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More on disk brakes and wheel ejection
TTT
May you have the wind at your back. And a really low gear for the hills! Chris Chris'Z Corner "The Website for the Common Bicyclist": http://www.geocities.com/czcorner |
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More on disk brakes and wheel ejection
Tim McNamara writes:
Well, this is still preliminary research and whilst it will undoubtedly put a bit of a rocket up the proverbial of many fork manufacturers from our point of view as riders of disc equipped bikes a little perspective is in order. Whilst it is looking like there seems to be an emerging problem the incidences of actual accidents that can be attributed to skewers undoing are clearly very small. Common sense coupled with a routine of skewer checking whilst out on the trails will most likely be enough to limit the problem to a very small risk. In short there is nothing here that suggests mountain bikers with disc brakes should panic and revert back to V-brakes. As they say in the science world, more research is needed. I disagree. A free body diagram shows that forces from a "rear of fork mounted" brake caliper exerts a downward force on the axle and that it is greater than a dropout without retention lips will hold under "normal" closure force. How QR skewers unscrew from vertical axle motion caused by these brake forces has been explained and proven by tests, leaving the "you didn't close it right" apologists out of the running. We don't need no steenkin further research, as they say. All that is needed is to move the caliper ahead of the fork, nothing more. In my estimation, this is the only reasonable solution that would conclusively solve the problem. I cannot understand what all the hand wringing is about. Just do it! This is fretting at its worst. Jobst Brandt Palo Alto CA |
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More on disk brakes and wheel ejection
wrote in message
... Tim McNamara writes: Well, this is still preliminary research and whilst it will undoubtedly put a bit of a rocket up the proverbial of many fork manufacturers from our point of view as riders of disc equipped bikes a little perspective is in order. Whilst it is looking like there seems to be an emerging problem the incidences of actual accidents that can be attributed to skewers undoing are clearly very small. Common sense coupled with a routine of skewer checking whilst out on the trails will most likely be enough to limit the problem to a very small risk. In short there is nothing here that suggests mountain bikers with disc brakes should panic and revert back to V-brakes. As they say in the science world, more research is needed. I disagree. A free body diagram shows that forces from a "rear of fork mounted" brake caliper exerts a downward force on the axle and that it is greater than a dropout without retention lips will hold under "normal" closure force. How QR skewers unscrew from vertical axle motion caused by these brake forces has been explained and proven by tests, leaving the "you didn't close it right" apologists out of the running. We don't need no steenkin further research, as they say. All that is needed is to move the caliper ahead of the fork, nothing more. In my estimation, this is the only reasonable solution that would conclusively solve the problem. I cannot understand what all the hand wringing is about. Just do it! This is fretting at its worst. Whether or not the calliper is moved on the forks there's a lot of expensive bikes out there that will not or cannot get retrofitted. How about Salsa or someone coming out with a front skewer with left handed threads for these bikes. Would that help? John Rees |
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More on disk brakes and wheel ejection
John Rees writes:
Well, this is still preliminary research and whilst it will undoubtedly put a bit of a rocket up the proverbial of many fork manufacturers from our point of view as riders of disc equipped bikes a little perspective is in order. Whilst it is looking like there seems to be an emerging problem the incidences of actual accidents that can be attributed to skewers undoing are clearly very small. Common sense coupled with a routine of skewer checking whilst out on the trails will most likely be enough to limit the problem to a very small risk. In short there is nothing here that suggests mountain bikers with disc brakes should panic and revert back to V-brakes. As they say in the science world, more research is needed. I disagree. A free body diagram shows that forces from a "rear of fork mounted" brake caliper exerts a downward force on the axle and that it is greater than a dropout without retention lips will hold under "normal" closure force. How QR skewers unscrew from vertical axle motion caused by these brake forces has been explained and proven by tests, leaving the "you didn't close it right" apologists out of the running. We don't need no steenkin further research, as they say. All that is needed is to move the caliper ahead of the fork, nothing more. In my estimation, this is the only reasonable solution that would conclusively solve the problem. I cannot understand what all the hand wringing is about. Just do it! This is fretting at its worst. Whether or not the caliper is moved on the forks there's a lot of expensive bikes out there that will not or cannot get retrofitted. How about Salsa or someone coming out with a front skewer with left handed threads for these bikes. Would that help? I didn't mention anything about prior equipment nor did the above comments. The question is what to do about the problem for the future. How the recall and retrofit occurs is a separate matter. That people are wringing their hands about whether it is a real problem and whether it even needs repair is the main problem here. There are many in this forum that are still defending the status quo. Left handed thread??? Please explain what effect that should have. We already discussed that inserting the skewer from the other side doesn't help much and only then when the lever snags something when it unscrews. However, the reason it unscrews is that it isn't holding and moves up and down in the dropout between braking and riding over bumps. Jobst Brandt Palo Alto CA |
