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Wheelbuilding issues
So I'm trying to build my first rear derailer wheel that's actually up
to the maximum safe level of tension the rim can handle. In the past I have built 1 front wheel, 1 rear derailer wheel, and 2 dishless rear wheels. These came out okay but not as high-tension and windup-free as possible. I'm using a new 36-hole 700C Sun CR-18 (575 grams, 23mm outside/18mm-ish inside width, eyelets not sockets, brushed), straight 2mm spokes (Sapim on one side and DT on the other due to an ordering error, and I didn't have the money for butted or I would have gotten them), brass Sapim nipples, and a new LX rear hub. This is going to be a 9-speed wheel for commuting, distance riding and loaded touring. I know all about how much 9-speed sucks strength-wise and am partially just building a 9-speed wheel and setting my bike up 9-speed to get a feel for how well such highly dished wheels can hold up. I have read The Bicycle Wheel and Sheldon Brown's wheelbuilding page several times. I'm using a tensiometer to check for inordinately loose/tight spokes, balanced tension, and to establish a standard for how much tension my future wheels with CR-18s can handle. I laced the wheel 3-cross using Tri-Flow to lube the spoke threads and white grease on the nipple seats. I accidentally dunked the non-drive side spoke threads in lube before I remembered not to (as advised on Sheldon's page), so I wiped a bunch of lube off with a rag and decided to see how the wheel would fare longevity-wise with lightly lubed non-drive spokes. The first mistake I made was overestimating how much tension this rim could take before beginning to overload and go potato-chip-shaped (this is also a reason I didn't just use degreaser on the lubed non-drive-side spoke threads - you wouldn't really have to worry about that with a strong enough rim even if it was highly dished, right?). In fact, I was a bit under the impression that with this rim I wouldn't be able to get the tension that high up at all before nipples started getting impossible to turn. This was a big mistake, I know now, but there is not exactly much material out there about learning to predict exactly what rims will be over-tensionable and which won't be, even though there are hints that such a clear distinction exists. Anyway, during what I then thought was not quite the end of the building process, I checked the wheel's centering and discovered the rim needed to be pulled over to the drive side by quite a bit. The drive side spokes were at I think (can't remember exactly) about 100-110 KgF average. At this point, the rim was true laterally and was mostly true radially and tension balanced with a few exceptions (see below). I figured it would be safe at this point to make the centering adjustement by just tightening all the drive-side spokes a half-turn, rather than loosening the non-drive spokes and tightening the drive ones. So I did that and when I spun the wheel immediately afterwards to check for typical small necessary lateral truing corrections, instead I saw that the wheel had become fairly potato-chip shaped. Up to this point I had not been following The Bicycle Wheel's procedure of adding layers of tension and then stress relieving to check for how close one is to approaching the rim's maximum safe tension - again, I didn't think it was really necessary with this rim to do so yet. After this occurred, I backed off all the drive-side spoke tensions by the half-turn I had just added. The potato chip shape remained. Then I backed off the tension by I think a quarter turn on both sides and it still remained. Afraid that I had permanently warped the rim, because the wheel didn't go back to being true, I then removed all tension from the spokes and reset them to the initial stage with the spoke threads just barely covered by the nipple, added a small amount of tension, did some very minor truing that one always needs to do at the beginning tensioning/truing phases, and saw that the rim was just as true as it was at this point the first time through, leading me to believe that my over-tensioning did not permanently warp the rim. The small bits of truing necessary did not match the shape of a slightly collapsed rim. My questions about this episode a If the rim was not permanently warped, what exactly is the reason that it did not go back to its previous true shape after I removed the tension I just added, and then some? I assume now that this is the same reason why a rim that's just gotten stress-relieved enough to overload it, as per The Book, will remain in the slight potato-chip shape even after you stop squeezing it, right? In later attempts at building this wheel, I added a quarter-turn layer of tension, stress-relieved it all around, saw a very slight potato-chip shape of maybe 2mm away from the centerline on either side happening as I spun the wheel in the stand, backed it off a half turn on both sides, all as per The Bicycle Wheel, and the result after the de-tensioning was that it was about as true as it was prior