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#31
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Spokes tension with hot rim
On Tue, 27 Jan 2009 13:58:12 GMT, Brian Nystrom
wrote: wrote: Dear Sergio, Probably not enough to regain the spoke tension lost when the the tire was mounted and inflated. Most wheels are built and tensioned bare, so their riding tension ends up noticeably lower because of the tire constricts when inflated. (Cheap wide single-wall MTB rims actually work the other way, gaining spoke tension with higher tire pressure, but I expect that we're talking about typical narrow 700c rims here.) Here's Dianne's page showing how increased tire pressure lowered spoke tension: http://www.geocities.com/dianne_1234...-inflation.htm Dianne found that 120 psi lowered 95 kgf bare-tire spoke tension ~13% to 81 kgf. Interesting. Just for laughs, I tried this on the front wheel of one of my bikes, a Mavic GEL280 rim (36 hole tubular) laced to a Record hub with DT Revolution spokes, with a Continental Sprinter tire. I pumped it up to 100 psi (my normal riding pressure and stuck a Wheelsmith tensiometer on it, then deflated the tire completely. It was really hard to tell if the tensiometer reading moved at all, but if it did, it was a matter of a few thousandths on the scale - essentially no difference. Any idea why this is? Is is just another tubular vs. clincher thing? Are DT Revolutions magic spokes? Is the Wheelsmith tensiometer junk? The glue absorbs the difference? They just don't make rims like they used to? Dear Bryan, Check a clincher, and check it at 120 psi. If the Wheelsmith tension gauge doesn't show a difference on a clincher at 120 psi, then the gauge is the problem. The Wheelsmith gauge is a different design than the Park tension gauge and might stick. I'll be surprised if tubulars behave differently than clinchers. The constriction is caused by the angle of the tire plies, which should be the same. A good analogy is that the tire plies work like a scissors jack as inflation expands them--notice how the scissors shorten as they expand? Here's a 24-second video of a Park gauge on a deflating MTB rim, which is a wide single-wall rim that confusingly causes the tension to drop: http://www.youtube.com/v/NeG5o3WX7Mw That should give you an idea of how small a change a tension gauge will show--the needle moves from a bit above mark 24 to just below it. And the gauge will move the other way on a 700c rim. The wide single-wall MTB rim behaves oddly because the tire ends up spreading the V of the rim, pulling the spokes at the bottom of the V outward more than the constriction pushes them inward. Cheers, Carl Fogel |
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#32
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Spokes tension with hot rim
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#33
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Spokes tension with hot rim
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#34
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Spokes tension with hot rim
On Tue, 27 Jan 2009 12:11:19 -0600, Werehatrack
wrote: On Sat, 24 Jan 2009 01:01:30 -0700, may have said: Such calculations would have to include the counter-effect of increased tire constriction as the heated tire's pressure increases. Given that your own testing demonstrated that the pressure gain due to practically-likely temp changes is miniscule, the chances of that factor making an important difference in the results seems small. [snip] Dear Werehatrack, You may be thinking of a tire that I dipped in boiling water, which produced no apparent pressure change. But that was just the contact patch and intended to test claims about skidding, which involves only the contact patch for a few seconds. In this thread, we're talking about prolonged rim braking, which is a much more impressive source of heat. Tim McNamara pointed out that Angel Rodriguez put temperature-change stickers on tandem rims and found ~250F in a very short time. From ~70F to ~250F is roughly 530 Rankine to 710 Rankine, about 33% higher absolute temperature and therefore probably about 33% higher tire pressure. A 100 psi tire might see about 130 psi. That kind of pressure increase would lead to noticeable tire constriction changes in spoke tension. Cheers, Carl Fogel |
