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#11
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dianne_1234 writes:
The University of Limerick Mountain Bike Club has collected some interesting failures. http://www.skynet.ie/~mtbclub/Photogallery/0001_Broken/ I see mostly pictures of a failed tight crank that unfortunately is focused on the pedal rather than the fracture. Just the same, it also shows the failure mode to be one of bending from standing on the bottom of the stroke as most previous pictures of crank failures have. That one interested me because in several photos I think I can see the darker side of the crack on the /inner/ side of the arm, as if the crack had originated *opposite* to the "standing on the pedal at 6:00" argument would suggest. Photos 8-10 are the ones. You will probably agree that the crank broke crosswise, no in torsion (spiral) or to the outside (for which there are no forces). Therefore, without going further into fracture analysis, it is safe to say that it broke inward from the standing load on the pedal. It also appears to me there might be a sudden change in cross section near the break, but I'm not familiar with the crank model. That is not ruled out, but as I said, the pictures are all focused on the pedal leaving the fracture blurred. We need a better photographer and one with a flash or other illumination. Jobst Brandt |
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#13
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On Sat, 12 Feb 2005 23:59:55 -0600, A Muzi
wrote: wrote: The University of Limerick Mountain BIke Club has collected some interesting failures. http://www.skynet.ie/~mtbclub/Photogallery/0001_Broken/ I'm curious how that rigid fork might have failed. The crack is on the left leg, on the back side, and has some light orange rust. The bent right leg I imagine might have collapsed as a result after the left one let go. #31~#34 are forks damaged by jumping. (Or actually, they were fine until it landed.) Dear Andrew, Another poster suggested trials-style riding, so I'm just asking to be sure. Do you mean dropping off a big ledge with the front wheel bashing into the flat ground at the bottom at a steep nose-down angle? (Push the fork back into the frame.) Or am I misunderstanding, and you mean flying jumps where the bike lands fairly flat at high speed on both wheels? (Splay the fork outward.) Carl Fogel |
#14
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wrote:
The University of Limerick Mountain BIke Club has collected some interesting failures. http://www.skynet.ie/~mtbclub/Photogallery/0001_Broken/ I'm curious how that rigid fork might have failed. The crack is on the left leg, on the back side, and has some light orange rust. The bent right leg I imagine might have collapsed as a result after the left one let go. wrote: #31~#34 are forks damaged by jumping. (Or actually, they were fine until it landed.) wrote: Another poster suggested trials-style riding, so I'm just asking to be sure. Do you mean dropping off a big ledge with the front wheel bashing into the flat ground at the bottom at a steep nose-down angle? (Push the fork back into the frame.) Or am I misunderstanding, and you mean flying jumps where the bike lands fairly flat at high speed on both wheels? (Splay the fork outward.) Sorry to be unclear. I meant the latter, as the fork goes the other way in the former, like this: http://www.yellowjersey.org/photosfr...t/NIMGAFRK.JPG As I recall from my youth, when we rode down a large hill then up a berm to get a couple of feet of air, the rear lands first followed by a great _thwack_ as the front hits. That's where I saw this type of failure first. I imagine it wouldn't be as destructive if one could manage to get both wheels to land at the same time. -- Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971 |
#15
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Bill Sornson wrote:
wrote: The University of Limerick Mountain BIke Club has collected some interesting failures. http://www.skynet.ie/~mtbclub/Photogallery/0001_Broken/ I'm curious how that rigid fork might have failed. The crack is on the left leg, on the back side, and has some light orange rust. The bent right leg I imagine might have collapsed as a result after the left one let go. Any opinions? There once was a site with pics Of breaks, and cracks, and strips Along came Carl Fogel The Usenet mogul And Dianne's modest thread was ripped PS: The University of LIMERICK was what I was... never mind. |
#16
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A Muzi writes:
As I recall from my youth, when we rode down a large hill then up a berm to get a couple of feet of air, the rear lands first followed by a great _thwack_ as the front hits. That's where I saw this type of failure first. Hmmm, yes, I remember bending the fork on my Hercules 3 speed in exactly the same way, increasing the fork offset by a good inch or more and making the tire rub the trailing edge of the fender, so that I had to bend it upwards just to be able to still ride the bike home. As I recall, I "repaired" the fork by running the bike into the back wall of the garage a few times until it looked about right. :-O |
#17
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On Sun, 13 Feb 2005 14:00:54 -0600, Tim McNamara
wrote: A Muzi writes: As I recall from my youth, when we rode down a large hill then up a berm to get a couple of feet of air, the rear lands first followed by a great _thwack_ as the front hits. That's where I saw this type of failure first. Hmmm, yes, I remember bending the fork on my Hercules 3 speed in exactly the same way, increasing the fork offset by a good inch or more and making the tire rub the trailing edge of the fender, so that I had to bend it upwards just to be able to still ride the bike home. As I recall, I "repaired" the fork by running the bike into the back wall of the garage a few times until it looked about right. :-O Dear Tim and Andrew, D'oh! I looked again at all the pictures and figured out that I had things backwards. This does indeed look like splayed-out pancake-landing after-jump damage, not the nose-down, drop-off-a-table, low-speed damage that I was wondering about. Thanks for de-confusing me. Carl Fogel |
#18
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wrote:
This does indeed look like splayed-out pancake-landing after-jump damage, not the nose-down, drop-off-a-table, low-speed damage that I was wondering about. It might equally be nose level (or slightly up - or even slightly down) hop-off-a-table, low-speed damage. James Thomson |
#19
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In article .com,
says... The University of Limerick Mountain BIke Club has collected some interesting failures. http://www.skynet.ie/~mtbclub/Photogallery/0001_Broken/ I'm curious how that rigid fork might have failed. The crack is on the left leg, on the back side, and has some light orange rust. The bent right leg I imagine might have collapsed as a result after the left one let go. Any opinions? They need to take better pictures. Most of them are of very poor quality. --------------- Alex |
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