Advice with MTB wheel/rim

[VincentBikes]

So I wrote this whole spiel about a spoke cannot go into compression as you have to apply a force on the one end and keep the other end fixed which a bicycle spoke is not (the one end just sits in the rim while the hub is supposed to apply a compression force according to Johan and this relates to your FEA boundary layer conditions which has to be defined very well in FEA or you get garbage information out) so that the hub can never stand on the bottom spokes as they will merely relief their tension, go to a no load condition in then slide into the rim but then the LAN Connection bombed out and I lost the whole thing I wrote so I will settle for Agree to Disagree. Maybe I will write it again later...

[kosmonooit]

Let's not forget Boundary Layer Delamination ...

[Wyatt Earp]

Let's not forget Boundary Layer Delamination ...

Noooooo, don't go there :lol:

As I said, I don't think the apple levitated, perhaps it sank

Just ignore me, I am just too chirpy today.

[Robrider]

Thanks Hannes and JB, I learnt something today. I never really considered things like this. I always assumed the top spokes increase their tension.

 

Now that we have proved that, I think the "hanging vs. standing" argument is becoming a bit of semantics, and I can see both sides.

 

Thanks for the interesting read.

[Johan Bornman]

So I wrote this whole spiel about a spoke cannot go into compression as you have to apply a force on the one end and keep the other end fixed which a bicycle spoke is not (the one end just sits in the rim while the hub is supposed to apply a compression force according to Johan and this relates to your FEA boundary layer conditions which has to be defined very well in FEA or you get garbage information out) so that the hub can never stand on the bottom spokes as they will merely relief their tension, go to a no load condition in then slide into the rim but then the LAN Connection bombed out and I lost the whole thing I wrote so I will settle for Agree to Disagree. Maybe I will write it again later...

 

Rusty, try again. This exact issue perplexes many people.

 

Try this experiment (although I'm sure I'm wasting my breath here since so-one tried any of the experiments I proposed).

 

Call your wife over and face her. Put your feet together, take her two hands in yours by making a hook with your fingers and both lean back until you form a triangle with the sharp end at your feet.

 

Reach an equilibrium so that the triangle is stable.

 

Note that your arms are in tension.

 

Now call your two children over and have them apply a 10kg force to your and her shoulder blades. They are both pushing against both of you. Note that your arms are still in tension but no longer as much. Your hands have not unhooked.

 

Same with the wheel. All the spokes support the hub and when it is loaded, the bottom spokes lose some tension but not all. Therefore those spokes support the load by losing some tension. The minute you overshoot their available tension the wheel collapses as the one in my photo.

[VincentBikes]

 

 

Same with the wheel. All the spokes support the hub and when it is loaded, the bottom spokes lose some tension but not all. Therefore those spokes support the load by losing some tension. The minute you overshoot their available tension the wheel collapses as the one in my photo.

 

I think it is about nomenclature. In engineering if something supports a load the component goes into compression stress. If it supports a load by hanging the load on it the component goes into tension. I think therefore it is your use of nomenclature that is confusing me. The spokes always stays in tension and can therefore never support/carry the load go into compression(normal riding conditions). I will come and visit you again and have a long cold one and some of those nice sandwitches and then we can discuss it. Maybe we must get the university to get a student to do his final year thesis on a Wheel FEA. That would be quite interesting.

[Kona Kula]

Ummm. So whats the outcome. Is this a good wheel?

[Bike Lore]

Ummm. So whats the outcome. Is this a good wheel?

 

I hope so. can't wait for the thing!!! and it is still being ordered.... ooi!! how am i going to survive the tension....

[Johan Bornman]

I think it is about nomenclature. In engineering if something supports a load the component goes into compression stress. If it supports a load by hanging the load on it the component goes into tension. I think therefore it is your use of nomenclature that is confusing me. The spokes always stays in tension and can therefore never support/carry the load go into compression(normal riding conditions). I will come and visit you again and have a long cold one and some of those nice sandwitches and then we can discuss it. Maybe we must get the university to get a student to do his final year thesis on a Wheel FEA. That would be quite interesting.

 

I humbly disagree. I think it is about a term and concept that is not discussed at engineering school. Perhaps the civils guys understand this better.

 

Allow me to cite an example that is similarly paradoxial but effectively the same.

 

Plain Concrete cannot support tensile loads.

 

Yet, a major feature of civil engineering is to use this material that cannot go in tension, to support loads in tension.

 

I'm talking lintels and similar pre-stressed concrete structures. I've been priviliged to walk through a lintel factory. These contrete beams are cast in what looks like gutters - long vessels. Inside the vessel along the length they lay some high-tensile wire and they stretch it. It looks like a guitar neck. Now they pour concrete over these wires and let it set. The wires are then cut from their tension pulleys and the concrete lintels are shipped for use.

