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#31
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Carlton Reid on QR safety
In article ,
Helen Deborah Vecht wrote: "Andy H" typed "Richard" wrote in message ... Snip - ......but as I neither sell, use, maintain, nor have any access to disk brakes or QR axles, I could add nothing useful to the debate. R. Then do just that, you have no potential problems do you? Do you have the statistics to hand? Andy H The problem is not statistical. The problem is anecdotal. Many here in the UK will know of a single catastrophic event that might have been the result of wheel ejection. A single catastrophe does not a statistic make but it does not mean there is not a problem. That IS the problem. Please comment upon the force diagram for front disc brakes. -- Michael Press |
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#32
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Carlton Reid on QR safety
On Sun, 05 Feb 2006 04:46:49 GMT, Michael Press wrote:
In article , "Andy H" wrote: "David Martin" wrote in message oups.com... Werehatrack wrote: Those of us who have seen your prior postings about the issue of disc brake ejections are fully aware of your position on the matter. Is it possible for you to accept the fact that for the majority of the readers, the evidence thus far published is not persuasive that there is a serious problem here which is not related to user error? Why do you claim to speak for the majority of readers, most of whom have expressed no public opinion on the matter? ..d Does the fact that the majority of people have expressed no public opinion (read; interest) speak volumes as to the severity of the problem? Do YOU know the relevant statistics to say that this is a major problem or design flaw? Life is inherently risky and I for one would rather check my qr's before a ride and have disk brakes than try to do what I do with rim brakes. I draw inferences from the fact that those who claim there is no problem refuse to comment upon the force diagram. You confuse inaction with refusal; they are not the same. Thus far, the number of incidents documented for which no user error could be identified is small, and there has been no analysis that I've seen showing that the rate of failure varies from what is found on non-disc-brake bikes. Yes, the force diagram indicates that a force can be present which could lead to this event, but the fact remains that in the direct experience of the majority of disc-brake-equipped riders, this force does not have the described effect. Their wheels are not leaping out, and their brakes are, in the main, stopping them safely and surely; as a result, they have a hard time seeing that there's a problem here. To make matters worse, this is not like the flaming Pinto syndrome, in which the result was easily duplicated in a test setting. Of course, as far as I can tell, no one seems to have tried to duplicate the wheel ejection event in a lab, either, or if they have tried, perhaps the results have not been conclusive or predictable; I haven't seen results published in any event. It is very hard to convince people that a problem is both real *and serious* when you don't have anything but math and a few isolated phenomena to offer as evidence. That the problem is real they may accept if they are math-literate, but since nearly everything has risk of one sort or another, it's also necessary to convince them that the problem is serious enough (not just in terms of potential harm should it occur, but more specifically in terms of the potential for the harm to come *to them* at all) before they will be persuaded that action is warranted or necessary. The paucity of demonstrated failures speaks volumes to the masses. Most of the reason I'm taking this position is that it is essential, if the problem is to be addressed, for those advocating change to understand that the task is not merely to show that something *can* occur, but that it is *likely*, and most importantly to demonstrate when, and how, that event is most likely to take place so that a genuinely repeatable demonstration of the risk is possible. Ford did nothing about the Pinto fuel tank until the crash test film was shown on national TV...and the Pinto was a popular car, with a large number of users who were potentially at risk. Bikes with disc brakes are not all that common to begin with, and a flaw in them will be of direct concern to fewer people, so the proponents of change will have to work even harder to develop a compelling argument in favor of mandatory action before the existing and potential consumers can be reached and convinced that they should not buy or use the product until the design has been made resistant to the described fault. As is true for most things, the majority responds only to those things that they both understand and believe are important to them. They remain silent when they are confident that they and their interests are not directly at risk. Thus far, they have been silent on the subject of disk ejection; most are probably unaware of the issue, in my opinion, and this reflects the lack of interest by the news dissemination channels, for whatever reason. But before it will be possible to get the word out, a much stronger case will need to be built, and the seriousness of the risk will need to be much more reliably demonstrable than it is at present. -- Typoes are a feature, not a bug. Some gardening required to reply via email. Words processed in a facility that contains nuts. |