to the last additional tension layer. On the initial build, if after my overtensioning I had just backed off the tension all around a bit more instead of starting over, would the wheel have gone back to trueness, presuming that all my nipple-turning had been accurate enough? Does it depend on exactly how overloaded and deformed the rim became? In The Book, it says that after you overload a rim during stress relieving, some truing will be necessary after you back it off half a turn all around. But none of the potato-chip shape from overloading is supposed to be remaining at that point, right? If it was, and you trued the rim in reaction to that, wouldn't everything just get really screwed up? So is the truing you'll be needing to do at that point just in reaction to inaccuracies in your nipple-turning? How exactly do all the rules about all this apply to rims of different types and weights? When you stress relieve a rim to test it for overload, are you supposed to be watching the rim for a potato-chip shape happening as you squeeze each group of 4 spokes and then stop if you see one, or should you just go through and stress relieve all the spokes and then check to see if the deformation occured somewhere in the process? There was another time when I stress relieved all around and then saw that the rim was in a shape that resembled the slight potato chip/saddle shape of an overloaded rim, but not quite. Whereas the usual shape is a series of curves where there's an apex veering to the left, followed by an apex veering to the right 90 degrees later, and an apex to the left another 90 degrees from that, etc. this series of curves went more like apex to the left followed by one to the right 45 degrees later, followed by the next one to the left 135 degrees later, followed by one to the right 45 degrees later, etc, such that both curves going to one side were still 180 degrees from each other, but the overall shape was weird. Again, this was after I tensioned and stress relieved the wheel. I figured that this was just a sign of overload but am still not really sure if I'm missing something. Does rim deformation just happen this way sometimes? Are there other variations on the typical imploded-rim shape? When stress relieving spokes, all internal stresses are relieved after you make one complete round of squeezing adjacent spokes beyond yield, right? If so, does that mean that if you were building up a rim that you absolutely knew was strong enough that difficulty in turning nipples was going to be the tension bottleneck for the wheel, you would only really have to stress relieve once, when you hit the point where no more tension can be added? I'm also wondering about how exactly techniques to eliminate spoke windup work. When you overshoot a quarter turn and then back up to eliminate windup, is the idea that somewhere in that extra quarter turn, the spoke's increasing torsional load will become enough to overcome the amount of friction between its threads and those of the nipple? What exactly keeps the spoke from winding up in the other direction when you back up the nipple? When you go to back up the nipple, isn't there just going to be more friction than you started with because now the spoke is tighter by a quarter turn plus whatever adjustment you wanted to make? Is it the best idea to keep one hand on the spoke you're adjusting as the other turns the spoke wrench, so that you can feel when a spoke is winding up and when it unwinds? Is it possible for a spoke to only unwind partially? I'm also wondering why hardly anything I've read about wheelbuilding mentions the possibility of tightening drive vs. non-drive-side spokes according to a ratio based on how much they pull the rim due to their differing angles, and how much tension each side will have in total when the wheel is done. The ratio is something like 8:5 for most 9-speed rears, isn't it? So why not just do your tensioning layers and truing adjustments by turning the drive side something like twice as much all the way through? If you just act like both sides pull the same amount and therefore you make even increments on both sides when you're tensioning, dishing, or truing, aren't you bound to create lateral/dish errors that must be dealt with using the same flawed process? I was experimenting with this and it seems like there may be something to it, but this time around I was confused about enough things that throwing this in the mix was more than I really wanted to deal with. In The Bicycle Wheel, it's written that wheels with unbalanced spoke tensions will equalize themselves in use. Is this just for the obvious reason that the spokes with low tensions will get looser and out of true in use, which causes all sorts of havoc, or is there something subtle I'm missing here that causes problems when some spokes are also inordinately high in tension, other than increasing the likelihood of eyelet cracking? Does this imply, for example, that a wheel with generally closely balanced, high tensions but a few spokes at inordinately high tensions for some reason