# Misinformation from experts?



## castofone (Dec 24, 2010)

There is a lot of dubious folklore about bicycle wheels. I recently picked up this gem from a commercial site (name withheld). It demonstrates a lack of understanding of basic wheel mechanics.


> The rear wheel on a multispeed bike is designed such that the spokes on the drive side of the wheel have higher spoke tension than the spokes on the non-drive side. Under load, like when you are riding your bicycle for example, only the spokes on the drive side of the wheel are supporting your weight. So a rear wheel with 36 spokes only has 18 spokes that are working to support your weight. Furthermore, in reality, far fewer spokes are actually supporting your weight, only the 4 or 5 spokes that are closest to the ground are really supporting your weight,...


There are two errors of fact there. I would hesitate to buy wheels from a wheel builder who a) believed that nonsense or b) not only doesn't understand wheel mechanics but either doesn't know that he doesn't know or is just full of bs. 

The saving grace is that you really don't have to understand anything much if you are just following traditional formulas and have a lot of experience with building wheels for different uses and weights but really, if they don't know they shouldn't pretend to know IME. Who was it who said It is better to shut up and appear ignorant than to open your mouth and remove all doubt.

Any other gems out there? Please post.


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## cfoster (Dec 20, 2007)

That's from our website.

I think you may have a misunderstanding of the subject material.

Furthermore, it's absolutely hilarious that out of all the wheel marketing BS advertised in the marketplace (via actual verbage, or implied performance via "design"), you managed to take offense to this?!

Here's a great resource of those whom are interested:

Sheldon Brown + Note Additional Available Further Reading Resources


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## cxwrench (Nov 9, 2004)

uhhmmm...to quote

"Furthermore, in reality, far fewer spokes are actually supporting your weight, only the *4 or 5 spokes that are closest to the ground* are really supporting your weight,... "

do you really think that's how it works?


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## gordy748 (Feb 11, 2007)

Sorry to sound like a dumba$$, but that does actually make sense to me. My reasoning is...

Gravitational force pushes the rider and bicycle weight downwards through the hub towards the ground. The only thing that supports that force is the spokes between the hubs and the ground. There is also force on the spokes leading to the top of the rim, but this force is pulling the top of the rim downwards, which is prevented from doing so by the horizontal spokes that ensure the rim cannot be deformed under normal load. So the lowermost spokes are, reasonably, the only ones supporting the rider and bicycle weight.

Mind that I am an economist and not a physicist, I'm happy to be wrong here in exchange for being educated on what's right!

As for the different tensions, I thought that the drive side spokes were closer to the center of the wheel, so needed to be higher tensioned to compensate...


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## JCavilia (Sep 12, 2005)

gordy, you don't know what you're wading into. there is a running debate for years about whether to describe the load as "standing" on the lower spokes.

it comes down to how one defines terms. But your analysis is not how it works. All the spokes are under tension, all the time. So the spokes on the bottom are pulling the hub _down_, so they can't be supporting the load in the sense you suggest. Spokes can't "push" - they're not rigid enough.

What is true is that the spokes on the bottom undergo a change in tension -- it is lessened, compared to all the others. That's why some say the hub "stands" on them. The load is actually supported by all the other spokes at that time. The ones on top pulling up toward the rim, the ones at the sides pulling to keep the rim from squashing out under that load. Looking from the ground up, the ground pushes up on the bottom of the rim, the rim tries to deform outward under that load, the spokes at the sides prevent that, allowing the load to be borne by the spokes at the top and sides. 

I shall say no more, except to agree with the OP that the assertion that only the driveside spokes support the load is bunk. If the tension is so unbalanced that the left spokes go slack, the wheel will go out of true and break spokes constantly. The higher-tensioned spokes do more work, but the others don't do nothing.


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## shinewheel (Jan 14, 2011)

Couldn't one answer this fairly simply by reading tensions with a tension meter in the various spoke positions both loaded and unloaded?
I'm a believer in load being supported predominantly by the lower spokes, and on the rear drive side, but am open to learning differently.


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## BWWpat (Dec 17, 2009)

Awe this debate. The entire wheel plays its part in the structure of the wheel. This is not debatable. When I first started in the bike world I thought the hub hung from the rim, but when I truly thought about it, looked at the forces being applied, played with tensions, built wheels incorrectly just to see what would happen, the conclusion was pretty simple.

The top spokes keep the wheel from collapsing while the bottom spokes absorb your weight. If the top spokes held your weight, they would increase in tension equivalent to your weight but they don't. Oddly enough the bottom spokes decrease in tension equivalent to your weight which is why we put tension into the spokes in the first place.

Yes its hard to wrap your mind around. but the reality is the bottom spokes are holding you while the top spokes are holding the wheel together. But in all the entire wheel supports the entire wheel, and taking one part away makes it no longer a wheel.

If you have another theory on how a wheel works please provide proof as I am open to new ideas. I love this stuff, I have built thousands of wheels. If I'm wrong I have no problem admitting it, but all the math from many sources supports our claims.


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## JCavilia (Sep 12, 2005)

shinewheel said:


> Couldn't one answer this fairly simply by reading tensions with a tension meter in the various spoke positions both loaded and unloaded?
> I'm a believer in *load being supported predominantly by the lower spokes*, and on the rear drive side, but am open to learning differently.


Damn; I said I'd resist ;-)

Not unless you use the word "supported" in what I'd call a peculiar way. To say a load is "supported" agianst gravity by something below it, the load must be exerting a _compression_ force on that member. You don't need a tension meter to know that the lower spokes remain under _tension_. If they went slack, your wheel would be a mess, constantly going out of true and breaking spokes from fatigue. The lower spokes are _pullling (down)_ not _pushing (up)_. They are _incapable_ of pushing.

So if by "support" in an upward direction you mean "not pull down as hard," you can call it "support." But that's not what the word means to me.

I really should go now.


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## TomH (Oct 6, 2008)

Heres a probably too simple understanding from a few engineering classes...

Any spoke below the axle (more than 90 degrees or parallel), your weight contributes to a tension loss. Any spoke above the axle (more than 90 degrees), your weight contributes to a tension gain. ALL spokes should undergo a change in tension relative to position/angle to maintain equilibrium. 

It should be impossible to isolate a few spokes and say they're holding the weight exclusively, the whole wheel works as a system.


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## Pirx (Aug 9, 2009)

JCavilia said:


> Damn; I said I'd resist ;-)


Alright, then I'll do the dirty work for you:

A) The contribution of the non-drive side spokes to supporting the force at the hub is, within small fractions of a single percent, the same as the one from the drive-side spokes.
B) If we take the expression "working to support the weight" to mean that the spokes carry an _increased_ load in response to the force exerted on the hub, then it is _exclusively_ the spokes outside of a roughly 15-degree or so wedge at the bottom that "support the weight". Of course, only the additional load on the top spokes contributes to generating the required upwards force. In other words, the situation is pretty much the opposite of what was described in the passage quoted by the OP. In a sense we could say that, in fact, the hub is "suspended from the top spokes", rather than "standing on the bottom spokes". What happens is simply that the spokes on top pull harder (upwards) than the spokes on the bottom.


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## Mike T. (Feb 3, 2004)

Yeah this topic is very interesting to us wheelbuidy types. It's been covered to exhaustion by poster *meltigfeather* over at MTBR.com. *'feather* is a structural engineer by profession and he specializes in pre-stressed (pre-tensioned?) structures of which a bicycle wheel is a good example. Concrete bridge beams are another - they have cables or rods inside them and without such structure a plain simple cement beam wouldn't support much at all.

The lower spokes support the downward lpad (upwards pressure?) until that pressure exceeds the tension in the spoke, then the nipple unseats from the rim and you're in big trouble.

Tests have been done (I can't quote them) and it was found that the de-tensioning of the lower spokes far exceeded the increase in tension of the upper spokes or side spokes.

And don't shoot the messenger here as 'feather is the engineer and the expert on pre-stressed structures, not me.


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## shinewheel (Jan 14, 2011)

When you get on the bike the only appreciable change in spoke loading is in the lower few spokes. I would say they are supporting your weight. A reduction in tension can still support a load.
I agree a lot of this is semantics, I'm more interested in whether anyone has performed the test I posed about change in tension in various spoke positions when the bike is loaded.


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## Pirx (Aug 9, 2009)

Mike T. said:


> Tests have been done (I can't quote them) and it was found that the de-tensioning of the lower spokes far exceeded the increase in tension of the upper spokes or side spokes.


This is correct.



shinewheel said:


> When you get on the bike the only appreciable change in spoke loading is in the lower few spokes.


