Crash strategy?
11-19-19, 10:49 AM
#76
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Just stop. You're not helping your case here.
and your first instinct is wrong. Instinct also tells you that you should put your hands out to try to stop the fall and/or protect your head. That works well for our monkey brains and walking speed but our monkey brains fool us when we get faster than walking speed.
I'm not speaking to instinct. When you're starting a roll it's better to initiate with your hand nearer the ground than handlebar height. That comes from being taught by true experts who are much more skilled than you or me, a large number of repetitions, and practical experience. If you're turning over with your hands waist high, that's how you land on your back. That's OK if you know how, but it's not how you want to start a roll.
Look up Kote gaeshi and the hand placement for a break-fall throw as opposed to allowing the attacker to roll out.
Additionally, you aren't going to "roll" all that far. If you let go of the bike, chances are that the bike is going to travel further than you and it will hit you, risking further injury. Holding onto the bike provides at least a little crumple zone so that the body doesn't take the full brunt of the impact. If nothing else, hanging onto the bars keeps you from putting your hands out.
I'm not sure how to approach this, since it's based on a lot of incorrect assumptions. Presumably because as you admit, you have no knowledge or formal experience in break-falls and tumbling.
First, let's nail it down that if we're talking about a roll it's primarily an over the front incident. There isn't any "crumple zone" - the bike isn't going to hit underneath you, or crumple or anything like that.
Second, it's a literal roll, not just bouncing on the ground turning over and over. It doesn't matter how far you roll, except that it's far enough to spread out the change in momentum.
When you do roll, you're going farther than the bike will slide. It's better to have separation from the bike than to get tangled up with it. But more importantly, you can't actually perform a roll while holding onto a bike.
11-19-19, 10:57 AM
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Enough talk. Let's see some video of testing. Start with a person stepping out of a speeding car .... won't be much to argue about after that, probably.
11-19-19, 10:57 AM
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How about you give us a vector diagram for momentum. I can run the vector diagram for momentum in my head and the vector for the momentum downwards is infinitesimally small compared to the size of the forward momentum...especially in your 100 mph scenario. You are the one making the claim, show us how it works.
11-19-19, 10:57 AM
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Okay. Firsdt of all ... sorry, but the idea that speed is irrelvant is Nonsense. Your speed increases the force with which you hit (F=MA.) If you are falling standing, or falling while moving forward at 20 mph, you will Not hit with the same force. Sorry, it's physics.
Anyone who doubts this, have a friend drive you down the highway; when the car hits 65 mph, gently step out of the car. You will only be falling six inches so you come back and tell us about it. Thanks.
As for reaction time---it is partly training, partly reflex.
I Always fight to stay up because I Don't Like Crashing. Can't pinpoint why ... maybe the damage to the bike, maybe the damage to the rider ... some reason.
If I have time.
Some crashes have been so fast, I was hitting pavement before I could move ... maybe a slight twist, but nothing to mitigate the force. other times, I have used a variety of techniques, with more or less success. If I practiced more, I would do it more naturally, but still, some wrecks happen way too fast.
But not all of them. People can Claim that if I could fall with control, I could ride with control and stop the wreck. Those people simply do not know,. Others claim that there is never time to do anything but flop around. Those people simply do not know.
I have been riding on the road, in traffic, for fifty years. I have a bunch of miles off-road. I have crashed a fair bit.
Thing is ... no one needs to validate me. I live my life, so when someone comes along and tells me what I have done is impossible ... okay. Whatever you need to believe.
I will check myself, when someone I respect contests a point. Sometimes my experiences were real but my interpretations were incorrect. obviously I am not infallible or I wouldn't be writing in a thread about crashing.
Anyone who doubts this, have a friend drive you down the highway; when the car hits 65 mph, gently step out of the car. You will only be falling six inches so you come back and tell us about it. Thanks.
As for reaction time---it is partly training, partly reflex.
I Always fight to stay up because I Don't Like Crashing. Can't pinpoint why ... maybe the damage to the bike, maybe the damage to the rider ... some reason.
If I have time.
Some crashes have been so fast, I was hitting pavement before I could move ... maybe a slight twist, but nothing to mitigate the force. other times, I have used a variety of techniques, with more or less success. If I practiced more, I would do it more naturally, but still, some wrecks happen way too fast.
