I know this can be an emotional issue for a lot of us, but my goal here is to get us thinking about what really makes cycling safer. If you choose to wear a helmet or not wear a helmet, the world is a better place if more of us choose to ride a bike more often. ❤

I remember being like 9 or 10 years old in my hometown and a cop "pulled me over" on my bike. Because I was wearing my helmet, he gave me a "ticket" that was a coupon for a free soda and piece of pizza at a local restaurant. I never know when I'll get another free soda and piece of pizza for it, so I've always worn my helmet ever since. It's been 25 years. I'm not kidding that one little thing stuck with me so hard as a child.

Dutch bike commuters rarely wear helmets, but then again, they have amazing bike infrastructure.

4 years ago, I was riding my bike on campus through a fairly empty parking lot. I had been an experienced cyclist at this point, riding between 15-30 miles a day in Manhattan as a commuter with no helmet. I went on that ride with no traffic around. Next thing I know, I woke up in the ED with a splitting headache and 6hrs had passed. It was 3am. I must have somehow lost control by hitting a crack or a rock and fell towards the back of my head. Ended up with postconcussional syndrome, permanent memory problems, and a hematoma towards the back of my skull that thankfully didnt lead to a brain bleed or more damage. A helmet would have prevented all of that. I still don't like to wear helmets, but I do. I think you have great points and I actually agree with your stance, but at the end of the day a helmet is still safer - and sometimes you just get unlucky.

One of the biggest concerns in sharing the road with cars is in getting doored. Sometimes getting doored means flipping over the door and landing headfirst. Even without flipping over, you're likely to hit your head.

It was interesting to hear her mention that one reason she wears a helmet is because she knows if she's ever in an accident that's the first thing people will ask. I go all in on visibility for basically the same reason. If I get hit I want there to be no doubt about whether the driver could see me or not.

I’m pretty pragmatic about it. It’s been a long time since I’ve fallen, but if I fall, I don’t want to end up with a traumatic brain injury. It’s like wearing a seatbelt while driving - obviously my intent is to never use it, and it’s been decades since I’ve been in a collision, but I’m still going to wear it every time. That said, if I use a rental bike somewhere and no helmet is available it’s not going to stop me from biking.

If my head is injured, I risk losing my personality, my livelihood, and risk putting my loved ones in a horrible position of having to “unplug me”. Wearing a helmet is just so easy, and stories I’ve heard from friends who work in the ER confirm they are very effective. Even when commuting, I just don’t trust cars, people, dogs etc.

I love this conversation! It’s videos like this that pushed me to study transportation engineering, I want to make a safer urban environment for everyone

Dude, this video is amazing. I especially enjoyed your outro about needing to have the conversation about improving city infrastructure, not just the conversation about helmets. The helmet conversation implies expected bike-vehicle crashes, whereas the infrastructure conversation doesn't want that to happen in the first place. Also, I wouldn't complain if you had a Shifter podcast.

Very interesting video! I am a cyclist from Brazil and it's really interesting to see the perspective from more developed countries. I live in a city that is very commended for its public transport infrastructure, but being a cyclist here feels absolutely like a survival experience. Wearing a helmet is pretty much mandatory if you value your life just for a matter of protecting yourself against the sheer exposure to traffic. It's not even really about you crashing, but other people crashing into you.

I only started wearing a helmet as an adult when I was cycling in the winter and needed to keep my touque from falling off in the high winds. After that, it became habit. Since then, I have lived in a province where adults were not required to wear a helmet, but did require under 18. I then got a new mindset: if you have something worth protecting, you will wear one. I never ride without a helmet in case you didn't suspect. :) I do understand how you ride without one and where, but you just never know when that sudden something will cross your path for that unexpected reason. Physics says that if you are travelling faster than running, and you fall, you will likely injure yourself. I ride around 20km/h, but can't run near that.

It might be anecdotal but one day my dad got in a bike accident where he was wearing a helmet. I saw the helmet because he'd fallen on the ground and it was ground flat on one side. My dad's still around, so that's enough of an incentive for me.

I currently commute most days on bike infrastructure in Denver, CO, USA. But I’m also 62. I don’t want to have a minor (or major) incident or even a simple fall and crack my head. So I wear a helmet. If I was 23 again, my answer may be different and I might go without a helmet. I think, as part of the decision risk assessment, age is also part of the equation.

It's weird the helmet laws in Australia. I've got buddies who'll ride their bikes with helmets to the skate park only to take them off when they go skate which is a significantly more dangerous activity.

To me it is easy. My house "never" burns, but I still pay for fire insurance. Same with bicycling: I "never" crash on my bike, but still use a helmet as an insurance to improve my chances if it should happen.

Thank you so much for this video with more factual debate on helmets. I got in a bike crash (very minor, dodging a car on a slippery bike lane) a couple years ago, the day after I got a helmet for the first time. When talking about it with people they always asked first "were you wearing a helmet". They would get so upset when I would answer, "why would that matter?", as my only injury was a scratch on my arm! The only way to get a productive discussion after that was to say first that yes, I had one, but no, it didn't help because there was a driver in the bike lane! People need to hear all this research you did and make a truely informed decision!

Almost 20 years ago now, I got hit by a car as a teen on my bike (pretty bad, broke a leg and some other bones). That experience, ironically, made me realize I didn't need the helmet every ride. It's not the most important safety equipment. What matters is a bike that works (brakes!), good lights, visible clothing, and a strong, vested interest in your own survival. Paying attention, understanding the road and what drivers and others around are likely to do, etc., will prevent the vast majority of incidents. I still wear a helmet on many rides, especially if the roads shared with cars will be tight/fast. I don't bother around town. I have been harassed occasionally by well-meaning strangers, usually from their car next to me at a stop light. I also spend every summer on motorcycles and with no doors on my Jeep. Both of those things are probably a greater danger than not wearing a bike helmet, but no strangers ever harass me about it in public. The indoctrination is real.

It’s absolutely stunning to hear a proper conversation about an ordinary, daily subject. I’m happy that it made sense to me and helped me make a choice (an adhd that struggles to make choices by overspread the factors in the matter and getting lost quickly, not sure if I’ve explained myself correctly). Thanks (:

The main reason I don't wear a helmet, and it's not one I've seen mentioned elsewhere, is that it reduces what I can hear. The friction against my hair, the air forced down around the helmet past my ears, combine to make it so much more difficult to tell when/how close/how fast a car/van/motorbike is about to overtake. You can glean so much from hearing a car engine and tyres behind you, and awareness of your surroundings is by far the most important thing keeping you safe.

