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.
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?
Downhill helmets and Motocross helmets may look similar, but there is a key difference between them.
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.
Helmet testing at Moelfre Hall. Aaron Hilton violates the keep-the-rubber-side-down rule - hugely so. Turnip Towers photo
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.
Kali's Prana Downhill helmet passes the US DOT and the European ECE 22.05 helmet standards, but does not pass the SNELL standards. Recent information indicates that this may be a good thing. Ian Hylands photo
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.
Alex Mancini Supermans into a rock garden at Contermanskloof, South Africa - probably happy that his helmet is certified to withstand a sharp impacts. Steven Morrow photo
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.
Kali Protectives Founder Brad Waldron at work with one of his full-face DH helmets. Ian Hylands photo
Talking Helmets With Kali's Brad Waldron
Brad Waldron, a long-time helmet designer and a product-testing fanatic, agrees that a more compliant shell offers more protection for lower-speed impacts typically seen in DH and Park riding. We asked Brad to comment on the differences between Moto and Downhill helmets, and the possible benefits of less-rigid shell construction. -RC
Yes, on average DH helmets are more flexible. One of the biggest reasons for this is that the DOT test for MX helmets requires a penetration test that forces the use of a stiffer shell. The test basically drives a pointed anvil directly through the shell.
SNELL believes that having a more rigid shell saves lives at the highest end of the crash spectrum, while sacrificing concussions on the lower end. I just had this discussion at the Indy motorcycle show with SNELL. I think there are arguments to this as well, but arguing the benefits of SNELL is not where I am looking to go in this discussion.
Rigid shells are worse at low-speed impacts. I believe that you want the shell to deform as soon as reasonably possible. Remember, a body in motion stays in motion until acted upon by a force. If your head hits a hard shell, your brain will continue in motion until it hits the other side of your skull. If on the other hand, the shell starts to break down and the foam is soft enough, then the dissipation of energy is starting quicker and your brain moves slower. Slowing down your brain moving inside your head is a good thing.
Our technology is to in-mold the foam with full-shell helmets, we found that when we in-molded, but did not change the stiffness of the shell, that we saw little benefits. When we made the shell much less stiff, we lowered g-forces 20-percent and more. So I am a big fan of less-stiff shells. There are limits though. You have to balance and tune the shell's stiffness to make sure it is not too soft. This kind of testing takes much time and energy. Not everyone is willing to put in an effort of such magnitude.
Brad Waldron, a long-time helmet designer and a product-testing fanatic, agrees that a more compliant shell offers more protection for lower-speed impacts typically seen in DH and Park riding. We asked Brad to comment on the differences between Moto and Downhill helmets, and the possible benefits of less-rigid shell construction. -RC
Yes, on average DH helmets are more flexible. One of the biggest reasons for this is that the DOT test for MX helmets requires a penetration test that forces the use of a stiffer shell. The test basically drives a pointed anvil directly through the shell.
SNELL believes that having a more rigid shell saves lives at the highest end of the crash spectrum, while sacrificing concussions on the lower end. I just had this discussion at the Indy motorcycle show with SNELL. I think there are arguments to this as well, but arguing the benefits of SNELL is not where I am looking to go in this discussion.
Rigid shells are worse at low-speed impacts. I believe that you want the shell to deform as soon as reasonably possible. Remember, a body in motion stays in motion until acted upon by a force. If your head hits a hard shell, your brain will continue in motion until it hits the other side of your skull. If on the other hand, the shell starts to break down and the foam is soft enough, then the dissipation of energy is starting quicker and your brain moves slower. Slowing down your brain moving inside your head is a good thing.
Our technology is to in-mold the foam with full-shell helmets, we found that when we in-molded, but did not change the stiffness of the shell, that we saw little benefits. When we made the shell much less stiff, we lowered g-forces 20-percent and more. So I am a big fan of less-stiff shells. There are limits though. You have to balance and tune the shell's stiffness to make sure it is not too soft. This kind of testing takes much time and energy. Not everyone is willing to put in an effort of such magnitude.
