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#11
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Tire-making: bead stress, tire width, math, woe........
On Aug 22, 2:28*pm, DougC wrote:
On 8/22/2011 1:18 PM, thirty-six wrote: The wire stiffens the connection with the rim so that the tyre stays in place. *The wire's strength is of no particular importance, it's the resistance to bending which is key. *... I don't know if I believe that. It would mean that you could take a clincher tire and cut both beads completely through--and then mount & inflate it and still have it stay on the rim, with just as much pressure as with the beads uncut. Obviously the beads are placed under great tension in use, since for ~100 years steel was the only material used and in the last several decades the only other material used has been kevlar (which is also a high tensile strength material). Dear Doug, Jobst cut tire beads and mounted tires, a test repeated by Damon Rinard: http://www.sheldonbrown.com/rinard/tirebead.htm Cheers, Carl Fogel |
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#12
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Tire-making: bead stress, tire width, math, woe........
On 8/22/2011 4:29 PM, carl fogel wrote:
On Aug 22, 2:28 pm, wrote: On 8/22/2011 1:18 PM, thirty-six wrote: The wire stiffens the connection with the rim so that the tyre stays in place. The wire's strength is of no particular importance, it's the resistance to bending which is key. ... I don't know if I believe that. It would mean that you could take a clincher tire and cut both beads completely through--and then mount& inflate it and still have it stay on the rim, with just as much pressure as with the beads uncut. Obviously the beads are placed under great tension in use, since for ~100 years steel was the only material used and in the last several decades the only other material used has been kevlar (which is also a high tensile strength material). Dear Doug, Jobst cut tire beads and mounted tires, a test repeated by Damon Rinard: http://www.sheldonbrown.com/rinard/tirebead.htm Cheers, Carl Fogel That's wonderful! I never would have guessed. It still doesn't explain the need for steel or kevlar however. By my own research, a steel bead costs about one-tenth what a kevlar one does. If making a folding tire was as simple as cutting slits in a steel bead, and tension on the bead doesn't hold the tire on, then why didn't bicycle tire companies just sell them that way? {,,,I would also note that [in the US] the CSPC rules regarding bicycle tires require them to remain on the rim while rolling a certain distance when deflated--so any tire with several inches of slack would still not be legal for sale,,,} |
#13
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Tire-making: bead stress, tire width, math, woe........
DougC wrote:
On 8/22/2011 1:30 PM, DirtRoadie wrote: Just for clarification, when you say "bead strength" or "stress on the bead," you seem to be referring to the tensile force on the wire or whatever material provides the reinforcement of the bead. Is that correct? Yes that's correct. What I'd like to be able to predict is, given a tire's width (cross-section area) and knowing an inflation pressure it should reach, how much tensile strength do the beads need to have. There is also the issue of the security of the interface between rim and tire at the bead. Essentially, with a secure enough bead "hook," the rim would serve in place of the tire bead. Not with any modern tire. The only tires that were retained by a hook-bead rim were the (cotton) cord-bead tires used previous to 1920 or so at the latest. One image, from 1913- http://www.norcom2000.com/users/dcim..._rims_k25d.jpg I have not found anything written that indicated that the tiny ridges on the edges of modern clincher bicycle tires plays any part in keeping them on the rim. By way of further example, a tubular tire requires nothing but the tire itself (no extra circumferential reinforcement) to withstand applicable pressures. The physics of inflation pressure a tubular tire are considerably different than a clincher. The bead need not be contiguous to hold a tire to a rim. This from Jobst, responding to Terry Morse: " Someone (Damon Rinard?) did an experiment to show this by cutting the bead of a tire in several places, and it still held pressure fine. That someone was I and Damon repeated the experiment after heated debate here on wreck.bike erupted when I pointed out that it is primarily the clinch that holds tires on rims. " Full text he http://yarchive.net/bike/blowouts.html -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 |
#14
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Tire-making: bead stress, tire width, math, woe........
