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#1
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Spoke tension question
Hello,
I've been using a set of wheels with CXP22 rims and Shimano hubs. When checking the bike over I noticed that a number of spokes on the rear wheel were very loose. I started tweaking them up, but the wheel went out of true. Not being experienced with wheels, I took it down to the LBS, explained the problem and asked them to true and tension it. Checking the wheel, I've found that while it's nice and true, there's a lot of variability in spoke tension on the non-drive side and some of the spokes have a lot less tension in them than others. My favourite ride is a 10 mile climb, followed by a 10 mile descent. The road surface for the first couple of miles of the descent is pretty bad. Lots of potholes and cracks, resulting in a rough and bumpy ride. I'm not a lightweight either, so I'm sure the wheels aren't having an easy time. Do I need to worry about the variability in spoke tension? Thanks Gary |
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#2
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Spoke tension question
On Thu, 05 Jan 2006 03:30:03 +0000, Gary Robinson wrote:
Checking the wheel, I've found that while it's nice and true, there's a lot of variability in spoke tension on the non-drive side and some of the spokes have a lot less tension in them than others. This is a sign of either a bent rim, or a poor build, or both. Actually, if they just re-trued a bent rim, that would be a bad build by definition. It's easy to get the wheel true, while the spoke tension is highly inconsistent. Say a given spoke is too loose, but the adjacent spokes on the other side are also too loose. Then the wheel might be true, but out of round. On the other hand, if a given spoke is too loose, but the same-side spokes next to it are too tight, then the wheel might look both true and round. But in these cases the wheel will not stay true. -- David L. Johnson __o | Accept risk. Accept responsibility. Put a lawyer out of _`\(,_ | business. (_)/ (_) | |
#3
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Spoke tension question
Do I need to worry about the variability in spoke tension?
First of all, it's important to know that the left and right side spokes of rear wheels for derailer bikes, and on several other types of rear wheel, use different tensions. There's more tension on the drive side spokes, which isn't a good thing but is inherit to any wheel where the spoke-end centerline is going to end up anywhere but exactly between the two flanges. It's unclear whether you know this or not. The rest of the conversation actually gets pretty complex, especially when you get into whether the shop did a good/honest job or not. I can tell you now that whether they did or not, they did a common one for the situation. Tension balance among all spokes on each side of a wheel is important/beneficial for a few reasons. Large disparities in tension make wheels susceptible to become damaged prematurely at best and fail at worst. Most wheels out there on dealer-level bikes are built good enough that these aren't issues, but aren't as well tension balanced as they could be by a long shot (and the argument exists and is pretty good that 8/9/10 speed wheels are all damage prone and unsafe for basically the same reaons that a shoddily tension-balanced wheel is). Truly precise tension balance, beyond the "pretty reasonable" norm, gets you an additional level of long-term durability that occurs for different physical reasons than the ones that make wheels with slack spokes die early. Some wheels aren't capable of this for reasons having to do with the construction method and precision of the rim. In general, the way that a conventional spoked bike wheel supports weight is by the built-in tension loads on each spoke taking turns temporarily absorbing the compressive loads the wheel encounters as you mount the bike, ride along, hit stuff, etc. At any one time on a 32 or 36 spoke 26" or 700 wheel, the load on the wheel is shared by about 4 spokes. That number changes for wheels of different sizes and spoke counts. Anytime that a wheel is loaded so much that any of the spokes lose all their tension (go slack), it's possible for the wheel to become damaged, or fail in some (usually but not always extreme) cases. Clearly, this indicates that it's not good to have spokes that are slack or near-slack before you even get on the bike. If the tension imbalance in your wheel is extreme enough, which sounds possible, the wheel could fail or become damaged as a result. It most likely was already damaged from being ridden in the conditions you describe with loose spokes, and those spokes probably became loose because the wheel was always undertensioned or poorly tension balanced. The type of damage that occurs most often is that the rim becomes deformed. Once this has occurred, and it usually already has by the time someone gets into the type of situation you're describing (big rider, big bumps, bike that actually gets ridden, noticeable spoke tension issues after a shop has already laid hands on it), it's impossible to make the wheel both true and tension balanced at the same time. If you understand the basics of how wheel truing works -tighten a spoke and the rim moves in that spoke's direction-, you can probably understand why. The only way a wheel can be both as perfectly true and perfectly tension balanced as