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#21
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Velocity Fusion Max Tension?
1234 writes:
If you thing it's over-tensioned, stress-relieve the wheel by putting it on the floor and pressing down on opposite sides of the rim. This is not stress relieving. Correct, the rim is quite flexible and deforms easily, so spoke tension doesn't increase enough. Stress relieving is not accomplished by pushing the rim parallel to the axle. That's always true, especially when you push with two hands (as Jeff said, "on opposite sides of the wheel"). But there's at least one exception: if the rim is pushed all around its circumference, not just on two opposite sides. The Rolf stressor box does just this: the hole in the table supports the rim while the cup presses the hub down. This tensions all the lower side spokes simultaneously. Rolf avoids wheel collapse by reducing the tension in the top side spokes at the same time. What is less apparent is that doing this by hand and doing it incrementally at different places around the rim does not accomplish what is needed. In the tensor box, tension of the down-side spokes is doubled while up-side tension goes to zero, thus not overloading the rim in circumferential compression. Besides, doing this manually is hard to accomplish on wheels with fewer than a 24 spokes, the requires force being greater than hands can readily exert and for excessive contact pressure. Jobst Brandt |
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#22
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Velocity Fusion Max Tension?
Thanks Jeff
I still didn't see any tension specs. But I don't think they publish them, or did I miss them also? John |
#23
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Velocity Fusion Max Tension?
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#24
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Velocity Fusion Max Tension?
Jasper Janssen wrote:
On 13 Nov 2005 09:18:36 -0800, "Ed" wrote: Do tell why it is impossible to create sufficient tension by pushing parallel to the axle. Only a few mm of hub to rim 'axial' displacement are required. This does not seem out of reach for mans current ability with machines. What do machines have to do with doing this by hand, exactly? Jasper doing this 'by hand' often involves machines. The leverage of a spoke wrench or the crank arm stress relief lever of Sheldon Brown are examples. Even if JeffWills' method of' 'pushing on the rim' worked, I'd rather have something like turns of a nut to help me control the process. I'm not talking hydraulics, here. Michael Press' statement was not limited to hand operation. (guessing at your meaning) Ed |
#25
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Velocity Fusion Max Tension?
john wrote:
Thanks Jeff I still didn't see any tension specs. But I don't think they publish them, or did I miss them also? John you need to call them. theoretically, it's specialist info. |
#26
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Velocity Fusion Max Tension?
In article
om, "Ed" wrote: Michael Press wrote: In article .com, "JeffWills" wrote: Ben Munson wrote: Thanks in advance, Ben "I may have overtensioned" Munson If you thing it's over-tensioned, stress-relieve the wheel by putting it on the floor and pressing down on opposite sides of the rim. If it "sproings" into a potato-chip shape, it's overtensioned. Back off the tension two turns and start truing again. Final tension should be less than the amount that potato-chipped the wheel.(This is Jobst's method- it works for me.) This is not stress relieving. The `sproings' sound is the sound made by spokes untwisting that were wound up when turning the nipples with the spoke wrench. Stress relieving is not accomplished by pushing the rim parallel to the axle. Not enough additional tension can be put on the spokes in this way. Do tell why it is impossible to create sufficient tension by pushing parallel to the axle. Only a few mm of hub to rim 'axial' displacement are required. This does not seem out of reach for mans current ability with machines. Let's consider change in spoke tension from lateral displacement of the rim. According to Damon Rinard's measurements of lateral stiffness a gravitational load of 11 kg deflects the wheel by only 0.002 m. And according to the graph in _The_Bicycle_Wheel a rim displacement of 0.002 m corresponds to a negligible increase in spoke tension. A 200 kg man putting half his weight on one side of a rim and half on the other will increase the rim displacement to about 0.02 m. This is enough to increase spoke tension by 50 N. Still far short of the spoke squeezing method. It would take a rim displacement of about 0.03 m to increase spoke tension by 200 N. The force and displacement is far greater than I would care to apply to _my_ wheel. Let's do a calculation. We squeeze two spokes together at their centers and calculate the increase in tension. Spring constant for a spoke: k = 1.23 x 10^6 N/m Length of a spoke: L = 0.3 m Lateral displacement of center of a squeezed spoke: s Stretched length of a spoke from lateral displcement: 2 * sqrt((L/2)^2 + s^2) = L * sqrt(1 + (2s/L)^2) ~ L( 1 + 4s^2/(2L^2)) Change in length of the spoke from lateral displacement: 2s^2/L Increase in spoke tension from lateral displacement: 2s^2/L k = 2 / 0.3 * (1.23 x 10^6) s^2 = 8.2 x 10^6 s^2 So if we squeeze a spoke by 5 mm = 0.005 m at the center the increase in spoke tension is 200 N. The spoke squeezing method is simpler and less likely to damage a wheel than pushing the rim laterally. -- Michael Press |
#27
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Velocity Fusion Max Tension?
