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#121
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"Actually you are the first person to bring up this issue"
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#122
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"Actually you are the first person to bring up this issue"
Tim McNamara wrote in message ...
(Jonesy) writes: Tim McNamara wrote in message ... (Jonesy) writes: James Annan wrote in message ... So there you have it. At this rate, by the time next year's complaint comes in, they will presumably have forgotten this first one. How convenient for them. Those who thought that it wouldn't do to kick up a fuss because the poor manufacturers were doing their best, may wish to re-examine their approach. Or else studiously ignore this post in the vain hope that the problem will go away. Assuming, of course, that there actually *is* a problem. There's no doubt that there is a problem. That depends on how you define "problem," and where you draw the line. The problem is that current front disk brake design results in an ejection force being applied to the wheel under normal operation. If the wheel does not actually come out of the drop-outs, then it's less of a problem and more of a design compromise. But that's mere word play. There's no doubt that this force exists, both in free body diagrams and simple experiments anyone can try. I'm not sure where you get the idea that I question that the force exists. I will now allege that you are attempting to set up a strawman to defend your position, considering the part that I wrote about QRs to be *completely missing* from your response. This is not anecdotal, it's readily and objectively demonstrable. You could prove the existence of this problem in less than 60 seconds. The stories of wheel ejection due to this "problem" are indeed anecdotal. We do not know the initial conditions. In fact, one can almost guarantee that the accounts have an assumed *lack* of operator error. This *in and of itself* discredits the value of the accounts. So, there is a problem and there is no doubt about it. This is your *opinion*, not fact. his *is* a design flaw and a dangerous one at that. This assumes that wheel ejection will inevitably happen. An untenable position that you cannot hope to prove. The industry needs to fix it post-haste or they *will* suffer the consequences of millions of dollars in punitive damages sometime in the future. This assumes, again, that wheel ejection is certain. I draw the line in real-world application, not at the force-diagram level. I just plain don't accept anecdotal evidence as proof. As support of hypothesis, yes. As proof? No. There is a difference, and it is real. Well, then, do the very simple experiment with your disk brake equipped bike and prove the existence of the problem to yourself. I have read this half-assed experiment several times, and I will repeat: It is invalid for testing the system as used. Remove the air from your car tires. Drive around until the sidewall fails. Fatal flaw in the design! All sarcasm aside, how the wheel is fixed into place makes all the difference. The front disk brakes creates an ejection force in normal operation. That's as real-world as it gets. Whether the force results in an actual ejection is UNKNOWN. Read that over and over and over until you grasp the implications of it. The only question is how often it happens. That's a very pertinent question. If it doesn't happen often, then it's hard to define it as a problem. The ejection force occurs every time the brake is used. Every time. Now I know you are purposely misreading what I wrote in order to create your strawman. Remove the word "force" from your sentence. Now see how it fits with what I wrote. Every single time. I would hope that seems clear enough. The question of how often a wheel is ejected is important in the epidemiological sense, but from the standpoint of competent design the issue is moot. LOL. Hardly. If the wheel never comes out, then the "design flaw" is purely theoretical! there is no way that it is acceptable that the front brake creates this ejection force- which is of surprisingly large magnitude, exceeding the minimum clamping force requirements under the CPSC rules as has been previously discussed. This is only true if and only if the fork legs are independent of one another. They are not, in ANY fork design. In addition, testing of QR skewers has shown that the vast majority exceed that minimal standard. This is incompetent design, pure and simple. I will agree that it is a compromise. Not ideal, for certain. Guess what - almost all bicycle products are design compromises. That's why stems break, seatposts snap and frame welds fail. I agree that to the poor folks who experience catastrophic failure, it is a very serious problem. But to those folks who go year after year after year without any sort of evidence of difficulty, then the problem just plain doesn't exist. How many people with quadraplegia, traumatic brain injury, or who are just plain dead as a consequence of this design, are acceptable to you? People went year after year without being decapitated by plate glass windshields before safety glass was required- does that mean there was "no problem" with the use of plate glass in windshields? The appeal to emotion is a logical fallacy in and of itself. The acceptance of risk is part of the human experience. I am more in danger in my car than I am at any time on my bicycle, disk-brake-equipped or not. Save your teary-eyed drama - it has no place in a technical discussion. It'll be nice to