This is wrong, although it is true that, depending on the number of spokes and the exact position of the wheel, the unloading of the bottom-most spoke (note the singular) can be much larger than the additional loading or unloading of any other spoke. It turns out that with the exception of one to three spokes, the load is distributed fairly evenly. I should also note that the spokes that are near-horizontal, and thus do not significantly contribute to countering the external force, nevertheless carry a significant amount of strain as well.



shinewheel said:


> A reduction in tension can still support a load.


Yes, but that is because the load is carried by the top spokes.



shinewheel said:


> I agree a lot of this is semantics, I'm more interested in whether anyone has performed the test I posed about change in tension in various spoke positions when the bike is loaded.


Jobst Brandt has results from a finite-element analysis in his book, which is available online.


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## ohdee (Nov 9, 2007)

From the original quote, I disagree that only the DS spokes support a riders weight. Both sides contribute the same for a radial load.

I'll stay out of the "standing" vs "hanging" debate. Been there, done that. It comes down to one's own interpretation.


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## cxwrench (Nov 9, 2004)

Pirx said:


> Alright, then I'll do the dirty work for you:
> 
> A) The contribution of the non-drive side spokes to supporting the force at the hub is, within small fractions of a single percent, the same as the one from the drive-side spokes.
> B) If we take the expression "working to support the weight" to mean that the spokes carry an _increased_ load in response to the force exerted on the hub, then it is _exclusively_ the spokes outside of a roughly 15-degree or so wedge at the bottom that "support the weight". Of course, only the additional load on the top spokes contributes to generating the required upwards force. In other words, the situation is pretty much the opposite of what was described in the passage quoted by the OP. In a sense we could say that, in fact, the hub is "suspended from the top spokes", rather than "standing on the bottom spokes". What happens is simply that the spokes on top pull harder (upwards) than the spokes on the bottom.


if it were any other way, how would this work?


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## Pirx (Aug 9, 2009)

ohdee said:


> I'll stay out of the "standing" vs "hanging" debate. Been there, done that. It comes down to one's own interpretation.


I think the confusion there comes from switching from absolute forces to force differences. But, yeah, it's better to not dig any more into this, I agree.



cxwrench said:


> if it were any other way, how would this work?


Don't ask me...


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## gordy748 (Feb 11, 2007)

Ahhh... I get it. The bike and rider is effectively suspended in mid air, trapeze-like. They pull the top of the rim downwards with the up-pointing spokes, while the rim is prevented from collapsing by tension from the side-pointing spokes.

So with enough weight (e.g. one Roseanne Barr) you could simply unscrew all the lower-most spokes and nothing would happen. Until she started pedaling off...


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## Kerry Irons (Feb 25, 2002)

*Review before the test*



JCavilia said:


> gordy, you don't know what you're wading into. there is a running debate for years about whether to describe the load as "standing" on the lower spokes.
> 
> it comes down to how one defines terms. But your analysis is not how it works. All the spokes are under tension, all the time. So the spokes on the bottom are pulling the hub _down_, so they can't be supporting the load in the sense you suggest. Spokes can't "push" - they're not rigid enough.
> 
> ...


For those who subscribe to fantasy theories, or simply do not understand how tensioned structures work, please review this post REPEATEDLY until you come to understanding. It will be on the test!


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## JCavilia (Sep 12, 2005)

*EXACTLY, gordy*



gordy748 said:


> Ahhh... I get it. The bike and rider is effectively suspended in mid air, trapeze-like. They pull the top of the rim downwards with the up-pointing spokes, while the rim is prevented from collapsing by tension from the side-pointing spokes.
> 
> So with enough weight (e.g. one Roseanne Barr) you could simply unscrew all the lower-most spokes and nothing would happen. Until she started pedaling off...


You might not be a physicist, but you learn quick.


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## Pirx (Aug 9, 2009)

Kerry Irons said:


> For those who subscribe to fantasy theories, or simply do not understand how tensioned structures work, please review this post REPEATEDLY until you come to understanding. It will be on the test!


Actually, hist last sentence in the post you quoted, "_The higher-tensioned spokes do more work_,[...]" is incorrect (the incremental load, and the associated strain, is pretty much exactly the same, on both drive- and non-drive side spokes). But otherwise I agree, he gave a very lucid explanation of the situation.


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## JCavilia (Sep 12, 2005)

*Perform a test*



shinewheel said:


> When you get on the bike the only appreciable change in spoke loading is in the lower few spokes. I would say they are supporting your weight. A reduction in tension can still support a load.
> I agree a lot of this is semantics, I'm more interested in whether anyone has performed the test I posed about change in tension in various spoke positions when the bike is loaded.


Sit on your bike, not moving, and have somebody take a big wire cutter and cut 4 or 5 spokes at the bottom of each wheel. I'll bet you ten thousand dollars (just to pick a figure) that the wheels will still hold you up. Then tell me those spokes were "supporting your weight."


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## JCavilia (Sep 12, 2005)

Kerry Irons said:


> For those who subscribe to fantasy theories, or simply do not understand how tensioned structures work, please review this post REPEATEDLY until you come to understanding. It will be on the test!


A blurb like that from Kerry Irons feels like getting an honorary degree


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## cxwrench (Nov 9, 2004)

JCavilia said:


> Sit on your bike, not moving, and have somebody take a big wire cutter and cut 4 or 5 spokes at the bottom of each wheel. I'll bet you ten thousand dollars (just to pick a figure) that the wheels will still hold you up. Then tell me those spokes were "supporting your weight."


exactly!


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## MerlinAma (Oct 11, 2005)

JCavilia said:


> Damn; I said I'd resist ;-)
> .


You've done such a good job I WILL resist trying to add anything!


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## Pirx (Aug 9, 2009)

JCavilia said:


> Sit on your bike, not moving, and have somebody take a big wire cutter and cut 4 or 5 spokes at the bottom of each wheel. I'll bet you ten thousand dollars (just to pick a figure) that the wheels will still hold you up. Then tell me those spokes were "supporting your weight."


Excellent example! :cornut:


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## danl1 (Jul 23, 2005)

TomH said:


> Heres a probably too simple understanding from a few engineering classes...
> 
> Any spoke below the axle (more than 90 degrees or parallel), your weight contributes to a tension loss. Any spoke above the axle (more than 90 degrees), your weight contributes to a tension gain. ALL spokes should undergo a change in tension relative to position/angle to maintain equilibrium.
> 
> It should be impossible to isolate a few spokes and say they're holding the weight exclusively, the whole wheel works as a system.


I'd say just the right number of classes. Enough to understand what's going on, not so many that you look clear around and climb up your own arse.

If we were analyzing the same structure in anything other than a vertical wheel context, we'd be saying that the radial tension keeps the axle centered, and also keeps the rim from deforming to the point of it's structural collapse. The real strength of a wheel is in the strength of the circle, and the bits in the middle are really only doing the job of keeping it round. 

To take yet another view, set a load on the top of a bare rim. it'll collapse pretty easily. Build the same rim (well, before it was ruined) into a wheel, continue to ignore the axle, and it'll take a great deal more weight - many multiples. 

So while you are absolutely right, there's one factual thing you got wrong - but it really only proves your point more. The changes in tension turn out not to be 'Top Half' and 'Bottom Half', but "Bottom Few" and "All the rest." In effect, the lowering of tension in those few bottom spokes, paired with the increased tension in all the rest, focuses the circumferential compression forces of the rim towards the load point, essentially trying to make the load point bulge outward, and resisting the 'inward' force of the ground. 

It turns out that a wheel "stands" on it's rim, and the combined spoke forces of all the spokes help it do that.

This 'standing on less tension' stuff is an argument of mathematical semantics. As a way of looking at things it's not invalid, but isn't helpful in conversations with those that don't trade in mathematical gibberish. And really, a bit more applicable to other types of tension-balanced structures than to wheels. While it has validity for one part of the force load discussion, it should be discussed only in the context of it's contribution to the roundness and planarity that really provide a wheel with strength. It's an argument in paired forces, and a wheel is just a bit more complicated than that.


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## rruff (Feb 28, 2006)

JCavilia said:


> What is true is that the spokes on the bottom undergo a change in tension -- it is lessened, compared to all the others. That's why some say the hub "stands" on them. The load is actually supported by all the other spokes at that time. The ones on top pulling up toward the rim, the ones at the sides pulling to keep the rim from squashing out under that load. Looking from the ground up, the ground pushes up on the bottom of the rim, the rim tries to deform outward under that load, the spokes at the sides prevent that, allowing the load to be borne by the spokes at the top and sides.