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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230 Comments
Or else is was my half shell.
Now I know I need to spend the extra money to get a DH specific one, which I will do.
www.kaliprotectives.com/moto/prana-frp
It is also worth noting that a lot of the latest research indicates neck trauma may be the primary cause of concussion. The theory is that your brain detects the impact in your neck, and forces your body to go limp because a limp body sustains less overall injury than a stiff one (that's why drunken falls often result in less serious injury than the same fall by a sober person). From what I have read the jury is still out on whether neck braces help with concussion (they do help in other ways), but it is worth thinking about.
What would you say about that ? In my opinion this article is some kind of advertisment
despite this article, ill keep rocking my SHOEI VFX-W best helmet money can buy and it shows. one helmet for everything.
Are you sure that the lower end remedy is no longer ASTM? That was the whole reason that helmet and standard exists. I'm willing to bet it's a website glitch. I have a lower end remedy, which I bought specifically because it met those standards...
So if you're wearing that SNELL MX lid waiting for that big impact, you're getting less protection in the lower spectrum, and a bunch of small concussions are just as bad, if not worse than a biggie. Personally, I've had three concussions and although I'm still sane, I noticed some changes (i.e. short term memory isn't as good as it was).
Like chazdog said, this issue needs further research, but until the clouds split and rays of deeper knowledge illuminate the both the leg and fuel powered cycling worlds, I'll stick with common sense, do my homework and buy a helmet that fits my needs.
This might be of interest www.youtube.com/watch?v=RXUdpqbxLn0
keep it simple!:
1.helmet , to protect the melon!
2.full finger gloves, the first thing that hits the ground (hands)!
3.some form of protector that includes kidney protection , it's easier to lose a kidney/s than snapping your neck!
4.knee pads.
99999999999999999999.neck brace , lots of cash for a piece of plastic,instead of wasting you money on one get a decent helmet!.
This post is also 7 years old!
This coming from someone who knows the dynamics behind this question, has been through two D3 carbons and is currently riding a SE2.
One the other hand if you are thrown from a dh bike and land head first into a tree or a rock, theres a decent chance that your head will experience a change in velocity of close to the riding speed before the crash.
I'm not trying to argue for one helmet or the other. I just feel that this article, and some of the responses, are linking speed of the vehicle be the driving argument for one helmet type versus the other. The actual impact that must be withstood is due to the change in velocity that the head experiences over what period of time.
but, is DOT = Good?
or is DOT too much?
I do believe Moto helmets fit much nicer for much less money. You can get DOT moto helmets for $70-170.
How about Fly Racing Kinetics? They have a dual density foam for highspeed and slowspeed impacts?
I'm assuming you guys have watched a SuperCross race before, or especially James Stewart. Those guys lawn dart 20 feet all of the time in motos (LOWSPEED IMPACTS) and knock themselves the f*ck out.
What would you say about that ? In my opinion this article is some kind of advertisment
What this article failed to shed light upon is the fact that, yes, moto helmets are not meant for downhill, but they arent meant for MOTOCROSS RACING ON DIRT TRACKS EITHER!!!! They are meant for extremely high speed crashes into pavement. With no rocks or trees. I have personally witnessed multiple pro-level mtn bike racers who crashed while using mountain bike downhill-specific helmets. They completely destroyed the helmets, and were put into severe comas. AND can now no longer ride any type of bicycle, and struggle to perform basic functions in day to day life. TBIs are dangerous.
So I guess the question is- would you rather be "saved" from the small and medium impacts, since they "matter'???? Or would you rather have some small concussions, albeit with some brain damage------- but still be able to function in your daily life????
.
F*** this article
Despite this article, I still personally feel safer in my mx lid, and thats largely what matters to me. If i dont feel safe i cant ride fast, having cracked and destroyed two remedys in just over a year i'm sticking with motocross lids. Its also worth considering that high level dh is achieving motocross level speeds in places, on ground featuring rock gardens and other features with high impact and penetration potential (the reason for the troy lee d3 beefing up over the old d2). Ultimate protection is still important, like the neck brace for example, you'll risk a bone for the sake of your spine, i'll risk a small concussion for the sake of my skull.