see all that wonderful, properly-controlled data from the laboratory testing. Think of it like Microsoft Windows: *you* are the testing lab. This is a diversionary argument. Controlled testing will answer the question. Until then, proof doesn't exist. If one were to give weight to the anecdotal evidence, then I would have to judge "no problem" to be the norm, and "problem" to be in the vast minority. Perhaps I am just unwilling to bury my head in the sand and to adopt the attitude of "well, it hasn't happened to me so it's all right." Nor should you. Nor should you grasp at straws and pretend that a few accounts mean anything as far as actual data goes. This is a serious problem with the potential to be life threatening; it is unacceptable and needs to be corrected. Merely your opinion. If the design cannot be corrected then it should be removed from the market and all existing installations of this equipment should be recalled and replaced. *IF* independent testing discovers that, I will agree 100%. But if there are mitigating factors, and this phenomenon is limited to a few select conditions, then I would not go so far as a total recall. Again, if the wheel is never ejected, then the "problem", effectively, does not exist. The designers and manufacturers of these products should have spotted this problem before the first fork was made. It's not like this is obscure and arcane knowledge. It is not as clear cut as you want to believe, either. Your opinion is not fact, nor is it very meaningful in the debate, UNLESS you have hard data that you wish to share. I don't want opinion, or anecdotal evidence, or supposition from climate professionals pretending to be engineers. Proof comes in the form of repeatable experiments, performed with the proper controls. Until that time, I will regard Mr. Annan's pursuit with all the attention it deserves. -- Bob Jones |
#123
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"Actually you are the first person to bring up this issue"
Super Slinky wrote in message et...
He and Jobst Brandt think that everyone besides them are too stupid to understand their sophomoric force diagrams. Step forward Adrian Carter of Pace Racing, and Bob Davis of AriZona Cycles, both of whom make disk brake + QR forks, and both of whom are on record as claiming that a disk brake cannot eject a wheel even without a QR present at all. The typical bike has a dropout angle more or less parallel with the head tube. On my bike this means that using the brake pad as a pivot, the axle hits the dropout at about a 45º angle, which nullifies about 70% of Mr. Annan's ejection force. Bzzt. Wrong, thanks for playing. But don't flatter yourself by pretending that this is a "sophomoric" error, I'd hope that any reasonably bright 15 year old schoolchild would be able to set you right. And in spite of the arrogance of James and Jobst that nobody understands their techno-babble, the truth is quite complex and nobody knows everything that is going on down there. Wait! First it's "sophomoric", but now it's too complex for anyone to understand. I see lots of people throwing up a smokescreen of petty trivia to do with "substandard QRs", knurling, the diameter of the hole in the hub body, but the essential details are clear and straightforward. Even if somebody was to do a first class physics research paper on the subject, it would merely be an academic exercise, because we have a better method for gauging the danger: real world experience. Like the real world experience listed on my web page? Somehow that gets the snide dismissal of "anecdotal" when it doesn't suit your purpose. Why doesn't everyone who is worried about this just switch to a through-axle fork? Beats me. I guess it isn't as much fun as bitching and whining. Beats me why the manufacturers don't say that their disk brake + QR forks are not suitable for use. I guess it isn't as profitable as selling them, and then selling an upgrade as the rider finds out his wheel won't stay in place. James |
#124
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"Actually you are the first person to bring up this issue"
"tcmedara" wrote in message
news:26p7c.20734$Cf3.17366@lakeread01... James is an ordinary bloke. He has raised what you acknowledge to be a valid concern. Where is the evidence that this valid concern has been treated with appropriate seriousness by those who (a) make money by selling the product abnd (b) have the resources to conduct more rigorous tests? That's a whole different problem, and one I could agree with you on. Based on the current facts, this may be worth looking into. Annan did contact the CPSC and was told they didn't see a problem, despite the facts that he offered. Other than Annan not liking the answer, why shouldn't we accept that answer from the very agency charged with the protection of consumers in the US from defective products. So you've had a serious crash, a friend is paralysed for life, a number of experts agree with your analysis that there is a problem and, lacking the necessary resources, you contact the consumer safety body. They come back and say not to worry, they've asked the manufacturers and they say there isn't a problem, but provide zero evidence to back this up. You are clearly satisfied by this response. The fact that most of us would not be says, I think, more about you than about us. The burden of proof should be on Annan in my opinion, not the CPSC. They looked at it, they said "no problem", so what more should they do? Provide some evidence to suggest that rather than ignoring it they have done some kind of analysis. This is not a theoretical