#33
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Carlton Reid on QR safety
James Annan wrote:
Carlton Reid has a puff piece about a new "Secure QR system" on bikebiz: http://www.bikebiz.co.uk/daily-news/article.php?id=6427 While promoting this new mechanism as "safer" than the existing system, he also insists that "industry experts say QRs are safe, when used correctly". This assertion is backed up with a quote from "industry expert" Bob Burns (actually Trek's *lawyer*), which is nothing more than a boilerplate denial dating to a few years ago when the QR/disk issue first surfaced. Strangely, alongside this there is no space in his article for these quotes from people who actually have some relevant engineering and technical experience: to which the response may as well be: "strangely, there's no space in this article for any evidence of this supposed disaster ever being attributable to anything other than inability to use a q.r." --- Chris Juden, Technical officer, CTC: "It's not just scaremongering, but all hangs together and makes perfect sense. In fact I'm kicking myself for not thinking of it before." strange how he hadn't noticed disk brakes ejecting /before/ reading chicken littles tale of doom... "changes must be made to the way disk brakes and front wheels are attached to forks" Jobst Brandt, author, "The Bicycle Wheel": "The more I see on this the more I find the defense of the status quo stranger than fiction. Why are writers trying to say that it can't happen? What motivates writers to claim that disc brakes as currently offered are not a hazard? as above, how are we not swamped with reports of ejected disks here on r.b.t? the chicken littles, would /LOVE/ to jump aboard if ejection was actually an occurrence. The mechanism has been clearly stated, the forces have been identified in magnitude and direction, and credible descriptions of failures have been presented. What's going on here! There is no easter bunny. Believe it!" i'll believe it when i see it. i've been riding disk 3 years - never any slippage or ejection. and i still ask among others i meet with negative results. strange how reality seems to be so easily discounted around here. John Forester, author, "Effective Cycling": "All that I can say is gross negligence." another one suckered into the hysteria. Unnamed Marzocchi Tech Support: "It is recommended that an 8" rotor is not used on a standard axle fork because the forces exerted on the wheel can potentially pull the axle out of the dropouts." un named? that's credible james. especially when force is /less/ for an 8" disk compared to 6". Brant Richards, On-One: "From the next batch, our rigid forks will have dropouts which are angled forward at 45degrees or thereabouts. This is because when I was coming home, and pulling a stoppy outside my driveway, I kept finding the front wheel shifted in the dropout." and his axle faces were serrated? and his dropouts were made of what? Dave Gray, Surly: "You are correct. I've noticed the problem on my Karate Monkey fork." as above, steel fork. Ben Cooper, Kinetics, describing his experiment: "Conclusion: From the above, there seems to be an effect from the disc brake which causes the quick release to loosen." --- eh? "loosening" is not slippage or ejection. And even more strangely, although he mentions the ongoing Walmart case concerning children's bikes, and refers repeatedly to user error, he also didn't find space to mention the recent out of court settlement in which a manufacturer paid off an (experienced adult) rider who was seriously injured by a front wheel ejection on a disk+QR fork. James bottom line, we still have yet to see any disk brake ejection. james, you get 10 points for effort in trying to create this storm, but alas, your teacup of evidence is bone dry. stick to climatology if you want to keep your name in the headlines - this is a q.r. user competency issue, not a disk brake design issue. what's next? the crusade against fundamentally unstable two-wheelers? |
#34
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Carlton Reid on QR safety
