Does the hub/axle hang from or stand on the spokes ?

[Johan Bornman]

Newton taught us this. For every action there is an equal and opposite reaction. I.e. if you press at the top of the wheel the bottom of the wheel is pushed back equally as hard by the ground. As the wheel's rim will also want to form a slightly ovalized shape as it is "squashed" it tends to want to pull the horizontal spokes as it tries to do this.

 

 

 

Yes. I you press down on the top of a wheel, it does ovalise. However, only bearings support loads like that. Most wheels support loads from an axle at the centre of the wheel. Newton says you push down on the axle, the road pushes back towards the axle.

[Brian Fantana]

I'm not sure what you mean by "this concept", since you didn't include a quote or reference and my comment may thus be off.

 

However, there is no difference between a wire-spoked wheel and a cable spoked wheel. Both wheels support the load in tension and the spokes/cables never go into compression and in fact, can't go into compression. I don't comprehend what the lecturer tried to show.

By saying "this concept", I meant the title of the thread. What you said in your second paragraph is exactly what the lecturer wanted to show, ie: there is no diffence between a "normal spoked" or cable spoked wheel. I agree that a correctly tensioned wheel will always have tensile stress in all spokes, and there is no compression of spokes when the wheel is loaded(even though the spokes @ 12:00 will experience more tensile stress than those @ 6:00 the spokes @ 6:00 will still experience tensile stress). I just mentioned compression to state that a spoke is designed to experience tensile stress and not compression. I think the lecturer wanted to challenge the dominant logic of students, to get us thinking in a certain direction.

Edited December 17, 2010 by Stephan

[Johan Bornman]

By saying "this concept", I meant the title of the thread. What you said in your second paragraph is exactly what the lecturer wanted to show, ie: there is no diffence between a "normal spoked" or cable spoked wheel. I agree that a correctly tensioned wheel will always have tensile stress in all spokes, and there is no compression of spokes when the wheel is loaded(even though the spokes @ 12:00 will experience more tensile stress than those @ 6:00 the spokes @ 6:00 will still experience tensile stress). I just mentioned compression to state that a spoke is designed to experience tensile stress and not compression. I think the lecturer wanted to challenge the dominant logic of students, to get us thinking in a certain direction.

 

Thanks, I'm on the same page as you now.

[The Drongo]

@ dom estique ated

 

All things being equal !!!

 

Nice Rack - I only have one for a single bike.

 

[Topwine]

Yes. I you press down on the top of a wheel, it does ovalise. However, only bearings support loads like that.

 

No, You don't even need a bearing to support a load like that, the rim can do it on its own. All the hub do, is transfer the load from the fork to the rim VIA the spokes. Capish ?

[Wyatt Earp]

No, You don't even need a bearing to support a load like that, the rim can do it on its own. All the hub do, is transfer the load from the fork to the rim VIA the spokes. Capish ?

Spot on, however a solid axle might not roll so well :lol:

[The_Break]

I think you should try your plucking and write down the notes. They will vary, but I do believe we agree on one thing. All spokes are still under tension. Hook up with a Muso and get us those notes.

 

My theory is still correct either way you look at it.

[Johan Bornman]

I think you should try your plucking and write down the notes. They will vary, but I do believe we agree on one thing. All spokes are still under tension. Hook up with a Muso and get us those notes.

 

My theory is still correct either way you look at it.

 

 

You don't need a muso to detect a change in tone. Try it, you may be surprised.

 

Yes, spoke tension does vary within the wheel. That's 'cause the rim and spokes are not uniform. I measure most rims and they're often ovalised by up to 4mm over their 600 or so diameters. Further, the extrusion is not perfect and, the valve hole plays a role in localised strength as well. Therefore spoke tension in a perfectly true wheel is not even.

 

However, we're only interested in the change of tension. We can't express this in notes since they may or may not be multiples or fractions of 256Hz. We use the change in tone instead. Any ear can pick that up.

 

If I understand you right, in your model, the top spokes will gain tension (go to a higher tone) and the bottom ring a couple of Hz lower. This is very, very easy to prove wrong and you don't need a tuning fork, musician, tensiometer or any measuring device to test.

 

What concerns me is your disclaimer - no matter what we find, your model is still right.

[Topwine]

 

What concerns me is your disclaimer - no matter what we find, your model is still right.

 

Dear Johan

 

What concerns me, or rather amuses me, is the fact that you stubbornly refuses to accept the fact that the top spokes increases in tension and that the hub hangs from the top, and not stand on the bottom spokes. No matter what scientific evidence are provided, you just refuses to believe, and say you "observe" otherwise. I am at the point of declaring your views as utter nonsense, if you cannot provide "any" scientific thesis or evidence for your continuing ignorance of the science behind this all.

