Need some help on spokes

[ZeroPlay]

 

Mr Bornman advocates the use of a "musical ear" to tune his wheels' date=' almost like tuning a guitar. What will happen if you cannot hear his melodious "twang"????? 

[/quote']

 

Big H, so does Brad Hunter, who put Velomax wheels on the map. He designs, has built and oversees production of some of the best factory built wheels available - and advocates twang rather than the tensiometer.

 

 

I think the idea is to combine the tension meter and the "twang" methods.

 

Different spokes have a different tone "twang" for the same tension depending on many things (length, thickness, double butted, where the cross each other, etc...), so one would use the tension meter to get a reference "twang" from one spoke that is the correct tension.  You then know what the correct tension sounds like for the particular wheel (or at least one side of the wheel) you're working on and you can compare the other spoke's "twang" to this one.

 

[Sequoia]

Johan is spot-on with regards to his analysis. The problem is that people try using a common sense approach to things which they don't understand. You get it with most sciences. There are many sources on the web coming out in support of Johan's views.  This guy did a finite element analysis of a bicycle wheel.

http://www.astounding.org.uk/ian/wheel/index.html

His conclusion: "From these figures, I conclude that it is perfectly reasonable to say that the hub stands on the lower spokes, and that it does not hang from the upper spokes. It is also wrong to say that the force distributes all around the rim and all the spokes contribute to holding up the hub - over a third of the spokes have an effect that pulls the hub down! "

Sheldon Brown also has a link to a guy's site who tested the lateral stiffness of various wheels. Quite interesting reading, even though his sample size is a bit small.

Lastly - No-one who is even slightly open-minded could possibly believe that just because something is new and made by XYZ-company, it must be the best. Companies are in it for the money. They want to sell. There are various ways of selling, but when selling to cyclists, using big words and shiny materials have worked since the first pedals were screwed to cranks.

Sequoia2007-12-19 02:02:38

[Johan Bornman]

 

Nicely explained. You mentioned students - what do you teach?

 

I teach wheelbuilding and bicycle repair and maintenance. I have a general and advanced wheelbuilding course and several repair and maintenance courses ranging from basic to fixing shock absorbers. All the courses together and you have a bike mechanic's qualification. I used to teach framebuilding too but sadly no-one wants to buy iron frames anymore.

 

 

 

I posted the info on spoke tensions and I made the same observation at the time - the tension range is huge. On that score' date=' have you considered that the tensions may have to do with rim fatigue as well as spoke life. i.e. too high a tension brings on rim failure sooner.

 

[/quote']

 

Indirectly yes. But generally, no. Once the wheel is tensioned, the rim is pulled into a teat around the spoke. As the wheel rotates, that teat pulsates and becomes lower at the bottom of the rotation and then returns to its maximum position for the rest of the rotation. That movement does fatigue the rim. However, it doesn't matter from what starting position the teat moves, its range of movement is determined by the rider's weight. It is movement inside that range that fatigues the aluminium, not the size of the teat. On a well-designed rim this fatigue limit is less that the rim's useful life. I.e. its braking surface is worn out first.

 

However, if the rim is hard anodised, a teat immediately cracks the surface of rim around the spoke. Those cracks then propagate into the aluminium and you have a rim that fails prematurely.

 

The shape of the rim is also a huge factor here. A deep V is more durable than a box section.

 

I said the tension indirectly contributes to rim failure because it is actually that initial set of crazed cracks that fails the rim, not the tension itself. Rims should be capable of taking more tension than the nipples can deliver.

 

This is not the case for most carbon rims and they have their own special problems.

 

 

 

Moving on to your other statement: "V-shaped rims have an inherent strengh that can get away without sockets." The highest stressed point on the rim due to deflection in the load affected zone is the inner (point of the V) and outer (top of braking) surface. While such rims have greater vertical stiffness' date=' I would suggest the peak stress at the inner and outer surface is much the same. Invariably such rims also have lower spoke counts and spoke tension is consequently higher, therefore the stress imposed on each eyelet is higher. I believe, manufacturers choice to leave out sockets on deep section rims has more to do with their inability to fit them into the narrow confines at the bottom of the V than inherent rim strength. My experience, while limited, bears out that these type of rims highly prone to fatigue failure around the eyelet.

 

 [/quote']

 

I think your assertion of maximum stresses in a V rim are correct. Some manufacturers overcome the problem by putting extra material in the groove of the V. Others don't bother and as you observe, they crack quickly. But also take the anodising into account. It is usually the biggest factor.

 

Mavic managed to make a nice socket which they fitted to the CXP33. It only pulls on the inner wall (and totally relieves the outer wall of spoke tension), and takes the anodising cracks out of harm's way. Further, they managed to drill it so that the spokes line up better. Most deep section rimms are drilled straight-through so that the spokes have to bend just where they enter the rim and that puts additional stress on both components.

 

I have seen many wheels which were dangerously undertensioned, yet the rims are still cracked. This is purely an anodising issue.