But not all of them. People can Claim that if I could fall with control, I could ride with control and stop the wreck. Those people simply do not know,. Others claim that there is never time to do anything but flop around. Those people simply do not know.
I have been riding on the road, in traffic, for fifty years. I have a bunch of miles off-road. I have crashed a fair bit.
Thing is ... no one needs to validate me. I live my life, so when someone comes along and tells me what I have done is impossible ... okay. Whatever you need to believe.
I will check myself, when someone I respect contests a point. Sometimes my experiences were real but my interpretations were incorrect. obviously I am not infallible or I wouldn't be writing in a thread about crashing.
Agreed because no two crashes are exactly the same. I look at this as I'm playing the odds, which I believe are a lot better if I hold onto the handlebars. Letting go too soon results in giving up in getting control back, and a very high probability that I will injure my hands and/or arms when I hit the ground. There may be crashes where letting go could be the right strategy, I suppose, but I wouldn't bet on my ability to sort them in real time from the ones where I have demonstrated to myself that I do better hanging on.
I think we should all take our own recollections of what we did during crashes with a grain of salt. Everything I've ever learned about human memory suggests that we're likely filling in blanks with guesses and inferences without even knowing it.
I've only gone over the handlebars once in 50 years of riding and that was at the bottom of a hill in San Francisco, I don't think it's very common on flat roads. The vast majority of single-bike accidents I've seen or experienced have involved the bike flipping out from under people for various reasons.
11-19-19, 10:59 AM
#81
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I'm pretty sure you're wrong about physics, too, @wphamilton. I suggest you listen again to what the others are saying. They've convinced me, and you haven't.
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11-19-19, 11:00 AM
#82
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No, you won't. The force you experience is going to be related to the initial speed and the final speed and how much time it takes to change. Falling from a moving bicycle and the force involve is influenced more by the forward momentum and the changes in speed than by the vertical change in momentum. Essentially, you are an elastic body hitting another much, much, much larger elastic body. One will bounce a lot and the other won't. Thus all the force goes into the smaller body.
That's why hitting the ground at 100 mph is going to leave a serious dent.
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11-19-19, 11:03 AM
#83
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I have. The forward momentum goes to zero and the vertical momentum goes to zero. The change in vertical momentum is very small because the velocity is small. The change in the horizontal momentum is huge (and thus the force is huge) because the change in velocity is very large.
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11-19-19, 11:07 AM
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I'm pretty sure you're wrong about physics, too, @wphamilton. I suggest you listen again to what the others are saying. They've convinced me, and you haven't.
But if you want an easy way to visualize the problem, think about an iced-over lake. There's a thin film of water, super-slick. You're somehow going 200 mph, on an skate jet or something (made up device). You fall off, from 2 feet high. How hard do you hit the ice?
edit: disregard atmospheric considerations. 200 is just an example to make it clear.
Last edited by wphamilton; 11-19-19 at 11:14 AM.
11-19-19, 11:10 AM
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I have. The forward momentum goes to zero and the vertical momentum goes to zero. The change in vertical momentum is very small because the velocity is small. The change in the horizontal momentum is huge (and thus the force is huge) because the change in velocity is very large.
11-19-19, 11:24 AM
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Says you. Why don't you show the rest of us how my "case" is wrong?
The "true experts" aren't doing rolls at 20 mph. They know better than to try it. As for having your hand nearer the ground, are you going to say that you should actually try to put your hand on the ground during the roll? I've been looking at a lot of Judo videos and none of them put a hand on the ground to initiate a roll. The shoulder is the first body part to hit the ground in all the videos I've seen.
Yep. Looked it up.
The guy getting thrown never touches the ground with his hand. Where his hand is when the throw is initiated has not relationship to how he hits the ground.
Nope. No "formal" training. Just a crap ton load of practical experience and a lifetime of not experiencing broken bones while crashing. I have also watched a lot of crash videos and there is very little travel of the riders' bodies following the crash. Riders who crash seldom roll more than a few feet even when there is a downward slope in a crash. Even if you tucked and rolled, you aren't likely to roll more than once over.
