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Helmets
yk wrote: The price range from $10 - $200. What are the differences ? Are expensive helmets safer or more aero-dynamically designed ? What to look for besides fit and color ? TIA Three things to look for in a helmet, fit, fit and ohh yes, fit. More expensive ones may be 'cooler' in terms of temp and looks but all are approved to the same 'low' standrards of safety in terms of height and speed. 4 ft and 14 MPH... |
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#22
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Helmets
On point! Hell-mutt nazis never address rotation/shear brain injuries. The
statistical data is corrupt but The conspiracy of ignorance masquerades as common sense. wrote in message ... I grant you that. He might have made it to dead sooner w/o the helment. I don't remember anyone blaming his broken neck on the helmet. |
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#24
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Helmets
mark wrote: wrote ... mark wrote: In other words, look for fit, color, an acceptable level of ventilation and a reasonably sturdy retention system. And keep in mind that they really won't help much at speeds over 12-15 mph, and they won't do much good in the typical cyclist/car collision. It depends. If you go head first into a windshield, it will absorb some of the energy, as will the windshield itself. It is certainly better than nothing, but it is not designed to provide full protection from that type of impact. If you are launched into the air, it will absorb the energy of the fall from whatever height your head reaches, up to about 6' (IIRC), due to the acceleration of gravity, and maybe will have some capacity leftover to absorb some deceleration from any frontal impact. All in all, your higher brain tissue may be left intact while the rest of your body (including brain stem)gets beat to hell. I would say that it will do a lot of good in a typical collision, but it will not always be enough. That's nice, I'll be sure and go through the windshield the next time a car hits me, and I'll make sure not to get launched more than 6' into the air. Stop taking it so personally and you might realize that I was trying to explain what protection a helmet does provide, and what it doesn't. If you think about it, your head is only about 4' from the ground when you're on a bike. No matter how hard you are hit, your head will only accelerate toward the ground from that height unless the angle of collision somehow catapults you higher or into the ground. So, in fact, contrary to your original statement, a helmet provides significant protection to the brain in most types of collisions, but it is the only part of the body that is protected to any degree. If you don't want to use a helmet, fine, but at least don't go around spreading nonsense. |
#25
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Helmets
Alex Rodriguez wrote:
ANSI or SNELL sticker is important. Alex, I see this all the time (especially on ride event applications). Guess what? If your helmet is less than 10 years old, it is NOT ANSI certified. And it's there's only a very slim chance it's SNELL certified. Most helmets sold in the US are CPSC certified. See: http://www.bhsi.org/standard.htm Art Harris |
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#28
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#29
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Helmets
On 7 Jul 2005 12:49:35 -0700,
wrote: wrote: wrote: If you think about it, your head is only about 4' from the ground when you're on a bike. Um, you might want to measure that. Um, I would, except I'm nowhere near my bicycle. Is it less than 6'? The answer is yes, so it doesn't matter. No matter how hard you are hit, your head will only accelerate toward the ground from that height unless the angle of collision somehow catapults you higher or into the ground. So, in fact, contrary to your original statement, a helmet provides significant protection to the brain in most types of collisions, but it is the only part of the body that is protected to any degree. You seem to be assuming the "collision" will involve only a rider toppling to the flat ground. Things are a bit more complicated. Um, no, hence the statement "unless the angle of collision somehow catapults you higher or into the ground". Um, you seem to be making the mistake of thinking that the acceleration of gravity is somehow more when you are falling toward the ground as a result of being hit from the side. First, very few topples to flat ground are serious problems. People have been falling off bikes ever since bikes were invented. Those people land on their head only in vanishingly rare cases. IOW, those incidents aren't worth worrying about. (Contrary to modern belief, people actually survived riding bikes in pre-helmet days!) All irrelevant since I wasn't talking about "topples", but bull****, nevertheless. If you don't get an arm out to break your fall, you very likely will bounce your head off the pavement, and the fall from the height your head is at at the time of the crash is sufficient, physiologically speaking, to bash your brains out. The events that are used to promote helmets are those that cause permanent injury or death. The vast majority of those events involve collisions with moving motor vehicles. In