 

 

[ZeroPlay]

 

JB' date=' I don't understand one aspect of your detailed explanation above.

 

If the tension of the spokes on the lower portion of the wheel decrease as they rotate surely that would imply that the opposite spokes would increase in tension correspondingly?

 

 

[/quote']

 

It is quite hard to visualise, but it doesn't happen the way you describe. Only the bottom spokes reduce in tension, the rest stay the same. It is exactly like a car tyre. Have a look at a parked car. The bottom of the tyre is squashed flat without the top part stretching downwards.

 

If you are familiar with Newton's laws and understand them, it'll help you to think of it as a force that attracts an equal and opposite force. The wheel presses on the road and the road presses back. The "press" is between the hub and the road and the area above the hub remains unaffected.

 

If that fails to switch on the right neurons, visualise the wheel horisontally. You are holding it by a long extended skewer with a handle on each side and pushing it against a wall.

 

 

 

... or just visualise bashing Johan Bornman over the head with your wheel - even if you still don't understand what the hell he's talking about, it'll bring a smile to your face (and others too, I suspect), thereby "reducing the tension".

 

[Johan Bornman]

Big H' date=' so does Brad Hunter, who put Velomax wheels on the map. He designs, has built and oversees production of some of the best factory built wheels available - and advocates twang rather than the tensiometer.

 

[/quote']

 

Let it go. It is summer and there are lots of ugly buzzing flies around. It goes with the territory.

 

In the process of getting a 20 spoke powertap hub for my daughter' date=' planning on mating it to an Easton rim tempest 2 clincher with cx rays. JB, would you do this for me?

[/quote']

 

I could do it for you. We are going to sukkel to get the right lenght of those spokes though. I'll calculate the lenghts quickly and see what is available.

 

[Johan Bornman]

I think the idea is to combine the tension meter and the "twang" methods.

Different spokes have a different tone "twang" for the same tension depending on many things (length' date=' thickness, double butted, where the cross each other, etc...), so one would use the tension meter to get a reference "twang" from one spoke that is the correct tension.  You then know what the correct tension sounds like for the particular wheel (or at least one side of the wheel) you're working on and you can compare the other spoke's "twang" to this one.
[/quote']

 

I think too much emphasis has been placed on the importance of plucking the spokes. I only use it as a final confirmation that a) the spokes are up to tension and b) that none of the spokes in the wheel show some large anomoly.

 

On front wheels all spokes resonate at the same frequency and on back wheels, the left and right hand side produce two different frequencies.

 

As you point out, various spokes will resonate at different frequencies, but for a single wheel the tone should be in tune, so to speak. However, a tone or a reading from a meter is only a final confirmation that nothing odd is going on inside there.

 

 

[Johan Bornman]

Cut cut cut...

 

 This guy did a finite element analysis of a bicycle wheel.

http://www.astounding.org.uk/ian/wheel/index.html

His conclusion: "From these figures' date=' I conclude that it is perfectly reasonable to say that the hub stands on the lower spokes, and that it does not hang from the upper spokes. It is also wrong to say that the force distributes all around the rim and all the spokes contribute to holding up the hub - over a third of the spokes have an effect that pulls the hub down! "

Sheldon Brown also has a link to a guy's site who tested the lateral stiffness of various wheels. Quite interesting reading, even though his sample size is a bit small.

 

Cut cut cut.

 

[/quote']

 

I also have a set of FEA results here done for a 36-spoke wheel. I haul it out when I'm doing a course and I have students (especially engineers) who become argumentative. I use it as a giant club to make them shut up.    (see, I can also do smileys)

 

However, it is quite easy to prove this to yourself. Experiment warning:

 

Find a buddy with longish strong fingernails. You'll also need a bicycle and a table to hold onto.

 

Pluck the top and bottom spokes of the bike and memorise the tone. Now climb onto the bike and sit on it with all your weight. This is where the table comes in handy.

 

Ask buddy to pluck the spokes again. You'll notice that the top one stays the same and the bottom one now has a lower frequency. If you are really sharp with this experiment you'll come back to me and say a perfect result is not what you got.

 

I'll save that aha moment for when it is appropriate.

 

 

 

 

[snaphaan]

Thank you JB for a very informative thread.

 

[Johan Bornman]

Thank you JB for a very informative thread.

 

It's a pleasure Pieter and all the others who've expressed their thanks and support. I appreciate it guys. I hope to meet all of you one day over a 5l box of Tassies so we can finally solve all the riddles surrounding the physics of cycling.

[Conti]

johan, jy gaan seker se ek moenie dom vrae vra nie,

of hoelank is n stuk tou?

as jy n wiel bou? doen jy als self,rim ingesluit?

en hoeveel kos n gem. wiel en met watter wiel op die mark kan dit vergelyk word?