Ironically, I’m an ER nurse and I commute to work in inner city houston and sometimes I wear my helmet, sometimes I don’t. I believe always being aware of my surroundings and not riding like an asshole will protect me a lot more than any helmet can.

Dutch guy chiming in 🙂: I loved your thorough discussion of the whole bike safety conversation, and checking the facts to see what actually holds up. I'd say you're spot on, including your concluding statement: leave it up to people to decide whether they want to wear a helmet or not. In the Netherlands, nobody really tends to wear a helmet on their commutes, except perhaps old people on e-bikes. And small kids that get pressured by their parents to wear them. Everyone else: only when mountainbiking or fast road biking. Works out just fine 👍

All arguments in favor of bike helmets are equally valid for anything else where a head injury is possible, e.g. driving a car or just in a car, working on a construction site or walking barefoot in your bathroom. The question is what is the threshold where the risk becomes too high. I've thought about this and decided from a risk standpoint it makes more sense to wear a helmet inside a car, which is what I do now. I mean, even in Formula 1 or NASCAR they also do that. For some reason people look at me strange, so I guess it's more of a cultural than a rational thing.

I got doored by a car and still remember the sound of my helmet slamming into the asphalt. A friend of mine got rear-ended by a car and hit the car hood so hard the helmet split in half. In either of those situations the presence of a helmet wouldn't have changed whether we got hospitalized or not, but it absolutely changed the nature and severity of those injuries, which would not have been captured in a pure hospitalization count comparison study. It is absolutely true that the problem boils down to cars and lack of infra (both of my examples were car-caused and on streets with inadequate bike infra), but in light of my own personal experiences there's literally no way I'll ever not wear a helmet and not tell my own kids to do the same, at least until we have Amsterdams all around North America.

Crashed on my bike yesterday. The cause of the crash was my speed and shoddy cargo hauling solution leading to poor control of the bike when I hit a bump in the pavement. I scraped my left elbow and my palms a bit. I was riding on a walking and cycling path as I nearly always do. A helmet would not have prevented my crash, nor would it have given me any protection in this case. I wasn't wearing a helmet, but if I did I would be a bit disappointed in it. Thanks for nothing, lol. Thicker gloves and a thicker jacket would have protected me, but obviously a better cargo solution or simply riding slower would have prevented the accident in the first place. Curiously, the only thing my girlfriend told me when I came home was that I needed to start always wearing a helmet. My own take away from the accident is that I need to ride much slower on non smooth surfaces and fix a proper cargo solution that doesn't lower my control over the bike. Reminds me of my driving teacher who always told me that the only factor you really need to consider when it comes to preventing accidents is speed. Lower the speed and every other accident risk factor fades into irrelevance. Doesn't matter if you are looking at your phone if you are standing still. Doesn't matter if the road is slippery if you are driving slow. Doesn't matter if it's foggy and you have poor vision if you are driving slow. Your slow reaction time or slow decision making doesn't matter if you are driving slowly enough to orient yourself and make your decisions.

Why I wear a full face mountain bike helmet in urban environments: - In Australia we have a vicious bird (read small dinosaur) called the Magpie which will draw blood if you ride near it's nest in the Spring time. It prefers ears. - I mount a light on the helmet to look into the corners with handlebar light lighting the forward direction. Flashing light during daylight. - The light mount will handle a GoPro if you want to record what hit you! - Front peak provides good sun protection. - Naturally the helmet is painted like a "Boba Fett" helmet. Very informative, well researched and balanced discussion on helmets and bike safety.

I've been cycling over the entire span you described. There was no bike infrastructure, and nobody wore a helmet when I started. I may still have my old Bell helmet somewhere. I always wear a helmet, partly because I don't want a child to see me riding without one, and decide not to. By the way, there is a huge difference between a head injury and other injuries.

It's silly to go through a thought process to decide if you need a helmet or not every time you get on a bike. How fast am I going? is it raining? Is the traffic light or heavy? Is the road surface good? Am I familiar with the area? Make it an automatic action that you don't need to think about and you'll hardly ever forget it. I've been road and mountain biking (some races) for 40+ years and skateboarding when younger. I had multiple events where my head stuck the ground. The only one where I was laid up with a concussion, I was not wearing a helmet. It escapes me why people go through so much effort to validate their actions to not wear a helmet.

This resonates with me due to my experience as a motorcycle safety instructor. I got into M/C safety as a response to mandatory helmet legislation that was proposed in Illinois in the late '80s. The proposed legislation sought to reduce state funding of safety training programs in exchange for a mandatory helmet law, which struck me as an asinine argument. I had always strived to be a competent operator, but after I became trained I was shocked at how deficient my self-taught skills truly were. I became passionate about teaching the skills that scholarly research have shown contribute to accidents. The key skills accident-involved riders statistically lack include mental and visual skills for traffic perception, visual direction control, traction management, maximum straight-line braking, braking in a curve, swerving to avoid an obstacle, overcoming an obstacle, countersteering to maintain control in a curve, entering moving traffic from a stop, and lane position for visibility. These days I watch lots of bicyclists to judge their riding ability. Can you guess what skills most bicyclists on the road really suck at? The exact same ones that were demonstrated to contribute to motorcycle accidents. Poorly skilled bicyclists in traffic are at much greater risk for injury, especially head injuries. But even on protected bike lanes and trails, poor riding skills are definitely a risk factor. I'd love to see a nationally recognized, evidence-based bicycle training program that will help untrained riders achieve mastery over these critical skills, so they can be safer riders. And yes, I always wear a helmet, regardless of whether I'm on a motorcycle or a bicycle. I've known people with various degrees of TBI, and it's a lifelong tragedy. I don't want to put my family through that nightmare.

After all the info I loved your ending statement to just have more empathy for people who choose to do things differently than ourselves. That was my biggest takeaway and I appreciate it!