would all equalize in use? A final group of questions has to do with interactions between radial trueness, tension balancing, and rim imperfections. I got my wheel to a point several times where the total tension difference between the slackest and tightest drive-side spokes was about 30 KgF, with a few at about 95, a few at about 125-130, and most at about 105-120, and a similar bunch of disparities on the non-drive-side. This was at about the max safe tension for the rim using the Jobst method unless I'm very confused. There was still quite a bit of radial truing error, perhaps 1mm between high and low points, but it was arranged in the classic annoying pattern where the bumps are tighter spots and the dips are looser spots. In other words, if I just went through and made the tension on each spoke exactly the same without regard to how true it would make the wheel, then the wheel would be a total mess. I was left with the definite feeling that I was just encountering imperfections in the rim, since I worked on it for a long and it seemed like there was little further I could do without compromising either tension balance or reasonable trueness. On the other hand, I'm fairly new at this and I don't want to put undue blame on the rim. My question is just how bad are the tolerances on Sun rims, or CR-18s in particular for those who have lots of experience with them, and what kind of tension disparities do you usually end up with? Thanks for reading and replying, Nate Knutson |
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Wheelbuilding issues
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Wheelbuilding issues
there's too much confusion about this "as much tension as the rim can
handle" business. maximum tension is a technical specification defined by the rim manufacturer. exceeding it does not make the wheel stronger or stiffer - because the spoke modulus remains the same regardless of tension. excess tension can also lead to accelerated rim cracking. call sun for clarification, but tension in the range of 90-100 kgf on the sprocket side is more likely to be maximum spec. /even/ tension is more important that absolute tension. read sheldon's great article on wheelbuilding on how to get it right. Nate Knutson wrote: So I'm trying to build my first rear derailer wheel that's actually up to the maximum safe level of tension the rim can handle. In the past I have built 1 front wheel, 1 rear derailer wheel, and 2 dishless rear wheels. These came out okay but not as high-tension and windup-free as possible. I'm using a new 36-hole 700C Sun CR-18 (575 grams, 23mm outside/18mm-ish inside width, eyelets not sockets, brushed), straight 2mm spokes (Sapim on one side and DT on the other due to an ordering error, and I didn't have the money for butted or I would have gotten them), brass Sapim nipples, and a new LX rear hub. This is going to be a 9-speed wheel for commuting, distance riding and loaded touring. I know all about how much 9-speed sucks strength-wise and am partially just building a 9-speed wheel and setting my bike up 9-speed to get a feel for how well such highly dished wheels can hold up. I have read The Bicycle Wheel and Sheldon Brown's wheelbuilding page several times. I'm using a tensiometer to check for inordinately loose/tight spokes, balanced tension, and to establish a standard for how much tension my future wheels with CR-18s can handle. I laced the wheel 3-cross using Tri-Flow to lube the spoke threads and white grease on the nipple seats. I accidentally dunked the non-drive side spoke threads in lube before I remembered not to (as advised on Sheldon's page), so I wiped a bunch of lube off with a rag and decided to see how the wheel would fare longevity-wise with lightly lubed non-drive spokes. The first mistake I made was overestimating how much tension this rim could take before beginning to overload and go potato-chip-shaped (this is also a reason I didn't just use degreaser on the lubed non-drive-side spoke threads - you wouldn't really have to worry about that with a strong enough rim even if it was highly dished, right?). In fact, I was a bit under the impression that with this rim I wouldn't be able to get the tension that high up at all before nipples started getting impossible to turn. This was a big mistake, I know now, but there is not exactly much material out there about learning to predict exactly what rims will be over-tensionable and which won't be, even though there are hints that such a clear distinction exists. Anyway, during what I then thought was not quite the end of the building process, I checked the wheel's centering and discovered the rim needed to be pulled over to the drive side by quite a bit. The drive side spokes were at I think (can't remember exactly) about 100-110 KgF average. At this point, the rim was true laterally and was mostly true radially and tension balanced with a few exceptions (see below). I figured it would be safe at this point to make the centering adjustement by just tightening all the drive-side spokes a half-turn, rather than loosening