problem, it is a problem which is being reported by actual cyclists in the real world. In fact, two problems: QRs coming loose under repeated braking (not considered a problem with rim brakes) and an ejection force applied by the brake. The burden of proof should be, as always, with the suppliers of product to demonstrate that it is safe. Part of that means showing, where a valid concern has been raised, that it has been considered in due detail. The letters on James' site represent well-respected technical experts agreeing that there is a case to answer, cyclists agreeing that there is an apparent problem (two, actually, QR loosening and ejection force), and the major US public safety body doing f**k all. Key words -- there is a "case to answer" and "apparent problem" Poor basis for policy formulation. But excelelnt basis for requiring some kind of proof that the product is safe. Proof which, a year on, is still absent. Which tells us something, I think. As previously suggested, google on Ford Pinto fuel tank fires for details why that assumption is known to be false. I'm sure there's a spectrum of behaviour. Some companies will try to obfuscate, others will step up do what needs to be done. Surf around the CPSC site and look at the breadth of recalls going on across the country. Not all companies are engaged in nefarious deeds to cover product shortfalls. Companies may engage in different behaviours in different circumstances. The keyt is what their lawyers advise them to do. If they recall disc brakes, for example, will that bring hundreds of crashed mountian bikers out of the woodwork claiming for dental work and punitive damages? The lack of a single credible rebuttal is no grounds form an indictement. Actually it would be quite good grounds for an indictment in this case, given the quality of evidence and opinion supporting James. Whether that indictment would result in conviction is another matter. I don't think any company can survive long if they are forced to rebutt any and all criticisms posted on every web site out there. I have had two frame failures on my recumbent. The manufacturer subjected the first to extensive metallurgical analysis, and took pains to ensure that I was supplied with a replacement. By the itme the second failure happened - only the fourth in total out of all the bikes sold - they had changed the grade of aluminium used, unpgraded the headset, changed the manufacturing process and reinforced the area where the failure occurred. They did that based on three failure, with no injuries. Here we have at least two failures documented in detail, one ending in severe injury, and numberous "me-too" incidents. At the risk of promoting lawyers, that's really where the courts come in. No it's not. Courts are for recriminations. I think the guys involved would be perfectly satisfied with an engineering solution to prevent a recurrence of the problem, no lawyers involved. I have a view that it is the lawyers who are preventing a more open discussion of the issues. have you ever heard of a single front wheel ejection (as opposed to a wheel falling out under gravity due to being unsecured) on a rim-braked bike? They've been around for a century or so, so there should be plenty to choose from. It's not about what I may or may not have heard of. Your question is valid, but remains (like this whole debate) in the realm of the theoretical. No, the debate is not theoretical. James' wheel ejected catastrophically causing him to crash. So did Russ', with disastrous consequences. Are there actually more wheel ejections now, or are they just more apparent to those looking for them? As stated: what is the mechanism by which wheel ejection could be caused in a rim-braked bike? This issue is specific to disc brakes. -- Guy === May contain traces of irony. Contents liable to settle after posting. http://www.chapmancentral.co.uk 88% of helmet statistics are made up, 65% of them at Washington University |
#125
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Babble from "tcmedara"
x-no-archive: yes
X-Newsreader: NN version 6.5.0 #2 (NOV) "tcmedara" writes: I may be stretching the analogy a bit, but the point remains -- until there is statistically significant evidence of correlation between front wheel ejection and disk brake use, there's nothing to act on. There's no "problem" that needs to be solved -- by either the gov't regulatory agencies or the manufacterers. I'll be the first to change my tune if a) someone can demonstrate a cover-up, rather than just assert one; and b) show that the QR/disk effect is resulting in real incidents out on the trail. Extremely good point. It occurs to me that all this fuss that cyclists make about broken glass, thorns, etc., is similarly just anecdotal evidence unsupported by any properly controlled large statistical study. And even if it turns out that broken glass does cause punctures, do punctures necessarily lead to injurious accidents? At the moment bicycle accident hospital records don't always record the necessary information. We need a proper epidemiological study to establish just how many people actually do get injured as a result of punctures caused by broken glass. Until we have such data we really don't know if broken glass on roads and cycle paths is a problem. -- Chris Malcolm +44 (0)131 651 3445 DoD #205 IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK [http://www.dai.ed.ac.uk/homes/cam/] |
#126
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"Actually you are the first person to bring up this issue"