Let's talk about more common crashes which are usually falls to the side. Over the bar crashes are rare. Even over the bar crashes seldom end with the rider going straight over the bars. They usually fall to the said as the bike and rider pivot around the front steering axis.
Go look at some of the videos of people crashing with their bikes. If they let go of the bike, the bike becomes an unguided missile that can go anywhere. As for performing the roll while holding onto the bike, you can do it. Again, a roll from a fall is only going to be a fraction of a circle. You won't roll over several times.
I'm not speaking to instinct. When you're starting a roll it's better to initiate with your hand nearer the ground than handlebar height. That comes from being taught by true experts who are much more skilled than you or me, a large number of repetitions, and practical experience. If you're turning over with your hands waist high, that's how you land on your back. That's OK if you know how, but it's not how you want to start a roll.
The guy getting thrown never touches the ground with his hand. Where his hand is when the throw is initiated has not relationship to how he hits the ground.
Go look at some of the videos of people crashing with their bikes. If they let go of the bike, the bike becomes an unguided missile that can go anywhere. As for performing the roll while holding onto the bike, you can do it. Again, a roll from a fall is only going to be a fraction of a circle. You won't roll over several times.
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11-19-19, 11:32 AM
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I'm not interested really interested in "convincing" people about a physics problem, especially when they're arguing with me. I'll give you the facts, take it or not.
But if you want an easy way to visualize the problem, think about an iced-over lake. There's a thin film of water, super-slick. You're somehow going 200 mph, on an skate jet or something (made up device). You fall off, from 2 feet high. How hard do you hit the ice?
edit: disregard atmospheric considerations. 200 is just an example to make it clear.
But if you want an easy way to visualize the problem, think about an iced-over lake. There's a thin film of water, super-slick. You're somehow going 200 mph, on an skate jet or something (made up device). You fall off, from 2 feet high. How hard do you hit the ice?
edit: disregard atmospheric considerations. 200 is just an example to make it clear.
There's your mistake. The horizontal momentum does not go to zero until you stop rolling or sliding. Figure out how long that takes, to derive the horizontal force of impact (ie,from friction or hitting something). The vertical force of impact, as you discovered, is exactly the same as you'd have with zero forward velocity.
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11-19-19, 11:40 AM
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@wphamilton, I'm saying your experience of a happy ending after a 65-mph crash may have created a belief for you that is unfounded. You got very lucky, and I think it has led to a misunderstanding.
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11-19-19, 11:54 AM
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Step out of the car, please.
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11-19-19, 12:07 PM
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@wphamilton, I'm saying your experience of a happy ending after a 65-mph crash may have created a belief for you that is unfounded. You got very lucky, and I think it has led to a misunderstanding.
11-19-19, 12:11 PM
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There is no "mistake". If you slide or roll it make little difference. The amount of time needed will be a little longer than if you hit the ground with all the momentum in one direction but it will be small enough that it won't make much difference. Hitting the ground at 20 or 100 or 200 mph with a glancing blow isn't going to be all that different from hitting the ground at those speed directly. The end result will be similar.
And the bolded part is absolutely ridiculous.
11-19-19, 12:39 PM
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As for having your hand nearer the ground, are you going to say that you should actually try to put your hand on the ground during the roll? I've been looking at a lot of Judo videos and none of them put a hand on the ground to initiate a roll. The shoulder is the first body part to hit the ground in all the videos I've seen.
Actually you generally do put your hand on the ground. Moreover, a large part of the significance of the hand placement is where it moves your shoulder. Ideally, the palm or back of the hand, the bent arm, the shoulder and the opposite hip are approximating a curve in the same plane.
If, after Kote gaesh I keep your arm high, and pull your balance forward and then arcing down, you will tend to flip in the air and hit flat. If I take it low in the same motion, your flip can be a gentle roll. The difference is where your balance is when you begin torquing over. Relating to the bike, if you keep holding your handlebars over the top, your shoulders will be too high for an easy roll.
I can do a shoulder roll while holding my arm in against my side. It's considered too advanced for beginners and discouraged in practice because it's easy to get the body position wrong.
Yep. Looked it up. https://www.youtube.com/watch?v=ll1GCzl4Bxg
The guy getting thrown never touches the ground with his hand.
