Jul 17, 2001 8:25 AM
|I need some helpful sugestions. I have broken two spokes in the last week. This is all happening on the non drive side at the spokes elbow. The wheels consist of Mavic Open Pros (32 hole) with Chorous Hubs and 14/15 double butted DT spokes. I weigh 205. I have noticed after the seconed time on closer examination of the hub that where the hole is on the hub seems to be a little deformed. Anybody have similar experiences and or suggestions on what to do next?|
|Get thyself to a good LBS!||grzy mnky|
Jul 17, 2001 9:28 AM
|Spoke tension, or more accurately incorrect tension is usually the cause. However at 205 lbs. you can really start applying some force (this is good) and you may be fatiguing the spokes - nothing lasts forever. The deformation at the hub is normal. You should visit a good LBS with a skilled wheel builder and work with them. You may need a rebuild - no real reason why the mentioned components can't work for you, but good hand built wheels are superior to anything from a machine - what you pay for is what you get. Picking up Jobst Brandt's book "The Bicycle Wheel" while you're at said LBS will give you a lot of good insight - even if you never plan to build a wheel yourself. It's a fairly quick read and reasonably priced at around $20.|
Jul 17, 2001 1:02 PM
|I took it to a new shop at lunch and they said almost the exact same things that you mentioned. They said that it should be a fine set up for me also. I will try again. I will find out in a couple of days if it is succesful. |
thanks again, slim
|re: Broken Spokes!||d_alex|
Jul 18, 2001 4:19 AM
|From what I have read recently, using semi-radial spoking is a good preventative for non-drive spoke breakage on heavily dished wheels. This should b possible with a 32 spoke wheel. Have you considered moving up to a 36 spoke wheel? At your weight, it would be a good idea.|
Jul 18, 2001 7:49 AM
|Thanks for the info d_alex. I am going to try this one more time and if I get another broken spoke then I will pass on your suggestion. At this point the next thing to do is make some changes and yours makes good sense.|
Jul 18, 2001 8:46 AM
|not sure where you heard this (do you have a source?), but the non-drive side has lower tension than the drive side so one would think that if you're getting a failure then low tension could be the cause. Now radial spoking actually increases tension due to the geometry of low angles, but the spokes are shorter so their working range is lower making it easier to exceed their ideal envelope. Ultimately it's a bunch of trade offs and the devil is in the details - I could see it going either way. The non-drive side radial spoking is as much a fashion statement as anything else (Brandt and the UBI/DT Manual). I should check and see what Sheldon Brown has to say. |
I guess the bottom line in my mind is that he really shouldn't be having any problems if the wheel is built correctly. His requirements aren't that unusual.
Jul 18, 2001 9:35 AM
|I once saw a custom-built wheel, which had 4x spoking on the drive side, and 2x on the non-drive side. The drive sides were straight gauge, whereas the non-drive were DB.|
Jul 18, 2001 2:03 PM
|I agree with gizzer. I think a good wheel tuning by a guy who understands what he is doing will solve the problem permanently. I'm not too surprised, I see a lot of broken spokes because 8 and 9 speed rear hubs are dished so much that they require a pretty good build.
I'm pretty conservative regarding spoking patterns, but I think that I understand the logic behind the half/radial theory, I just don't do it. It actually is supposed to help two ways:
1. You can run all of the non-drive spokes from the inside of the hub. This gives them a little less angle and consequently requires a little more tension to center the rim.
2. Radial spoking doesn't have any spokes that run forward from the top of the hub. In a conventional crossed spoke wheel, those spokes are slightly detensioned when the hub is rotated by pedaling forces.
Jul 18, 2001 3:00 PM
|The advocates of "non-drive side radial spoking (do you ever get the unnerving feeling you're delving too deeply into a specialism for social health?)", claim that the leading (unextended under torsion) spokes become too loose because the net tension on that side of the wheel is less. This is both part fallacy, and a reason to do the opposite, and lace the wheel fully tangentially:
It presumes that because the spokes are less highly tensioned, they will stretch more than otherwise. This isn't the case, as spoke elongation is a function of the characteristics of the metal, not the current tension; only tension so low that the spoke was unloaded enough that it could move freely in the hub would increase the chances of fatigue failure, and this doesn't happen.
More to the point, if the leading spokes are slacking due to torsion, then the trailing spokes are bearing some torsional stress, transmitted through the hub body: and therefore should be tangential for the same reason the drive-side is: to prevent fatigue failure from fretting at the spoke/ hub interface.
I'd put it all down partly to the vagaries of fashion, and partly to DT Revolution spokes: the preponderence for very narrow spokes means that spoke twist is more of a problem in wheels these days... and these leading non-drive spokes are the first to relieve themselves if the builder doesn't do it first.
|I may do this for my master's thesis!||Rusty McNasty|
Jul 20, 2001 5:07 AM
|Let's see: a finite-element analysis of 1)common 3x and common 4x 2)3x-semi-radial ouside 3) same, but radial inside 4)4x and 3x, 2x, semi-radial. Sounds like I'll be making a lot of wheels, though!|
|Cut to the Chase....||grzy mnky|
Jul 20, 2001 3:58 PM
|Just visit Stanford and dust off Jobst Brandt's thesis.... ;-) |
Of course the best would be to use it to build upon - the analysis tools and technology are so amazing these days! Good luck!
|just for interest||Jofa|
Jul 20, 2001 4:12 PM
|Apparently Jobst found out that some shy fellow had conducted in-depth investigations into the dynamics of spoked wheels before him, and demonstrated all the ' wheel stands on its spokes' stuff already, but was never well-publicised; Jobst of course has, fairly, declared this at every oppurtunity recently, reluctant to take credit for the discoveries which everybody supposed he himself had originated. I can't remember who or when, but scrutiny of rec.bicycles.tech should turn up the name, just for research interest.|| |