Is that why people are confused? Does anybody here know what a free body diagram is? It is great for visualizing what is going on, because spokes essentially act as force vectors. 

Look at the wheel in the zero load state. The spokes are in pretension and radiate from the hub, pulling on it equally in all directions. Assume it is radially laced just to make the visualization easier. Now add a vertical load... the bike's dropouts result in a downward force on the hub, which *must* be countered by changes in spoke tension. So, there must be a net increase in vertical force vectors acting on the hub via the spokes, that *exactly* offsets the negative vertical force via the dropouts. 

When it is said that the "lower spokes support the load", it is because... they do. In a typical wheel they are the ones that are by far effected the most. Their loss in tension results in a positive vertical vector acting on the hub, balancing the downward force of the dropouts. None of the spokes in the wheel experience a significant increase in tension... there is an overall reduction in spoke tension for the entire wheel.

Of course you can remove the lower spokes if you like and the wheel can still support a load... though it will be much weaker than before. The load paths simply change. You can remove all but the top spoke if you like and it will still support a static load... but that doesn't resemble what is going on in an actual pretensioned wheel. 

Maybe it would be helpful to look at *why* the lower spokes support most of the load. It is because there is a concentrated load being applied there, via the ground to the tire to the rim. The rim distorts vertically resulting in a loss in spoke tension. A stiffer rim will spread the load to more spokes, but the net change in the vertical force vectors must always equal the downward force at the dropouts. In other words, the stiffness of the rim affects the peak change in spoke tension and the length of the zone at the bottom of the wheel that is effected. If the rim was infinitely stiff, the lower and upper spokes would contribute equally to countering vertical forces.


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## meltingfeather (Dec 16, 2009)

I'm just going to post once. I was invited to this discussion and don't contribute to this forum at all, as you can see. 
This topic has gone 'round and 'round over the years, and I expect that it will continue.
I will say that pretensioned structures are very counter-intuitive. Many engineers have trouble with the concepts when they are introduced in structural analysis, so it is not surprising that many others have trouble with the concepts as well.
A pretensioned structure relies on the pretensioned state for its structural integrity, so while the cutting spokes out of a wheel example might seem logical to some, it fundamentally changes the nature of the structure and also doesn't have the result you wager that it will.
Since a wheel works as a unit, for most it is sufficient to say that the wheel supports the load.
For those who are interested in the structural analysis of the wheel and want to delve further into the distribution of forces within it, there is no other conclusion than that the spokes at the bottom of the wheel do the vast majority of the work to support the load, whatever you want to call it, *though it takes all the spokes, the rim, and the hub for this to be able to work*.
It is interesting that one poster cited JB's FEA work on a wheel right after denying the conclusion that it supports.
The key to understanding the concept of pretensioning is that it is a change the equilibrium state of the structural members from a simple structure. This shift in the zero point is critical to the structural performance of the wheel and is undoubtedly where the semantic arguments begin.
From a structural performance standpoint, less tension is the same as compression when talking about force reactions. The bottom spokes see a compressive load and they shrink in reaction to it according to their modulus of elasticity and geometry. Where they start and stop stress-wise is irrelevant (as long as they remain below yield strength).
One person mentioned a free body diagram and that is one useful teaching tool that is applied in this scenario that demonstrates unequivocally what I am saying. You can sum the forces exerted on the hub by each and every spoke, accounting only for the vertical component of the force. What you will find is that the minute increases in all spokes except for the highly affected few at the bottom does not sum to even close to offseting the load. That's 2+2=4 easy.
Among people to whom this understanding is critical (structural engineers), there is no debate or question on this issue. That should also be an indication.
For people applying simple logic to individual pieces of a structural unit in an attempt to refute what has been understood for many many years, I would suggest focusing your energy on learning if you want to understand or figuring out why you care, rather than trying to refute established fact. I recognize the difficulty of some of these concepts, but that does not change the reality of the system.
:thumbsup:


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## Mike T. (Feb 3, 2004)

Exactly. What the "bikes hang from spokes" crowd don't consider is that a wheel is only a wheel when it's in its finished form - tensioned. Until then it's just a bunch of flimsy parts. They talk of "chop lower spokes and chop upper spokes - which ones make the most difference to wheel integrity?" They forget that if lower spokes are chopped then the load-bearing ability of their "wheel" is no more than an unspoked rim. If the upper spokes are chopped in their "wheel" then immediately, before *any* load is applied, the lower spokes become untensioned to zero and those spokes lose all ability to support weight. But that's not a surprise as the instant they cut their spokes, the wheels ceases to be a wheel anyway.

It doesn't matter how many times they say it, they can't change science and facts - lower spokes support weight and they will do that until the load exceeds their tension and the wheel collapses and that load will be *far* greater than the one that would collapse the rim if they were cut. They should try that little experiment.


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## Mike T. (Feb 3, 2004)

meltingfeather said:


> I was invited to this discussion


Ahhh yes, I still have a modicum of pull around here (Mike puffing out his chest). 

Thanks *'feather*. Ol' buddy.


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## Pirx (Aug 9, 2009)

rruff said:


> So, there must be a net increase in vertical force vectors acting on the hub via the spokes, that *exactly* offsets the negative vertical force via the dropouts.


So far so good.



rruff said:


> When it is said that the "lower spokes support the load", it is because... they do. In a typical wheel they are the ones that are by far effected the most.


A) You might want to read what was said before. It all depends on what you mean by "support the load". In an abstract sense that can be understood to be true, but there's a connotation to this phrasing that is plain false, see Cavilia's example above. 

B) Yes, the bottom few spokes are *a*ffected the most.



rruff said:


> None of the spokes in the wheel experience a significant increase in tension... there is an overall reduction in spoke tension for the entire wheel.


Now you're just fantasizing. The above is completely false. Look up the reference I gave. People have done the calculations, and it turns out, not surprisingly, that most spokes experience an increase in tension when the wheel is loaded.



rruff said:


> Of course you can remove the lower spokes if you like and the wheel can still support a load... though it will be much weaker than before.


As long as the wheel is standing still, as a matter of fact the wheel will be stronger if you don't remove too many spokes. Certainly if you only remove the bottom three or so that will be the case.



rruff said:


> The load paths simply change. You can remove all but the top spoke if you like and it will still support a static load.


If you do that, your rim will collapse under all but the lightest loads. In a bicycle wheel, both rim and spokes play a role.



rruff said:


> Maybe it would be helpful to look at *why* the lower spokes support most of the load. It is because there is a concentrated load being applied there, via the ground to the tire to the rim.


Your premise is false, and so is your conclusion. As an aside, the question of how a tire transmits the load to the wheel is a fascinating one, too. I am still waiting for somebody to bring up this question in here. That will provide for days and days of fun without end. Suffice it to say, no, the tire does _*not*_ transmit a concentrated load to the wheel. Similar to how the spoked wheel itself works, in the case of an air tire (and radically different from, say, a full-rubber tire) the rim is in fact _suspended_ in the tire, and held by distributed forces from the tire bead.



rruff said:


> If the rim was infinitely stiff, the lower and upper spokes would contribute equally to countering vertical forces.


Yes, this is exactly true.


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## Pirx (Aug 9, 2009)

meltingfeather said:


> It is interesting that one poster cited JB's FEA work on a wheel right after denying the conclusion that it supports.


Since it is me you are referring to here, I'll just note that I am obviously not denying "the conclusion [JB's] analysis supports". To keep this brief:
a) Semantics _does_ matter in this discussion. It's not like this has not been explained before, so I won't elaborate any further.
b) I have done computations similar to JBs' myself. What you find, as a matter of fact, is that the sum of the contribution of the changes in load of the upper spokes is not negligible at all, even if it is less than the contribution of the lower spokes. In addition, the load scenario of JB's analysis corresponds to a naked wheel sitting on a flat surface. I'll just note that a wheel suspended in an air tire experiences a very different load scenario, and leave it at that.


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## MongoEric (Aug 18, 2011)

Structural Engineering PE here; a few points to make.

1. There is a big difference between less tension and compression. The change in forces may be the same, but many members (structural elements) have strength in tension but none in compression. That is how most simple trusses are designed. 

2. You can think of the spoke as similar to cables, very strong in tension, no strength in compression. Wouldn't a wheel built with cables instead of spokes work. In fact, isn't that what emergency spoke replacments are? 

3. The concept of freebody diagrams are key. Without movement the sum of the forces must equal zero, and unless there is a major disaster (big movement of the hub) there is no relative movement. If this is not me talking, it is Issac Newton.


