Advice with MTB wheel/rim

[Johan Bornman]

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.

 

 

 

 

 

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

Lets proceed civilly then.

 

How do you propose the spokes (and which spokes) support the load on a hub? You say I talk bollocks, give us your view.

[Bike Lore]

I think it is time that we stop this topic. it does not seem like anyone is going to move on there views and the post are become more and more patronize. it was truly an insightful discussion and JB arguments was thought provoking and it absolutely okay to disagree. Personally i have respect for anyone that is able to put there preconceived ideas away and really attempt to understand the alternative point of view without getting personal or generalizing. and it is clear that JB had this skill not like other people on this form. I my self need to work in this skill. I would advice everyone to always treat other peoples views with respect and not to become condescend. Nor should one trough there qualifications around to quickly.

 

thank you everyone for the energy that was put in and the advice that what given. I really hope my new tubeless wheel will be awesome.B)

[Topwine]

Lets proceed civilly then.

 

How do you propose the spokes (and which spokes) support the load on a hub? You say I talk bollocks, give us your view.

 

First, spokes is unable to support any meaningful compression forces, it would buckle to easily. (too thin and long). Therefore, the main load or force support is through tension forces inside the spokes. By pre-tensioning all the spokes, you let the rim support the load from the hub. When you jump the bike (or climb onto it for that matter, only the magnitude of the force differs) the force is downwards onto the hub. The hub then wants to move down, but is restricted from doing so by all the spokes north of the equator pulling it up, with the top most northerly one carrying the most load. These top spokes then transfer the load onto the rim which will tend to want to move the rim down onto the ground, where mother earth makes contact with it at the bottom point and provides the equal, but opposing force. therefore the rim will tend to deform at the bottom as well as the top.

 

Regards

[Bike Lore]

First, spokes is unable to support any meaningful compression forces, it would buckle to easily. (too thin and long). Therefore, the main load or force support is through tension forces inside the spokes. By pre-tensioning all the spokes, you let the rim support the load from the hub. When you jump the bike (or climb onto it for that matter, only the magnitude of the force differs) the force is downwards onto the hub. The hub then wants to move down, but is restricted from doing so by all the spokes north of the equator pulling it up, with the top most northerly one carrying the most load. These top spokes then transfer the load onto the rim which will tend to want to move the rim down onto the ground, where mother earth makes contact with it at the bottom point and provides the equal, but opposing force. therefore the rim will tend to deform at the bottom as well as the top.

 

Regards

 

thanks Topwine for summarizing. I have attempted to say the same with my pictures-post before. I think there are some wording in the counter arguments that are leading to misunderstanding . I think the word compression is used to loosely. in the previous post the word compression is used when the tension in a spoke decreases from it preset value. even though it can't go in the true compression due to its slenderness ratio (effective length / cross aria) being to high it apeare to go in to compresstion becuse the pre-stress reduces. but i think we need to give this a rest now.

[Gatiepie]

Fish gut, provided it is specc'd to have a similar tensile strength as stainless steel, make for a perfectly good spoke.

 

.....

 

That's how fishgut can support a wheel. The challenge is to find gut strong enough and find a method of affixing it to the hub and rim.

 

If you use a stronger rim (which is just a beam), then you'll involve more spokes and take even less tension away per spoke.

 

A wheel is a pre-stressed structure and therefore the spokes can support a compressive load up to the point where they go slack.

 

I want to do two experiments. I will build a wheel with spokes that are not tensioned (using 1.5mm steel cable for spokes) and one that is tensioned with the same type of spokes (will use cable tensioners). I foresee that the wheel without the spokes tensioned will be usable in a straight line and will show that the hub hangs on the rim. The other wheel will be tensioned then we need some crazy dude to test the durability of it by jumping with it. Any takers? And anybody who want to sponsor two hubs and two rims for science? You can have it back afterwards :-)

 

If this all works I will get some thick building line (that yellow fish gut stuff) and replace the cable with it so we can take some pictures and make videos.

[kosmonooit]

My attempts to find a FEA animation of said topic have failed ...

 

 

http://www.youtube.com/watch?v=-apBdyxcWZA

 

About rims/wheels: going to be building myself a set just for fun with Hope Pro rear and Extralite Lefty front hubs , what the collective wisdom on the ZTR Crest rims?

 

And spokes options?