the non-drive spokes and tightening the drive ones. So I did that and when I spun the wheel immediately afterwards to check for typical small necessary lateral truing corrections, instead I saw that the wheel had become fairly potato-chip shaped. Up to this point I had not been following The Bicycle Wheel's procedure of adding layers of tension and then stress relieving to check for how close one is to approaching the rim's maximum safe tension - again, I didn't think it was really necessary with this rim to do so yet. After this occurred, I backed off all the drive-side spoke tensions by the half-turn I had just added. The potato chip shape remained. Then I backed off the tension by I think a quarter turn on both sides and it still remained. Afraid that I had permanently warped the rim, because the wheel didn't go back to being true, I then removed all tension from the spokes and reset them to the initial stage with the spoke threads just barely covered by the nipple, added a small amount of tension, did some very minor truing that one always needs to do at the beginning tensioning/truing phases, and saw that the rim was just as true as it was at this point the first time through, leading me to believe that my over-tensioning did not permanently warp the rim. The small bits of truing necessary did not match the shape of a slightly collapsed rim. My questions about this episode a If the rim was not permanently warped, what exactly is the reason that it did not go back to its previous true shape after I removed the tension I just added, and then some? I assume now that this is the same reason why a rim that's just gotten stress-relieved enough to overload it, as per The Book, will remain in the slight potato-chip shape even after you stop squeezing it, right? In later attempts at building this wheel, I added a quarter-turn layer of tension, stress-relieved it all around, saw a very slight potato-chip shape of maybe 2mm away from the centerline on either side happening as I spun the wheel in the stand, backed it off a half turn on both sides, all as per The Bicycle Wheel, and the result after the de-tensioning was that it was about as true as it was prior to the last additional tension layer. On the initial build, if after my overtensioning I had just backed off the tension all around a bit more instead of starting over, would the wheel have gone back to trueness, presuming that all my nipple-turning had been accurate enough? Does it depend on exactly how overloaded and deformed the rim became? In The Book, it says that after you overload a rim during stress relieving, some truing will be necessary after you back it off half a turn all around. But none of the potato-chip shape from overloading is supposed to be remaining at that point, right? If it was, and you trued the rim in reaction to that, wouldn't everything just get really screwed up? So is the truing you'll be needing to do at that point just in reaction to inaccuracies in your nipple-turning? How exactly do all the rules about all this apply to rims of different types and weights? When you stress relieve a rim to test it for overload, are you supposed to be watching the rim for a potato-chip shape happening as you squeeze each group of 4 spokes and then stop if you see one, or should you just go through and stress relieve all the spokes and then check to see if the deformation occured somewhere in the process? There was another time when I stress relieved all around and then saw that the rim was in a shape that resembled the slight potato chip/saddle shape of an overloaded rim, but not quite. Whereas the usual shape is a series of curves where there's an apex veering to the left, followed by an apex veering to the right 90 degrees later, and an apex to the left another 90 degrees from that, etc. this series of curves went more like apex to the left followed by one to the right 45 degrees later, followed by the next one to the left 135 degrees later, followed by one to the right 45 degrees later, etc, such that both curves going to one side were still 180 degrees from each other, but the overall shape was weird. Again, this was after I tensioned and stress relieved the wheel. I figured that this was just a sign of overload but am still not really sure if I'm missing something. Does rim deformation just happen this way sometimes? Are there other variations on the typical imploded-rim shape? When stress relieving spokes, all internal stresses are relieved after you make one complete round of squeezing adjacent spokes beyond yield, right? If so, does that mean that if you were building up a rim that you absolutely knew was strong enough that difficulty in turning nipples was going to be the tension bottleneck for the wheel, you would only really have to stress relieve once, when you hit the point where no more tension can be added? I'm also wondering about how exactly techniques to eliminate spoke windup work. When you overshoot a quarter turn and then back up to eliminate windup, is the idea that somewhere in that extra quarter turn, the spoke's increasing