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## rruff (Feb 28, 2006)

Pirx said:


> It all depends on what you mean by "support the load". In an abstract sense that can be understood to be true, but there's a connotation to this phrasing that is plain false, see Cavilia's example above.


It is only a false connotation if you do not understand how a wheel supports the load. 



> People have done the calculations, and it turns out, not surprisingly, that most spokes experience an increase in tension when the wheel is loaded.


Did I say something that contradicted that? No. What I stated was 100% true... please read it again. The increase in tension is *insignificant* compared to the relatively huge decrease in tension for the lower spokes... and if you add them up you get a large net decrease. 

I've made an FEM of a wheel myself, BTW. And here is one that is posted on the internet... please look it over. Ian's Bicycle Wheel Analysis



> As long as the wheel is standing still, as a matter of fact the wheel will be stronger if you don't remove too many spokes. Certainly if you only remove the bottom three or so that will be the case.


I'm excited to see how you determined that...


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## Pirx (Aug 9, 2009)

rruff said:


> Did I say something that contradicted that? No. What I stated was 100% true... please read it again. The increase in tension is *insignificant* compared to the relatively huge decrease in tension for the lower spokes... and if you add them up you get a large net decrease.


I read it again, and what confused me was your sentence "_there is an overall reduction in spoke tension for the entire wheel_". I realize now what you meant by that, but I still think the phrasing is a bit misleading. Be that as it may, it seems we agree.



rruff said:


> I've made an FEM of a wheel myself, BTW. And here is one that is posted on the internet... please look it over. Ian's Bicycle Wheel Analysis.


Nice! I hadn't seen that one before. What was the FEM code you used? Homegrown?


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## rruff (Feb 28, 2006)

Pirx said:


> Nice! I hadn't seen that one before. What was the FEM code you used? Homegrown?


That isn't me. I made several models on some free software about 5 years ago, and did not publish the results. I just looked for it and can't find it... hope it didn't get lost when I switched computers...

Found it... LISA was the name of the software.


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## ergott (Feb 26, 2006)

JCavilia said:


> Sit on your bike, not moving, and have somebody take a big wire cutter and cut 4 or 5 spokes at the bottom of each wheel. I'll bet you ten thousand dollars (just to pick a figure) that the wheels will still hold you up. Then tell me those spokes were "supporting your weight."


The problem with this example is you are not factoring in the stiffness of the rim. I could give you a rim that will hold your weight with 4 spokes holding the hub up. Not good science.


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## castofone (Dec 24, 2010)

Mr Meltingfeather has given us some insight into a special way of thinking about prestressed structures. It is convenient from the point of view of this modelling to view the few spokes at the bottom of a wheel as "supporting" the wheel even thought they do less work than all the other spokes.

Economists have similar models that show how the unemployed "support" the economy.

Unless you are working with that type of modelling it makes zero sense to think of the spokes that do the least are "supporting" the wheel. Its just not relevant to everyday common sense understanding and in fact just serves to muddy the water.


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## rruff (Feb 28, 2006)

castofone said:


> It is convenient from the point of view of this modelling to view the few spokes at the bottom of a wheel as "supporting" the wheel even thought they do less work than all the other spokes.


They are doing *more* work than the other spokes. They are the ones that are experiencing by far the biggest change in tension... and a subsequent change in length. This is the actual definition of work via physics, and it is applicable to this case.


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## flatsix911 (Jun 28, 2009)

rruff said:


> It is only a false connotation if you do not understand how a wheel supports the load. Did I say something that contradicted that? No. What I stated was 100% true... please read it again. The increase in tension is *insignificant* compared to the relatively huge decrease in tension for the lower spokes... and if you add them up you get a large net decrease.
> 
> I've made an FEM of a wheel myself, BTW.
> *And here is one that is posted on the internet... please look it over. Ian's Bicycle Wheel Analysis*
> I'm excited to see how you determined that...


This is an excellent Finite element (FE) analysis and should put the question to rest for good 
I am also a PE and the condensed summary is partially quoted below non tech types ...:thumbsup: 




> *Analysis of a Spoked Wheel*
> Ian's Bicycle Wheel Analysis
> 
> 
> ...


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## tednugent (Apr 26, 2010)

i'm wondering why are people getting hung up about the lower couple of spokes vs. the top, etc...

like people said, they all work together as a system.

all the arguments are based on a static system (ie at rest), which is one piece of the puzzle. Still interesting to read.

since it is a dynamic system, there is more to look like....throw in acceleration from the chain drive into the mix, throw in effects of braking into the mix, then things get more interesting, because of more spokes really come into play.


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## orange_julius (Jan 24, 2003)

tednugent said:


> i'm wondering why are people getting hung up about the lower couple of spokes vs. the top, etc...
> 
> like people said, they all work together as a system.
> 
> ...


At the risk of extrapolating my limited engineering knowledge too far, compressional waves propagate at speeds of kilometers per second in solid material. So do traverse waves. So you are talking dynamical response times of microseconds or much less, hardly material in the case of bicycles and bicycle parts/wheels.


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## JCavilia (Sep 12, 2005)

castofone said:


> Mr Meltingfeather has given us some insight into a special way of thinking about prestressed structures. It is convenient from the point of view of this modelling to view the few spokes at the bottom of a wheel as "supporting" the wheel *even though they do less work than all the other spokes.*Economists have similar models that show how the unemployed "support" the economy.
> 
> Unless you are working with that type of modelling it makes zero sense to think of the spokes that do the least are "supporting" the wheel. Its just not relevant to everyday common sense understanding and in fact just serves to muddy the water.


Well said, but I would change the emphasized clause to read, "even though they are exerting their force in the opposite direction from the other spokes, which are the ones "supporting" the load in the ordinary meaning of the term.


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## tednugent (Apr 26, 2010)

orange_julius said:


> At the risk of extrapolating my limited engineering knowledge too far, compressional waves propagate at speeds of kilometers per second in solid material. So do traverse waves. So you are talking dynamical response times of microseconds or much less, hardly material in the case of bicycles and bicycle parts/wheels.


Not really speaking in terms of the science in vibrations.. it's another aspect to consider when a wheel rolls down a road. 

Putting it into layman's terms because not everyone here has a science background....

In the dynamic environment, you also look at the loading of the wheel from the aspect of how the chain-cassette-hub-wheel interaction of the forces, the affect of the loading from using the brakes, as well cornering forces when you're taking a corner... it's more complex.

the 2D model is a good starting point when you "fix" a lot of the variables in the question you're trying to answer. Of course things change a bit when you start reducing the spoke count, different lacing pattern, etc.

The 2D model is a good starting point, but not the end-all of all questions, because it only focused on answering a specific question.

That's always a problem when someone uses FEA.... other people are too quick to jump into conclusions.

If it was really this simple, wheel manufacturers wouldn't spend much time on the R&D and there would be no progress/advancements in the wheel realm of the bicycle.


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## orange_julius (Jan 24, 2003)

tednugent said:


> Not really speaking in terms of the science in vibrations.. it's another aspect to consider when a wheel rolls down a road.
> 
> Putting it into layman's terms because not everyone here has a science background....
> 
> ...


Tednugent, I don't disagree with you regarding need for analysis that is more comprehensive. What I don't agree is your saying that a dynamical model is necessary. But I think that you and I have different definitions of what "dynamical model" means. To me it means needing to do time-domain finite-difference type of modeling. I think you take it to mean, a (static) model that considers the state of the (more comprehensive) system. 

Anyways, this is becoming sidetracked ... :-D.


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## tednugent (Apr 26, 2010)

orange_julius said:


> Tednugent, I don't disagree with you regarding need for analysis that is more comprehensive. What I don't agree is your saying that a dynamical model is necessary. But I think that you and I have different definitions of what "dynamical model" means. To me it means needing to do time-domain finite-difference type of modeling. I think you take it to mean, a (static) model that considers the state of the (more comprehensive) system.
> 
> Anyways, this is becoming sidetracked ... :-D.


As I mentioned earlier, a single FEA model with very specific assumptions made, isn't quite the end-all of all information.

That is the danger of a sharing a FEA model--- as I mentioned, some people are quick to jump to conclusions and always refer that that model as their proof.

There is more information when what a single FEA provides. There more things to analyze.


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## rruff (Feb 28, 2006)

JCavilia said:


> Well said, but I would change the emphasized clause to read, "even though they are exerting their force in the opposite direction from the other spokes, which are the ones "supporting" the load in the ordinary meaning of the term.


Which spokes are "supporting" the load when their is no load? This isn't a trick question. All the spokes are in tension when there is no load whatsoever. Does that mean they are supporting some invisible load? What sense does that make?