#36
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Spokes tension with hot rim
On Wed, 28 Jan 2009 15:17:10 GMT, Brian Nystrom
wrote: wrote: On Tue, 27 Jan 2009 13:58:12 GMT, Brian Nystrom wrote: wrote: Dear Sergio, Probably not enough to regain the spoke tension lost when the the tire was mounted and inflated. Most wheels are built and tensioned bare, so their riding tension ends up noticeably lower because of the tire constricts when inflated. (Cheap wide single-wall MTB rims actually work the other way, gaining spoke tension with higher tire pressure, but I expect that we're talking about typical narrow 700c rims here.) Here's Dianne's page showing how increased tire pressure lowered spoke tension: http://www.geocities.com/dianne_1234...-inflation.htm Dianne found that 120 psi lowered 95 kgf bare-tire spoke tension ~13% to 81 kgf. Interesting. Just for laughs, I tried this on the front wheel of one of my bikes, a Mavic GEL280 rim (36 hole tubular) laced to a Record hub with DT Revolution spokes, with a Continental Sprinter tire. I pumped it up to 100 psi (my normal riding pressure and stuck a Wheelsmith tensiometer on it, then deflated the tire completely. It was really hard to tell if the tensiometer reading moved at all, but if it did, it was a matter of a few thousandths on the scale - essentially no difference. Any idea why this is? Is is just another tubular vs. clincher thing? Are DT Revolutions magic spokes? Is the Wheelsmith tensiometer junk? The glue absorbs the difference? They just don't make rims like they used to? Dear Bryan, Check a clincher, and check it at 120 psi. I would, but that wouldn't mean much to me, as I only ride tubulars on the road and I never inflate the front wheel to more than 105 psi, usually 95-100. If this phenomenon doesn't affect the performance of my wheels under the conditions I use them, I really don't care about it. Do any of you have tubulars you can test this on? If the Wheelsmith tension gauge doesn't show a difference on a clincher at 120 psi, then the gauge is the problem. The Wheelsmith gauge is a different design than the Park tension gauge and might stick. I can believe that. I tried it again using the method that Jim suggested. It revealed a very slight variation from reading to reading, but still no obvious difference between 0 and 100 psi. BTW, this was tested on a radial-laced wheel, which I would assume would be a worst-case scenario. I'll be surprised if tubulars behave differently than clinchers. The constriction is caused by the angle of the tire plies, which should be the same. A good analogy is that the tire plies work like a scissors jack as inflation expands them--notice how the scissors shorten as they expand? Ah, that sounds like a plausible explanation. I guess what we need is "radial" bike tires, eh? Here's a 24-second video of a Park gauge on a deflating MTB rim, which is a wide single-wall rim that confusingly causes the tension to drop: http://www.youtube.com/v/NeG5o3WX7Mw That should give you an idea of how small a change a tension gauge will show--the needle moves from a bit above mark 24 to just below it. And the gauge will move the other way on a 700c rim. The wide single-wall MTB rim behaves oddly because the tire ends up spreading the V of the rim, pulling the spokes at the bottom of the V outward more than the constriction pushes them inward. Just for yucks, I tested this on a Mavic CrossMax wheel with a tubeless tire, with the gauge set across the narrow (more flexible) dimension of the spoke. I checked it at 40 psi (the most I ever run in the tires) and at zero. There was a very slight gain in tension - considerably less than 1Kgf - at zero psi. All I can conclude at this point is that for the wheels I ride at the pressures I use, this phenomenon is insignificant. Dear Bryan, Or that your Wheelsmith gauge sticks. Try it on a clincher to see if it works. Cheers, Carl Fogel |
#37
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Spokes tension with hot rim
wrote:
On Wed, 28 Jan 2009 15:17:10 GMT, Brian Nystrom wrote: wrote: On Tue, 27 Jan 2009 13:58:12 GMT, Brian Nystrom wrote: wrote: Dear Sergio, Probably not enough to regain the spoke tension lost when the the tire was mounted and inflated. Most wheels are built and tensioned bare, so their riding tension ends up noticeably lower because of the tire constricts when inflated. (Cheap wide single-wall MTB rims actually work the other way, gaining spoke tension with higher tire pressure, but I expect that we're talking about typical narrow 700c rims here.) Here's Dianne's page showing how increased tire pressure lowered spoke tension: http://www.geocities.com/dianne_1234...-inflation.htm Dianne found that 120 psi lowered 95 kgf bare-tire spoke tension ~13% to 81 kgf. Interesting. Just for laughs, I tried this on the front wheel of one of my bikes, a Mavic GEL280 rim (36 hole tubular) laced to a Record hub with DT Revolution spokes, with a Continental Sprinter tire. I pumped it up to 100 psi (my normal riding pressure and stuck a Wheelsmith tensiometer on it, then deflated the tire completely. It was really hard to tell if the tensiometer reading moved at all, but if it did, it was a matter of a few thousandths on the scale - essentially no difference. Any idea why this is? Is is just another tubular vs. clincher thing? Are DT Revolutions magic spokes? Is the Wheelsmith tensiometer junk? The glue absorbs the difference? They just don't make rims like they used to? Dear Bryan, Check a clincher, and check it at 120 psi. I would, but that wouldn't mean much to me, as I only ride tubulars on the road and I never inflate the front wheel to more than 105 psi, usually 95-100. If this phenomenon doesn't affect the performance of my wheels under the conditions I use them, I really don't care about it. Do any of you have tubulars you can test this on? If the Wheelsmith tension gauge doesn't show a difference on a clincher at 120 psi, then the gauge is the problem. The Wheelsmith gauge is a different design than the Park tension gauge and might stick. I can believe that. I tried it again using the method that Jim suggested. It revealed a very slight variation from reading to reading, but still no obvious difference between 0 and 100 psi. BTW, this was tested on a radial-laced wheel, which I would assume would be a worst-case scenario. I'll be surprised if tubulars behave differently than clinchers. The constriction is caused by the angle of the tire plies, which should be the same. A good analogy is that the tire plies work like a scissors jack as inflation expands them--notice how the scissors shorten as they expand? Ah, that sounds like a plausible explanation. I guess what we need is "radial" bike tires, eh? Here's a 24-second video of a Park gauge on a deflating MTB rim, which is a wide single-wall rim that confusingly causes the tension to drop: http://www.youtube.com/v/NeG5o3WX7Mw That should give you an idea of how small a change a tension gauge will show--the needle moves from a bit above mark 24 to just below it. And the gauge will move the other way on a 700c rim. The wide single-wall MTB rim behaves oddly because the tire ends up spreading the V of the rim, pulling the spokes at the bottom of the V outward more than the constriction pushes them inward. Just for yucks, I tested this on a Mavic CrossMax wheel with a tubeless tire, with the gauge set across the narrow (more flexible) dimension of the spoke. I checked it at 40 psi (the most I ever run in the tires) and at zero. There was a very slight gain in tension - considerably less than 1Kgf - at zero psi. All I can conclude at this point is that for the wheels I ride at the pressures I use, this phenomenon is insignificant. Dear Bryan, Or that your Wheelsmith gauge sticks. No, that's not a problem, as I took multiple readings, removing and replacing the gauge every time. It works smoothly. Try it on a clincher to see if it works. I don't have any to test. Seriously, I don't own any road clinchers. |
#38
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Spokes tension with hot rim
On Thu, 29 Jan 2009 15:59:09 GMT, Brian Nystrom
wrote: wrote: On Wed, 28 Jan 2009 15:17:10 GMT, Brian Nystrom [snip] Dear Bryan, Or that your Wheelsmith gauge sticks. No, that's not a problem, as I took multiple readings, removing and replacing the gauge every time. It works smoothly. Try it on a clincher to see if it works. I don't have any to test. Seriously, I don't own any road clinchers. Dear Bryan, Let us know when you manage to find a 700c clincher tire. Seriously. :-) Cheers, Carl Fogel |
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