torsional load will become enough to overcome the amount of friction between its threads and those of the nipple? What exactly keeps the spoke from winding up in the other direction when you back up the nipple? When you go to back up the nipple, isn't there just going to be more friction than you started with because now the spoke is tighter by a quarter turn plus whatever adjustment you wanted to make? Is it the best idea to keep one hand on the spoke you're adjusting as the other turns the spoke wrench, so that you can feel when a spoke is winding up and when it unwinds? Is it possible for a spoke to only unwind partially? I'm also wondering why hardly anything I've read about wheelbuilding mentions the possibility of tightening drive vs. non-drive-side spokes according to a ratio based on how much they pull the rim due to their differing angles, and how much tension each side will have in total when the wheel is done. The ratio is something like 8:5 for most 9-speed rears, isn't it? So why not just do your tensioning layers and truing adjustments by turning the drive side something like twice as much all the way through? If you just act like both sides pull the same amount and therefore you make even increments on both sides when you're tensioning, dishing, or truing, aren't you bound to create lateral/dish errors that must be dealt with using the same flawed process? I was experimenting with this and it seems like there may be something to it, but this time around I was confused about enough things that throwing this in the mix was more than I really wanted to deal with. In The Bicycle Wheel, it's written that wheels with unbalanced spoke tensions will equalize themselves in use. Is this just for the obvious reason that the spokes with low tensions will get looser and out of true in use, which causes all sorts of havoc, or is there something subtle I'm missing here that causes problems when some spokes are also inordinately high in tension, other than increasing the likelihood of eyelet cracking? Does this imply, for example, that a wheel with generally closely balanced, high tensions but a few spokes at inordinately high tensions for some reason would all equalize in use? A final group of questions has to do with interactions between radial trueness, tension balancing, and rim imperfections. I got my wheel to a point several times where the total tension difference between the slackest and tightest drive-side spokes was about 30 KgF, with a few at about 95, a few at about 125-130, and most at about 105-120, and a similar bunch of disparities on the non-drive-side. This was at about the max safe tension for the rim using the Jobst method unless I'm very confused. There was still quite a bit of radial truing error, perhaps 1mm between high and low points, but it was arranged in the classic annoying pattern where the bumps are tighter spots and the dips are looser spots. In other words, if I just went through and made the tension on each spoke exactly the same without regard to how true it would make the wheel, then the wheel would be a total mess. I was left with the definite feeling that I was just encountering imperfections in the rim, since I worked on it for a long and it seemed like there was little further I could do without compromising either tension balance or reasonable trueness. On the other hand, I'm fairly new at this and I don't want to put undue blame on the rim. My question is just how bad are the tolerances on Sun rims, or CR-18s in particular for those who have lots of experience with them, and what kind of tension disparities do you usually end up with? Thanks for reading and replying, Nate Knutson |
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Wheelbuilding issues
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Wheelbuilding issues
"Nate Knutson" wrote in message om... (Nate Knutson) wrote in message . com... In The Bicycle Wheel, it's written that wheels with unbalanced spoke tensions will equalize themselves in use. I thought I'd add pre-emptively that this is not the phrasing used in the book, but just how I read and remember it. I can't post a direct quote here because I don't have a copy with me. I don't understand how that could be. The tightest spokes are the least likely to loosen, and the loosest spokes are the most likely to loosen. I don't recall reading anything like that in The Book. Art Harris |
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Wheelbuilding issues
Arthur Harris wrote:
"Nate Knutson" wrote in message om... (Nate Knutson) wrote in message . com... In The Bicycle Wheel, it's written that wheels with unbalanced spoke tensions will equalize themselves in use. I thought I'd add pre-emptively that this is not the phrasing used in the book, but just how I read and remember it. I can't post a direct quote here because I don't have a copy with me. I don't understand how that could be. The tightest spokes are the least likely to loosen, and the loosest spokes are the most likely to loosen. I don't recall reading anything like that in The Book. Page 105 of the third edition, under Balancing Tension: "If spokes are not equally tight they will equalize during use and cause misalignment." -- Warren Block * Rapid City, South Dakota * USA |