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## rruff (Feb 28, 2006)

tednugent said:


> There is more information when what a single FEA provides. There more things to analyze.


What exactly... and what do you expect to change?


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## cfoster (Dec 20, 2007)

I'd like to take a second and offer a personal note to the RBR community.

Castofone began this thread a few days ago, I replied shortly thereafter. My reply was short, and perhaps a bit snide in its undertone. I apologize for my reaction, and could have been more professional. Afterall, we're all here to share a communal cycling interest/spirit.

It's not justification, but I think I was a bit reactive becuase we've all been down this road before regarding this topic, here at RBR and MTBR. As individuals and as a community, I think we've grown in understanding. All the time taken to communicate simple and complex data associated with a bicycle wheel's function benefits everyone. On top of that, for those whom are interested there are plenty of reading resources available regarding this topic.

This topic has been discussed in exhaustive detail at MTBR, about this time last year. The MTBR posting activity got a little heated, and unfortunately resulted in unnecessary implied or stated derogatory messages.

For anyone who is really interested in developing an understanding of this topic, there's a quick 317 post thread at MTBR here:

MTBR Resource

It's a lot of reading, but it's really worth your time to follow it from start to finish. 

At bicyclewheelwarehouse, we build bicycle wheels. We're interested enough in our work to dedicate our lives to it. JB, Sheldon Brown, RRUFF, MeltingFeather is all required reading here. Admittedly, I do not possess an engineering degree. But I do not lack the ability to develop an understanding of topic material, regardless of complexity. During the course of the MTBR thread, I delved deep into as much associative topic material as I could. Almost instantly the topic veers from bicycle wheels, and begins to reference many of the aforementioned terms in this RBR thread. And through it all, the realization that the math has already been done was consistent. Subsequently, (and at present), attempts to reanalyze the bicycle wheel I believe now bear the burden of proof. As the burden has already been addressed in previous analysis.

I've mentioned it before, I'm open to new ideas, and principles based on fact. For Castofone to say or connote that "I'm an expert" and that my fact is now more correct than another's, due to a reference of select but contradictory "science", at the expense of excluding volumes of referenceble studies, published authors, and contributing scientists that take pride in referencing their factual knowledge for the purview of their peers, is also unprofessional.

It is my hope that the RBR community jumps over to the MTBR post to read through all the info exchange, and I hope that I can grow personally and professionaly here at RBR, to be more inclusive of new ideas and participation.


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## tednugent (Apr 26, 2010)

rruff said:


> What exactly... and what do you expect to change?


If you noticed how the model was constrained and the load was specifically applied at the 3 points.

Since the weight (of a unicyclist or bicyclist) is applied through the axle, thus through the hubs, why not apply an arbitrary load there also in addition to the load applied to say... the air pressure/ground. -- that's another way to look at it.

next one is applying that affects of the von-mises stress on the rim itself.

How about the load when you're applying a rotating force? Ie, you're pedaling?

How about the affects of the rim brake?

How about cornering?

How about the cross section profile of the rim? How does its geometry affect it?

How about a reduction in spoke count?

There are lots of questions engineers think about and try to figure out.

Someone at Mavic probably had an idea of Isopulse, and needed to do various models to prove it out, probably before testing....


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## ergott (Feb 26, 2006)

@ Foster.

What is the context of what the OP grabbed from your site? Link?


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## cfoster (Dec 20, 2007)

ergott said:


> @ Foster.
> 
> What is the context of what the OP grabbed from your site? Link?


Here's the link from our site.

BWW Wheel Buying Guide

When I typed this "guide" out, my intention was to apply my understanding of wheel function as it applies to wheel components that we stock and sell. I realize now that we should perhaps ammend our website to convey that point specifically. Shimano low flange hubs, "conventionally" (read non-off-set spoke bed, OSB) drilled rims, etc. If someone were to apply some sort of mathematical absolute, they could quickly negate the value of our guide, but the new found value would still not apply to what we do.

That's our world, that's my viewpoint. Having the benefit of this thread, I recognize that maybe there does exist a rear multi-speed/cassette wheel product that was designed/engineered to a degree that completely absolutely/100% mitigates conditions present in the wheels that we specialize in. If that's the case, and if we stock/sell that wheel, I'd have to update the verbage in our guide to exclude those specific wheels from our general statement about "only the rear wheel drive side", etc. 

I haven't come across such a wheel yet though, although some of the stuff we've played with does well to close up the disparity. Perhaps some specific combination of an OSB extremely stiff rim + a high-low rear hub flange design + specific lace patterns reaches that end?


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## castofone (Dec 24, 2010)

rruff said:


> They are doing *more* work than the other spokes. They are the ones that are experiencing by far the biggest change in tension... and a subsequent change in length. This is the actual definition of work via physics, and it is applicable to this case.


♫Mud, mud, glorious mud ♪

They experience a change in tension by _relaxing_. You try doing that at work and see if the boss agrees that you are working harder. 

And just to be accurate from the point of view of the proper definition of "work" (F*d), they are doing _negative_ work which from any sane interpretation is the same as _less_ work. 

It seems that the one and only context in which you can fruitfully conceive of the reverse being true is in the Alice in Wonderland context of pretension modelling. And who among wheel builders and bike riders is familiar with or cares about that? 

Look, if you go around saying the spokes at the bottom of a wheel are the ones "supporting" the wheel or that they are "working" harder the rest of world will immediately assume you mean those spokes are working in compression to support the wheel. And if you say it with lots of fancy words some of us will think it must be true, but it's not.


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## cxwrench (Nov 9, 2004)

wow...i get it now. i'm only a little over 100 posts into the MTBR thread and it's been enlightening to say the least. it is actually a pretty simple concept once you open your mind up just a bit so that you can understand what is happening. and holy sh*t is that guy Turveyd a complete trolling idiot. back to the thread, so i can learn some more. thanks guys!


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## castofone (Dec 24, 2010)

Well actually Turvyd does suffer from a lack of self control and is given to rudeness but he's not totally wrong. He is fundamentally correct when he says the wheel is supported from the spokes that are not below the hub.

If you go around saying the spokes below the hub support the wheel most of the world will assume you are saying the bottom spokes support the wheel in compression. In fact it is only in the abstruse world of finite element analysis that this is conceptually true but even then its not true in fact. The spokes never lose all tension unless the wheel is over loaded. To say that the spokes below the hub support the wheel is a convenient fiction. Even in the same modelling it is equally valid (but less convenient) to say the wheel is supported by all the spokes except the bottom ones. For the sake of convenience for the FEM, and only for that, it makes sense to say the bottom spokes support the wheel. For most of the world and in the common sense understanding of mechanics it is incorrect and misleading. 

So if you are going to say the wheel is supported by the bottom few spokes it behoves you to qualify that statement with an appropriate addendum for example "from the point of view of conventional finite element modelling" or words to that effect and then add that although they "support" the wheel they never go into compression. Otherwise your words will be taken as nonsense. Better I think not to say it at all and speak to the world in language and concepts that we understand.


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## tednugent (Apr 26, 2010)

castofone said:


> Well actually Turvyd does suffer from a lack of self control and is given to rudeness but he's only wrong in some trivial ways. He is fundamentally correct when he says the wheel is supported from the spokes that are not below the hub.
> 
> If you go around saying the spokes below the hub support the wheel most of the world will assume you are saying the bottom spokes support the wheel in compression. In fact it is only in the abstruse world of finite element analysis that this is conceptually true but even then its not true in fact. The spokes never lose all tension unless the wheel is over loaded. To say that the spokes below the hub support the wheel is a convenient fiction. Even in the same modelling it is equally valid (but less convenient) to say the wheel is supported by all the spokes except the bottom ones. For the sake of convenience for the FEM, and only for that, it makes sense to say the bottom spokes support the wheel. For most of the world and in the common sense understanding of mechanics it is incorrect and misleading.
> 
> So if you are going to say the wheel is supported by the bottom few spokes it behoves you to qualify that statement with an appropriate addendum for example "from the point of view of conventional finite element modelling" or words to that effect and then add that although they "support" the wheel they never go into compression. Otherwise your words will be taken as nonsense. Better I think not to say it at all and speak to the world in language and concepts that we understand.


A model is only as good as its estimations when the model was set up. You can't really discredit all Finite Element models. If the model doesn't match reality... something is definitely wrong with the model on how it made, how it's constained, how the force(s) are applied, etc.

So, really, what you have to say is based on "Ian's Bicycle Wheel Analysis Model"....

But, as I mentioned... some people are too quick to jump into conclusions and came it's the word of God.