The guy getting thrown never touches the ground with his hand.
He can't, because the other Black Belt is holding his wrist. But you fixated on the wrong point. I'm telling you about how hand position at the start affects the roll or fall. I don't care if his hands are touching the ground or not.
Notice in the first demos - slow ones - how low the hands are and how easy the roll looks. The later ones are faster, but still low hands allowing the roll (although he adds part of a break-fall technique at times). None of them are high-hand turns that compel a break-fall instead of a roll. You need to keep looking for videos, or else accept my word for it. I'm only blue belt not black belt, but this is very basic for Akido.
11-19-19, 12:49 PM
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I've only dumped a handful of times, but IIRC each and every time it was an instantaneous thing. No time for planning or even altering how I landed.
Worst one I had was the front wheel going sideways and sending me straight down onto concrete. No chance to change a thing, in terms of direction, what I landed on, whether to roll or anything. Slid. Got bad abrasions. At ~25mph I can't see how I could have done things differently.
11-19-19, 12:56 PM
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Look, you say you won't argue physics with someone who hasn't studied it ... I won't argue physics with someone who doesn't understand it. Anyone, I don't care if his diploma says "Master of Physics," who claims speed doesn't affect force of impact is an idiot. if speed didn't affect impact, there would be no need for safety systems, helmets, none of that ... because a 0 mph impact---that is, No impact---would deliver the same force as an infinitely fast impact. But we all know that the force of impact increases with speed----We All Know That. Or---we Should.
Again, do the test on video. Step out of a car travelling 65 mph. and just walk away unruffled.
Anyone who has watched sportbike racing has seen riders come off at hellacious speeds ... and walk away after sliding. Sometimes, though ... they die. You survived once and somehow decided that landing at any speed is the same. I suggest you be a Real scientist, and repeat the experiment a few times to verify the data.
Not much more to say here. Video, or you got nothing.
11-19-19, 01:19 PM
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There is no "mistake". If you slide or roll it make little difference. The amount of time needed will be a little longer than if you hit the ground with all the momentum in one direction but it will be small enough that it won't make much difference. Hitting the ground at 20 or 100 or 200 mph with a glancing blow isn't going to be all that different from hitting the ground at those speed directly. The end result will be similar.
You absolutely need to find or estimate the time it takes to come to a stop, because the force you feel is the momentum change divided by the time it takes. Literally all of your horizontal momentum is accounted for in this phase (remember your vectors). Once you have done that, then you've accounted for all of the momentum changes and you'll know that vertical momentum is changed in a short time during the initial impact, and horizontal momentum is changed in the period where you are slowing along the ground. Exclusively in that phase.
Your mistake was in assuming that all of the momentum "goes to zero" in the fleeting moments of initial impact.
Regarding your answer to noglider, I'm afraid you got that wrong as well. You will find yourself sliding at 200 mph across the ice. If you believe that part of that impact is from the 200 mph, then where do you think that momentum went??? You're still the same mass, still the same velocity, therefore still have the same momentum.
11-19-19, 01:27 PM
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So to sum up, the best strategy for avoiding injury in a crash is to land on a sheet of ice. Got it.
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11-19-19, 01:27 PM
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Your point is well taken. My comments were focused on recreational cycling. But, I would agree that those who race and may have gone down more than once or twice can train themselves to react instinctively. All you have to do is see a crash in Moto GP to know that the racers have prepared to take appropriate measures. I have some friends who have been good enough to be invited to Olympic trials with the US. They tell me I'm a solid rider but I know I'm not like them or even near "real" cyclists.
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11-19-19, 01:48 PM
#100
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At this point, I'm not sure if I'm supposed to take up judo or physics to deal with the hypothetical situation that could possibly arise under just the right circumstances to allow me to perfectly time a shift in my hand position during landing, but I'm going with neither.
I'm surprised a gymnast, a third base coach and a professional stone-skipper haven't weighed in.
Right now, I'd like to call in a plumber because this thread is circling the drain.
I'm surprised a gymnast, a third base coach and a professional stone-skipper haven't weighed in.
Right now, I'd like to call in a plumber because this thread is circling the drain.
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