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More on disk brakes and wheel ejection
John Rees writes:
Well, this is still preliminary research and whilst it will undoubtedly put a bit of a rocket up the proverbial of many fork manufacturers from our point of view as riders of disc equipped bikes a little perspective is in order. Whilst it is looking like there seems to be an emerging problem the incidences of actual accidents that can be attributed to skewers undoing are clearly very small. Common sense coupled with a routine of skewer checking whilst out on the trails will most likely be enough to limit the problem to a very small risk. In short there is nothing here that suggests mountain bikers with disc brakes should panic and revert back to V-brakes. As they say in the science world, more research is needed. I disagree. A free body diagram shows that forces from a "rear of fork mounted" brake caliper exerts a downward force on the axle and that it is greater than a dropout without retention lips will hold under "normal" closure force. How QR skewers unscrew from vertical axle motion caused by these brake forces has been explained and proven by tests, leaving the "you didn't close it right" apologists out of the running. We don't need no steenkin further research, as they say. All that is needed is to move the caliper ahead of the fork, nothing more. In my estimation, this is the only reasonable solution that would conclusively solve the problem. I cannot understand what all the hand wringing is about. Just do it! This is fretting at its worst. Whether or not the caliper is moved on the forks there's a lot of expensive bikes out there that will not or cannot get retrofitted. How about Salsa or someone coming out with a front skewer with left handed threads for these bikes. Would that help? I didn't mention anything about prior equipment nor did the above comments. The question is what to do about the problem for the future. How the recall and retrofit occurs is a separate matter. That people are wringing their hands about whether it is a real problem and whether it even needs repair is the main problem here. There are many who are still defending the status quo in this forum. Left handed thread??? Please explain what effect that could have. We already discussed that inserting the skewer from the other side doesn't help much and only then when the lever snags something when it unscrews. However, the reason it unscrews is that it isn't holding and moves up and down in the dropout between braking and riding over bumps. Jobst Brandt Palo Alto CA |
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More on disk brakes and wheel ejection
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#7
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More on disk brakes and wheel ejection
Quoth Jobst:
We don't need no steenkin further research, as they say. All that is needed is to move the caliper ahead of the fork, nothing more. In my estimation, this is the only reasonable solution that would conclusively solve the problem. That would require re-desining the calipers, n'es-ce pas? What about changing the angle of the wheel slot in the fork ends to make it perpendicular to the braking reaction force? This would seem a lot easier to do. Forgive me if this has already been suggested and dismissed for some good reason--I haven't been reading all of the posts in this looooong thread. Sheldon "Four O'Clock" Brown +-----------------------------------------------------------+ | Sometimes the only thing more dangerous than a question | | is an answer. --Ferengi Rule of Acquisition #208 | +-----------------------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide http://captainbike.com http://sheldonbrown.com |
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More on disk brakes and wheel ejection
John Rees writes:
I disagree. A free body diagram shows that forces from a "rear of fork mounted" brake caliper exerts a downward force on the axle and that it is greater than a dropout without retention lips will hold under "normal" closure force. How QR skewers unscrew from vertical axle motion caused by these brake forces has been explained and proven by tests, leaving the "you didn't close it right" apologists out of the running. We don't need no steenkin further research, as they say. All that is needed is to move the caliper ahead of the fork, nothing more. In my estimation, this is the only reasonable solution that would conclusively solve the problem. I cannot understand what all the hand wringing is about. Just do it! This is fretting at its worst. Whether or not the caliper is moved on the forks there's a lot of expensive bikes out there that will not or cannot get retrofitted. How about Salsa or someone coming out with a front skewer with left handed threads for these bikes. Would that help? I didn't mention anything about prior equipment nor did the above comments. The question is what to do about the problem for the future. How the recall and retrofit occurs is a separate matter. That people are wringing their hands about whether it is a real problem and whether it even needs repair is the main problem here. There are many in this forum that are still defending the status quo. Well, I didn't see the rest of the discussion. Your post stands as the first in the thread on my newsreader. The post you