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## Winter Rider (Dec 13, 2011)

Skimming thru this thread.. mostly very reasonable replies sans the baggage I often read elsewhere.

Take your tension meter.. have someone sit on the bike.. and measure the spoke tensions on the bottom 3 spokes. Then do it with no one on the bike... what does that tell you? 

Then do same with the top 3 spokes....... same routine.. what does that tell you?

While the Park tension meter is best used horizontal.. it should give acceptable readings in those mounted postions. 

Be interesting to have someone do this<<<<.


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## ziscwg (Apr 19, 2010)

JCavilia said:


> Sit on your bike, not moving, and have somebody take a big wire cutter and cut 4 or 5 spokes at the bottom of each wheel. I'll bet you ten thousand dollars (just to pick a figure) that the wheels will still hold you up. Then tell me those spokes were "supporting your weight."


I'll take that bet, but I get to use a tri spoke wheel!!!


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## rruff (Feb 28, 2006)

castofone said:


> It seems that the one and only context in which you can fruitfully conceive of the reverse being true is in the Alice in Wonderland context of pretension modelling. And who among wheel builders and bike riders is familiar with or cares about that?


So reality is Alice in Wonderland to you?

Riddle this. You have a bicycle wheel with no load... then you add a load and the sum of spoke tensions has declined. How is this possible? Does that blow your mind? How can the effect of adding a load make the sum of tension less?

If your are having trouble with this, I'd hate to see what you do with quantum physics...


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## rruff (Feb 28, 2006)

castofone said:


> For the sake of convenience for the FEM, and only for that, it makes sense to say the bottom spokes support the wheel. For most of the world and in the common sense understanding of mechanics it is incorrect and misleading.


It amazes me that you continue to insist that we all cater to your lack of understanding. Were you an Inquisitor in the dark ages in some previous life?


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## Pirx (Aug 9, 2009)

castofone said:


> And just to be accurate from the point of view of the proper definition of "work" (F*d), they are doing _negative_ work which from any sane interpretation is the same as _less_ work.


Nonsense. It all depends on your system perspective. The work done _on_ the system is positive, so the energy of the system (wheel plus spokes) increases, and is stored as elastic energy. What rruff said was entirely consistent with this.



castofone said:


> Look, if you go around saying the spokes at the bottom of a wheel are the ones "supporting" the wheel or that they are "working" harder the rest of world will immediately assume you mean those spokes are working in compression to support the wheel. And if you say it with lots of fancy words some of us will think it must be true, but it's not.


Nobody is saying they work in literal compression. What the rest of the illiterate world things is not very important.



castofone said:


> In fact it is only in the abstruse world of finite element analysis that this is conceptually true but even then its not true in fact.


There is a rigorous sense in which this is true. 



rruff said:


> So reality is Alice in Wonderland to you?


You know, the one thing I would really like to know is this: How much of the significantly higher deformation of the bottom spokes is really caused by the particular way the force is applied to the wheel, which corresponds to having the naked wheel on a rigid surface. I have a very strong feeling that the picture will change substantially if you include an (air) tire in the simulation. I wonder if anybody has done this. I have found some simulations like that for car and truck wheels, but those rims are very different. But in these cases you see a much more uniform load distribution, and I expect to find the same for the bicycle wheel.


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## rruff (Feb 28, 2006)

Pirx said:


> You know, the one thing I would really like to know is this: How much of the significantly higher deformation of the bottom spokes is really caused by the particular way the force is applied to the wheel, which corresponds to having the naked wheel on a rigid surface.


It isn't a "naked wheel on a rigid surface" but some assumptions must be made concerning how the load is distributed from the tire to the rim. 

Here is a study where they actually instrumented a wheel and measured it while riding. Looks about the same as the FEMs.

http://www.duke.edu/~hpgavin/papers/HPGavin-Wheel-Paper.pdf


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## Pirx (Aug 9, 2009)

Ahah, interesting. Darn, I even had that paper on my computer. So, here's what I did: I scanned in the data for the 2X wheel, and put a spline through it, the result is attached, see below. This should be compared to Fig. 11 in the paper by Gavin. It's a rough approximation, and obviously I did not enforce periodicity (a Fourier approximation would have been better than a spline for this, but I had the spline handy, so what the heck...), but that's good enough for this. I then looked at a couple of integrals over a full revolution to get a sense of the relative contribution of tension versus de-tension (aka "compression"... ). As I suspected, with the actual wheel, the load is indeed more evenly distributed.

First, I looked at the average change in tension that a spoke undergoes during one revolution. It turns out that on average, there is a positive strain of about 10ms (ms=microstrain). The average during compression is -65ms, the average during elongation is 36ms. So, for the actual wheel, you do get an _increase_ in tension, on average.

Next, I looked at the contribution of various angles to the actual force, by multiplying the strain data with the cosine of the angle. The result is that about 76.5% of the force comes from the de-tensioned spokes (the ones within an about 55-degree wedge at the bottom), and 23.5% comes from the rest. So, yes, most of the force to carry the load does come from unloading the spokes at the bottom, but the 23.5%-contribution of the top spokes is certainly not negligible.

View attachment 250539


P.S.: Feel free to check my numbers, I threw this together quickly, so I may have made a mistake somewhere.


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## Pirx (Aug 9, 2009)

I forgot to attach this one: This is what the contribution of the spokes to the vertical force looks like, as a function of spoke angle. It's just the cosine of the angle times the strain, so this is in arbitrary units. You would have to multiply with a stiffness to get the actual force derivative.

View attachment 250544


Somewhat interestingly, there are two ranges of angles where the spokes are actually pulling the hub down, rather than holding it up.


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## castofone (Dec 24, 2010)

rruff said:


> It amazes me that you continue to insist that we all cater to your lack of understanding. Were you an Inquisitor in the dark ages in some previous life?


That's just silly.

Do you believe that the rest of the world sees the problem through the prism of finite element analysis? Or do you not see that it can be expressed in terms common to all? Do you really think it is appropriate to use an expression that is only valid in the particular world of FEA but contrary to common understanding?


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## tednugent (Apr 26, 2010)

castofone said:


> That's just silly.
> 
> Do you believe that the rest of the world sees the problem through the prism of finite element analysis? Or do you not see that it can be expressed in terms common to all? Do you really think it is appropriate to use an expression that is only valid in the particular world of FEA but contrary to common understanding?


.....Why do you keep bad mouth FEA?

The question what do the each of the spokes do under load of the rider IS FEA. In the simplist form, each spoke is a element.

In it's layman's terms, what people are saying is correct about the bottom few spokes. If you want to argue, then they'll get into the weeds of things and things get more technical.

If you want to really understand.... learn the jibberish engineers and scientist speak.

here is an example of compression leading into plastic deformation of a spoke


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## Pirx (Aug 9, 2009)

tednugent said:


> here is an example of compression leading into plastic deformation of a spoke


I am sorry, but I don't buy that one, at least not from what I can see in the picture. For the spoke to fail in this way via compression buckling, the rim would have to be severely damaged as well, yet this one looks pristine. In The sharp kink in the spoke is suspicious as well. Something else has been going on here.


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## Mike T. (Feb 3, 2004)

Pirx said:


> I am sorry, but I don't buy that one, at least not from what I can see in the picture. For the spoke to fail in this way via compression buckling, the rim would have to be severely damaged as well, yet this one looks pristine. In The sharp kink in the spoke is suspicious as well. Something else has been going on here.


It's a classic case of arboreal trauma.


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## kbwh (May 28, 2010)

I had to look that up, Mike T. And then I had a good chuckle.

Interesting thread, by the way. Thanks all.


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## Mike T. (Feb 3, 2004)

kbwh said:


> I had to look that up, Mike T. And then I had a good chuckle.


On reflection, the term "arboreal intervention" might have been better.


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## kbwh (May 28, 2010)

Must have been traumatic for the poor branch, though.

@Pirx: Just to be sure: Zero degrees in your diagram is up? Reading the diagram upside down wouldn't be a first.


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## tednugent (Apr 26, 2010)

Pirx said:


> I am sorry, but I don't buy that one, at least not from what I can see in the picture. For the spoke to fail in this way via compression buckling, the rim would have to be severely damaged as well, yet this one looks pristine. In The sharp kink in the spoke is suspicious as well. Something else has been going on here.



yes... it took a really good whack trying to attempt a bunnyhop over a large log while mountain biking. The attempt failed....rim is fine.

If I had attempted and failed with a rim that is say.... 20 spoked, you would definitely see damage to the rim.


