet than mountain riders. More expensive road helmets (such as the Giro Synthe) often have extensive design, engineering, and testing involved to reduce aerodynamic drag. The video below gives you an inside look at design process of that wind cheating brain protector.
Next, consider the helmet retention system, which includes straps that run in front and behind your ears and clasp together under your neck. The helmet will also have some sort of a ratcheting mechanism that adjusts to the circumference of your head. Each type of ratchet offers different advantages. If you like to make adjustments on the fly for instance, Lazer offers helmets with a small dial on top of the helmet for easy and quick access.
While helmet features like these are important to consider, the real reason to wear a helmet is to protect your brain. Magnetic snap-on eye shields are awesome, but useless if the helmet doesn’t provide adequate protection in a crash. That leads up to the main structural technologies that protect your noggin in a worst-case scenario.
Most helmets are made of EPS (expanded polystyrene) foam liner bonded to a harder shell. Helmets have not strayed far from the proven foam liner/hard shell design since EPS foam was first used in the mid-1970s.
EPS foam helmet liners begin life in the form of small beads of styrene that are later paired with an expanding agent. As the beads are heated, they expand, and are then packed into a mold of the helmet shape. Less expensive helmet models will feature a shell that’s taped or glued to the outside of the EPS. In-mold technology, seen on higher-end models, allows the foam and shell to be molded together.
This process allows for more aggressive and aerodynamic features to be incorporated, along with increasing the helmet’s impact absorption capabilities. In-mold also allows for more ventilation while maintaining structural rigidity. Helmet shells protect the foam from abrasion due to regular wear and tear, and vary from polycarbonate to carbon fiber. Shell material, ventilation, and engineering costs will also play a role in determining price.
Kali cone-head construction (click to enlarge). Photo courtesy of Art’s Cyclery
When your helmeted head hits the ground, the helmet you are hopefully wearing will absorb most of the impact force. This happens through a combination of the shell and EPS foam deforming, engineer talk for getting crushed, with the foam absorbing most of the force. Denser foams require more force to cause deformation, which some manufacturers interpret as a reason to make very dense, thin helmets, which still meet the safety testing requirements. Critics point out that dense foam creates more impact resistance in the helmet, but actually passes more impact force on to your head.
Some helmet companies, such as Kali Protectives, use multiple density EPS construction. This allows for much more control over how the forces are distributed through the helmet. Kali’s Cone-Head technology allows multiple-density designs with lower density foam closer to the head and higher-density foam closer to the shell. This creates crumple zones within the helmet for more effective dispersal of impact forces across more of the helmet, which does a better job of keeping the forces from being transferred to your head.