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#11
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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? 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. 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 |
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#12
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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. 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." 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. James |
#13
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James Annan vaguely muttered something like ...
"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 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 ... and varying the pads, configuration of forks, bumps etc as well as having a 'control' set. Maybe they are running more tests and you have interim results ? Did they have a specification to work to for the tests ? -- Paul ... (8(|) Homer Rules !!! "A tosser is a tosser, no matter what mode of transport they're using." |
#14
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"S o r n i" wrote in message ...
Helen Deborah Vecht wrote: Umm... I used to have a grip of 100lb... girlie What are you doing Friday night? Note the tense. Unfortunately it's relevant in Helen's case. -- Dave... |
#15
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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 ;-) 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 |
#16
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in message , jim beam
') wrote: 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. Darth Ben of Kinetics carried out his own independent tests and observed slippage under braking, with properly tightened skewers; and published his results on the net. If this happens in 0.01% of bicycles that's still an awful lot of very nasty crashes. The fact that it doesn't happen in 99.9% of bicycles is good news but does not prove there is no problem. -- (Simon Brooke) http://www.jasmine.org.uk/~simon/ ;; better than your average performing pineapple |
#17
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"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. -- Helen D. Vecht: Edgware. |
#18
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"Just zis Guy, you know?" typed
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 ;-) ^^^ Wrong smiley, Guy. :-( -- Helen D. Vecht: Edgware. |
#19
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Helen Deborah Vecht vaguely muttered something like ...
"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. I'd suggest it may well be more than that .. and there should, if using good engineering principles, be a large margin for error. IMHO all bike equipment has to cope well with maxima. And beyond ... -- Paul ... (8(|) Homer Rules !!! "A tosser is a tosser, no matter what mode of transport they're using." |
#20
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Helen Deborah Vecht writes:
"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. Measuring grip strength is actually a pretty common activity. http://snipurl.com/93vp 100 - 200 lbs is consistent with athletic men. |
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