 

There comes a point when you have to man up and concede that you have made the wrong conclusions and move on.

[eggsovereasywithteandtoast]

...the world is flat they said ...

[Guest Big H]

Dear Johan

 

What concerns me, or rather amuses me, is the fact that you stubbornly refuses to accept the fact that the top spokes increases in tension and that the hub hangs from the top, and not stand on the bottom spokes. No matter what scientific evidence are provided, you just refuses to believe, and say you "observe" otherwise. I am at the point of declaring your views as utter nonsense, if you cannot provide "any" scientific thesis or evidence for your continuing ignorance of the science behind this all.

 

There comes a point when you have to man up and concede that you have made the wrong conclusions and move on.

 

Verdwyn net en raak weg jou verwaande akademiese klein twak.

[Wyatt Earp]

Verdwyn net en raak weg jou verwaande akademiese klein twak.

But........die akademiese twak has a valid point, where is the evidence, there is a difference between evidence and observation.

As for tapping the spokes and getting a different sound, well seems to me like someone watched the Triplets of Belleville.

Now Bruno's grandma uses a tuning fork which will emit a better pitch (and a more accurate pitch, time and again) than the dull and lifeless human finger or nail which is not capable of resonating at the frequency required.

[Guest Big H]

But........die akademiese twak has a valid point, where is the evidence, there is a difference between evidence and observation.

As for tapping the spokes and getting a different sound, well seems to me like someone watched the Triplets of Belleville.

Now Bruno's grandma uses a tuning fork which will emit a better pitch (and a more accurate pitch, time and again) than the dull and lifeless human finger or nail which is not capable of resonating at the frequency required.

 

If you have built the sewer manholes as you said you will surely know where the difference between pure first principle design of a sewer manhole and the practical construction of the sewer manhole in he field is. The twain seldom meets. I build my own wheels using a spoke tensiomemter but my final check is the "twang". I am totally tone deaf but have learnt my own interpretation of the "twang"

 

"Les Triplettes de Belleville" analogy is just a continuation of your fued and not really an intelligent observation.

Edited December 19, 2010 by Big H

[Guest Big H]

Maybe here is the answer..... and educated one and not one by young kids that graduated form low class South African institutions of learning.....

 

J. Engrg. Mech. Volume 119, Issue 3, pp. 439-455 (March 1993)

 

C. J. Burgoyne 1 and R. Dilmaghanian2

1Univ. Lect., Engrg. Dept., Univ. of Cambridge, Trumpington St., Cambridge CB2 1PZ, United Kingdom

2Formerly, Steel Construction Inst.

 

Issue Date: March 1993

 

Bicycle wheels achieve their structural efficiency by making use of prestressing in three ways. Tests show that the bottom spokes carry virtually all the load by compressive forces, which reduce the tensile prestress set up in the spokes when the wheel was made. The test results are compared with an analysis that considers the spokes as a disk that can carry force in one direction only. This is shown to give good agreement, as does an analysis that considers the rim as a straight beam on an elastic foundation. The behavior of the wheel with an inflated tire is also considered, and it is shown that good comparisons with theory are obtained if the reaction from the road is assumed to be distributed over a specific length of the rim. Prestressing is shown to be important also in the mechanism by which the various forces are transmitted through the tire from the road to the rim.

 

©1993 American Society of Civil Engineers"

[Wyatt Earp]

If you have built the sewer manholes as you said you will surely know where the difference between pure first principle design of a sewer manhole and the practical construction of the sewer manhole in he field is. The twain seldom meets. I build my own wheels using a spoke tensiomemter but my final check is the "twang". I am totally tone deaf but have learnt my own interpretation of the "twang"

 

"Les Triplettes de Belleville" analogy is just a continuation of your fued.

Yes I certainly understand the difference between first principle and the practical in the field, but let's just get one thing clear, the principles still need to be applied.

:lol: As *** praat n' siekte was het hulle jou lankal al in n' lood kis begrawe onder die paaie wat jy glo so bou.

Seems like you need to get your head out the sewer and leave behind the need to try and bully people by trying to make them believe that when you have hands on experience, you may declare yourself qualified.

I think you are where you are because you are not a very subservient type of individual and have probably never held wayleaves in your two russian fingered hands.

As dit by klank en frequencies kom sal ek jou naam liederlik gat maak

[Guest Big H]

Jobst Brandt wrote a whole book on the subject. He did a bunch of finite element analysis, as well as actual laboratory experimentation. Go read it.