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#21
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Helen Deborah Vecht said...
James Annan typed "A light hand force of 5 lbs was Umm... I used to have a grip of 100lb[1]. Of what would 5lb be representative? [1] measured by hand surgeon doing research. -- girlie A bike rider using the brake but not wanting to lock the wheel or go OTB? What do you think would happen if you used that 100lb grip on the brakes going 15.5 mph? Oy, this topic is getting very tired, and all the dweebs trying to concoct a grand conspiracy theory about it is just pathetic. In fact, I would suspect that the typical grip on the brake lever at 15.5 mph would be much less than 5 lb. |
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#22
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Bonehenge said...
I'm on the Board of Directors for a mountain bike advocacy group with almost 700 members in our chapter, and thousands more across other states. I also work at a very busy bike shop. We are located in the US within driving distance for Plattekill Mountain, Mount Snow, and other competitive downhill locations. I have no connection to any manufacturer, bike, fork, or anything else. News of wheel ejections on disc brake equipped bikes would travel very fast, along the lines of "Did you hear what happened to my buddy?" The tale would grow taller as it passed down the line, and eventually everyone would have a "buddy" who had this happen. This is news that would travel quickly at events and festivals. No one that I know has EVER heard of this, 'nor do we see forks with damaged QR seating areas coming in for service at the shop. Should I wear a "sandwich board" to Interbike looking for someone who is familiar with this widespread problem? Forgetting to close the QR dosen't count! G Barry The only place you will hear about it is on Usenet and a few UK based message boards. I believe there is one clear case of it happening--to James Anaan. But instead of him coming to the common sense conclusion that his case was a perfect storm of bad ingredients, he runs around like Chicken Little telling everyone the sky is falling. He had a steel tandem fork without retention lips and a very unfortunate dropout angle. The tandem allows extraordinary leverage and braking forces. You won't be doing an endo by locking the front brake on a tandem. The dropouts were angled perfectly to allow the wheel to pop out if the disc brake pad was a pivot. No retention lips. The painted dropouts meant that the only thing that was really holding the wheel to the fork was the friction of the paint on steel. In the very beginning, he had an interesting story to tell. Now he is like Don Quixote, trying to create a reality that never existed. |
#23
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SuperSlinky wrote:
Bonehenge said... News of wheel ejections on disc brake equipped bikes would travel very fast, along the lines of "Did you hear what happened to my buddy?" If your buddy was Russ Pinder then it might have done just that... The only place you will hear about it is on Usenet and a few UK based message boards. I believe there is one clear case of it happening--to James Anaan. But instead of him coming to the common sense conclusion that his case was a perfect storm of bad ingredients, he runs around like Chicken Little telling everyone the sky is falling. It probably was a perfect storm of bad ingredients, but perfect storms of bad ingredients can happen, and if they can still be avoided without too much extra trouble then there's no good reason not to avoid them. Unless you think complacency is a good reason. Or you could just bluster about saying it hardly ever happens, so it's not a problem. Like Chernobyl, for example... Pete. -- Peter Clinch Medical Physics IT Officer Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital Fax 44 1382 640177 Dundee DD1 9SY Scotland UK net http://www.dundee.ac.uk/~pjclinch/ |
#24
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James Annan wrote:
jim beam wrote in message ... polite as always. james, the point is not my "single case" but the lack of cases that you present to the contrary. post some pics of forks evidencing slippage if you please. http://www.velotech.de/saz_12_-_03_-_05.pdf which I found by googling a previous post of mine in r.b.t, so don't pretend you haven't seen it before. Unfortunately, I can't find the rebuttal that you presumably offered, so I'd be grateful for a reminder. i have deep regret that 1. my german is not strong enough to follow all of the text 2. that i don't have either the time or the ax to grind to look for this stuff. only when i show up on r.b.t. do i ever get to see articles like that, so please james, emotive language like "don't pretend you've never seen it before" merely serves as antagonism. now, to address your cannondale point, it is clearly a carefully guarded response, but i fail to see how you'd expect anything else Is this really all you can bring yourself to say about it? Let me remind you of their test: "A light hand force of 5 lbs was applied to the brake lever every 10 seconds for 3 seconds duration. This caused braking torque to be applied to the wheel. The drums had 3 equally-spaced cleats (0.5" high the same as those used on wheel fatigue test T027) to create bumps for the front wheel to go over." And then we have: "Conclusion: "The conclusion is that the braking action of disc brakes is not causing the quick release mechanism to unscrew. This test is unable to cause loosening. At this time there are no reasons to believe that anything is missing or over constrained in this test." i did read it, thanks. what is restatement trying to achieve? You describe that as "carefully guarded, but i fail to see how you'd expect anything else"! Remember that this is not just something they happened to have done and offered to throw into the ring, but a piece of work they were specifically commissioned to do by the CPSC in order to investigate whether there was a potential danger. Have you really no "reasons to believe that anything is missing or over constrained in this test"? You have no opinion beyond "carefully guarded, but i fail to see how you'd expect anything else"? I would be equally amused to hear Mark Hickey's assessment of this test, and Tony Raven's, too. you're just too busy being a victim to make progress in this. if you're serious about getting traction, why don't /you/ commission an independent test from a reputable third party and have your attorney submit it? habeus corpus. any attorneys here want to represent james? |