Michael Press wrote:
In article om, "Ed" wrote: Michael Press wrote: In article .com, "JeffWills" wrote: Ben Munson wrote: Thanks in advance, Ben "I may have overtensioned" Munson If you thing it's over-tensioned, stress-relieve the wheel by putting it on the floor and pressing down on opposite sides of the rim. If it "sproings" into a potato-chip shape, it's overtensioned. Back off the tension two turns and start truing again. Final tension should be less than the amount that potato-chipped the wheel.(This is Jobst's method- it works for me.) This is not stress relieving. The `sproings' sound is the sound made by spokes untwisting that were wound up when turning the nipples with the spoke wrench. Stress relieving is not accomplished by pushing the rim parallel to the axle. Not enough additional tension can be put on the spokes in this way. Do tell why it is impossible to create sufficient tension by pushing parallel to the axle. Only a few mm of hub to rim 'axial' displacement are required. This does not seem out of reach for mans current ability with machines. Let's consider change in spoke tension from lateral displacement of the rim. According to Damon Rinard's measurements of lateral stiffness a gravitational load of 11 kg deflects the wheel by only 0.002 m. Damon Rinard applied a load at one point on the rim which was free to flex, all spokes could react. Dividing the load and applying it to more points reduces the freedom, less displacement at the point of the load results (see the posts of Diane_1234, Jobst Brandt in this thread). And according to the graph in _The_Bicycle_Wheel a rim displacement of 0.002 m corresponds to a negligible increase in spoke tension. Sorry, but I don't see what you're referring to as I peruse my copy. using your 300mm spoke, "The Bicycle Wheel"'s 35.5mm half flange width, simple case of radial spoking, the rim to spoke hole radial distance is sqrt(300.00^2 - 35.500^2) = 297.892mm With an immobile rim, a pure axial hub displacement of 2mm results in a length of sqrt(297.892^2 + (35.500+ 2.000)^2) = 300.243mm for an increased spoke length of 0.243 mm. using your Spring constant for a spoke the resulting tension change is 1.23 x 10^6 N/m * 0.243 x 10^-3 m = 299N The axial force required (per spoke) would be about spoke tension * 37.5 / 300.243 This is attainable in the home, but us mere 80kg folks will need some mechanical advantage to handle 36 spoke wheels. please check this, its late at night. A 200 kg man putting half his weight on one side of a rim and half on the other will increase the rim displacement to about 0.02 m. This is enough to increase spoke tension by 50 N. Still far short of the spoke squeezing method. It would take a rim displacement of about 0.03 m to increase spoke tension by 200 N. The force and displacement is far greater than I would care to apply to _my_ wheel. I think this all comes from the Rinard data. I wouldn't do it that way either. snip spoke squeeze calc The spoke squeezing method is simpler and less likely to damage a wheel than pushing the rim laterally. The point of yours that I questioned was that it is impossible to create sufficient tension by pushing parallel to the axle. You have not addressed this other than for the limited two point loaded case and using one point load data. Perhaps that is the case to which you meant to confine your remark. Thanks for your reply. Ed |
#28
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Velocity Fusion Max Tension?
Ben Munson wrote: On 2005-11-13 06:28:12 -0800, "Qui si parla Campagnolo" said: Ben Munson wrote: I am building a non-dished track wheel with 700c Velocity Fusions. What is the max spoke tension for this rim? Without heating any of the usual strong personalities up to simmer, does anyone have knowledge of its real-world limits? Is there a comprehensive place to get this information online? If not, is there a reason nobody has started one? Thanks in advance, Ben "I may have overtensioned" Munson 100 kgf is what you ought to be looking for. For a symmetrical hub, both sides. I have built hundreds of Fusions and that's what I use. Thanks Peter! That's the kind of info I like. Is there much variance in your tension between Aeroheads to Fusions to deep Vs? I am going to be moving on to some Deep V mountain bike wheels for my pops after this little learning experience. He is a heavyweight, so all of this gets more critical. Ben Munson No, the same for all three..Using enough spokes, and not a too light rim and proper tension is what makes wheels work. Nothing wrong with 36h wheels. |
#29
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Velocity Fusion Max Tension?
On 13 Nov 2005 20:44:05 -0800, "Ed" wrote:
Jasper Janssen wrote: On 13 Nov 2005 09:18:36 -0800, "Ed" wrote: Do tell why it is impossible to create sufficient tension by pushing parallel to the axle. Only a few mm of hub to rim 'axial' displacement are required. This does not seem out of reach for mans current ability with machines. What do machines have to do with doing this by hand, exactly? doing this 'by hand' often involves machines. The leverage of a spoke wrench or the crank arm stress relief lever of Sheldon Brown are examples. And neither of them involve hub/rin axial displacement. Even if JeffWills' method of' 'pushing on the rim' worked, I'd rather have something like turns of a nut to help me control the process. I'm not talking hydraulics, here. The operation *as described* was putting the wheel on the floor and pushing on the rim. Please tell me what kind of 'turns of the nut' Rube Goldberg device you've got worked out for that. Michael Press' statement was not limited to hand operation. Yes, it was. Jasper |
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