[Johan Bornman]

I want to do two experiments. I will build a wheel with spokes that are not tensioned (using 1.5mm steel cable for spokes) and one that is tensioned with the same type of spokes (will use cable tensioners). I foresee that the wheel without the spokes tensioned will be usable in a straight line and will show that the hub hangs on the rim. The other wheel will be tensioned then we need some crazy dude to test the durability of it by jumping with it. Any takers? And anybody who want to sponsor two hubs and two rims for science? You can have it back afterwards :-)

 

If this all works I will get some thick building line (that yellow fish gut stuff) and replace the cable with it so we can take some pictures and make videos.

 

Gatiepie, the untensioned wheel is not a pre-stressed structure and will behave completely differently from the pre-stressed (tensioned) one. In fact, the untensioned wheel behaves like the wine guy (sorry, can't see your name in this view) proposes.

 

We see this when we build wheels up to the point where the spokes are in tension, the hub moves when you tension the opposite spoke. As soon as you can get a ring from the spoke when plucked, it is pre-stressed and then the rim moves towards the hub and the hub remains static inside the web.

 

Come pay me a quick visit. I'll demonstrate this for you in 20 minutes.

[Johan Bornman]

thanks Topwine for summarizing. I have attempted to say the same with my pictures-post before. I think there are some wording in the counter arguments that are leading to misunderstanding . I think the word compression is used to loosely. in the previous post the word compression is used when the tension in a spoke decreases from it preset value. even though it can't go in the true compression due to its slenderness ratio (effective length / cross aria) being to high it apeare to go in to compresstion becuse the pre-stress reduces. but i think we need to give this a rest now.

 

Hannes, the word compression was never used loosely. Not by me in anyway. I've always stated that the bottom spokes get compressed, but remain in tension.

[Johan Bornman]

First, spokes is unable to support any meaningful compression forces, it would buckle to easily. (too thin and long). Therefore, the main load or force support is through tension forces inside the spokes.

 

 

That is exactly what I've been saying and I want to point out that I never said the spokes go into compression. The photo I published shows clearly what happens when the spokes go into compression.

 

 

By pre-tensioning all the spokes, you let the rim support the load from the hub.

 

The term pre-tensioning is problematic and suggests something else. Rather use tensioning or pre-load.

 

 

When you jump the bike (cut cut) the force is downwards onto the hub. The hub then wants to move down, but is restricted from doing so by all the spokes north of the equator pulling it up, with the top most northerly one carrying the most load.

 

No. This would be true only if the top spokes hang from a hook in the sky. If it weren't for the bottom spokes, the wheel would be free to move down, as indeed it does when it is in the air on its way to landing.

 

All the spokes (within the deformation paramater I want to keep out of here for simplicity sake), north, west and east keep their tension the same and only the bottom ones lose some of their tension.

 

These top spokes then transfer the load onto the rim which will tend to want to move the rim down onto the ground, where mother earth makes contact with it at the bottom point and provides the equal, but opposing force. therefore the rim will tend to deform at the bottom as well as the top.

 

This is where it goes pear-shaped.

 

You stated correctly that there is a force on the hub and it is opposed by an equal force from terra firma pushing upwards. Equal and opposite. You can't now have a third force pulling upwards from the top of the rim. That would mess up the algebra.

 

I think this is the crux of it all.

[Plentipotential]

Chain Reaction Cycles

 

Hope Pro II hub, Mavic 819 UST and 1.8-2.0 mm spokes.

 

R 2321.67 throw on a tyre, I bought Conto Race King UST, R 339.33. Add in a few bits and pieces and they pay for the freight. Collected at the post office, costs include everything.

 

The utter rubish being spouted forth here on this forum about the Mavic 819 is not to be believed. Tubeless is the way foreward IMO and from a fellow heavy weight the 819 is bullet proof, forget the weight saving with other rims, if you want to save weight go on a diet. I have broken a lot of bike parts but this combo is solid and good value for money and the CRC custom wheel build has not let me down.

[Johan Bornman]

cut cut cut cut

 

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.

 

 

Your haven't given any consideration to fatigue.

 

If you make the spokes thicker, the load is taken up by less spokes and it puts greater stress on the rim at the spoke holes.

 

If you make the spokes thinner, the load is distributed over more spokes and the rim takes less strain and fatigues slower. 99% of rim failures are fatigue failures.

 

If you make the rim and spokes thicker, you're building a motorbike wheel. Strong enough is strong enough, but strength is not durabillity.

 

This is a complete aside to the "how the spokes support their load" debate and I don't want to confuse the two.

[Johan Bornman]

Chain Reaction Cycles

The utter rubish being spouted forth here on this forum about the Mavic 819 is not to be believed. Tubeless is the way foreward IMO and from a fellow heavy weight the 819 is bullet proof, forget the weight saving with other rims,

 

Utter rubbish? I think I explained why this is an inferior rim. Perhaps you would like to be brave enough to tackle me on my specific points rather than make sweeping statements.