responded to and quoted was undated, makes it tough for me to located the original thread.. That's a problem between you and your newsreader. It has no effect on presenting technical arguments, suggesting that others "think about it" is a bit rude, especially when the writer hasn't done so. Loosening screws is a common occurrence in machinery for sound reasons. Tightening a screw takes more torque than loosening so with random roughness and motion, loosening is the preferred direction of rotation. By your logic screws should not be lying along roads where they have unscrewed themselves from their designed position. Why even have a dropout? Since there isn't a yellow motorcycle chasing XC riders around in races to make quick wheel changes, why is there a need for a super quick release on a mountain suspension fork in the first place? I take it you don't ride bike. I for one prefer to change my flat tires using a patch kit and not needing a wrench to remove the wheel. When I start a ride I also like to grab a suitable wheel from by "armory" and quickly and simply attach it to my bicycle. How about a closed dropout with a new standard for attaching the front wheel? I see, you are trying to make friends with the many bicyclists who enjoy having easily changeable wheels. I don't think you are being any more realistic about this than your tightening theory. At about this point your admonition to "think about it" comes to mind. Why stick with a design that predates: - Mountain bikes. - Suspension forks. - Disc brakes. The time seems to have arrived to rethink the entire front wheel attachment. That and the concept of four wheels on a car, front engines and doors that open to the rear and many other things that have shown their worth pragmatically over millions of vehicles. maybe we should review the air cooled ace engine and solid axles again. I'm sure you should think about it! Jobst Brandt Palo Alto CA |
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More on disk brakes and wheel ejection
anonymous snipes rudely from cover:
The hand-wringing is over the solid fact that very few of these failures occur. The fact that they DO occur does not imply that there is a fundemental design flaw in the system. While I do agree that the system is not optimal, the entire bicycle, from frame to tires, is a compromise. Strength, weight, convenience, efficiency. Everything. Just because you are too lazy to review the tests and incidents that have been presented doesn't mean there is no evidence and no obvious design flaw in the current arrangement of disk brakes. Just about any moderately astute mechanical engineer recognizes the magnitude of this flaw on inspection, without ever making a measurement. There is also the inconvenient fact that the failures are not a given, and do not happen 100% on all disk-brake/fork systems. This implies that some PART of the system may be more at fault than another, and that the design is adequate (if not optimal) but the execution, in some cases, is inadequate. Dangerously so, in fact. Talk to the rider in the wheelchair whose wheel separation brought focus to this problem that was previously pushed aside because there were no serious injuries YET. Mountain bikers are expected to fall. Why failures are less common than one might expect has also been statistically explained here on this forum. If you were interested, you could look this up in deja news or Google. I will not do your library search. So, I have a solution that is easier than cheaper than your's: If someone is worried about disk brakes and ejection, they should convert to a non-disk-brake system. Cheap and easy. Others can ride their booby trapped bicycles while remembering to not leave the wheels in the frame over a longer number of rides and not to make hard braking stops such as upon landing from a jump. I'm not going to hold my breath over getting real data on this. "Because I said so," or "because it's theoretically possible" aren't good enough answers. As you snipe from the sidelines, manufacturers and merchant are giving their liability serious thought. Of course as a non combatant you can offer all sorts of inane solutions to what you consider a non-problem. I don't understand what motivates you to take this stance that benefits no one. I'm sure you have not testified in a bicycle liability suit but your smug style and off kilter advice would not be seen favorably by the court or the jury. Jobst Brandt Palo Alto CA |
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More on disk brakes and wheel ejection
Sheldon Brown writes:
We don't need no steenkin further research, as they say. All that is needed is to move the caliper ahead of the fork, nothing more. In my estimation, this is the only reasonable solution that would conclusively solve the problem. That would require re-designing the calipers, n'es-ce pas? What about changing the angle of the wheel slot in the fork ends to make it perpendicular to the braking reaction force? This would seem a lot easier to do. I think we went through all that. As long as the braking forces are down and the wheel loads are up, the axle will move and the QR will unscrew. Therefore, changing the dropout slot orientation is only a bandaid and does not attack the underlying problem. The caliper must be in front so that its reaction forces are in the same direction as the wheel load forces. Only then will the reliable retention of the wheel be assured. Forgive me if this has already been suggested and dismissed for some good reason--I haven't been reading all of the posts in this looooong thread. Well, it hasn't been put this way before but it has been part of the argument for caliper placement. I'm glad you brought it up again so that that aspect does not get lost. Jobst Brandt Palo Alto CA |
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