Interesting article thats added meat to a malnourished issue, but i'm not going to decide solely based on one article based largely on information from 7 years ago. This issue needs further debating and research, would have been good to get troy lee, bell and 661 involved as they all are the big moto and dh helmet makers, no offence to kali.
Look at it simply, motocross bikes travel faster, they need better helmets to cope with the higher impacts of possible crashes.
DH helmets are engineered to be lighter (therefore cheaper and more aesthetically pleasing) because there aren't as many certification tests they need to pass because DH bikes are slower.
Do the bloody math. motocross lids protect you better!
Why would MX riders still be using MX lids if DH lids protected better?
You guys just believe anything a couple of people say when writing an article with basically no credible back up sources of info.
As for the foam if it is too stiff your head will experience a larger force than with DH engineered foam. As a result you willl experience more brain trauma from a MX helmet with stiff foam. The world cup riders could possibly be on the limit of DH helmets but it seems doubtfull as they are the testers of most products. It's quite likely the helmets are modeld around what they experience and need to withstand.
Not entirely convinced by the part about the spikes, I think you could easily encounter very sharp objects on a DH track.
Another thing is that a lot of carbon lids are a lot stiffer than composite lids which might make them less safe in some cases but of course safer in other.
A third thing is the question about weight. While my TLD Air mx helmet is pretty damn heavy, My One Gamma mx helmet is lighter than my old Giro DH helmet so you can't say that a DH helmet is lighter than a MX helmet. In most cases it's probably true but you should make sure it is if you think that's important to you.
All I'm saying is that it might not just be DH vs. Mx but also model vs. model and material vs. material.
The downside of this is that some of the smaller manufactures (and Aus being a much smaller market than elsewhere) cannot justify providing these helmets to Aus Standards out of their own pocket on a yearly basis and for every model, so they do not get sold in Australia as they have not passed AS Certification.
With my Son my primary concern is a high speed impact with a tree or rock. If he has a serious impact is is going to be a brutally hard hit. For this brutal impact I side with the DOT dirt bike helmet...What it was designed for right?
Of further concern to me is when I fit him (or me) in a Troy Lee, Fox, or Giro I can push these helmets forward into his/my mouth...This bothers me.....While head protection is primary, teeth are also on the list..Have a helmet slid forward into your mouth and say goodbye to your Chiclets!
As an MX guy I remain unimpressed with some of what I see in DH MTB helmets.
Cheek padding needs to be upgraded from fluff to something more substantial....This is what holds your face back right?
The helmet nose needs to be long enough to give your teeth a fighting chance.
The faster you are and the harder you race the more helmet you need.
The flexy thing makes sense...Upgrade the rest of the DH helmets to suite race pace and I will be a buyer.
Until then I consider what is currently on the market good for slower weekend warriors.
Just my opinion.
I wish that Motorcyclist hadn't removed the article from their site that I referenced above, as it was very thorough in describing the problems they found with SNELL helmets in their testing. That said, the NYT story linked to in the article covers some of the same ground in suggesting that stiffer helmets aren't always better -- even in some very high energy crashes. And in my experience with MTB, most of our crashes fall well below the threshold that SNELL and even DOT test for. And that would be fine, except that the stiffness employed for those worst-case-scenario impacts could make riders more vulnerable to serious or even life-threatening injuries in the types of crashes that are most common in motocross and DH.
I ride Northstar in Lake Tahoe and a lot of other brutal DH courses here in the area, so my own head protection is very much on my mind. For what it's worth, the most substantial DH helmet I've tried on is the Fox V3R, which has a very moto feel to it, with a larger shell and more padding than most DH helmets (including Fox's lower-line models). It's also certified to the ASTM standard mentioned in the article. If I were looking for something for my son to wear, I'd definitely give that one a look (and for the record, I have no relationship with Fox). Thanks again for sharing.
The stiffness of the SNELL helmet is indeed overkill for 99% of what we do and your point is both well received and appreciated.