those cases, it's very common for the impact speed to be much higher than the 14 mph - that is, to greatly exceed the rated capacity of a bike helmet. But your head still accelerates to the ground at the acceleration of gravity. Perhaps you're imagining that the typical car-bike collision involves simply knocking the cyclist to the ground. But AFAIK, that's never been demonstrated to be the case. Nope, I'm assuming that the typical collision involves getting knocked sideways hard as hell but falling toward the ground at the acceleration of gravity. And even if it were, there's no reason to think the head's impact with the ground would be at only 14 mph. Crashes like that are very chaotic, in the mathematical sense. The only way a car will knock you into the ground at 14 mph is if it is going 14 mph in the direction of the ground when it falls on top of you. Crashes like that are very chaotic, in the mathematical sense. Again, recalling my statement "unless the angle of collision somehow catapults you higher or into the ground", which added to the case of a perfect sideways hit covers _all_ the possibilities of the maximum acceleration toward the ground in that chaos. IOW, the motion of the cyclist's body would be extremely random. It's entirely possible that the cyclist would be energetically "flipped" and have his head impact the ground at higher speed, even if it managed to miss impacting the car itself. Thank you. That would be covered by "catapults". Whatever the details of the mechanics, it's good to keep one fact firmly in mind: Helmets are NOT working as claimed. Head injury rates are not being improved by helmet wearing, and indeed seem to be worsening somewhat. Bull****. Cite needed. There may be other factors involved, but one likely one is that a helmet certified for only a 14 mph impact is - guess what? - actually good only for a 14 mph impact! It protects the head from an impact of 14mph. That says nothing about the speed of the cyclist or a car in a car/bicycle collision. It is also stupid to suggest that no one ever has a bicycle slide out from under them with a resulting bounce of the head off of the pavement, in which case the forward speed of the bicycle is completely beside the point and the impact will usually be very much like simplest case- the acceleration of the head from the height it was before the crash to the ground. If you don't want to use a helmet, fine, but at least don't go around spreading nonsense. Dear SSTW, Below is an idealized rider on a bicycle, travelling sideways after being accelerated to 20 mph by a careless driver and about to hit a 6-inch-high curb: H ----- 20 mph @ 60 inches above ground | | | CM ---- 20 mph @ 36 inches above ground | | | | _____________________________________ |_| 6-inch curb The collision with the curb is likely to spin the rider's head H around his center of mass CM at an impressive rate. I think that this was the point of Frank's example of knocking the bottom of an upright pencil sideways--the rotation around the center of mass can be much faster than the acceleration due to gravity. For a more dramatic demonstration, stand a yardstick upright and give its base a sideways kick with your foot--the top end of the yardstick slams to the floor much faster than it would if it had simply toppled sideways. For fun, someone might calculate the speed at impact of the head of a 5-foot-high "yardstick" under these three conditions: The first calculator on the page below will solve the first example if you put 5 into the foot-field and click outside: http://hyperphysics.phy-astr.gsu.edu...aj.html#tracon 12.2 mph horizontal 5-foot stick dropped from 60 inches (no wind drag) (17.9 fps = 12.2 mph) xx.x mph vertical 5-foot stick toppling sideways, base remains in place, (no wind drag, falling chimney) xx.x mph vertical 5-foot-stick whose idealized bottom is struck by a 20 mph massive object (no wind) A bike and rider, of course, are weighted toward the head end, so the analogy is crude, but the idea of rotation speed increasing fall speed seems quite plausible. Another example would be a 60-inch-high bicyclist's head rotating sideways down onto the hood of a 36-inch-high car hood after being struck by the 18-inch-high car bumper at 20 mph: Head at 60 inches ____________________ | / | | / | | ________/car hood at 36 inches | | / | | / | | _/ ___bumper at 18 inches | | \ ___ ___ | | \____/ \---------------------/ \- |________\___/_____________________\___/____ As Frank pointed out, the calculations are rather tricky, since all sorts of things happen that a crude ASCII diagram can't cover--the driver above might jam his brakes on just as he strikes the bike, so that the rider is sent flying sideways, but rotates downward and hits the ground, not the hood of the car, because the car begins slowing violently just after it hits the rider. Carl Fogel |
#30
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Helmets
Do you wear a helmet in your car? No? Why not? You're more likely to
incur a head injury in your car than on your bike. Why not protect yourself? How about wearing a kevlar vest? No? Not worried about getting shot? The risk is small, but it's there, nonetheless. Have you got those little sticky things on the floor of your tub/shower? No? Egad! Talk about a risk taker! I hope you have plenty of insurance. |
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