Thank you for this info! There's something that needs to be included in the calculations, I would think: crashes not related to vehicles. Vehicles were not part of my 3 most memorable crashes over the past 30 years, or so. Two were from coming across patches of "black ice" and I was glad I was wearing a helmet when my head hit the road (once) and the paved bike path (the second time). The third was from leaves in the street, slippery from the rain. Watch out for those slippery leaves! I know these are only personal experiences, though, but I know that conditions can come up by surprise. (So, even if you're not next to cars, I would vote for a helmet, because things sometimes happen. Even if it's infrequent, you frequently need your head.) Also, I get way more pressure (in the US) to not ride at all. Hardly anyone mentions my helmet. Of course, we must keep building more and more protected bike lanes (that are maintained all year round). Yay for bike infrastructure! And I'll make it a point not to harshly judge anyone I see without a helmet or me if I find myself without one, for some reason. Thanks again.

I was certain there couldn't be reasonable argument AGAINST wearing a helmet but your conversation really gave me food for thought. The statistics were interesting (it seems cycling is a lot more safe than I had assumed) but they didn't really change my mind. Because in the end it's not about what's statistically most likely to happen but the particular situation I might end up in. But the experiment showing that car drivers are less careful when a cyclist is wearing a helmet really makes me think.

Helmet laws were lobbied hard by automobile companies. It made bikes appear more dangerous than they are, and made cycling more of a hassle. Now, with less people riding, and car drivers often being actively antagonistic, we pretty much have to wear a helmet in situations where people in saner societies wouldn't. When I was a kid, bicycling was the dominant way to get to school. Now, that's a rarity.

Super thanks to Cailynn for the extensive research and to both of you for the detailed yet concise presentation!

I suspect the chance of an accident also varies by region. Some of the math in this video is a little sophomoric though. Yes, there are other injuries aside from head injuries that send one to the hospital, but stroke and other brain injuries tend to be far more dire then, say, a broken arm or other bone. Even a 60% reduction in that would be pretty compelling to me. Sure, most people never have an accident. The same might hold true for cars and seatbelts. Still, I live in Somerville MA, and they put up white painted “ghost” bikes to commemorate bike deaths. One is in an area I often bike by. What is the downside of wearing a helmet? Messy hair?

Personally I wear a helmet at all times. Several reasons, the two main ones being that I have done so for 30+ years (so it’s a habit by now) and also because there is very very little safe bike infrastructure where I live. So I am among cars about 90% of the time. This also taught me to „ride as if nobody can see me“, aka always assuming that I am, for all intents and purposes, invisible to car drivers. This strategy has prevented bad things from happening on several occasions, both on a bicycle as well as on a motorbike. Some (!) of my fellow two wheeled riders - motorized or otherwise - are frankly reckless and move about like they own the place, without even looking at what happens around them. And as soon as one of them gets swiped, everyone is all over why car drivers are THE issue. That is not to say that there are no issues there mind you, because there are plenty. Bro…you and your bike are about as wide as the average A-pillar from the perspective of a car driver. There is no difference there whether you are on an omafiets or a Hayabusa. If you are in the right spot, the driver can physically not see you. I don’t care if you might have the right of way. I would rather yield and live than insist on ROW and leave a nice Bull‘s Eye on a windscreen and having my membership of the Being Alive Club revoked permanently. Also, everyone traveling on two wheels should remind themselves occasionally that their crumple zone is a LOT smaller than that of even the most basic car. No matter how much you were in the right, you will always draw the shortest straw as far as injuries go. No amount of helmet will change that. A fender bender on a car might be a trip to the morgue for you.

Thanks for this really insightful / big-picture / historical approach to this topic! I almost didn't watch the video because of the nature of exchanges I've had on the topic before, but I'm really glad I did. I especially appreciated looking at this through the PR & Dr. (x2) lenses. I certainly learned things I didn't know and hadn't considered before. That only talking about helmets in the context of discussions of bike safety is myopic is an especially compelling point. A broader consideration--and recasting--of 'bike safety' seems like something really worth exploring further. Dare I suggest a dedicated playlist with a broad scope of sub-topics? I personally wear a helmet at all times while riding and will continue to do so, as my rides virtually always include roads shared with cars where the posted speed limit is 40mph and actual speeds are what they are--and I'm a creature of habit for whom maintaining this habit will be safest. Watching this has given me greater empathy for those who make other choices, based on their circumstances, like the one you describe in the last segment.

Very interesting discussion! I always wear a helmet but in my California commute I am forced to merge directly into 45mph/70kph traffic and there are numerous opportunities to be right hooked. Maybe I’d reconsider if I could ride on a protected path

The study I want to see is: How does the choice to wear a helmet, corralate with riding style? My hypothesis is that risk averse people will choose a helmet, and risk takers will be more likely to not wear a helmet. Risk averse people will cycle cautiously and have a lower crash rate, risk takers will do sketchier things on their bike, and have a higher crash rate. So it makes sense for helmets and injuries to corrolate, but the underlying cause could be the the cycling style of the rider.

Not wearing a helmet does not make you an idiot but traumatic brain damage will.

This might be your best video yet. You treat the subject fairly and comprehensively. Helmet fundamentalism™ is a real problem. I almost always wear a helmet, and I could be a poster child for helmet advocacy, as my helmet probably saved my life once and reduced my probable injury several times. But I do not think helmet wearing is paramount, and mine is a nuanced view. SKILL is a big factor in a cyclist’s safety, one I hope you touch upon eventually. I have taught safe cycling, and with my many years and miles of cycling on roads and streets, I feel I’m safer than most even when I’m bareheaded and others are helmeted. I am pretty good at predicting road users’ behavior, and I’m good at being predictable to others. These skills are very valuable. I also evaluate my role in near hits, because when the “other guy” seems to be at fault, maybe I at least played a role.

I don’t wear one if that’d make me not ride my bike due to heat/inconvenience. It’s better to ride than not to ride, helmeted or helmetless! Statistically there are more traumatic head injuries per unhelmeted km in cars and on foot, so if i’m not wearing a helmet on foot or when i get a ride on a car… yeah!

A helmet is like the seatbelt of your car. You don’t need it until you do. I went to the ER twice to get my face stiched and my brain and neck checked. Because of accidents while commuting and not wearing a helmet. The first one was because a dog ran across the bike path and struck my front wheel, the second one was because the skewer of my front wheel worked itself loose. In both cases it was a head first dive into the tarmac. Both times i was riding slowlc … ca. 20km/h.

I had a very serious accident in the early morning a couple years back,which resulted in a hospital stay with a concussion,stitches,road rash,smashed eyeglasses.I wasn't wearing a helmet then ,but ever since then I've worn one

I've been riding my bicycle more than 3000 miles a year for over 50 years - I raced USCF in my 20's and have ridden extended tours all over the country. I always wore my helmet. The one time I fell off my bike and cracked my helmet was on an errand to the bank about 5 years ago. It's never about if your going to fall but when.