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Wheelbuilding issues
"Arthur Harris" writes:
"Nate Knutson" wrote In The Bicycle Wheel, it's written that wheels with unbalanced spoke tensions will equalize themselves in use. I thought I'd add pre-emptively that this is not the phrasing used in the book, but just how I read and remember it. I can't post a direct quote here because I don't have a copy with me. I don't understand how that could be. The tightest spokes are the least likely to loosen, and the loosest spokes are the most likely to loosen. I don't recall reading anything like that in The Book. Nate is right. According to page 111 of the German edition Jobst writes (translated back to English): "If the spokes are unequally tensioned, these differences will even out in use and the wheel will come untrue." I don't understand it either. Christian |
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Wheelbuilding issues
Christian Odenthal writes:
In The Bicycle Wheel, it's written that wheels with unbalanced spoke tensions will equalize themselves in use. I thought I'd add pre-emptively that this is not the phrasing used in the book, but just how I read and remember it. I can't post a direct quote here because I don't have a copy with me. I don't understand how that could be. The tightest spokes are the least likely to loosen, and the loosest spokes are the most likely to loosen. I don't recall reading anything like that in The Book. Nate is right. According to page 111 of the German edition Jobst writes (translated back to English): "If the spokes are unequally tensioned, these differences will even out in use and the wheel will come untrue." I don't understand it either. The spokes will not change but the rim will, assuming the wheel runs over average bumpy roads that momentarily impart high stress to the rim. Under these conditions, the rim will gradually conform to tension distribution and thereby change individual preloads of the spokes. The rim adapts and this alters spoke tension. Jobst Brandt |
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Wheelbuilding issues
Nate Knutson wrote:
So I'm trying to build my first rear derailer wheel that's actually up to the maximum safe level of tension the rim can handle. In the past I have built 1 front wheel, 1 rear derailer wheel, and 2 dishless rear wheels. These came out okay but not as high-tension and windup-free as possible. I'm using a new 36-hole 700C Sun CR-18 (575 grams, 23mm outside/18mm- ish inside width, eyelets not sockets, brushed), straight 2mm spokes (Sapim on one side and DT on the other due to an ordering error, and I didn't have the money for butted or I would have gotten them), brass Sapim nipples, and a new LX rear hub. This is going to be a 9-speed wheel for commuting, distance riding and loaded touring. I know all about how much 9-speed sucks strength-wise and am partially just building a 9-speed wheel and setting my bike up 9-speed to get a feel for how well such highly dished wheels can hold up. I have read The Bicycle Wheel and Sheldon Brown's wheelbuilding page several times. I'm using a tensiometer to check for inordinately loose/tight spokes, balanced tension, and to establish a standard for how much tension my future wheels with CR-18s can handle. I laced the wheel 3-cross using Tri-Flow to lube the spoke threads and white grease on the nipple seats. I accidentally dunked the non-drive side spoke threads in lube before I remembered not to (as advised on Sheldon's page), so I wiped a bunch of lube off with a rag and decided to see how the wheel would fare longevity-wise with lightly lubed non- drive spokes. The first mistake I made was overestimating how much tension this rim could take before beginning to overload and go potato-chip- shaped (this is also a reason I didn't just use degreaser on the lubed non-drive-side spoke threads - you wouldn't really have to worry about that with a strong enough rim even if it was highly dished, right?). In fact, I was a bit under the impression that with this rim I wouldn't be able to get the tension that high up at all before nipples started getting impossible to turn. This was a big mistake, I know now, but there is not exactly much material out there about learning to predict exactly what rims will be over-tensionable and which won't be, even though there are hints that such a clear distinction exists. Anyway, during what I then thought was not quite the end of the building process, I checked the wheel's centering and discovered the rim needed to be pulled over to the drive side by quite a bit. The drive side spokes were at I think (can't remember exactly) about 100-110 KgF average. At this point, the rim was true laterally and was mostly true radially and tension balanced with a few exceptions (see below). I figured it would be safe at this point to make the centering adjustement by just