#25
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James Annan wrote:
I would be equally amused to hear Mark Hickey's assessment of this test, and Tony Raven's, too. I'm staying out of this. My views are well known and there is not a lot of point repeating them in the church of the faith. I did plan to do what no-one seems to have done and go and find out what 5lbs force on the brake lever was like. I know I don't squeeze my brakes as hard as I possibly can so I know 100lbs is not realistic. However I have no idea at present what 5lbs represents in my normal range of braking. Is it top end, bottom end, middling? Can anyone here say yet because until they can then ridiculing the figure absent realistic reference points is conviction not scientific enquiry. Damn, I just got sucked in. Tony |
#26
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jim beam wrote in message ...
James Annan wrote: jim beam wrote: James Annan wrote: snip "The conclusion is that the braking action of disc brakes is not causing the quick release mechanism to unscrew. This test is unable to cause loosening. At this time there are no reasons to believe that anything is missing or over constrained in this test." james, did you check out the pics i posted of my own disk brakes? Yes, but if you thought I'd be interested in a single case of "my wheel didn't slip" then you have missed the point very very badly indeed. polite as always. james, the point is not my "single case" but the lack of cases that you present to the contrary. post some pics of forks evidencing slippage if you please. dismissal of evidence that contradicts your accusations does not add credibility to your case. bottom line is this; put yourself in the position of a manufacturer. are you going to pay attention to a guy on the net who, with respect, misses a vital part of their analysis, then descends to personal attack when challenged, or are you going to rely on your distributor network's return data? This from Mr. Sock Puppet! It's too rich! Did it ever occur to you that few people pay attention to your counterexample not only because it's somewhat beside the point, but that you've proven yourself unreliable here on rbt? James may be "a guy on the net," but at least he makes his name and his qualifications known. By your own reasoning, we should give no credence to you. trust me, i have been carefully on the lookout for potential ejection problems among all the people i've ridden mountain with since you raised this issue, and you may be interested to learn that i have actually seen one case of slip! but problem is, there was no ejection and it was clearly attributable to an open cam skewer, badly crudded up, that the rider couldn't be bothered to close properly. so, like a broken chain that's attributable to it not being fitted correctly or an under-clamped brake cable slipping and causing brake failure, the only disk wheel slippage i've seen was due to incorrect skewer deployment. and even then, if i hadn't been specifically looking for the slippage, the rider would never have known because he hadn't, nor had he /ever/ had, any problems! certainly not anything as serious as ejection. now, to address your cannondale point, it is clearly a carefully guarded response, but i fail to see how you'd expect anything else in the face of a serious liability threat that's not supported by any statistical evidence. It wasn't a carefully guided response. It was a confidential communication between Cannondale and the CPSC and under the circumstances both of them probably have a legal duty to be forthright about the facts regardless of the legal consequences. Furthermore, to the extent statistics has a bearing on this issue, it also should clue you in to why your counterexample doesn't count for much. Does the fact that I could take photographs of thousands of upright SUVs mean that SUVs don't have a rollover problem? mtb brakes changed from cantilever to linear p.d.q. once it was established that incorrect usage combined with fouling could send a rider over the bar. i don't know the numbers, but i'll wager there were not many o.t.b's before manufacturers made the switch, however statistically unlikely. unless disk brake ejection is actually evidenced, then who is going to fix a problem that doesn't exist? Now, have you any "reasons to believe that anything is missing or over constrained in this test"? Inquiring minds want to know... James |
#27
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On Wed, 15 Sep 2004 15:05:32 +0100, Helen Deborah Vecht
wrote: James Annan typed "A light hand force of 5 lbs was Umm... I used to have a grip of 100lb[1]. Of what would 5lb be representative? [1] measured by hand surgeon doing research. The grip force required to lock up the wheel is far less than that with any useful braking system, of course. Still, it appears to me that they designed a passable test rather than an exhaustive one. If so, they may have shot themselves in the foot; should a later determination show that their test was flawed *and that they had reason to know this*, the investigators will not be pleased. I agree with another poster's statement; a variety of application pressures, a range of bump sizes with simulation of jumping (some of which is "landed" with the brakes engaged), and a higher stress and load level in general seems to be merited. In their partial defense, I will note that they seemed to be focusing solely on the issue of whether common, normal vibration levels in low-stress riding could result in QR loosening. I'm pretty sure that's the wrong question, and in any event, they tested only one QR design. Combined with the lack of test conditions that simulate the popularly-expected potential failure mode scenarios, I feel that it is best to regard this test as not dispositive of disc brake safety in and of itself. All that said, I'm still going to keep riding the bike that has a front disc. I'm not convinced that there's a significant wheel ejection hazard in the type of riding that I do. -- Typoes are a feature, not a bug. Some gardening required to reply via email. Words processed in a facility that contains nuts. |
#28
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Helen Deborah Vecht wrote in message ...