No, it's not complicated, because I've lived my whole life in my body and I know what feels safe and what doesn't. At least, that's what everyone thinks, but some people go on to then assert that what makes sense based on their personal values/risk assessments and environments should be applied (even mandated) to everyone. Great material for considering nuances! Context makes such a huge difference, whether it's public policy debates, personal decision-making based on environment/routing/speed, and psychology/culture. If all the energy directed at shaming pedestrians/cyclists for not exhibiting safety equipment and safe behavior was directed at making cars less deadly by making them smaller, lighter, slower, able to detect and override unsafe driving behavior or removing them from cities entirely, that'd do a lot more good than marginally increasing helmet-wearing.

I've been cycling about 30 years. There was about a 5 year window where I didn't wear a helmet cause I was a teenager and mom and dad weren't around. The uncle I lived with in college abrasively got me to wear it and the habit stuck. 6 years later, my bike fell apart while I was commuting and I woke up in the hospital with only 3 skull fractures, a ruptured ear drum, and a mild concussion. You will not be able to slap one on when you need it.

So personal annecdote. When I was around 12 years old, I had a biking accident. Something weird happened and my front tire came to a full stop forcing me to flip over my handlebars. I was wearing a helmet and landed on the ground dazed and confused. My arm was broken. My legs covered in road rash, the bike landed on my broken arm. And I was in pain, when I got home and my dad picked me up we took off my helmet and found a large dent in the helmet The plastic was ripped and crumpling off, the Styrofoam were caved in, and I felt so bad that I broke the helmet. But my parents were more happy that I was. That impact would have had a huge injury on my head if it were not for the crumple design of helmets. And while most people probably aren't doing intense biking, why would you want to risk the injury. Infact why would you not want to wear a helmet, what happened to me was like an act of God, and I still don't know what caused it.

Amazingly concise breakdown of topic. I'm rapidly approaching 30K on my e-bike commute; every kilometre, helmeted. Yet two weeks ago I found myself on an evening e-bike tour through the heart of Rome, helmetless, because the option was available. So many details revealed in this video's analysis helped me understand why I was able to make that decision in Rome. Excellent content Tom!

I was recently one of the 600+ people hospitalized after a crash. Everyone from the EMT to various staff at the hospital all asked me if I was wearing a helmet. I answered yes and then they said oh good. Then i told them it didn't matter because I didn't crash into the fence with my head, I crashed into the fence with my face and the helmet didn't help (or hurt to be fair). The crash was because of a stupid decision and I sure won't do that again but I do ride in all situations so I will continue to wear a helmet. Loved the info on risk assessment and risk behavior.

I was leaving in Sweden and never wore a helmet except during the winter! Every winter I fell at least once. Now I moved to the US and I always wear a helmet but I wouldn’t feel judged if I didn’t. I just choose to wear it because I think the likelihood for me to fall here is higher.

This is an interesting/emotional one for me. I was cycling home from work in a designated shared bike/pedestrian pathway and one of the only places where my route crossed a road I was hit by a car making an illegal turn from the wrong lane. I hit the windshield and then was flown through the air and onto the pavement. Among other injuries, my helmet wad smashed and I had a concussion. I've never seen a Canadian city where the infrastructure is so good, I'd feel comfortable without a helmet. And now when I see a cyclist without a helmet, I feel a bit of a pit in my stomach thinking of how much worse than things might have been if I wasn't wearing a helmet. My first time on a bike after my accident, I came across an accident where a cyclist was on the ground in a bike lane after being hit by a car. Her head was on the ground with out a helmet to protect her, I started shaking and got the bus the rest of the way home. This was all in BC, now I'm in Halifax and I find drivers here are less used to cyclists and I definitely wouldn't feel safe anywhere near a road here without a helmet. That said I have done a cycling tour of Paris without a helmet and felt completely safe there. I haven't cycled in Calgary, so don't know much about the infrastructure there. I totally understand and respect the other side of this, but feeling like my helmet probably saved my life on a route I thought was pretty safe and had good infrastructure still makes it difficult for me to see people without helmets.

The more cyclists, the less cars. The less cars, the less deaths.

I'm all for wearing a lid (and I do 95% of the time) but all the hand-wringing is such cringe victim blaming, and helmet laws are demonstrably counter-productive. if you care about cyclists, BUILD SAFE INFRASTRUCTURE.

great video. i get angry everytime i read in the local newspaper "bicyclist hit by car, injured, didnt wear helmet", so basically the bicyclist gets blamed for getting himself injured. Its unbelievable

That is a cool video, and I love the message that infrastructure in cities must be improved if we want more people on alternative means of transportation. However, perhaps because I am not in North America and this shaming etc. is not really that common where I am in Europe, I have never been bothered about it. As a teenager I rode a bike on highways and on very dangerous roads actually, now that I think about it, and never it crossed my mind to get a helmet. I am wearing one now, 15 years down the road when I picked up cycling again, because my significant other bought me one and asked me to be careful. I said alright, I've awful hair anyway, I don't mind a helmet. Then one day on a winter morning commute I slipped on a black ice patch on a right turn on a perfectly curated bike lane in the most perfectly maintained (well not on that morning as it seems) section of my commute. I damaged my rear mech, and right brake lever, hitting my head hard on the asphalt on the right side of my head. Man that would have HURT without a helmet. This is why I continue to wear a helmet, not because of a law or public opinion. I did not get from the video the counter point - why don't you want to wear a helmet? What is the cons here? Am I helping new world order by wearing a helmet? I get confused on that part.

Could you please add a bibliography of all studies used by Cailynn Klingbeil in the video? It would be very useful

Secondary to well designed safe separated cycling infrastructure, the upright cycling position on comfortable relatively heavy city bikes I believe is a significant reason why helmets are not often worn in places like the Netherlands. Many other countries like the US, Canada, Australia, UK are dominated by forward leaning lightweight sports bikes which are much easier to go over the handlebars when braking heavily. Afterall Sports cyclists ('Wielrenners') and mountain bikers in the Netherlands also almost always wear helmets. Choose the right tool for the job I say.

Thank you for both of your efforts to present this information. Your discussion referenced a lot of published research. I tried looking for some of those references, specifically the 2013 BC study comparing the risk of various modes of transportation. I could not find that paper. Granted, I didn't spend a lot of time. I was surprised that you didn't link to or at least list the publication titles in the video description. I know it would be a lot of work to do so for a video posted 9 months ago but I would be very interested and I assume other viewers may be too.