tightening all the drive-side spokes a half-turn, rather than loosening the non-drive spokes and tightening the drive ones. So I did that and when I spun the wheel immediately afterwards to check for typical small necessary lateral truing corrections, instead I saw that the wheel had become fairly potato- chip shaped. Up to this point I had not been following The Bicycle Wheel's procedure of adding layers of tension and then stress relieving to check for how close one is to approaching the rim's maximum safe tension - again, I didn't think it was really necessary with this rim to do so yet. After this occurred, I backed off all the drive-side spoke tensions by the half-turn I had just added. The potato chip shape remained. Then I backed off the tension by I think a quarter turn on both sides and it still remained. Afraid that I had permanently warped the rim, because the wheel didn't go back to being true, I then removed all tension from the spokes and reset them to the initial stage with the spoke threads just barely covered by the nipple, added a small amount of tension, did some very minor truing that one always needs to do at the beginning tensioning/truing phases, and saw that the rim was just as true as it was at this point the first time through, leading me to believe that my over-tensioning did not permanently warp the rim. The small bits of truing necessary did not match the shape of a slightly collapsed rim. My questions about this episode a If the rim was not permanently warped, what exactly is the reason that it did not go back to its previous true shape after I removed the tension I just added, and then some? I assume now that this is the same reason why a rim that's just gotten stress- relieved enough to overload it, as per The Book, will remain in the slight potato-chip shape even after you stop squeezing it, right? In later attempts at building this wheel, I added a quarter-turn layer of tension, stress- relieved it all around, saw a very slight potato- chip shape of maybe 2mm away from the centerline on either side happening as I spun the wheel in the stand, backed it off a half turn on both sides, all as per The Bicycle Wheel, and the result after the de- tensioning was that it was about as true as it was prior to the last additional tension layer. On the initial build, if after my overtensioning I had just backed off the tension all around a bit more instead of starting over, would the wheel have gone back to trueness, presuming that all my nipple-turning had been accurate enough? Does it depend on exactly how overloaded and deformed the rim became? In The Book, it says that after you overload a rim during stress relieving, some truing will be necessary after you back it off half a turn all around. But none of the potato-chip shape from overloading is supposed to be remaining at that point, right? If it was, and you trued the rim in reaction to that, wouldn't everything just get really screwed up? So is the truing you'll be needing to do at that point just in reaction to inaccuracies in your nipple-turning? How exactly do all the rules about all this apply to rims of different types and weights? When you stress relieve a rim to test it for overload, are you supposed to be watching the rim for a potato-chip shape happening as you squeeze each group of 4 spokes and then stop if you see one, or should you just go through and stress relieve all the spokes and then check to see if the deformation occured somewhere in the process? There was another time when I stress relieved all around and then saw that the rim was in a shape that resembled the slight potato chip/saddle shape of an overloaded rim, but not quite. Whereas the usual shape is a series of curves where there's an apex veering to the left, followed by an apex veering to the right 90 degrees later, and an apex to the left another 90 degrees from that, etc. this series of curves went more like apex to the left followed by one to the right 45 degrees later, followed by the next one to the left 135 degrees later, followed by one to the right 45 degrees later, etc, such that both curves going to one side were still 180 degrees from each other, but the overall shape was weird. Again, this was after I tensioned and stress relieved the wheel. I figured that this was just a sign of overload but am still not really sure if I'm missing something. Does rim deformation just happen this way sometimes? Are there other variations on the typical imploded- rim shape? When stress relieving spokes, all internal stresses are relieved after you make one complete round of squeezing adjacent spokes beyond yield, right? If so, does that mean that if you were building up a rim that you absolutely knew was strong enough that difficulty in turning nipples was going to be the tension bottleneck for the wheel, you would only really have to stress relieve once, when you hit the point where no more tension can be added? I'm also wondering about how exactly techniques to eliminate spoke windup work. When you overshoot a quarter turn and then back up to eliminate