 

How do they support loads in tension? By loading the lintel, the bottom part of it is tensioned and the top compressed.

 

For those who don't get this, have a snack. Break a boudoir biscuit and note how the top part compresses and the bottom part pulls apart (goes in tension). It breaks exactly like a non -re-stressed lintel would have broken.

 

The fact that the concrete lintel is pre-stressed, means that you can apply tension to it and it will support a load. As you know, it isn't tensioned beyond the tension in the wires, therefore it remains in compression.

 

The wire-spoked wheel is the same. It supports a load by losing some of its tension in the bottom spokes. Not all, just some.

[Bike Lore]

The wire-spoked wheel is the same. It supports a load by losing some of its tension in the bottom spokes. Not all, just some.

 

then ask your self why/how does it loosen it tension? what is the cause... the point being; the force is transfer via the top pointing spokes to the rim which then pushes the rim in to the ground. the deformation of the rims is countered by the horizontal spokes. if the bottom spokes did not loosen it tension the hub will not be in equilibrium and it will continue to move down. yes it does move initially down due to the sum of the forces. when this happens the distance between the hub and the contact point shrinks and the tension in the bottom spokes are relieved. the bottom spokes never(i hope for my inner lining sake ) pushes against the hub and the wheel. it just pulls less.

 

I should add that up to the point where the tension in the lower spoke has decreased from the pre-tension to zero the tension in the top spokes has not increased due the the loading of the wheel. after this the tension will start to increase.

 

but i think we need to stop this now. it was interesting doing the calculations and discussing this with my fellow engineers and scientist at work over brake times but the problem is solved.

 

now lets get back to the serious stuff like riding my bike. today is interval day

[Weight Weenie]

Pleasure Hannes.

The valves don't come cheap at round about R100 a pop....(don't quote me on that price though!)

The valve cores are replaceable.

In my opinion it is better to use proper UST or Tubeless ready tyres with Stans rims as these tyres have a different bead design to normal tyres. These tyres also tend to be more expensive....especially in South Africa.

This bead then fits better into the bead socket interface ("BST") that Stan's rims use.Bead Socket Technology

 

* By eliminating the bead hook and lowering the sidewall by 2-3mm we reduce the weight of the rim. Some of this material can be used in the center part of the rim making it stronger and stiffer.

* The curve of the rim sidewall is the same shape as the bead of the tire so they fit together like a ball and socket joint. This design will help reduce the strain on the tire bead while creating a tighter seal.

* By lowering the sidewall of the rim we also reduce the mechanical leverage the tire has on the rim. This will make the rim stiffer and last longer by eliminating flexing that can cause cracking.

* With these short sidewalls the tire should not hit the rim and pinch flat as often as standard rims, either with or without tubes. This design will allow you to run lower pressures and use 4mm more of the tire than ever before. The tire will have larger air volume giving you better traction.

 

Nope sorry I disagree, the whole idea behind the Stan's tubeless system is to do away with tubeless (UST) tyres and rims, making for a cheaper lighter combo, ie. you can use a normal rim and a normal foldable tyre and seal it with the sealant/tape/rim strip and have a 'tubeless' setup. BUT as some normal beads are to weak and tend to jump from the normal rims, Stan's started making his own rims with the BST technology so that a normal tyre can sit on his rim like a UST tyre does on a UST rim and not jump off or burp air. (look at the vid on the stans site, he uses a C-clamp on the tyre bead and it does not burp on the stans rims, the others setups do) Thus all the UST advantages but less cost and weight and you can use almost any tyre. (ok normal tyre sidewalls are weaker than UST sidewalls, thats the ceveat)

 

On my ztr 355 rims, UST/tubeless ready tyres were almost impossibble to get on/off, normal tyres go on and off by hand without tyre levers. Apparently I had the rim taped up with insulation tape to build it up so Juan took that off and now they are fine and UST will go on/off easily.

 

Thus that rim is actually made for normal tyres, you dont need to use UST if you dont want to.

[Bike Lore]

Nope sorry I disagree, the whole idea behind the Stan's tubeless system is to do away with tubeless (UST) tyres and rims, making for a cheaper lighter combo, ie. you can use a normal rim and a normal foldable tyre and seal it with the sealant/tape/rim strip and have a 'tubeless' setup. BUT as some normal beads are to weak and tend to jump from the normal rims, Stan's started making his own rims with the BST technology so that a normal tyre can sit on his rim like a UST tyre does on a UST rim and not jump off or burp air. (look at the vid on the stans site, he uses a C-clamp on the tyre bead and it does not burp on the stans rims, the others setups do) Thus all the UST advantages but less cost and weight and you can use almost any tyre. (ok normal tyre sidewalls are weaker than UST sidewalls, thats the ceveat)

 

On my ztr 355 rims, UST/tubeless ready tyres were almost impossibble to get on/off, normal tyres go on and off by hand without tyre levers. Apparently I had the rim taped up with insulation tape to build it up so Juan took that off and now they are fine and UST will go on/off easily.