This was a super interesting video, and covered the nuance that I suspected probably existed. I've been wanting to occasionally ride helmet free and felt the shame you all talked about here, and am re-assessing that now. I'm also trying to figure out how to bike commute when we go back to work in January. Thanks for doing this Cailynn and Tom!

Ugh thank you for this!! I live in BC so I have to wear one to avoid a ticket but when I lived in Scotland I never wore one and nobody ever asked me about it. They did ask “where’s your high-vis vest?” Which makes so much more sense to me. Be seen so you don’t get hit! I love a leisurely ride with my hair flowing in the wind. I still do it occasionally but I can’t relax as much because I’m so anxious about a cop driving by 😞. Anyway, love your videos. Thanks!

I think if you are on protected bike paths then its fine. In Denmark (Copenhagen where I am), no one wears one since almost all streets have separated bike paths with our own lights, etc. However, if you find yourself mingling with cars to the point they are passing and the lane is just some paint on the street and you are sometimes very close **cough those buses cough** then a helmet seems feasible.

Several years ago, I went down after hitting a patch of oil on a rainy day. If I hadn't been wearing a helmet, it would have been my head sliding along that curb.

I can’t remember not loving my bike. I was hit by a drunk driver on my way home from 3rd grade in the 1960s. Extreme head injury, 3 months of coma. Recovered but not without lifetime issues.the next year I bought another bike, at almost 70, I have 6 bikes and ride them all with a helmet and rear view mirrors, and a front /rear camera. I would never decide for another person what they do or not do. I never want to be that injured again. Personal choice. I don’t understand why taxpayers pay for roads for cars but if you don’t have safe bike lanes, too bad.safe bike lanes should be a part of retroactive improvements and new planning. IF YOU BUILD IT, THEY WILL COME!!! Thanks for all your hard work on these bike related matters.

Thanks for a KZfaq video that made me think. I wear a helmet all the time when riding because my wife asks me to. OTOH, here in my (U.S., car-favoring) town, I go far out of my way to avoid traffic. I take alleyways and side streets because I'm retired and thus have time. I ride for my health, so it's a little ridiculous for me to worry about how long I'm on the bike. After a lifetime of "driving for a living", just pulling the car out of the garage is work to me so I only use the car when have to. Without my wife's request, I still might wear a helmet, because that is where I mount my most reliable rear-view mirror (yeah I know- I'm a dork)

I've broken 2 helmets in accidents. I bought my first helmet in 1990 after riding for many years without one (in fact in the UK no-one wore a helmet, even for racing when I started serious cycling in around 1970 when I wanted to get fit for sailing). I got knocked off (and out) on my way home from work and decided to get one for my 13 mile each way commute. Fortunately I was on my way to work when a cat ran across the road and attempted to run through my front wheel. I ended up in hospital for a fortnight and off work for 3 months. I was a paraplegic for several days and still suffer partial paralysis over 30 years later. The helmet suppliers gave both my wife and I new helmets and used my old one for display. 18 months later I came off a hired mountain bike in Yorkshire and seriously modified my face and got knocked out again. OK it was icy limestone and it looked worse than what it was but it was another broken helmet. My first accident prompted most members of my cycle club to get helmets and now I always wear one though I much preferred being bare-headed. I'm 82 now and still ride though much less than formerly and with a little electrical assistance. You're not an idiot. It's your choice (though with the US health business it may be a bigger risk than here, in the UK). With my experience I think I'd be an idiot not to wear one.

Great Video! I have appx 50,000 miles riding, 7000 as a commuter and perhaps half my miles on group rides with 4-20 riders. I agree with "Shifter" that the need for a helmet varies with riding conditions and that over emphasis on helmet safety can overshadow other more important issues. Somehow, I've never crashed (on pavement that is - I've had 2 minor mountain bike crashes) but I've witnessed 3 "cracked helmet" crashes, numerous minor crashes, and one helicopter evacuation. But none of the cyclists I've witnessed crashing were seriously injured or killed unlike a friend of mine killed in a car crash or the hundreds of thousands killed annually in cars and the hundreds of thousands killed by avoiding the relatively safe and healthy exercise of cycling (to say nothing of the mental health benefits of riding with friends!!!) So, those who think helmets should absolutely be worn at all times by all people in all situations, might consider wearing their helmets while in a car or airplane since that is where most people will be when they crash, not on a bike. Nonetheless, despite my many miles of crash free cycling experience, I wear my helmet 99.9% of the time. I would especially advise new riders early in their cycling learning curve to wear their helmets at all times, at least until they get past their first minor crashes which statistically speaking are practically inevitable during the first 2 or 3 thousand miles of riding. (Don't let this scare you, almost all beginner bike crashes result in very minor injury - band aides not stitches - or no injury at all) I'd also add that if forced to choose between giving up my helmet or giving up my rear view mirror, I'd keep my mirror and give up my helmet but of course, I use both. I use the mirror to evaluate the competency of drivers passing, or for situational awareness in traffic, or on group rides who might be following too closely when stopping. I mount my mirror to my helmet visor or to my eyeglasses rather that to the bike handlebar for two reasons: helmet or eyeglass mounted mirrors are "suspended" by your body and legs so the image is not jiggled as on a handlebar mirror, and secondly because you can adjust your range of vision with a slight head swivel. Just be aware that when you turn your head you tend to turn your bike in the same direction so concentrate on not swerving when turning your head. May the road rise to meet you (but not as you crash!) - Dan Ford of Fruita, Colorado

Nice background, nice people, great conversation! I came off my bike a few years back on a greasy bend here in Dublin. It happened in an instant and I was wearing my helmet and cycling shorts. I became intimate with the road surface through my ankle, hip bone, shoulder and helmet encased head. I jumped up and continued home where I struggled to undress and shower once the adrenaline stopped pumping. My helmet and shredded bib shorts went into the bin and my wounds healed quickly with help from the local ER. They sent me to a plastic surgeon who spoke about skin grafts but I convinced her I’d heal quickly. The most interesting part was they also sent me to a trauma surgeon who examined me and then gave me a very interesting lecture on how my helmet acted as a ‘lubricant’ as I slid across the tarmac on my LHS eventually coming to a stop without hitting anything. He said the helmet did its job in this particular case but would not have prevented whip lash injuries had I hit an obstacle with my head. He was quite pleased with his lecture as was I with the outcome.