[Topwine]

Dear Johan

 

You are not doing your reputation any good by continuing to show your ignorance about structural design and force distribution. Having just spoken to another professional mechanical engineer to confirm, I can safely say you don't know what you are talking about. I certainly won't let you build my wheels !

 

Can I kindly suggest you make an appointment with a professor at a reputable engineering university (not college) to explain or demonstrate to you how forces in a spoked bicycle wheel are distributed.

 

Amen

[Plentipotential]

Utter rubbish? I think I explained why this is an inferior rim. Perhaps you would like to be brave enough to tackle me on my specific points rather than make sweeping statements.

 

All this from a man who once posted the following on this forum. "Stanchions are anodised for several reasons. Anodising is extremely hard (second only to diamonds)"

 

To the layman all this techno talk can, on the surface (pun intended) appear very impressive at first glance, however the proof is in the actual using of the products. The Mavic 819 is a bullet proof rim, and no, aluminium on aluminium is not a corrosion problem. As stated by yourself on the 1st page of this thread, and I quote " 2. The nipple retaining collar is an aluminium-on-aluminium joint which is a corrosion bomb waiting to explode. These collars often just rot off. Coastal riders in particular should avoid this technology. The same goes for Ksyrium and other Mavic rims with nipples that screw into the rim."

 

However, brass, which contains 63% copper, is a problem, copper being the alloy not to be mixed with aluminium. If aluminium-on-aluminium was a corrosion bomb then aluminium as a product would eat itself, no?

[Johan Bornman]

All this from a man who once posted the following on this forum. "Stanchions are anodised for several reasons. Anodising is extremely hard (second only to diamonds)"

 

 

I'll deal with this in that particular post. Didn't know you took exception to that.

 

 

To the layman all this techno talk can, on the surface (pun intended) appear very impressive at first glance, however the proof is in the actual using of the products. The Mavic 819 is a bullet proof rim, and no, aluminium on aluminium is not a corrosion problem. As stated by yourself on the 1st page of this thread, and I quote " 2. The nipple retaining collar is an aluminium-on-aluminium joint which is a corrosion bomb waiting to explode. These collars often just rot off. Coastal riders in particular should avoid this technology. The same goes for Ksyrium and other Mavic rims with nipples that screw into the rim."

 

However, brass, which contains 63% copper, is a problem, copper being the alloy not to be mixed with aluminium. If aluminium-on-aluminium was a corrosion bomb then aluminium as a product would eat itself, no?

 

The brass in nipples is nickel plated and remains good for years and years of use. I have only good things to say for brass nipples.

 

However, I've posted several photos and given detailed explanations of X819 and Ksyrium problems where the aluminium corrodes, making it impossible to tune the aluminium nipples in these wheels.

 

If you think aluminium-on-aluminium corrosion doesn't exist, I have news for you.

 

Shimano learnt from Mavic's woes and developed a similar system without the stress risers.

[Tieffels]

First, spokes is unable to support any meaningful compression forces, it would buckle to easily. (too thin and long). Therefore, the main load or force support is through tension forces inside the spokes. By pre-tensioning all the spokes, you let the rim support the load from the hub. When you jump the bike (or climb onto it for that matter, only the magnitude of the force differs) the force is downwards onto the hub. The hub then wants to move down, but is restricted from doing so by all the spokes north of the equator pulling it up, with the top most northerly one carrying the most load. These top spokes then transfer the load onto the rim which will tend to want to move the rim down onto the ground, where mother earth makes contact with it at the bottom point and provides the equal, but opposing force. therefore the rim will tend to deform at the bottom as well as the top.

 

Regards

 

Ja, your understanding of the concept is greatly dependant on where you start with the analysis. You start at the hub and work towards the rim, I suggest start at the rim and work towards the hub..

 

In what you said above you assume the rim is quite rigid, which it is not as per JB suggestion and the FEM thingy. As the rim is subjected to a load from the ground, be it your weight or a rock at the bottom of a drop, the rim deforms and displaces inwards towards the hub, relieving some of the pretension in the spoke affected by the deflection zone of the rim. And the stronger the rim, obviously the smaller the deflection zone and less spokes are affected. Also the rim might bulge out due to conservation of mass as per the FEM pics, so the tension in some horizontal spokes also increase.

 

As per your previous posts you understand force vectors, so now you simply sum the vertical components of the tension in all the spokes and that is the force that the hub sees and transfers to the frame of the bike, which is countered by your weigh or slows you down in the case of a drop-off.

 

Easy