 

Thus that rim is actually made for normal tyres, you dont need to use UST if you dont want to.

 

wow that is gr8. I have spoken to my LBS en they will help me with some rim tape and a valve. oi I should just resist buying a front wheel....

[VincentBikes]

I humbly disagree. I think it is about a term and concept that is not discussed at engineering school. Perhaps the civils guys understand this better.

 

Allow me to cite an example that is similarly paradoxial but effectively the same.

 

Plain Concrete cannot support tensile loads.

 

Yet, a major feature of civil engineering is to use this material that cannot go in tension, to support loads in tension.

 

I'm talking lintels and similar pre-stressed concrete structures. I've been priviliged to walk through a lintel factory. These contrete beams are cast in what looks like gutters - long vessels. Inside the vessel along the length they lay some high-tensile wire and they stretch it. It looks like a guitar neck. Now they pour concrete over these wires and let it set. The wires are then cut from their tension pulleys and the concrete lintels are shipped for use.

 

How do they support loads in tension? By loading the lintel, the bottom part of it is tensioned and the top compressed.

 

For those who don't get this, have a snack. Break a boudoir biscuit and note how the top part compresses and the bottom part pulls apart (goes in tension). It breaks exactly like a non -re-stressed lintel would have broken.

 

The fact that the concrete lintel is pre-stressed, means that you can apply tension to it and it will support a load. As you know, it isn't tensioned beyond the tension in the wires, therefore it remains in compression.

 

The wire-spoked wheel is the same. It supports a load by losing some of its tension in the bottom spokes. Not all, just some.

 

 

Like I said some of those nice sandwitches and a long cold draught..................

[Topwine]

Wow, this was fun. It was of course a loaded question initially by me. Having a Mechanical Engineering degree, I quite enjoyed the debate.

 

So in conclusion then, we have determined that Johan talks a lot of bollocks when he makes this statement,

 

"Jumping your bike doesn't put strain on the spokes at all" ,

 

The jumping force is indeed transferred from the hub through the spokes onto the rim where the counter force is provided by the ground at the impact zone.

 

Thanks guys

[Johan Bornman]

Wow, this was fun. It was of course a loaded question initially by me. Having a Mechanical Engineering degree, I quite enjoyed the debate.

 

So in conclusion then, we have determined that Johan talks a lot of bollocks when he makes this statement,

 

"Jumping your bike doesn't put strain on the spokes at all" ,

 

The jumping force is indeed transferred from the hub through the spokes onto the rim where the counter force is provided by the ground at the impact zone.

 

Thanks guys

 

Degrees seem to be no substitute for savvy. Admit that you did not ever spend ten minutes discussing or analysing a wire-spoked wheel at varsity. And since then you just stirred up your old prejudices and smugly satisfied yourself that you know how it works.

 

I also take it you have not read any literature on the topic. If so, please divulge which ones.

 

I also take it that you will not attempt to explain the photo of a typical car-impacted wheel.

 

I also take it that you have not tried the experiment that I cited.

 

I also take it you have have not tried to apply a spoke tensiometer to a loaded and unloaded wheel.

 

I also take it that you know it all and won't do any of the above.

 

I also take it that you cannot explain why a wheel behaves like I describe when removing a bulge in the rim by tensioning the spokes directly at the bulge and not at the opposite side.

 

If you read through the arguments above you'll noticed that the chief protagonists against my proposal are vascilating between prejudice and a breakthrough in understanding. There has been no conclusions.

 

Fact is: Jumping your bike does not increase strain on the spokes (and we're negating the fact that the rim changes shape) but reduces strain on the bottom spokes in the load affected zone.

 

Jump bikes don't need thicker spokes, they need thicker rims to distribute the load over more spokes.

 

Debate my arse. You insulted me with your so-called loaded question and then sat back without any contribution at all. Look up debate in the dictionary.

[Topwine]

Johan

 

In all respect, I have no interest in humiliating you, but if you continue like this, I might have no choice. You clearly have no understanding of how force vectors work or how forces are distributed in structures.

 

 

 

 

Fact is: Jumping your bike does not increase strain on the spokes (and we're negating the fact that the rim changes shape) but reduces strain on the bottom spokes in the load affected zone.

 

Jump bikes don't need thicker spokes, they need thicker rims to distribute the load over more spokes.

 

 

Your "facts" are based on inferior understanding of force vectors and load distribution. Jumping your bike are going to require thicker rims AND thicker spokes, or MORE spokes of the same diameter. The force is distributed THROUGH the spokes ONTO the rim. You can have it no other way, only in your imagination.

 

I can explain all your "points" but before you grasp this basic concept here, I'll be wasting my time.

 

Best