Just an anecdote from Denmark here: I used to live in Copenhagen and rode my bike from and to work every day. The commute was about 10km each way, and most of the way was with separated bike lanes. In the 5 years I rode every day on this route, I was hit by a car no less than 3 times and one of the times I was slung on the hood and only came off the car when he stopped. All 3 times happened because the driver just crossed the lane without looking. Granted it was a very stupid section of road where parked cars would block the line of sight for cars going to the right (across the bike lane). One of the times I am pretty sure the helmet saved my life or at least saved me from a seriously bad time since even with the helmet on I got a pretty serious concussion. I'm wearing a helmet, and I am teaching my kids to wear one too. I think the argument of riders taking more risks because of helmets is a stupid one. I feel unsafe in traffic with cars no matter what I am wearing. I have also broken enough bikes on my mountain bike to know that gear does not equal immortality, and I also knew that before I went to the hospital. You can't say that gear makes people reckless without in the same sentence a mention that the helmet actually works and saves lives.

Brilliant video! Thanks so much for diving into this emotionally charged issue. I’ll be bookmarking this video and recommending it as needed in the future. Cheers! John 😊

I totally get where you're coming from. But I also seem to have a lot more decision fatigue than you do, lol, and don't want to have to constantly analyze what my journey is going to be like. It's just so much easier to put on the helmet when I head out on my bike. It just seems like such a waste to not wear a helmet, imo. The risks are small, I agree, but the consequences are potentially huge and those need to be weighed appropriately as well--the ~60% reduction in injury in the case of an accident could be the difference in a traumatic brain injury that lands you in care for months or indefinitely or lets you walk away, you know? To me, basically any small inconvenience that can keep me from being stuck, potentially paralyzed in a hospital bed for an indefinite amount of time is 100% worth it since that seems like one of the worth possible fates. And I think you might be underestimating the risk on bike paths--my only accident in many years of bike commuting in both traffic and shared paths on a bike was on a separated shared park trail when an oblivious pedestrian stepped out from behind a tree into my path without looking and clipped me--it's caused a permanent knee injury and I'm glad I had a helmet on because I have no memory of what my head was doing--so it's not just cars you have to worry about. In any case, I've gotten a helmets with perks like a visor and ear flaps that incentivize wearing it--I don't have to deal with sunglasses, which I hate messing with, or with wind noise. And I bought a backpack with straps that make carrying it around in shops much less of a pain. There are ways to deal with all of the annoyances it brings AND still benefit from the safety. We can still advocate for more separated lanes and reduce our risk of head injury should we get into an accident on them.

I personally always wear a helmet. Doesn't matter if I'm mountain biking, gravel biking or commuting. That's just my personal choice and comes from my personal experience of a few very close calls. I think it's up to the individual rider. I choose to wear one, but at the same time won't damn someone else for their personal choice to not wear one.

Had my first bike accident last week. Went over the handlebars. Broken finger, messed up knee, broken eye socket. CT scans were clear. If I hadn’t been wearing my helmet, I’m sure I’d have had a serious head injury.

I appreciate this discussion so much. Thank you for putting this info out there for us to help make our own informed decisions.

This was thoughtful and informing! Thank you for deep diving into the topic!

Whoa! I really loved this! What seemed like a cavalier question about safety turned into a fantastic, in-depth, and well informed cycling safety discussion. As an individual whose been in a major cycling accident (while not wearing a helmet) I have to say I think I'll be wearing mine without exception for the foreseeable future; However Cailynn's research, and your discussion, have definitely changed the way I think about cycling safety in general. Thank you!

I loved this video. I have rode for 40 years and had my share of crashes. I have never hit my head. I wear a helmet since I typically have to mix with traffic between the shared paths but it is just there on the off chance I get hit at an angle and hit my head. I make sure to have my lights working and keep my bike maintained and this has kept my incidents very low. This is such a great channel. Thanks for the great information.

Thank you both for this fascinating conversation. I do realize that a foam hat will do little to protect me if I get right-hooked by a: dump truck, cement truck, semi, or bus (I've heard about and seen all of these). I still wear it, because I've fallen off my bike a number of times; they were all slow speed and my fault, and one of these days I might hit my head. I'd rather have a concussion than a concussion with a skull fracture. Also, governments don't do well with nuance.

I ride a lot with my bike since childhood and I believe I am on the more aggressive side of the riding styles out there. But I would also consider myself somewhat "expert" since I am also riding downhill races and road bike races. Also commute daily here in Berlin. And from my experience of crashing and seeing other is, that yes you rarely fall on your helmet. But when you do, a helmet is your life insurance. And always remember - nobody ever wanted to crash but it will happen (somewhat by definition) when you don't expect it. So yes, my takeaway is there a are more important things we and our cities can do to stay safe - so don't ride like Rambo without any lights and reflector on you or your bike at night and expect that you are safe because of a helmet. Also cities must understand that we will probably die when we hit a car driving 50 km/h probably not because of brain damage but damage to internals and organs (I know) - so telling riders to wear a helmet but not doing anything for infrastructure is not doing shit. But please never compromise on obvious safety. For me a helmet is still a no brainer - pun intended.

Great video, thanks! Excellently researched Caitlyn, and I really enjoyed the tone and conversational style presentation. As an Australian, I hope this video and more conversations like it can push us to change the helmet laws.

I don't commute by trike and never will since I work from home, but I always wear a helmet on my tricycle rides. I'm already severely disabled partially due to neurological issues, I don't need to hit my head in a tricycle accident to make it worse.

Ironically, the best place to wear a cycle helmet is on protected infrastructure. There's a good chance a cycle helmet will provide some protection if you fall off your bike at low speed. Cycle helmet certification tests generally involve a drop onto a surface from a couple of metres, so that's the sort of collision they're designed to withstand. If you're mixing with cars, then the cycle helmet is only likely to be of much use in a very low speed collision (

Great video. Fascinating data. Thanks. Two years ago I came off my bike at very slow speed when my front wheel ‘went from under me’. Trees on both sides of the track, which I didn’t hit, but I just rolled across the ground and was just shook up. Three months later I was in a hurry to get to the doctors and miss timed a ‘bunny hop’ and hit the pavement (sidewalk) hard. Brick wall to the left and steel railings on the right. I landed on my left shoulder which triggered arthritis which is a constant reminder. Two weeks ago I was working on some scaffolding and walked at speed into the end of a scaffolding tube (that should have been protected). I wasn’t wearing my hard hat. Hospital and stitches was the result. I always wear a safety hat on my bike and those two falls were lucky that I didn’t hit my head. I’ll carry on wearing it. Those stitches were painful, even WITH anaesthetic. I am not usually accident prone!