A more flexible design is definitely on my radar now as we are in the market for a new helmet.
I have not seen the MTB Fox V3 in person, but until recently we have been looked long and hard at the MX V3R and it seemed a decent choice, but(after reading your article) turned it down because of the SNELL cert.
Looking online the two helmets appear to be identical, are vented the same, they are both constructed of CF, and they weigh exactly the same (took some homework, but I found the MX/MTB helmets weigh identical).
I would be very interested to hear if you know these to be different helmets or is the paint job just different?
The MX version is SNELL rated and the MTB version does not have the SNELL cert, however I wonder if the MTB helmet may be the same helmet without Fox having sought SNELL certification for this particular version?
I assume FOX pays considerably for SNELL certification and I wonder if they just pass it over to save money on the MTB V3?
Thanks in advance for your help and thanks again for the great article!
Peace
The best way to look at this is an analogy, would you rather drive a 3/4 inch thick steel plated car around or a standard car. Which would be safer? You might say o well if I hit something with a armored car i will just destroy whatever I hit (the hummer/big sub theory) but realistically in a bicycle crash with you head meeting tree, rock, earth the tree rock or earth will win. Dh specific helmets are like regular cars designed to absorb impact not just transfer it to your body. Another great example which maybe someone can speak to that has been in the situation, when an armored vehicle (or effectively an mx helmet) is hit with a huge amount of force say running over an a mine or explosive charge, the people inside are safe (which is better than dead) but are shaken up pretty badly (i don't mean bruises either, very serious permanent damage!!)
Yes, F=m*a. Acceleration (m/s^2) is the rate of change in an object’s velocity (m/s). In a physical system, velocity is measured as a vector , ie. it has a direction within the 3D field which is the resultant of the sum of all the component inputs.
For example, assuming you are riding forwards on flat ground when you crash. You go over the bars while doing 16m/s (about 50km/h). Assuming that you end up 1.5m off the ground before you start coming down again, V^2 = Vo^2+2a(X-Xo), then you are falling in the Y axis at about 5.4m/s when you hit the ground. Velocity is a vector though, so you need to add the 16m/s you were doing in the X axis. The resultant vector (since this example is only happening in a 2D plane, apply simple trigonometry) V=16.9m/s.
In reality when you hit the ground you’re not actually going to stop dead (pardon the pun), you’re head is probably going to bounce. That’s too hard to explain without diagrams though so let’s keep it simple and assume you’ve hit a tree. This brings us back to F=m*a.
So your 58cm head which weighs say 5kg + about an extra1 kg for an mtb full face helmets weighs in at 6kg. Your helmet is decelerating against the tree, going from 16.9m/s to zero m/s essentially instantaneously. In order for the maths to actually work though we’ll need to assume that your helmet takes 0.1s to slow to a stop. So a = 16.9m/s / 0.1s = 169m/s^2. For comparative purposes gravity is about 9.8m/s^2.
Force on mtb helmet Fmtb = 6kg * 169m/s^2 = 1014 N
To convert this back to g-force on the helmet, 6kg *9.8m/s^2 = 58.8 N, this is the ‘normal’ weight of your head and helmet. 1014N / 58.8N = 17.2 G
Let’s say you were wearing a moto helmet that weighed closer to 2kg.
Fmoto = 7kg * 169m/s^2 = 1183 N
Again in G’s, 7*9.8 = 68.6N so 1183/68.6 = 17.2G
As you can see, relating back to G’s gives a somewhat opaque representation of the actual magnitude of the impact as it ends up expressed relative to your weight which hides the real world impact on severity as a result of increasing helmet weights.
Similarly, the 17.2G can’t be related back to the 275G limit set in Snell M2010 as that is a measure of how much of the force generated by a 500kg anvil with a surface area about 11cm square hitting the helmet at 7.75m/s transfers through to your head. Incidentally, that equates to 38,750 N or about 645 G. Even top fighter pilots and astronauts have blacked out by the time they reach 10G, yes I know it's a completely different mechanism but it gives an idea of the general limits of the human body compared to these tests.