jim beam wrote: bottom line, we still have yet to see any disk brake ejection. james, you get 10 points for effort in trying to create this storm, but alas, your teacup of evidence is bone dry. stick to climatology if you want to keep your name in the headlines - this is a q.r. user competency issue, not a disk brake design issue. what's next? the crusade against fundamentally unstable two-wheelers? Fundementally, it's all about James' ego. That's why he busts out his yawn-inducing troll every four months or so. Funny thing - no movement at all in my Shimano XT QR on Marzocchi Flylight 80. Commuter with slicks - lots of hard, high-g braking. Lever got closed at about 80 degrees, which is a little less than normal for me. His chatter, along with the sycophantic "me toos", seems to have no effect on the ability of the QR to do its basic function. Heh. E.P. |
#35
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Carlton Reid on QR safety
jim beam wrote:
i'll believe it when i see it. i've been riding disk 3 years - Clearly you're one of the many who don't need disks riding nothing off-road but the wimpier trails of Marin. bottom line, we still have yet to see any disk brake ejection. So what happened to Russ Pinder, someone who knows how to tighten a QR and checked his before his fateful ride? You're really offensive with your adamant refusal to acknowledge the failures that have happened. Greg -- "All my time I spent in heaven Revelries of dance and wine Waking to the sound of laughter Up I'd rise and kiss the sky" - The Mekons |
#36
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Carlton Reid on QR safety
jim beam wrote:
James Annan wrote: Brant Richards, On-One: "From the next batch, our rigid forks will have dropouts which are angled forward at 45degrees or thereabouts. This is because when I was coming home, and pulling a stoppy outside my driveway, I kept finding the front wheel shifted in the dropout." and his axle faces were serrated? and his dropouts were made of what? What clamping force did he apply to the QR? Was it perhaps less than it should have been due to poor lubrication? What was the geometry and centre of mass of the bike+rider+panniers? What is the maximum instantaneous braking force it is possible to apply for this configuration? No thanks, I'll stick to a design that doesn't rely so heavily on so many unknowns and variables. Adding serrations to directly resist pullout of a critical component is not good design, it's a kludge required to make a fundamentally flawed design work most of the time. See if you can find a qualified mechanical engineer who disagrees. -- Benjamin Lewis Now is the time for all good men to come to. -- Walt Kelly |
#37
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Carlton Reid on QR safety
Michael Press typed
The problem is not statistical. The problem is anecdotal. Many here in the UK will know of a single catastrophic event that might have been the result of wheel ejection. A single catastrophe does not a statistic make but it does not mean there is not a problem. That IS the problem. Please comment upon the force diagram for front disc brakes. I am neither a physicist nor engineer; many here are. I will leave comments to those more qualified. -- Helen D. Vecht: Edgware. |
#38
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Carlton Reid on QR safety
On Sun, 05 Feb 2006 20:31:15 +0000, Michael Press wrote:
Please comment upon the force diagram for front disc brakes. Are there any besides Annan's hand-drawn on a photo? That one omits the vertical load the forks put on the spindle, which at maximum braking effort will be weight of the rider plus ( bicycle minus front-wheel) . To eject the spindle the force trying to do so from the geometry of the brakes will need to be greater than that vertical load _plus_ the frictional force from the clamping of the spindle -- be it QR or hex nut. To do the calculations you need to know the coefficient of friction between tyre & road, and the location of the Centre of Gravity of the rider+bike combination as well as the location of the brake pads, the front wheel & brake diameters, and the wheelbase. Because the CoG of recumbents is somewhat lower than an upright, the braking forces can be greater (10-15% -- not as much better as some believe) so I would expect a genuine problem to turn up first on disk-braked 'bents. I've been reading the HPVA mailing lists and alt.rec.bicycles.recumbents for many years and don't remember seeing this problem mentioned. OTOH, maybe 'bent riders know how to do up a QR properly. Mike |
#39
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Carlton Reid on QR safety
Mike Causer writes:
Please comment upon the force diagram for front disc brakes. Are there any besides Annan's hand-drawn on a photo? That one omits the vertical load the forks put on the spindle, which at maximum braking effort will be weight of the rider plus ( bicycle minus front-wheel) . To eject the spindle the force trying to do so from the geometry of the brakes will need to be greater than that vertical load _plus_ the frictional force from the clamping of the spindle -- be it QR or hex nut. To do the calculations you need to know the coefficient of friction between tyre & road, and the location of the Centre of Gravity of the rider+bike combination as well as the location of the brake pads, the front wheel & brake diameters, and the wheelbase. You can isolate the forces of interest more simply by noting the ratio of wheel OD to brake disk diameter and from that assess forces (assuming a traction coefficient of one, which is appropriate for knobby tires on stiff clay or road tires on dry pavement). The rear portion of the disk rotates upward through the brake caliper that stops the wheel and thereby receives an upward force of wheel:disk ratio times the load on the wheel, even tough the downward force on the dropout is only half the wheel load, each dropout carrying half that load. I think that calculation accurately states the problem and should make apparent why this is a bad design. Forget about GC and other calculations that muddy the straight forward relationship between downward and upward forces on the dropout in question. I think caliper position is an obvious main item for discussion. Jobst Brandt |
#40
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Carlton Reid on QR safety
Werehatrack wrote: On Sat, 04 Feb 2006 13:24:51 -0800, "G.T." wrote: David wrote: James Annan wrote: Werehatrack wrote: Those of us who have seen your prior postings about the issue of disc brake ejections are fully aware of your position on the matter. However, those who read Carlton's article on Bikebiz might think it safe to draw the conclusion that "industry experts say QRs are safe, when used correctly", even though numerous industry experts have quite clearly expressed the contrary view. They will also not know that one case was recently settled in favour of the rider. James Out of court settlements almost always include a statement that the plantiff is not admitting liability. It is often less costly to pay a small settlement than it is to defend the claim, particularly if the jurisdiction is known to be plaintiff-favorable. That first plantiff should be defendant. True, as is the statement so amended. And in fact, in most such cases, getting an out-of-court settlement also has two other beneficial results for the defendant; it ends the case completely without any opening for it to continue through some sort of appeal, and it precludes the possibility that the case can be used as a precedent. Given the combination of cost of defense, the possibility that the suit might initially be lost (and thereby often bring on a spate of me-too suits), the hazard that the defense expense might dwarf the actual settlement if an appeal is (or must be) filed, and the hazard that the finding might be cited in other cases as a precedent, there's lots of reason to shut down the process by making an offer to settle even when the case isn't necessarily all that strong for the plaintiff. The fact is that most cases settle -- except med mal, where the consequences of settlement are significant (doctor gets reported to national registry, premiums go through the roof), and the chances of winning generally are high. Notwithstanding what you read in the news, it is the rare case when a plaintiff wins a med-mal case. Products cases -- even big ones -- usually settle unless there is an exceptionally low chance of liability or the probable award is way lower than plaintiff's demand. Also, some companies just try everything, and some companies settle everything. Toro -- the lawmower company -- puts everything into mediation. Make a claim, go to mediation. In some states, the impetus to settle is being reduced by defendant-friendly changes to statute, often made under the guise of "ending lawsuit abuse". Sometimes, what's billed as an abuse-control measure turns out to be a PLI-defense attorney's nightmare...because the defense lawyers don't get paid the big bucks for doing the slam-dunk early dismissal filings, they only make the big bucks when the case goes on long enough to rack up some worthwhile billable hours. You have been reading too many Grisham novels. Every time some tort reform package is put together, it usually gets smushed like a bug. All I see are statutes creating new claims for relief and not ending them, particularly in the employment field. Look for subtle and stealthy moves by PLI defense attorneys, and more open ones by plaintiff lawyers, to get plaintiff-friendly changes made if their billable hours drop too low. They both have a vested interest in keeping the process alive. There is very, very little legislation proposed by defense lawyers, and most of that is "law improvement" legislation, e.g., clarificaiton of a poorly drafted statute or process-related changes like amending the rules of civil proceedure. Most all of that is done on a bi-partisan basis. Most of the defense-friendly tort reform legislation is proposed by industry or professional organizations including the AMA and the Chamber of Commerce. On the other hand, ATLA and some of the plaintiff's attorneys groups do propose or oppose legislation more vigorously -- which generally means a welter of Erin Brockovich commercials until the legislation passes or fails. -- Jay Beattie. |
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