windup, is the idea that somewhere in that extra quarter turn, the spoke's increasing torsional load will become enough to overcome the amount of friction between its threads and those of the nipple? What exactly keeps the spoke from winding up in the other direction when you back up the nipple? When you go to back up the nipple, isn't there just going to be more friction than you started with because now the spoke is tighter by a quarter turn plus whatever adjustment you wanted to make? Is it the best idea to keep one hand on the spoke you're adjusting as the other turns the spoke wrench, so that you can feel when a spoke is winding up and when it unwinds? Is it possible for a spoke to only unwind partially? I'm also wondering why hardly anything I've read about wheelbuilding mentions the possibility of tightening drive vs. non-drive-side spokes according to a ratio based on how much they pull the rim due to their differing angles, and how much tension each side will have in total when the wheel is done. The ratio is something like 8:5 for most 9-speed rears, isn't it? So why not just do your tensioning layers and truing adjustments by turning the drive side something like twice as much all the way through? If you just act like both sides pull the same amount and therefore you make even increments on both sides when you're tensioning, dishing, or truing, aren't you bound to create lateral/dish errors that must be dealt with using the same flawed process? I was experimenting with this and it seems like there may be something to it, but this time around I was confused about enough things that throwing this in the mix was more than I really wanted to deal with. In The Bicycle Wheel, it's written that wheels with unbalanced spoke tensions will equalize themselves in use. Is this just for the obvious reason that the spokes with low tensions will get looser and out of true in use, which causes all sorts of havoc, or is there something subtle I'm missing here that causes problems when some spokes are also inordinately high in tension, other than increasing the likelihood of eyelet cracking? Does this imply, for example, that a wheel with generally closely balanced, high tensions but a few spokes at inordinately high tensions for some reason would all equalize in use? A final group of questions has to do with interactions between radial trueness, tension balancing, and rim imperfections. I got my wheel to a point several times where the total tension difference between the slackest and tightest drive-side spokes was about 30 KgF, with a few at about 95, a few at about 125-130, and most at about 105-120, and a similar bunch of disparities on the non-drive-side. This was at about the max safe tension for the rim using the Jobst method unless I'm very confused. There was still quite a bit of radial truing error, perhaps 1mm between high and low points, but it was arranged in the classic annoying pattern where the bumps are tighter spots and the dips are looser spots. In other words, if I just went through and made the tension on each spoke exactly the same without regard to how true it would make the wheel, then the wheel would be a total mess. I was left with the definite feeling that I was just encountering imperfections in the rim, since I worked on it for a long and it seemed like there was little further I could do without compromising either tension balance or reasonable trueness. On the other hand, I'm fairly new at this and I don't want to put undue blame on the rim. My question is just how bad are the tolerances on Sun rims, or CR-18s in particular for those who have lots of experience with them, and what kind of tension disparities do you usually end up with? Thanks for reading and replying, Nate Knutson Spoke alignment is key to having the wheel turn out to be durable. In short, the shortest distance between two points is a straight line. Take a thread and stretch it along the path of each spoke to see how close the are to straight. This has nothing to do with tension itself, but it does have to do with how spokes respond in dynamic loading and unloading. When you work aligned spokes you get more equal response. I agree with the other posters responses about the expected elasticity of stainless spokes and even tension. I have had very good and very bad experiences with Sun rims. I think some Sun rims come through with very bad quality control. Peter White, of Peter White Cycles, has mentioned this in his write up on wheels. I have tossed CR-18s in the recycling bin due to this. It is very frusrating to go through an entire rear build and arrive at that point. I am not suggesting that you throw out your work, but I expect to get tension balance between 5 & 10% while having lateral and radial true better than 0.3mm. My expectation is met on all wheels I send out and I have found some Sun rims that will allow this. I have also found more than a few Sun rim samples that wouldn't even come close. It is up to you and your pride as to what you want to do next. -- |
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