An engineering standard or specification such as M2010 responds to a documented set of required performance criteria. Therefore it WILL NOT give an optimal functional outcome for a completely different set of criteria. SNELL and DOT aren’t even targeted at Moto Cross applications, they’re designed to cater for Highway environments. If you crash your Hayabusa at 300 km/h SNELL is probably spot on, you’ll be dead anyway, just not necessarily from head injuries. Motocross helmets need to comply with the same standards so that you’re allowed to wear your helmet from your garage to your nearest MX track, not because it’s the best protection for you once you’re off road.
MX tracks make sure they do not have trees and giant boulders in the middle of the track for the rider to hit....Dh courses are littered with potential death traps. Hitting a big tree or rock with ones head at only 15 MPH or less could be life ending. At 30 mph it would be life ending....There is no MX comparable here...Something to consider.
Last weekend my Son rode with a soon to be pro MX star. His father (my buddy) rode with me in the shuttle truck and we compared notes...After comparing notes our thinking that DH is much more dangerous than MX....Surprised? I was!
Comparing notes on injuries per race there were many more on the DH races than at the MX track. Every local DH race this year had major injuries (ambulance and broken bones or worse). According to my buddy about 30% of the MX races have a crash that involves an ambulance or broken bones. Considering how long the MX guys ride for (20 minute moto, plus qualifying, plus practice) the differences are staggering!
I wonder if in part this is a result of MTB riders wearing lessor protective equipment?
I thought you might find this interesting....I certainly did.
In any case, I do think moto seems to be accelerating a bit in terms of injuries lately -- today's four-strokes are so fast and today's riders are so skilled that it seems like a lot of riders spend endless spans on the injured list. This is Racer X's injury report midway through the 2012 MX season: www.racerxonline.com/2012/06/15/injury-report-budds-creek
Again, I certainly understand your reservations in the helmet debate. As a dad, it's up to you to follow your conscience in choosing your son's gear. My article wasn't meant to condemn moto helmets or their designers; I only wanted to provide some often-overlooked bits on the helmet debate as it pertains to DH. Good luck, and have fun out on the hill with your son.
Something else to note; Once the inner foam has been crushed or compacted it is far less equipped to dampen impacts in that same area. A softer helmet could sustain multiple small impacts that compress the foam and then leave little protection for the big impact.
Also the article said that there is new evidence concerning DEATH linked to soncussions whichyou sustain from small impacts. if thats not a serious injury i don't know what is.
Forgive me for not remembering his name, but I saw a documentary on a skier who was famous for having spectacular crashes. This buy was no bloke, he raced on an international level. Once, he crashed while skiing with his family and it was one too many for his brain to take. Now he wakes up every morning to his wife showing him pictures of his family because he doesn't remember them. His memory ''resets'' every time he goes to sleep.
This is an extreme case but it goes without saying that impacts to the brain, even the smaller ones, DO have consequences.
Are you sure?
You wouldn't happen to be thinking of the movie '50 First Dates' would you? What happens if he stays up playing COD all night, does he keep his memory, or does it always go at 2am or something?
You can't really compare MX/SX accidents because there is a lot of weight behind the bike. They have some pretty catastrophic accidents at low speed. IMO it's more important to look at individual helmet design and construction and use some common sense. Some things to consider: many companies use the same helmet manufacturer. In MX, O'neal and ONE Ind have typically been made by KBC. And they're not the only brands. Look at companies whose origins ARE helmet manufacture and design. These are the guys who do the R and D. Also, most of the better helmets will use a multi-block foam design to assist with getting the right amount of shock absorption depending on the area of the head/helmet and likely type of impact. It's basically styrene with bigger and smaller bubbles to create different densities. It's not new, AGV have used it in their road helmets for a long time.
So in a nutshell: Brain injury is caused by your brain impacting against your skull. Shock absorption is the answer. Therefore get a helmet with quality construction, a multi-block/density design and a strong but fairly soft shell. Composites like fiberglass/kevlar/carbon have proven effective. And don't forget correct fit. Fit is key.