[greatwhite]

Indirectly yes. But generally' date=' no. Once the wheel is tensioned, the rim is pulled into a teat around the spoke. As the wheel rotates, that teat pulsates and becomes lower at the bottom of the rotation and then returns to its maximum position for the rest of the rotation. That movement does fatigue the rim. However, it doesn't matter from what starting position the teat moves, its range of movement is determined by the rider's weight. It is movement inside that range that fatigues the aluminium, not the size of the teat. On a well-designed rim this fatigue limit is less that the rim's useful life. I.e. its braking surface is worn out first.

[/quote']

 

Ignoring the anodising, if you increase the preload (spoke tension), you will decrease the number of cycles required till fatigue failure. I agree with you though, anodising doesn't help at all in this regard.

 

The CXP 33 you mentioned elsewhere, was a well designed and made rim, but mass of material was on its side too - it was heavy.

 

[Ox_Wagon]

Here we go again........ <?:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

 

This guy did a finite element analysis of a bicycle wheel is fundamentally flawed in that it assumes:

1) No buckling of slender beams (Spokes)

2) It is possible to transfer a compression force from the spoke to the rim. NOT!  

http://www.astounding.org.uk/ian/wheel/index.html

So it is only possible for a rim to stand on the bottom spoke IF

1) You glue the nipple to the rim

2) Use REALY strong rim tape

3) Have a really strong inner tube, the Tubeless guys has a problem

 

Check the following tread:

https://www.bikehub.co.za/forum_posts.asp?TID=16361&KW=&PID=251045#251045

 

IanJ, your correct. The top spokes sees the combined weight of the rider plus the tension of the bottom spokes, this elongates the top spokes a bit which in turns shortens the bottom spokes reducing the tension.

Ox_Wagon2007-12-19 03:54:27

[Johan Bornman]

Ignoring the anodising' date=' if you increase the preload (spoke tension), you will decrease the number of cycles required till fatigue failure.

[/quote']  

I am not convinced that is so. The way I see it is that the initial deflection from pre-load is given once only, thereafter it is the number of cycles that fatigue it. Once the rim is fatigued (brittle), the high load will pull the spoke out though. But I stand to be corrected.

The CXP 33 you mentioned elsewhere' date=' was a well designed and made rim, but mass of material was on its side too - it was heavy.

 

[/quote']

Weight is in the eye of the beholder. A component weighs what it must weigh. In other words, the engineer had a job for it in mind and it was designed correspondingly. It is a very, very durable rim that is easy to true and stays true for a long time.

 

 

[Johan Bornman]

Here we go again........ <?:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

 

This guy did a finite element analysis of a bicycle wheel is fundamentally flawed in that it assumes:

1) No buckling of slender beams (Spokes)

2) It is possible to transfer a compression force from the spoke to the rim. NOT!  

http://www.astounding.org.uk/ian/wheel/index.html

So it is only possible for a rim to stand on the bottom spoke IF

1) You glue the nipple to the rim

2) Use REALY strong rim tape

3) Have a really strong inner tube' date=' the Tubeless guys has a problem

 

Check the following tread:

https://www.bikehub.co.za/forum_posts.asp?TID=16361&KW=&PID=251045#251045

 

IanJ, your correct. The top spokes sees the combined weight of the rider plus the tension of the bottom spokes, this elongates the top spokes a bit which in turns shortens the bottom spokes reducing the tension.

[/quote']

 

Like you say, here we go again.

 

Euler's buckling is only possible once the beam is in compression. The spoke never goes into compression, only reduced tension. IT IS ALWAYS IN TENSION.

 

Once once you exceed the thension you have in the bank with compression, then the nipple will lift and the wheel will collapse. It is the same with the spokes moving in the flange holes. Have a look at the scan from the book I posted earlier on.

 

But, I'm repeating myself. I have asked you before to perform the plucking experiment but you doggedly refuse. Perhaps it is time we organise a Hubber workshop and do a Wheel Understanding seminar.

 

 

[BikeMax]

 

It is like cooking fondant....... you can use the droplet in the water technique and you might get proper fondant' date=' but if you use a proper thermometer you WILL get proper results, even the most inexperienced of cooks.

 

[/quote']

 

Now that would be a bit like using a HR monitor to measure cycling intensity, when you could instead use a device, not unlike a thermometer, that measures output directly wouldn't it ?

 

Big H - you make me laugh sometimes

 

[Ox_Wagon]

So at least you agree that the above mentioned finite element analysis is flawed.  But if you agree that the all the spokes are ALWAYS in tension and no compression force can be transferred how does the hub press on the road with out effecting the tension of the top spokes? <?:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

On the "twang", I haven?t heard of the unit before nor have I seen any standard (SABS, DIN , ASME etc) on it nor instruments that measure it.  What is the conversion factor between "twang" and Force? As such I have difficulty excepting any ?experiment? where the "twang" is used as the only measurable to prove a theory that is not supported by engineering theory.

Lastly why on earth would a wheel collapse if it loses tension in ?the? bottom spoke or even the bottom 3 or 4 spokes? The rim may be damages but it would not collapse.