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Old 03-16-06, 01:08 PM   #1
coyotecrust
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black spokes break

"black spokes break

and black spokes creak"


true or false or somewhere in between?
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Old 03-16-06, 01:20 PM   #2
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are they anodized? are they dt spokes, or disposable wheel spokes?
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Old 03-16-06, 01:38 PM   #3
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among the people i know who build wheels and have experience in general, black spokes are regarded as detrimental to a wheel. mainly because of the crosses - squeeze the crosses on a silver spoked wheel and they slide and flex easily over each other and return to their original position, with black spokes, the drag and bind over one another, and dont return to their original position unless seperated by hand, the creeking you may be refering to are the spokes occasionally popping back into place after theyve 'walked' over to one side.

all my builds are done with silver spokes, unless the customer asks otherwise - by all means black spokes arnt weak by any means, but when working on a wheel things feel alot more refined and secure when the spokes are silver...
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Old 03-16-06, 01:44 PM   #4
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hi quality like dt or wheelsmith
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Old 03-16-06, 02:11 PM   #5
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Interesting, my ATB (Trek 820) is about a year old (used for commuting) and i've started hearing a funny creak from the front wheel if i'm in a strong wind. Could be the black spokes rubbing on each other?

Does this mean the wheels need truing? I check them when I do my weekly inspections and haven't noticed them going out of true. Only broke one spoke in 1 year, and that was because I was hauling too many books.
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Old 03-16-06, 02:51 PM   #6
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Originally Posted by The Great Stonk
among the people i know who build wheels and have experience in general, black spokes are regarded as detrimental to a wheel. mainly because of the crosses - squeeze the crosses on a silver spoked wheel and they slide and flex easily over each other and return to their original position, with black spokes, the drag and bind over one another, and dont return to their original position unless seperated by hand, the creeking you may be refering to are the spokes occasionally popping back into place after theyve 'walked' over to one side.
I tend to keep a bit of lube on the spoke crossings for this very reason...
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Old 03-16-06, 02:58 PM   #7
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I give a 1 year spoke breakage guarantee on all my handbuilt wheels.....except if you want black spokes. I find them to be more brittle at the elbows as well.
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Old 03-16-06, 03:58 PM   #8
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I see the black spokes fail far more often then plain SS spokes. The worst is the straight 15g unbranded spokes that come on just about every MTB these days.
A confession: I did build up my singlespeed with black 14/15 Dts because I wanted an all black/flat silver bike. So far so good.
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Old 03-16-06, 07:19 PM   #9
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I just checked our three, late model MTBs. Only one has black spokes. Naturally, it's the newest and most expensive.
Should I put lubricant where the spokes cross? If yes, what kind of lubricant? This bike is taken on trails, I'm concerned about dirt build up on any unprotected, lubricated surface. Thanks for any feedback.
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Old 03-16-06, 07:25 PM   #10
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Originally Posted by roccobike
I just checked our three, late model MTBs. Only one has black spokes. Naturally, it's the newest and most expensive.
Should I put lubricant where the spokes cross? If yes, what kind of lubricant? This bike is taken on trails, I'm concerned about dirt build up on any unprotected, lubricated surface. Thanks for any feedback.
I think that lube where the spokes cross would be counterproductive, especially for a mountain bike. Collected grit will make things worse, not better. Is my guess, at least. I've never had a bike with black spokes myself.
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Old 03-16-06, 07:40 PM   #11
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Originally Posted by timcupery
I think that lube where the spokes cross would be counterproductive, especially for a mountain bike. Collected grit will make things worse, not better. Is my guess, at least. I've never had a bike with black spokes myself.
That makes sense to me, especially with the type of riding I do. I'm just going to ride the bike. If I start to have spoke problems, I'll remember this thread and rebuild with silver spokes. Many thanks to the OP for sharing this info.
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Old 03-16-06, 10:59 PM   #12
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That makes sense to me, especially with the type of riding I do. I'm just going to ride the bike. If I start to have spoke problems, I'll remember this thread and rebuild with silver spokes. Many thanks to the OP for sharing this info.
That is just what I reccomend. If you break one, replace the spoke. When you break the second one, build the wheel.
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Old 03-16-06, 11:44 PM   #13
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Anyone have anything more than anecdotal evidence? so far I am seeing the "black spokes are inferior" thing in several ways:

1. For the same rim, hub, lacing, and spoke size, black spokes will break or creak more when subjected to the same uses/stresses.