"Slacker" wrote in message ... Forgive me, but I'm still a little confused. If the wheel is installed properly there is no problem, so what issue are we talking about? Almost any item can be misused a little and remain safe. Are you guys just trying to cover every single possible act of incompetence and/or stupidity? Nope. but tight enough QRs to be perfectly OK for a rim-brake bike will potentially be dangerous with disks. This is hardly a great act of stupidity or incompetence. |
#127
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"Actually you are the first person to bring up this issue"
Just zis Guy, you know? wrote: So you've had a serious crash, a friend is paralysed for life, a number of experts agree with your analysis that there is a problem and, lacking the necessary resources, you contact the consumer safety body. They come back and say not to worry, they've asked the manufacturers and they say there isn't a problem, but provide zero evidence to back this up. I would like to emphasise that this isn't just about Russ Pinder, although of course his case is well publicised. It isn't even about the other serious crashes I have heard about, several of which required hospital stays and lengthy rehab. From my POV, it's about the _next_ failures, which are readily preventable. Companies may engage in different behaviours in different circumstances. The keyt is what their lawyers advise them to do. If they recall disc brakes, for example, will that bring hundreds of crashed mountian bikers out of the woodwork claiming for dental work and punitive damages? One thing is pretty certain: the manufacturers will not open themselves up to a large number of compensation claims when they finally admit there is a problem. No-one is pretending that a large number of cyclists have been hurt by this, but clearly a modest number have been. For all the pre-emptive vitriol about ambulance-chasing lawyers, the only lawyers that have been heard from so far are those of the manufacturers, issuing their predictably evasive denials. Frankly, if they were worth their salaries, they should be warning their bosses of the unlimited punitive fines and even prison sentences that they could face were any evidence of a cover-up or concealment come to light. Just in case anyone is in any doubt about the matter, manufacturers and retailers have an absolute duty to report any _suspicion_ of a problem to the CPSC (rather than waiting for conclusive proof sufficient to convince the most obstinate). According to my recent correspondent, Avid technical support said: "You most certainly have a big problem with your fork dropouts and/or the QR. I'd get this fork/QR issue handled before you ride any further." Yet the fork manufacturer (two of them, in fact) brushed him off with denial and advice to try a better QR (he was already using Shimano). They are treading a very dangerous path here. James |
#128
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"Actually you are the first person to bring up this issue"
A Muzi wrote:
But the one case where a wheel actually left the fork has a very unusual fork end, exactly wrong, and also lacking LLips. I'm puzzled as to what motivates people to make statements like this which are so obviously false and trivially disproven. There are _several_ cases of wheels leaving the forks mentioned on my web pages (and the linked STW threads), and only two of them involved tandems with badly angled dropouts and no lawyer lips. The rest were all standard commercial MTB forks. James |
#129
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"Actually you are the first person to bring up this issue"
tcmedara said...
Couldn't bear to trim it. I do believe you have said it better than I ever could. And it's just the sort of thing I was trying to get at. I'll take your implied advice now and just drop the subject. It's quickly turning into a Mike Vandeman-like discussion but without the humor. I'm always suspicious of self-righteous indignation and claims of martyrdom at the hands of government and big business. It's usually just a smoke cloud for some one looking to obfuscate the cracks in their own argument. I see we both came to similar conclusions independently. You think the oh-so-objective Mr Annan will ask to post your analysis on his site so readers can make up their own minds? Let us know. I'm not all that hopefull Tom I won't hold my breath about him publishing any point of views except his own. He seems to have a...mental block against anyone's opinion but his own. Besides, I have been kind of hard on him, but from where I sit he invites derision because of his own snide comments which he calls 'irony'. I wasn't necessarily implying that you give up the argument. God knows I have argued about things far past the point of doing any good, but you may help preserve your peace of mind if you accept the fact that he isn't going to be persuaded by anything you say. I just jumped in because I hate to see anyone fight the good fight alone. |
#130
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"Actually you are the first person to bring up this issue"
Tom Sherman said...
Super Slinky wrote: ...If the dropout was angled about 45? forward, there would be no ejection force at all.... Then why not design forks with disc brake mounts with this dropout angle to avoid the problem completely? I have always been willing to concede that James had a point, just not as good a one as he thought it was. The current design isn't ideal and could use some refinement. But considering all the failures possible on a mountain bike, it isn't anything to get excited about. |
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