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## Pirx (Aug 9, 2009)

kbwh said:


> Must have been traumatic for the poor branch, though.
> 
> @Pirx: Just to be sure: Zero degrees in your diagram is up? Reading the diagram upside down wouldn't be a first.


Yes, zero is up, 180 degrees is at the bottom.


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## Pirx (Aug 9, 2009)

I thought that it would also be instructive to compare the above plots with the case of a wheel laced with an ideally stiff rim. Below is a plot that shows the spoke strain as a function of angle for a wheel that has such a rim (this means there will be no deformation whatsoever of the rim). The blue curve is the same as the one in Gavin's paper, for a real (finite-stiffness) rim, the red curve is for an ideally stiff rim, under the exact same load, laced to the exact same spokes. For the experts, the red curve is just a cosine, which gives a decent approximation for the stiff-rim case. 

This shows the very significant effect that the deformation of the rim has. So, if you have one of those very deep-section carbon rims, then the distribution of the spoke strains will be much more even. In particular, both top and bottom spokes support the load to exactly the same degree, as has been said earlier. Also, again as expected, for the stiff rim, the spokes in the +/- 90-degree positions are unaffected. For the flexible rim, those spokes are stressed to withstand the flattening (and thus widening at the +/- 90-degree positions) of the rim.

View attachment 250611


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## ohdee (Nov 9, 2007)

I haven't read every post here but I do subscribe to everything meltingfeather (and a few others) have provided.

I consider the bottom spokes to do most the work (in the case of static gravity loads). From a fatigue standpoint, the greater loss of tension over time means they will fail sooner. That's why we see NDS spokes fail first, for the most part. They are already lower in tension, lose more tension due to vertical loads, and lose even more tension from pedaling torque (if they are the leading spokes). High changes in tension over time cause spoke failure.

Forget the the fact that the lower spokes actually lose tension, it's about the overall effect on the life of the spoke.


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## Pirx (Aug 9, 2009)

ohdee said:


> I consider the bottom spokes to do most the work (in the case of static gravity loads). From a fatigue standpoint, the greater loss of tension over time means they will fail sooner.


Uhmm, are you saying that the bottom spokes will fail sooner? 
Sooner than the top spokes??? 



ohdee said:


> That's why we see NDS spokes fail first, for the most part.


NDS spokes can fatigue first because the relative load amplitude is higher. But there's different modes of failure possible (e.g., at the nipple versus the bend, if any), so it depends.



ohdee said:


> They [NDS spokes] are already lower in tension, lose more tension due to vertical loads, and lose even more tension from pedaling torque (if they are the leading spokes).


Again, they lose more tension than what? The effect of pedaling loads on DS versus NDS spokes is not necessarily easy to predict, and obviously depends on the spoking pattern.


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## Kristatos (Jan 10, 2008)

This whole thread reminds me of a brewing forum I used to read and post in back when I did a lot of brewing. Someone would propagate some lame myth of brewing science and when all the biochemists piled on everyone else would get ticked at them for making the discussion too technical because it was easier just to continue going on believing in their myths than try to understand the science.


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## rruff (Feb 28, 2006)

castofone said:


> Or do you not see that it can be expressed in terms common to all? Do you really think it is appropriate to use an expression that is only valid in the particular world of FEA but contrary to common understanding?


It isn't the particular world of FEA, it is the particular world of pre-tensioned structures. It is way before computers. 

If you understood it, it would be "common" to your understanding. Apparently it isn't yet. A few of us who *do* understand it, have tried to explain it in the simplest possible terms. Instead of trying to understand or conceding that you don't get it, you keep claiming we are wrong or deluded.


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## sometimerider (Sep 21, 2007)

ohdee said:


> I consider the bottom spokes to do most the work (in the case of static gravity loads). From a fatigue standpoint, the greater loss of tension over time means they will fail sooner.


Oh, oh. I better go replace my bottom spokes.



(yes, I'm just kidding)


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## Mike T. (Feb 3, 2004)

rruff said:


> Instead of trying to understand or conceding that you don't get it, you keep claiming we are wrong or deluded.


But this is what always happens when this same subject comes up again. I remember it happening about 1/2 a dozen times over two forums (RBR & MTBR).


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## ohdee (Nov 9, 2007)

Pirx said:


> Uhmm, are you saying that the bottom spokes will fail sooner?
> Sooner than the top spokes???


Obviously the wheel spins. Lets say you kept it stationary and went through millions of vertical load cycles at the axel. The bottom spokes would fail first, therefore, I think they are "doing the work".


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## ohdee (Nov 9, 2007)

Mike T. said:


> But this is what always happens when this same subject comes up again. I remember it happening about 1/2 a dozen times over two forums (RBR & MTBR).


I don't know how many times I swore off posting in threads like these. :mad2:


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## bholwell (Jan 22, 2008)

Pirx said:


> I thought that it would also be instructive to compare the above plots with the case of a wheel laced with an ideally stiff rim.


Finally, someone posted something meaningful! +Rep points to you, sir.

I blame Jobst Brandt for all this trivial bickering.


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## bholwell (Jan 22, 2008)

Pirx said:


> So, yes, most of the force to carry the load does come from unloading the spokes at the bottom, but the 23.5%-contribution of the top spokes is certainly not negligible.


Thank you very much for sharing this info. I wish I could give you more rep.

/THREAD


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## MShaw (Jun 7, 2003)

Oh goody! A religious discussion! Next up: wheel stiffness. Then: what chain lube do I use?

It took till page 4 for someone to point out that some of the forces acting on the spokes were from the rim deforming at the bottom. 

I still don't get all the math (and probably never will!) so I'll stick to my happy little world view of 'it goes round and round and I don't particularly care why.' 

M


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## rruff (Feb 28, 2006)

Pirx said:


> This shows the very significant effect that the deformation of the rim has. So, if you have one of those very deep-section carbon rims, then the distribution of the spoke strains will be much more even.


You haven't closed the loop... ie how stiff is a "stiff" rim in reality? The stiffness never approaches your infinitely (not "ideally") stiff case.


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## Pirx (Aug 9, 2009)

rruff said:


> You haven't closed the loop... ie how stiff is a "stiff" rim in reality? The stiffness never approaches your infinitely (not "ideally") stiff case.


Oh yes, you are quite right. My example does not at all address the question of how stiff real rims really are. On the other hand, given that the rim inertial moment is proportional to the third power of the depth of the rim, if you go from a standard box rim to an aero rim of the same material, and if we're assuming, for the sake of argument, that the aero rim has, say, five times the depth of the box rim, then the deformation of the former will go down by a factor of more than 100 compared to the latter. Lots of assumptions and approximations, I know, but the order of magnitude should be about right.


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## rruff (Feb 28, 2006)

Pirx said:


> the deformation of the former will go down by a factor of more than 100 compared to the latter.


Nope... even if the shape is 100 times stiffer in vertical bending, this has much less effect than you'd think. A CX-Ray at 100kg tension is stretched ~1mm. In other words, if the bottom of the rim flexes upward 1mm, the spoke provides 100kg of lift. So how radially stiff is the rim *relative* to this? That is the important question. 

The radial stiffness of a shallow box rim is close to the "zero stiffness" case... but even a 100 times stiffer rim will be much closer to "zero" than "infinity". 

When get the time I'll dust off the FEM I made several years back. I used an XR300 rim, but this was not stiff enough to make a substantive difference compared to Ian or Jobst or Gavin's model.


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## Pirx (Aug 9, 2009)

rruff said:


> So how radially stiff is the rim *relative* to this? That is the important question.


Hmm, yes, you are right.



rruff said:


> The radial stiffness of a shallow box rim is close to the "zero stiffness" case... but even a 100 times stiffer rim will be much closer to "zero" than "infinity".


Good point, at least potentially. I have no good intuition about what the real numbers are, but you could be right.



rruff said:


> When get the time I'll dust off the FEM I made several years back.


That would be interesting. I have a little wheel FEM model here, too, but I have no idea when I'll have the time to look at that, let alone if I get to it before you. It's been a while, so it will take me a while to just remember what I had done at the time...


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## rruff (Feb 28, 2006)

Just for fun I put a tensiometer on the bottom spoke of a XR300 front wheel (18 spokes, CX-Rays), and I supported all of my 78kg on the handlebars, about even with the axle. The bottom spoke lost ~30kg tension, the two next to it ~15kg, and the rest didn't change enough to notice.