bike wheels get is if the rim is perfectly straight and round before it has any spoke tension acting on it. (And no wheel can be absolutely perfect in this regard, because rims are all stiffer at the seam and so they respond to tension differently there, making either tension disparities or radial truth disparities inevitable). It's also common for loose spokes to allow the nipple to move when ridden, making the spokes looser and perpetuating both the nipple-loosening and the rim-damaging problem. That the left spokes have tension differences that are easy to feel by hand isn't good, but how bad it is depends on how large the differences are and whether any spokes are completely slack, or close to it. 8/9/10 speed wheels usually have very loose left spokes, which sucks and makes these wheels inherently less durable (because even though the wheel has the very-tight right spokes to support it, the left ones still are forced to operate at very low or, in practice with many typical mass-produced wheels, basically no tension. This is especially true of wheels with light rims. That mass-produced wheels are usually built way under-tension and with poor tension balance anyway makes the problem a lot worse). It's easier to feel differences in tension between lower-tension spokes by hand than it is with higher-tensioned ones. Among the less-tensioned spokes, smaller variances in tension also result in easier to feel differences than they do on spokes in a higher tension range. So based on your description, it is possible that things are basically okay, and that the left-side spokes are all in the reasonable-but-not-stellar range, and that you managed to avoid significantly damaging the wheel when you were riding it with loose spokes before. However, it's not likely at all. What's probably going on is that the rim is now messed up and whoever trued the wheel compensated for that by letting spoke tensions be uneven, probably in the right side spokes as well, and also probably didn't do anything to correct a too-low-to-begin-with tension level, which most wheels that are having problems but aren't being abused are suffering from. And they also probably didn't make the tension balance on the wheel as good as it could be while still true, either, which is hard to do on a messed up rim. And it's also likely the wheel is laterally pretty true but far from as-good-as-it-gets radially. This is all fairly standard practice for shops, and whether it's particularly wrong or they should have told you or should have pointed you to a new wheel or whatever is a complicated discussion, and depends on how bad your wheel really is, which I can't tell from here. Most shop mechanics deal with a *lot* of wheels having some form of these problems. Mass-produced wheels that get ridden, especially by heavier riders, are basically guaranteed to have them, unless they get loved up before being ridden by someone who knows what they're doing and is willing to spend more time on them than an average bike shop can afford to spend on a wheel true at market rate. However, if this is to the point where any spokes on the wheel are completely slack, or obviously close to it, and the shop handed it to you that way with no warning and told you to ride it, that's irresponsible and wrong of them. Loose spokes do cause wheel failure in practice, just not very often. Where to draw the line in practice of how loose or imbalanced is too much is something that's basically glossed over day-to-day in most shops. And the reason I bother writing all this is because I'm also no lightweight rider, and this **** needs to be more understood so that heavy people can ride bikes. |
#4
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Spoke tension question
"Nate Knutson" wrote:
ups.com... Do I need to worry about the variability in spoke tension? First of all, it's important to know that the left and right side spokes of rear wheels for derailer bikes, and on several other types of rear wheel, use different tensions. There's more tension on the drive side spokes, which isn't a good thing but is inherit to any wheel where the spoke-end centerline is going to end up anywhere but exactly between the two flanges. It's unclear whether you know this or not. I'm not sure if I understood all of the wisdom (I'm pretty sure I didn't) and I'm not sure if you understand my English but I have to ask a question: what about Sram hubs (and probably some others too) which have flanges located symmetrically from the hub center (rim is exactly in the middle between the flanges)? They should allow to build wheels with equally tensioned spokes at both sides. However the distance between flanges is reduced. Are wheels build on these hubs stronger than "classic" ones? -- marcin www.enduro.95mb.com - it is in Polish however you can find here some pictures from an overhaul of Z1 FR SL and AVA RL (click on the "rower") |
#5
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Spoke tension question
Marcin J. wrote: what about Sram hubs (and probably some others too) which have flanges located symmetrically from the hub center (rim is exactly in the middle between the flanges)? They should allow to build wheels with equally tensioned spokes at both sides. However the distance between flanges is reduced. Are wheels build on these hubs stronger than "classic" ones? Yes, this makes for a stronger wheel. |
#6
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Spoke tension question
