Tech Tuesday: DH Helmet vs. Motocross Helmet: Which is Safer?

This Tech Tuesday, Pinkbike features a think-piece by Guest-Contributor Robert Beaupre, who pits conventional helmet logic against new information that challenges existing standards and postulates that a cycling-friendly helmet design which utilizes a more flexible shell better-protects the rider in comparison to sturdier Motocross lids that must pass more stringent tests. Many DH and park riders use Motocross helmets in the assumption that they offer more protection. Beaupre's essay gives much reason to doubt that logic. To enlist industry input, we contacted two helmet makers: Bell Sports and Kali Protectives. Bell Sports did not choose to participate. It's a good read. -RC


Moto VS DH - Which Helmet is Safer for Cycling?
Among many gravity riders, there is a common assumption that Motocross helmets are safer than full-face bicycle helmets. On the surface, that seems like a sensible notion: Motocross helmets are larger and heavier than mountain bike lids, and having more material between your head and the ground in a crash is a good thing, right?


Unfortunately, it may not be that simple. There is an ongoing debate in the motorcycle industry about how stiff a helmet should be to offer maximum protection. A number of critics have suggested that many motorcycle helmets, particularly those made to meet the demanding SNELL certification standard, are engineered to be so rigid that they actually offer less protection in the most common types of crashes. What does this mean to you as a mountain biker? If you choose to wear a Motocross helmet instead of a bicycle helmet when you ride downhill, it could mean a lot.

Which Test is Best?

To understand why the motorcycle helmet debate matters to bicycle riders, you have to understand the testing demands that these helmets are engineered to meet. Common testing procedures for motorcycle helmets seek to simulate the crashes that a rider could encounter on the road. The tests at helmet labs routinely drop helmets onto differently shaped objects from considerable heights. These intense impacts make sense considering the energy levels involved when a motorcyclist's head strikes the ground (or another vehicle) at highway speeds.

The testing used by the SNELL Memorial Foundation, a non-profit group that has certified motorcycle helmets for decades, involves even greater stresses than the standard Department of Transportation (DOT) testing that a helmet must pass to be sold in the U.S. The latest SNELL certification standard (M2010) requires that a helmet transmit less than 275 g-forces to the headform inside of the helmet in any part of the testing - a process that involves some very severe impacts.


According to critics, trouble arises from the substantial stiffness that motorcycle helmets must employ to manage these very severe impacts in the SNELL testing. In a sense, the energy absorbing EPS foam inside a helmet works the same way as the suspension on a mountain bike. Just as the suspension on your bike absorbs the energy and slows the impacts from bumps and drops, a helmet is made to absorb the energy that your head encounters in a crash.

In most crashes, the helmet's primary job is to slow your head down so it doesn't take the full force of the impact. It's the EPS foam inside of the helmet, rather than the helmet's outer shell, that handles most of this task. The foam is designed to compress upon impact, slowing your head as it does so. But if the foam fails to slow your head sufficiently, your brain will smack into the inside of your skull, causing a concussion. And if the helmet really fails at this task, the consequences are usually grim. The problem with a very stiff helmet liner - one engineered to withstand the brutal impacts a motorcyclist on the street could encounter - is the same problem you'd find with a downhill bike that's been set up specifically to withstand ten-foot drops to flat. The helmet with its super-stiff liner won't be compliant enough to cushion smaller impacts, just as the downhill bike with super-stiff suspension won't effectively cushion small and medium-sized hits.


When it comes to brain trauma, small and medium-sized hits matter. Neurologists have learned many new things about the effects of concussions in recent years, and the news usually isn't good for those who've suffered them. Repeated blows to the head have been correlated with chronic traumatic encephalopathy (CTE), a brain condition linked to the deaths of some retired NFL players. All of this has led researchers to suspect that concussions may be much more dangerous than previously imagined.

Critics also point to the fact that it doesn't take multiple concussions to change a person's life. Even a single concussion can cause problems with cognition and memory that can last indefinitely. James Newman, a former director of the SNELL Foundation, has estimated that impacts of 200 g's or more - 75 g's less than the figures required for Snell M2010 certification - typically correspond to severe brain injuries or worse.


Experts square off

So are the motorcycle helmets being made to SNELL standards too stiff? According to a 2005 article by Motorcyclist magazine, DOT helmets outperformed their SNELL counterparts in independent tests that were designed to simulate slow- to medium-speed crashes. This wasn't especially surprising, though, since DOT helmets aren't typically engineered to be stout enough to meet SNELL standards, which means they theoretically should be more compliant in small crashes.

What was surprising was that the DOT helmets also transmitted fewer g's than the SNELL-certified helmets in the highest-energy impacts as well, raising the question of whether SNELL testing had truly become too rigorous for its own good. Ironically, the best performer in the 32-helmet Motorcyclist test was a $79.95 DOT-certified helmet, which transmitted as much as 67 g's less in violent impacts than a $400 SNELL lid.

After publication of the article, SNELL issued a rebuttal that questioned Motorcyclist's testing methods (although since then, SNELL has moved toward requiring more compliant liners in its testing -- one of the chief points of the Motorcyclist article). But the rebuttal didn't stop the controversy from growing. The debate reached a boiling point in 2009 when Dexter Ford, the author of the 2005 Motorcyclist article, wrote a story on the issue for the New York Times. Shortly after that article ran, Motorcyclist fired Ford, a veteran of three decades with the magazine, allegedly due to boycott threats from helmet manufacturers. The 2005 story no longer appears on the Motorcyclist website.



Making the choice

All of these facts raise a number of concerns for mountain bikers who choose motocross lids. If it's true that some top-of-the-line motorcycle helmets may be too stiff for even highway motorcycle use, what does that mean to riders who use them for downhill, where the speeds are typically much slower? Are downhill riders better off choosing helmets that were engineered for the crashes they'll likely face on a downhill course, rather than those engineered for 75-mph trips into car barriers?

While that choice remains up to you as a rider, it's clear that there are some good reasons to think twice before opting for a motocross helmet over one engineered for bicycles. This is particularly true since ASTM F1952 - a downhill-specific helmet safety certification - now appears on many bicycle helmets, giving gravity riders a discipline-specific standard of their own. Regardless of where the controversy over helmets ends, choosing the right helmet for your type of riding deserves your attention - at least to the extent you value your head.

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