I'm still wearing one. I've had friends that had to get taken to the ER after they hit their face on a rock since they were only wearing a half face helmet, not full face. They were so massively injured that they were skipping like a scratched CD, saying the same lines over again, then forgetting what they had just said 15 seconds ago. Scared the hell out of me to see someone so injured with a broken nose, severe head trauma, and a split lip. He made a decently full recovery, but his face is still a bit bent and memory isn't quite as sharp. He was the lucky one. The other guy, a small company CEO, hit the back of his head while riding on a Lime scooter and became permanently braindead. He was not wearing a helmet. Another friend was riding his bike with a helmet, but fell down a flight of unmarked stairs in Seattle that he assumed was a ramp, killing him. The takeaways are that cities will never have perfect infrastructure, and that you should always err on the side of more safety equipment, not less. Because in a crash, even low-speed injuries can really injure someone if they hit their head on a curb, tree, rock, or pavement- no cars involved.

Really an absolutely excellent video, thanks! Thanks for not answering the question for us, but giving us a way to answer it on our own.

A great summary on helmets specifically, and risk assessment in general, much appreciated! We live in Germany, and are still at the stage where our kids are very quick to point out if we've forgotten our helmets - it's so engrained now that we grab and put them on almost without thinking. But it is a lovely feeling to ride without them (when we get the opportunity!)

I wear helmet. It took lot of time for me to decide to get one as I thought I do not need it. I did not see safety issue that significant and i generally did not like having caps on my head. However, one day a friend offered me to try his helmet. And it changed my mindset 180 degree. I was so thrilled that I bought helmet as soon as possible. Not for safety reasons. Just, for comfort. I always struggled with protecting my head from hard sun in summer. Tried wearing various head covers and nothing helped. Everything was more uncomfortable than having no cover. Until I put helmet on. I found out that is solution for my troubles. It covers my head, protecting me from the Sun, but also allowing air to flow freely and cool me down. Helmet is so lightweight that after short time you do not even feel it on the head. It was instant blessing I felt. On cold weather I put thin scarf under the helmet to protect me from the cold air. Again, very useful and comfortable. So, for years I wear helmet. Now, about safety. Helmet does have a role in enhancing safety. First thing is, if you use helmet of distinctive color (and especially if you put some reflective stickers on even light on it) it is highly noticeable and prevents lots of odd situations in traffic. I guess that is the most important role of helmet as safety device. Secondly, it does protect your head. If you fall from bike, for whatever reason, it is surely better that helmet takes impact with the hard surfaces than your head. When I was young attendee of alpine course, instructor told us that wearing helmet while mountain climbing is a must. But he said: "It will not save you from large boulder. If it hits you, even if it does not crack helmet or your scull, your neck would surely suffer hard injury. It will save you from small boulders and rocks that would not kill you but would tear apart skin on your head or face or break bones." I remembered that, and I find it applicable to biking too - if you fall from bike, helmet may save you and reduce serious injuries to minor ones. That said. I started riding bike when I was maybe 7. Now I am 54. I fell from bike numerous times, and my head never touched a ground. That also has something to do with me training martial arts when I was boy, so I do have instinct to handle the fall. So, my personal statistics does not advocate for wearing helmet. Nevertheless, I wear helmet. My son started biking at 7. He wears helmet from day one. It is not that we force him to do so, but we managed to teach him accept helmet as something natural, comfortable and safe. He treats helmet same as sunglasses. He actually had one incident, riding down the hill and he lost control, feel from the bike and slammed strongly with his temple to the edge of a sidewalk. That is the nastiest hit in the head you can imagine falling from the bike. That kind of blow in a head may be lethal. He wore helmet that took the hit and it saved him. Probability for such incident to happen is very low, but if it happens, it happens. Some would say: better be safe than sorry. He wears helmet all the time. No one has to tell him to. I do not advocate wearing helmet. Whenever I am involved in such discussion I just tell this same story and advise people to try it out. If one likes it, feels comfortable and maybe feels safer, then why not wearing it? If he does not feel like it, then he should not. It is just matter of preference.

Hi. This is the best treatise on bike helmets I have ever heard. If I could give you 10 thumbs up I would. I don't have a helmet and in 50 years I crashed 5 times, twice (when young) being stupid, twice caught out by ridges (railwayline syndrome) and once by rain. That last need never happen again because it was the result of chromium plated rims which meant no brakes in the heavy rain. They are obsolete. I once thought about helmets as I careered down hill at over 30mph about the consequences of a crash and I quickly thought "why a helmet and not a back brace, or full body armour"? If carrying on cycling was that dangerous then it was time to stop. 20 years later I'm still riding. In your friends history, she neglected to mention the UCI mandate of helmets. Before that helmets were rare but seemingly over night the helmet scourge struck. Ordinary cyclists riding alone felt the need to protect themselves the same as pros in the bunch sprint. Ridiculous. Another thing of interest is that here in the UK our Highway Code has followed some other European countries in establishing a hierarchy of harm to persuade those that do the most harm (drivers of ever larger vehicles) need to take more care around more vulnerable users (cyclists, pedestrians etc) and established a rule of passing at least 1.5 metres away. In my recentt experience this has helped enourmously. Well done with this vid yet again, really great.

Regarding the point about lower accident rates with rideshare bikes, not only are you sitting upright for better visibility and comfort, their design also usually permit you to be able to put your feet on the ground easily while still seated on the saddle. This can make it easier to safely stop with little to no notice, never mind balancing when waiting at a stop or red light. Most bikes sold in the US don’t let you do that.

I recently injured my leg in a bike crash. Interestingly enough, the first question from many people upon hearing my leg was hurt was "were you wearing a helmet?" (I wasn't). I've been chastised over and over again for it, which is sort of fair, but... I broke my leg. A helmet wouldn't have helped in this case. What would have helped is better traffic calming and bike separating infrastructure in my neighborhood, because my crash had a lot to do with turning at high speed to try and match the pace of traffic.