Gary Robinson wrote: Hello, I've been using a set of wheels with CXP22 rims and Shimano hubs. When checking the bike over I noticed that a number of spokes on the rear wheel were very loose. I started tweaking them up, but the wheel went out of true. Not being experienced with wheels, I took it down to the LBS, explained the problem and asked them to true and tension it. Checking the wheel, I've found that while it's nice and true, there's a lot of variability in spoke tension on the non-drive side and some of the spokes have a lot less tension in them than others. My favourite ride is a 10 mile climb, followed by a 10 mile descent. The road surface for the first couple of miles of the descent is pretty bad. Lots of potholes and cracks, resulting in a rough and bumpy ride. I'm not a lightweight either, so I'm sure the wheels aren't having an easy time. Do I need to worry about the variability in spoke tension? Thanks Gary Couple of things. If the rim is not round, the tension will jot be even on the left OR right side. If it's not round due to riding, impacts, etc, then a wheel can either have even tension and not be round or true or it can be round and true but with a used rim, the tension will vary. I would say on an older rim, getting the tension as close as possible is the key to a long term use w/o problem, not having it look good on a truing stand. |
#7
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Spoke tension question
Marcin J. wrote: "Nate Knutson" wrote: ups.com... Do I need to worry about the variability in spoke tension? First of all, it's important to know that the left and right side spokes of rear wheels for derailer bikes, and on several other types of rear wheel, use different tensions. There's more tension on the drive side spokes, which isn't a good thing but is inherit to any wheel where the spoke-end centerline is going to end up anywhere but exactly between the two flanges. It's unclear whether you know this or not. I'm not sure if I understood all of the wisdom (I'm pretty sure I didn't) and I'm not sure if you understand my English but I have to ask a question: what about Sram hubs (and probably some others too) which have flanges located symmetrically from the hub center (rim is exactly in the middle between the flanges)? They should allow to build wheels with equally tensioned spokes at both sides. However the distance between flanges is reduced. Are wheels build on these hubs stronger than "classic" ones? Wheels are all about triangles with the 'base' being the distance between the flanges. If that 'base' is too small, the wheel won't be reliable. Sram hubs make for good wheels as do all other hubs out there if the components chosen are appropriate for the rider and their needs and the build is a good one. |
#8
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Spoke tension question
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#9
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Spoke tension question
On Thu, 5 Jan 2006 13:25:31 +0100, "Marcin J." wrote:
what about Sram hubs (and probably some others too) which have flanges located symmetrically from the hub center (rim is exactly in the middle between the flanges)? They should allow to build wheels with equally tensioned spokes at both sides. However the distance between flanges is reduced. Are wheels build on these hubs stronger than "classic" ones? I built some American Classic hubs into Velocity OC, both 700c and 650c. The spoke tension is almost the same on each side of the hub. One might conclude that a dishless wheel is stronger but I don't think so. The distance between the flanges on these hubs is narrower than most other hubs and that doesn't make stronger. In my thinking, if you permit the distances between flanges approach zero, the lateral support of the rim becomes zero. |
#10
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Spoke tension question
Nate Knutson writes:
Do I need to worry about the variability in spoke tension? First of all, it's important to know that the left and right side spokes of rear wheels for derailer bikes, and on several other types of rear wheel, use different tensions. There's more tension on the drive side spokes, which isn't a good thing but is inherit to any wheel where the spoke-end centerline is going to end up anywhere but exactly between the two flanges. It's unclear whether you know this or not. I think the term would better be "right side" spokes, some hubs today having the drive (crossed spokes) on the left and radial on the right. The asymmetry arising from the gear cluster being on the right side and displacing the hub to the left. Besides, "drive side" sounds pretentious and has a ring of insider jargon that thrives in bicycling. The rest of the conversation actually gets pretty complex, especially when you get into whether the shop did a good/honest job or not. I can tell you now that whether they did or not, they did a common one for the situation. If spokes within one side of a rear wheel cannot be brought into uniform tension it means the rim has kinks in it that will prevent it from being a reliably true wheel. That is to say, it was either a faulty rim from the start (which is unlikely) or it experienced a damaging event (crash). Such rims can be rehabilitated, if the bends are not too abrupt, by bending the rim while the wheel is partially tensioned. It cannot be done reasonably without spoke tension. Jobst Brandt |
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