On Aug 22, 2:20*pm, DougC wrote:
On 8/22/2011 1:30 PM, DirtRoadie wrote: Just for clarification, when you say "bead strength" or "stress on the bead," you seem to be referring to the tensile force on the wire or whatever material provides the reinforcement of the bead. Is that correct? Yes that's correct. What I'd like to be able to predict is, given a tire's width (cross-section area) and knowing an inflation pressure it should reach, how much tensile strength do the beads need to have. * There is also the issue of the security of the interface between rim and tire at the bead. Essentially, with a secure enough bead "hook," the rim would serve in place of the tire bead. Not with any modern tire. The only tires that were retained by a hook-bead rim were the (cotton) cord-bead tires used previous to 1920 or so at the latest. One image, from 1913-http://www.norcom2000.com/users/dcimper/assorted/inanities/recumbent/... I have not found anything written that indicated that the tiny ridges on the edges of modern clincher bicycle tires plays any part in keeping them on the rim. I was not suggesting that the "secure enough bead hook" exists, just that a sufficient attachment between rim and tire at the bead would negate any need for the bead to have independent tensile (circumferential) strength. Others are describing the same thing in an actual experiment * By way of further example, a tubular tire requires nothing but the tire itself (no extra circumferential reinforcement) to withstand applicable pressures. The physics of inflation pressure a tubular tire are considerably different than a clincher. It was just an example showing that there is no need for the independent tensile strength of a bead to keep the tire from expanding radially and blowing off the rim as a result. Not intended to be a complete analysis of all forces involved DR |
#15
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Tire-making: bead stress, tire width, math, woe........
DougC wrote:
On 8/22/2011 1:18 PM, thirty-six wrote: The wire stiffens the connection with the rim so that the tyre stays in place. The wire's strength is of no particular importance, it's the resistance to bending which is key. ... I don't know if I believe that. It would mean that you could take a clincher tire and cut both beads completely through--and then mount & inflate it and still have it stay on the rim, with just as much pressure as with the beads uncut. Obviously the beads are placed under great tension in use, since for ~100 years steel was the only material used and in the last several decades the only other material used has been kevlar (which is also a high tensile strength material). That is not so nowadays. On modern rims, it is the shape of the interface between tire and rim not bead tension. Older "straight side" rims are a different matter. -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 |
#16
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Tire-making: bead stress, tire width, math, woe........
DougC wrote:
On 8/22/2011 1:30 PM, DirtRoadie wrote: Just for clarification, when you say "bead strength" or "stress on the bead," you seem to be referring to the tensile force on the wire or whatever material provides the reinforcement of the bead. Is that correct? Yes that's correct. What I'd like to be able to predict is, given a tire's width (cross-section area) and knowing an inflation pressure it should reach, how much tensile strength do the beads need to have. There is also the issue of the security of the interface between rim and tire at the bead. Essentially, with a secure enough bead "hook," the rim would serve in place of the tire bead. Not with any modern tire. The only tires that were retained by a hook-bead rim were the (cotton) cord-bead tires used previous to 1920 or so at the latest. One image, from 1913- http://www.norcom2000.com/users/dcim..._rims_k25d.jpg I have not found anything written that indicated that the tiny ridges on the edges of modern clincher bicycle tires plays any part in keeping them on the rim. By way of further example, a tubular tire requires nothing but the tire itself (no extra circumferential reinforcement) to withstand applicable pressures. The physics of inflation pressure a tubular tire are considerably different than a clincher. The bead need not be contiguous to hold a tire to a rim. This from Jobst, responding to Terry Morse: " Someone (Damon Rinard?) did an experiment to show this by cutting the bead of a tire in several places, and it still held pressure fine. That someone was I and Damon repeated the experiment after heated debate here on wreck.bike erupted when I pointed out that it is primarily the clinch that holds tires on rims. " Full text he http://yarchive.net/bike/blowouts.html -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 |
#17
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Tire-making: bead stress, tire width, math, woe........
ever ride on Specialized turbo's ?
Spec uses Roebling's old wire. |
#18
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Tire-making: bead stress, tire width, math, woe........