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## jbtrek1 (Dec 8, 2006)

I have been searching this and the MTBR forum for an answer to this question. Here is my question: if a new rear wheel build (powertap hub, HED 28h Belguim rims) using 2x-2x and DT rev spokes had a significant lateral deflection to the point of brake rub (rim brakes) on the ND side, what would you do? (I have never built a wheel with this problem in the past) The deflection occurs over certain bumps in the road, and while out of the saddle on big climbs. To add to the complexity, I am using a powertap hub that uses a "torque tube" to supply the torque to the ND side of the hub. I am leaning to use comps on both sides and go with a 2x-2x setup which is what my old wheel used. This is the build that Saris uses on their "factory wheels". I feel that Saris' solution is a bit of overkill and that only one side needs the thicker spokes, since the rim only deflects in one direction. Question is which side gets the Comp treatment? The drive side due to the high tension, or the ND side due to the low tension and drive torque supplied from this particular hub? It seems the larger bracing angle of the ND side would give a larger K value (spring constant) in the lateral direction than the Drive side, therefore one would want to increase the K value of the Drive side spokes (using thicker spokes) to make a more "dynamically balanced" wheel. I am a MechE, but do not specialize in tension structures. I weigh 150lbs and am an avid racer. This wheel is used for racing and training. 

Thanks!


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## rruff (Feb 28, 2006)

You should have started a new thread... but...

If you are using a S cassette, then the DS offset is way less than it could be. I lace the PT hubs 1x heads in on the DS to get some of that back. But I don't think you should be having this trouble with 2x both sides if it was well built. It is a stiff rim and there are plenty of spokes for your size. BTW... the stiffness is the same in both directions, unless spokes go slack. Can you measure the tension? Maybe it was built with too little?

First check something simple... grab the wheel with your hand and rock it back and forth. Does it feel loose? Clamp the rear QR *hard*, and see if that helps. PT hubs have a goofy axle arrangement... the NDS cap must be pressed very hard against the NDS bearing to provide any stiffness at all.


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## jbtrek1 (Dec 8, 2006)

Yeah, I wanted to start a new thread, but it wouldn't let me (don't use the forums too often and have never posted)...sorry about this. I also meant to post as a general reply, but it nested me under some other replies. Anyway, I know the PT hub does use a goofy axle system. My old PT hub was the 12mm axle, and it was threaded. It had 32h and 2x-2x on Comps with no problems. My new hub is 28h, which I justified by going with the Belgium rim over my old Open Pro. I do crank down on the QRs, and there is no hub play. It is shimano. I origninally built it to 120kg on the Drive side, and bumped it up to 127kg once I noticed the problem. This increase did not help. So, would the Comps go on the left or right, or should I just suck it up and put comps on both sides? I will stick with the 2x-2x for this (re)build.


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## JCavilia (Sep 12, 2005)

*poor reasoning*



ohdee said:


> Obviously the wheel spins. Lets say you kept it stationary and went through millions of vertical load cycles at the axel. The bottom spokes would fail first, therefore, I think they are "doing the work".


I don't think your conclusion follows from your premises, unless "doing the work" is synonymous with "undergoing more and deeper fatigue cycles."


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## rruff (Feb 28, 2006)

I can't believe that you have problematic flex between the hub and rim, if the spoke tension is that high. Was it stress relieved well? How many miles?


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## jbtrek1 (Dec 8, 2006)

rruff, I started a new thread. How do I delete my Reply in this one? Sorry to everyone about the Noob mistake!


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## BWWpat (Dec 17, 2009)

jbtrek1 said:


> rruff, I started a new thread. How do I delete my Reply in this one? Sorry to everyone about the Noob mistake!


What? A mistake!? GET EM!


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## scblack (Dec 20, 2011)

JCavilia said:


> Sit on your bike, not moving, and have somebody take a big wire cutter and cut 4 or 5 spokes at the bottom of each wheel. I'll bet you ten thousand dollars (just to pick a figure) that the wheels will still hold you up. Then tell me those spokes were "supporting your weight."


Another way to show your analysis is correct: 

Get a spoke which is not in a wheel. Grab each end and PULL to try to stretch it. No movement whatsoever.

Then, PUSH the ends of the spoke towards each other. The spoke will EASILY bend.

Now, please tell me, how a spoke that can't take an easy push with hand pressure, could POSSIBLY "support the weight" of a bike and rider?


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## Digger51 (May 12, 2006)

Ouch, now my head hurts. All I want to do is ride.


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## Mike T. (Feb 3, 2004)

scblack said:


> Now, please tell me, how a spoke that can't take an easy push with hand pressure, could POSSIBLY "support the weight" of a bike and rider?


Easy. You do realize we're talking about a *wheel* here eh, not just a handful of separate parts? That's kinda like expecting a Junior Engineer Golden Gate Bridge Erector Set (of parts) to carry 5000 cars/hour.

Load that spoke with lots of tension (as much as a wheel should have) and do the same to all the rest of the spokes in the wheel (otherwise you don't have a wheel; just an erector set of parts). Now you push up on the end of one of those spokes and you'll see that it won't bend until your push has exceeded the tension that this spoke is under. Shortly after that, if you keep upping the pressure, the rim will collapse because at that point, when the rim isn't loaded with spoke tensions pulling from the whole circumference, you just have a rim; not a wheel.


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## jbtrek1 (Dec 8, 2006)

Mike T., you made me think of this example. You could hang a 120kg weight from a single spoke held vertically at the opposing end by a vise. This would simulate tension of a single spoke in a wheel. Now apply upward "road" pressure (force) to the bottom of the spoke (the end with the weight attached). The spoke will support all of the force you apply until you exceed 120kg, at which time the spoke will start to bow.


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## Mike T. (Feb 3, 2004)

jbtrek1 said:


> Mike T., you made me think of this example. You could hang a 120kg weight from a single spoke held vertically at the opposing end by a vise. This would simulate tension of a single spoke in a wheel. Now apply upward "road" pressure (force) to the bottom of the spoke (the end with the weight attached). The spoke will support all of the force you apply until you exceed 120kg, at which time the spoke will start to bow.


You're probably right. I'm sure the engineers here will put us straight if you're not. And I'll bet if that vise was hung from a scale, it could measure the force exerted upwards on that weight - far in excess of the "bending" strength of the thin wire. And if the spoke was replaced with a kevlar thread, it wouldn't bend either even though that force would be passing up through it. Of course, some people around here won't be able to see this.


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## cxwrench (Nov 9, 2004)

scblack said:


> Another way to show your analysis is correct:
> 
> Get a spoke which is not in a wheel. Grab each end and PULL to try to stretch it. No movement whatsoever.
> 
> ...


read the mtbr thread referenced somewhere in here, and read this thread thoroughly. it takes a while (for some, me included) to get your head around the idea, but it makes perfectly good sense once you do. 
what a single spoke does when you're holding it in your hand has absolutely nothing to do w/ how it behaves in a wheel w/ tension.


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## scblack (Dec 20, 2011)

cxwrench said:


> read the mtbr thread referenced somewhere in here, and read this thread thoroughly. it takes a while (for some, me included) to get your head around the idea, but it makes perfectly good sense once you do.
> what a single spoke does when you're holding it in your hand has absolutely nothing to do w/ how it behaves in a wheel w/ tension.


Yes, I will do that, thanks.


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## JCavilia (Sep 12, 2005)

Mike T. said:


> You're probably right. I'm sure the engineers here will put us straight if you're not. And I'll bet if that vise was hung from a scale, it could measure the force exerted upwards on that weight - far in excess of the "bending" strength of the thin wire. And if the spoke was replaced with a kevlar thread, it wouldn't bend either *even though that force would be passing up through it*. Of course, some people around here won't be able to see this.


Wrong-o (IMHO). No force is passing "up" through that spoke. All the force on the spoke is downward. The upward force is merely partly balancing the downward force of the weight, thereby lessening the downward force on the spoke.


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## ohdee (Nov 9, 2007)

JCavilia said:


> Wrong-o (IMHO). No force is passing "up" through that spoke. All the force on the spoke is downward. The upward force is merely partly balancing the downward force of the weight, thereby lessening the downward force on the spoke.


Your honest opinion is wrong.


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## Mike T. (Feb 3, 2004)

JCavilia said:


> Wrong-o (IMHO). No force is passing "up" through that spoke. All the force on the spoke is downward. The upward force is merely partly balancing the downward force of the weight, thereby lessening the downward force on the spoke.


Wrong-o. An absolutely *equal* amount of force is passing up though that spoke as down through it or the spoke would go zinging through the center of the earth followed closely by the bike with the rider on it.

But you even contradicted yourself with this - "The upward force is merely partly balancing the downward force of the weight..........."

Thanks for agreeing with me.


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## kbwh (May 28, 2010)

Ah, Isaak N.


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