For years I rode, trained and raced road bikes. I rode about 200 miles a week and over the course of time I broke 2 helmets the hard way. People can do as they wish but I will choose to wear a helmet.

Great video, very helpful perspectives and thorough information!

Bikes have always been my main mode of transportation. (Mainly motorcycles) I'm a firm believer in helmets because I've seen what they can do and I've also seen how easily a simple fall can cause brain injury. I didn't really wear one for commuting on the bicycle but now that I got a 29er, I'm looking at name brand helmets. Fly racing has been my go to brand and they've got some good looking helmets. Also, those e-bikes? I'd go with a full face mtb helmet for that.

I've broken my arm and wrist on my bike while wearing a helmet. I've stopped wearing one for my commute or getting groceries. I ride slower and more carefully without the helmet. Love the coverage on this topic.

Would never make a negative comment on someone not wearing a helmet. My bicycle helmet shades my head while maintaining a breeze. It supports largest model "Da Brim" sun visor for even more shade out in the sun! Bottom of my "Da Brim" is black to further reduce brightness from indirect glare. My bicycle helmet mechanically supports largest bicycle rearview mirror! My blue eyes highly favor BOTH, shade, AND dark grey (not brown lenses) sunglasses! Senior handicapper on my "Hase" trike here, that may never need a helmet for safety. A helmet can also support electronics for communications, radio, lights, and reflectors too. Love both my "Hase" stream-lined rain fairing and my fairing-attached "Hase" rain poncho! Just remember the beautiful sound of rain on your childhood, hooded rain poncho. Love both cloudy riding days and actually riding in the rain! One then OWNS the bicycle trail, along with the wildlife. LOL! Multiple reasons for helmet wearing, beyond potential for safety!!! However, would NEVER argue here with someone who does not want to wear a helmet! Gary "Jason Stillwater" in the recumbent world.

Helmets save brain cells. I'm a cyclist and a physician who has worked in brain injury rehab. In severe multi-trauma with significant injuries to many body parts, a helmet probably won't save you from a brain injury (aka concussion) or death. If you do survive, what a helmet may do is lessen the degree of brain injury from severe to moderate or maybe even minor. Severe brain injury means that you have permanent physical damage to the brain that can be imaged on MRI or CT. This usually comes with loss of personality, loss of cognition (memory, attention, complex reasoning etc. etc.). You are not the same person you were before and may depend on others caring for you for the rest of your life. With a lesser degree of impact a helmet may save you from a moderate brain injury characterized by loss of memories extending beyond 24 hours before and after your injury, and loss of consciousness of greater than 30 minutes. Moderate brain injuries may include physical permanent damage to the brain with retention or recovery of many if not all cognitive abilities. With a bike helmet on you may end up with a mild traumatic brain injury. This includes loss of consciousness of 30 minutes or less. You may not even lose consciousness at all, but feel dazed or spaced out. There may be loss of memories for events a few hours before and after the event. The damage is physiological with no permanent brain damage. Most people get better within 2 to 12 weeks. And my two crashes? Both on Calgary bike paths. On one, a skateboarder jumped off a wall next to the path and wacked me off my bike. I did a pretty good roll and was OK with no symptoms of brain injury at all. My helmet was cracked to shit though (as it was designed to do). On the second though, an unrestrained dog ran under my front wheel. That's my last memory till I was in the shower at work wondering why I ached so badly. That was about 5 km from the crash site. Again, my helmet was smashed to shit. I have no idea whether I was unconscious or not. The dog owner obviously didn't care and didn't call EMS etc. I had to take a week off work as I couldn't concentrate enough to do intellectual work. Two weeks later though I was well enough to be the convenor of a conference in Toronto - on ........... traumatic brain injury. In both cases the helmet saved me from a greater degree of injury - in the second case possibly permanent. This is my own experience, but the stats back me up. So even the seemingly safest ride can be the one with the unforseen event. I don't leave home without my helmet.

For the last few years, I've been wearing a helmet while biking and skiing to keep my wife happy. I think in both of those sports, it used to be normal to not wear a helmet, but it is now thought of as a critical safety issue. A few weeks ago, I took a spill on my bike for the first time in 15 years. I just took a corner a little too fast while it was raining. I got pretty banged up and had some scratches on my helmet -- so I'm glad I was wearing it -- even though it would have likely been a minor scrape. While I now feel more comfortable wearing a helmet than not (especially in traffic), I'm fine if others decide to go without. I also think that bike injuries and fatalities are overblown in the statics because of people who do not ride safely (salmons), people who ride with unsafe equipment (no brakes), and people who ride without lights at night. Frankly, it's pretty scary how many people I see riding like this. I've considered starting or working with a charity to help lower-income people overcome some of these issues. Focusing on overall safety with some resources to help low-income people would go a long way in improving the bike statistics.

Here's a fun subversion of expectations. Flip the script and wear a helmet when you walk or drive somewhere, then point out that you're just as likely to get injured in this context.

When I was about 8 years old I rode home from a friend's house in the evening. We lived in a small village and it was winter so it was already very dark at 9 p.m. although there was no snow. When I crossed the street and wanted to drive onto the sidewalk my front tire slid on the edge and I fell. I cracked my skull open on the edge of the sidewalk. To this day I don't know how long I lay there on the street, in the cold but there were no people out at that time, no cars driving along the quiet village street. Everyone was already home. Inside, warming their feet at the fireplace. Thankfully I eventually regained consciousness but I was unable to scream due to the incredible pain and unable to think clearly. I somehow managed to walk the rest of the way home (a couple 100 meters) and my parents immediately drove me to the hospital where I spent about a month. I'm now 41 and don't have a lot of memory of what happened after I fell, but I vividly remember the moments before my head hit the sidewalk to this day. I'm lucky that this happened to me at an age, when my skull was still a little malleable and my growing body was able to heal quickly. If this happened to me today with my aging body and more brittle skull, the consequences could be dire. Here's the kicker though: nobody apart from myself was involved in that accident. I was not hit by a car, there was no one around. I just fell and it ended really badly. Is that a bias? I don't know. All I know is that I learned a lesson that day: You should wear a helmet when riding a bike - at all times. Period.

Exhausted making others feel better. I kindly provide these kinds of facts every time someone calls me out. Having been a commuting cyclist on three continents, it's just government laziness to place safety on the individual over correct infrastructure (cars could use safer infrastructure too). The risk assessment is simple: are you going fast, is there complex terrain, is your brain still growing; wear a helmet