"Paul - xxx" typed How was the 5 lbs measured ? As an ex Torque Control Engineer (Desoutter / Georges Renault) I feel the tests would be more relevant using a range of braking forces from light to as much as possible, commensurate with the force a human hand can exert ... This is, I believe' in the 100-200lb range and consistent with panic braking. IMHO all bike equipment has to cope well with maxima. Seems the real world question is how much lever force is required to lock up the rotor. Beyond that all you are testing is the lever strength. Given that disc systems are designed for single digit applications, and most levers accept no more than two fingers, using full hand grip strength is not valid. I found some data on grip & pinch strengths at http://www.bleng.com/pdf/grip1.pdf for anyone interested. Dave D. |
#29
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in message , Helen Deborah
Vecht ') wrote: "Paul - xxx" typed How was the 5 lbs measured ? As an ex Torque Control Engineer (Desoutter / Georges Renault) I feel the tests would be more relevant using a range of braking forces from light to as much as possible, commensurate with the force a human hand can exert ... This is, I believe' in the 100-200lb range and consistent with panic braking. IMHO all bike equipment has to cope well with maxima. The people who point out that if you slam on the brakes on a mountain bike you go over the top anyway are right, you know; I've seen it happen. And hydraulic disk brakes are very sensitive. So Cannondale's five pounds may in fact be typical of the maximum safe braking force; certainly my Hayes HFX-9 equipped Cannondale has very light brakes. My own guess would be that panic stop force is slightly higher but it certainly isn't very high. Of course by exerting more force you can lock the front wheel. But the injury consequent on locking the front wheel at speed is not greatly different from the injury consequent on the wheel ejecting at speed. This isn't to say that I believe disk ejection can't happen. I think there's enough independent testimony to indicate it can. But I believe that it is extremely rare in practice. Me? I ride a Lefty. -- (Simon Brooke) http://www.jasmine.org.uk/~simon/ ;; All in all you're just another hick in the mall -- Drink C'lloid |
#30
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in message , Just zis Guy, you know?
') wrote: Helen Deborah Vecht wrote: Umm... I used to have a grip of 100lb[1]. Of what would 5lb be representative? A rider on a disk-brake equipped Cannondale being very, very careful not to make the QR come undone ;-) There's two major objections to that account. Firstly, most disk brake equipped Cannondales do not have quick releases on the front. F series[1] and Chase hardtails, Scalpel, Jeckyll[1] and Prophet full suspension bikes all have Lefty 'forks' which don't have a removable front axle. Gemini[2] models have through axles front and rear. The only models I could find in Cannondale's 2005 'mountain' line up with both disk brakes and a front quick-release are the F600 and the remaining Jekyll. Secondly, as I've pointed out elsewhere on the thread the hand pressure required to lock the wheel with hydraulic disks is not very high and while I wouldn't like to say categorically that five pounds is the maximum safe braking pressure it's in the right ball park. [1] Some older models have Fatty forks which do have quick release; some low end models have non-Cannondale forks which do have quick release. Few of these also have disk brakes. [2] 2005 models certainly; it's possible that some older models have quick release. -- (Simon Brooke) http://www.jasmine.org.uk/~simon/ ;; Usenet: like distance learning without the learning. |
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