On Aug 22, 10:44*pm, DougC wrote:
On 8/22/2011 4:29 PM, carl fogel wrote: On Aug 22, 2:28 pm, *wrote: On 8/22/2011 1:18 PM, thirty-six wrote: The wire stiffens the connection with the rim so that the tyre stays in place. *The wire's strength is of no particular importance, it's the resistance to bending which is key. *... I don't know if I believe that. It would mean that you could take a clincher tire and cut both beads completely through--and then mount& *inflate it and still have it stay on the rim, with just as much pressure as with the beads uncut. Obviously the beads are placed under great tension in use, since for ~100 years steel was the only material used and in the last several decades the only other material used has been kevlar (which is also a high tensile strength material). Dear Doug, Jobst cut tire beads and mounted tires, a test repeated by Damon Rinard: *http://www.sheldonbrown.com/rinard/tirebead.htm Cheers, Carl Fogel That's wonderful! I never would have guessed. It still doesn't explain the need for steel or kevlar however. I've explained. By my own research, a steel bead costs about one-tenth what a kevlar one does. If making a folding tire was as simple as cutting slits in a steel bead, and tension on the bead doesn't hold the tire on, then why didn't bicycle tire companies just sell them that way? {,,,I would also note that [in the US] the CSPC rules regarding bicycle tires require them to remain on the rim while rolling a certain distance when deflated--so any tire with several inches of slack would still not be legal for sale,,,} |
#19
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Tire-making: bead stress, tire width, math, woe........
On Aug 22, 11:19*pm, AMuzi wrote:
DougC wrote: On 8/22/2011 1:18 PM, thirty-six wrote: The wire stiffens the connection with the rim so that the tyre stays in place. *The wire's strength is of no particular importance, it's the resistance to bending which is key. *... I don't know if I believe that. It would mean that you could take a clincher tire and cut both beads completely through--and then mount & inflate it and still have it stay on the rim, with just as much pressure as with the beads uncut. Obviously the beads are placed under great tension in use, since for ~100 years steel was the only material used and in the last several decades the only other material used has been kevlar (which is also a high tensile strength material). That is not so nowadays. On modern rims, it is the shape of the interface between tire and rim not bead tension. Older "straight side" rims are a different matter. Fact is, a kevlar beaded tyre will roll off a straight sided rim unless the tyre and rim are clean and grease free at their juncture and preferably something sticky is applied. A wipe with petroleum spirit of a rubber finished bead should suffice to make the bead sticky enough. This is not a practical long term solution. The bead rolls off precisely because it is flexible. Shape can be sufficient to retain the bead until the tyre flats. |
#20
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Tire-making: bead stress, tire width, math, woe........
AMuzi wrote:
ougC wrote: : On 8/22/2011 1:30 PM, DirtRoadie wrote: : : : Just for clarification, when you say "bead strength" or "stress on the : bead," you seem to be referring to the tensile force on the wire or : whatever material provides the reinforcement of the bead. Is that : correct? : : Yes that's correct. : What I'd like to be able to predict is, given a tire's width : (cross-section area) and knowing an inflation pressure it should reach, : how much tensile strength do the beads need to have. : : There is also the issue of the security of the interface : between rim and tire at the bead. Essentially, with a secure enough : bead "hook," the rim would serve in place of the tire bead. : : Not with any modern tire. The only tires that were retained by a : hook-bead rim were the (cotton) cord-bead tires used previous to 1920 or : so at the latest. : : One image, from 1913- : http://www.norcom2000.com/users/dcim..._rims_k25d.jpg : : : I have not found anything written that indicated that the tiny ridges on : the edges of modern clincher bicycle tires plays any part in keeping : them on the rim. : : By way of : further example, a tubular tire requires nothing but the tire itself : (no extra circumferential reinforcement) to withstand applicable : pressures. : : : The physics of inflation pressure a tubular tire are considerably : different than a clincher. : : : :The bead need not be contiguous to hold a tire to a rim. :This from Jobst, responding to Terry Morse: :" Someone (Damon Rinard?) did an experiment to show this by :cutting : the bead of a tire in several places, and it still held ressure : fine. :That someone was I and Damon repeated the experiment after :heated :debate here on wreck.bike erupted when I pointed out that it is rimarily the clinch that holds tires on rims. " :Full text he :http://yarchive.net/bike/blowouts.html I note that neither person claimed to have ridden the tire. Dynamic forces on the bead are much different from static. I don't find the experiment at all convincing. In fact, considering who's proposed it, I consider it anti-convincing. -- sig 126 |
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