2. There are proportionately more black spokes of all uses and applications on the market, so a greater percentage of spoke problems involve black spokes.

3. Black spokes are used more often in low-end applications, so we see them with problems more often.

4. Black and silver spoke problems occur at the same frequency proportional to application, we just take notice of it more now that we have the idea in our mind that black spokes might be worse.

I have no evidence, but it seems that only case #1 would mean that black spokes are actually more prone to problems. Am I thinking this through correctly?
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Old 03-17-06, 06:42 AM   #14
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I'm no expert on this subject, but I can't help but think this is the stuff urban legends are made of.

Bob
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Old 03-17-06, 06:53 AM   #15
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Jimmythefly has a very logical mind.

+1
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Old 03-17-06, 07:06 AM   #16
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I have not noticed any more problems with black spokes than silver.
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Old 03-18-06, 09:18 AM   #17
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Black spokes are anodized, and that's where the problem lies. Here comes the science (sorry);

Spokes, even DT Swiss, who claim they 'cold forge' them, as if drawing isn't cold-forging, d'uh, are heavily drawn, much more so than frame tubing, bar-ends, etc. They come from ~10mm stock, as a rule and undergo massive deformations. While this degree of cold-work makes them very, very strong, it obviously can't alter their Young Modulus. It won't make them stiffer, as that is a fixed material parameter, so even at much higher strength, they elastically deform the same amount as unworked material.

Now, spokes are generally made from 18-8 (304Sxx) stainless steel, of varying cleanliness. The degree of impurity, inclusions, unwelded voids, etc - the quality, is what affects the base material price, and so, to some degree, the final quality and price.

The highest quality ones generally come from manufacturers with the highest care and attention to detail, quality control installation. This is reflected in the accuracy of the cold-heading an manufacturer's mark on the head, the forming of threada nd the smoothness of the spoke surface.

It is this surface finish that is of paramount importance in the case of spokes in general, and black spokes in particular.

Anodising is, as most of you appreciate, an artifical thickening of the natural oxide skin of a material, brought about by electrolytic means. This however, unfortunately, unlike for example, stove-oxidising, a process seen in heat-treatment of ductile iron pipe means the oxide film is now also porous at its outer extremeity, and so will uptake dyes.

This is in general in a highly-worked, very strong material, a Bad Thing™. 304 stainless is very ductile when unworked, or annealed. At more than 90% reduction, it only has ten percent or less ductility remaining. This is more than most aluminium tubesets will offer, but more importantly, the absolutely massive impact toughness and resistance to crack propagation have been drastically reduced by all the locked up dislocation substructure (cold working).

Even the tiny elastic deformation that the unworked material could comfortably and unendingly absorb has a much more severe effect on hard-drawn material. Fatigue failure occur via what is termed microplastic deformation - tiny local stress concentrations vastly exceed the fatigue limit and yield stress, while remaining in the bulk sample comfortably under the yield limit. And in spokes, this adds up quickly.

As long as the surface is perfect, the likelihood of such micro-plastic deformation, due to miniscule stress concentrators is slim. Add a porous, incredibly hard (oxides tend to be), brittle layer, intimately bonded to a hardened, less tough substrate = recipe for sudden failure. Fatigue failures ALWAYS occur at the surface.

In short:


Blackened spokes, of ANY quality have an inherently higher likelihood of failure. BUT. Most good quality spokes will not come close to their fatigue limit or suffer sufficient stress for a crack to occur in the surface.
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Old 03-18-06, 11:17 AM   #18
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Originally Posted by Falanx
As long as the surface is perfect, the likelihood of such micro-plastic deformation, due to miniscule stress concentrators is slim. Add a porous, incredibly hard (oxides tend to be), brittle layer, intimately bonded to a hardened, less tough substrate = recipe for sudden failure. Fatigue failures ALWAYS occur at the surface.
This is the exact reason anodized rims have fallen out of favor. Adding a super-hard non-flexible layer on top of an underlying softer flexible material will eventually cause surface-cracks. Which propagates through and eventually cracks all the way. Spokes are stressed closer to yield and ultimate strength levels than any other part on the bike. So there's already some stretch in the material under tension, making surface-cracks that much easier to develop.
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Old 03-18-06, 11:23 AM   #19
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Originally Posted by Falanx
Black spokes are anodized, and that's where the problem lies. [snipped]
I thought black spokes were painted that color, but just looking at some black spokes that I have here (DT Swiss) makes me think that maybe they are anodized (just going by appearance). I was under the impression that anodizing was almost exclusively an aluminum surface treatment. Do you know for a fact that stainless steel spokes are commonly anodized?

Also, I understand that there are two basic types of anodizing treatments: cosmetic, and "hard". If my DT spokes are indeed anodized, they appear to be only cosmetically treated instead of hard anodized. The coating comes off fairly easily and doesn't seem to resist abrasion much at all. This would lead me to believe that the treatment wouldn't impart surface imperfections to the underlying material.
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Old 03-18-06, 11:23 AM   #20
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*Nods*

We should sit down over half-caff one day and set the materials engineering world to rights....
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Old 03-18-06, 11:29 AM   #21
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Originally Posted by Falanx
Fatigue failures ALWAYS occur at the surface.
I disagree. Impurities in the metal can cause stress risers too.
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Old 03-18-06, 12:10 PM   #22
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Quote:
Originally Posted by juicemouse
I disagree. Impurities in the metal can cause stress risers too.

No. They can't. Impurities are nothing more than statistical abberations in the lattice. Manganese atoms in maraging steels are impurities. Sulphur in any steel is an impurity, but unless those impurities cluster and become an inclusion, they alone will not exert enough effect to cause a failure. Inclusions and other point defects (voids/vacancy clusters, dislocation clusters forming ithe beginnings of cracks, gas bubbles) can however. The terminology is very explicit in these cases for a reason, and that reason is not to trip you up, but to ensure that the phenomenological situation is correctly ascribed.

Stress raisers in a material require dislocation pileup. One single impurity atom cannot cause a dislocation pileup because it has no way of hindering the dislocation line. Multiple clusters of impurity atoms that therefore are inclusions, however can, by a variety of means, most usually Orowan dispersion strengthening.

This isn't open to disagreement. It's basic materials mechanics and dislocation theory.

EDIT:

And as for the fatigue reference, fatigue failures occur at the surface of a component for a reason - because the surface of a component is always under the most stress - it has environmental stress-corrosion cracking effects, the greatest distance and therefore bending moment incurred from the 'free surface' of zero net stress, and no material ahead of it to share the greatest loading - as well as a distroted, not-even-close to perfect lattice in the surface region.

Last edited by Falanx; 03-18-06 at 12:31 PM.
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Old 03-18-06, 12:28 PM   #23
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Originally Posted by Falanx
No. They can't. Impurities are nothing more than statistical abberations in the lattice. Manganese atoms in maraging steels are impurities. Sulphur in any steel is an impurity, but unless those impurities cluster and become an inclusion, they alone will not exert enough effect to cause a failure. Inclusions and other point defects (voids/vacancy clusters, dislocation clusters forming ithe beginnings of cracks, gas bubbles) can however. The terminology is very explicit in these cases for a reason, and that reason is not to trip you up, but to ensure that the phenomenological situation is correctly ascribed.

Stress raisers in a material require dislocation pileup. One single impurity atom cannot cause a dislocation pileup because it has no way of hindering the dislocation line. Multiple clusters of impurity atoms that therefore are inclusions, however can, by a variety of means, most usually Orowan dispersion strengthening.

This isn't open to disagreement. It's basic materials mechanics and dislocation theory.
You're right. It was inclusions that I was thinking of. Materials science was a few years ago for me. Thank you for the clarification/correction.
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Old 03-18-06, 12:32 PM   #24
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Sorry, chap. I came across as really arsey on that one...
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Old 03-18-06, 12:46 PM   #25
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Originally Posted by Falanx
Sorry, chap. I came across as really arsey on that one...
No worries, I'm fairly thick-skinned.

Any input on my earlier post (#19)?
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