Spokes Rubbing

[Yellow Saddle]

I don't remember the debates and I can be bothered searching.

However, you may well know something I don't, so can you tell me what the bottom spokes on a wheel compress against (Apart from the inner tube)?

You can't be bothered doing some work yourself. If I give you one answer, you'll come back with another question and another and another. It is all there on the record. Do it yourself.

 

[Yellow Saddle]

It's obvious that a hub stands on its bottom spokes just like SS/Fixed are better at driving a rear sprocket because the chain is not pushing it through bends like on a derailleur equipped bike (it's also why riders of these bikes place such importance on chainline and get it as straight as possible)

Pushing what through the bends.

 

[Yellow Saddle]

It's like having a small terrier snapping at your trouser-leg.

I may be a terrier but you are the one that makes unfounded statements and refuse to back them up or have the grace that you've misrepresented someone. The terrier will back off when you prove your statement.

 

[Yellow Saddle]

I've not read The Bicycle Wheel or seen the old posts etc.

It is however relatively straightforward to analyse a bicycle wheel when static with a load applied at the axle. It has been done many times.

If I've time at the weekend (no promises) I'll run it through one of my design programmes (yes I'm an engineer ) to see what it predicts.

I've a pretty good idea what the results will show, but I'll wait and see.

I can't simulate rotation though!! so this is just a bit of fun (he says).

You'll have to run an FEA and for that you'll need dimensions. I can readily supply some if you let me know what you want. I have assisted several FEAs done on the topic. You can also get a full set of data from The Bicycle Wheel by Jobst Brandt.

A good experimental scientist doesn't set out with a pre-conceived result. A hypothesis is better to start off from.

 

[Ian H]

An old friend, late club-mate and frame-builder, once stated that he never laced his spokes at the last crossing because "they rubbed and wore through each other". I've never heard of any of his wheels failing, though. Cheap machine-built wheels used to be built that way — may still be for all I know.

 

[Salar]

You'll have to run an FEA and for that you'll need dimensions. I can readily supply some if you let me know what you want.

Thanks, if you have any section properties that would help.

I can't justify the cost of FEA programmes in my line of work. However I can simulate a wheel, spokes etc their properties and apply realistic loads at the axle.

The analysis will provide radial axial loads, spoke tension, displacements and (compression?).
I could do it longhand, but I'll let the PC do the work.

 

[Yellow Saddle]

Thanks, if you have any section properties that would help.

I can't justify the cost of FEA programmes in my line of work. However I can simulate a wheel, spokes etc their properties and apply realistic loads at the axle.

The analysis will provide radial axial loads, spoke tension, displacements and (compression?).
I could do it longhand, but I'll let the PC do the work.

If you are not going to do an FEA, I can't see how dimensions of say a rim section would help. You may as well rely on simple force diagrams which will give you the same result. Just assume a not-infinitely-stiff rim, use the strain figures for 2mm 18/8 stainless wire and assume an infinitely stiff hub. I don't know what a realistic load on the axle implies. This is super simple - half a person's average body weight. The direction of the force is a given and the direction of the resisting force from the road should also be obvious.

What is your hypothesis?

 

[Yellow Saddle]

An old friend, late club-mate and frame-builder, once stated that he never laced his spokes at the last crossing because "they rubbed and wore through each other". I've never heard of any of his wheels failing, though. Cheap machine-built wheels used to be built that way — may still be for all I know.

Your old friend had a strange view of how spokes interact. I also have never heard of any of my aunt Edna's wheels fail. Machine built wheels are always hand laced and an interlace at the last crossing is not an issue for productivity. For that matter, expensive machine-built wheels are also interlaced where appropriate. I don't see what point you make other than skirt your obligation to substantiate your claim.

 

[Salar]

@Yellow Saddle

I need to input properties of the sections to satisfy programme requirements, a straight forward plane frame analysis will give some basic results.

I could simulate tyre deformation by inputting springs, but for now I'll consider the rim as rigid.

This is all pretty basic stuff.

Hypothesis............Well, I'm expecting max tension in the upper vertical/ near vertical spokes, gradually reducing to virtually zero on the horizontal, then some minor compression in the vertical / near vertical spokes where the wheel touches the ground.

A simplistic demonstration as to why the top spokes only take tension is how guy ropes and tensile bracing works in structures.

The one variable is the spoke tension.

 

[Sea of vapours]

or now I'll consider the rim as rigid.

Intuitively, this doesn't sound like a reasonable assumption. I'm fairly confident that a rim without spokes can be compressed into an oval (I have no experience of so doing; it just seems reasonable). More to the point, I'm even more confident that the rim is circumferentially incompressible, at least to the degree where applying radial forces to it will distort it into an oval before inducing circumferential compression.

If those assumptions are correct then won't the wheel try to bow out / become ovoid in the horizontal plane? And if that's true won't the horizontal spokes experience [increased] tension due to resisting the wheel's tendency to become ovoid?

That's just a musing really, and very probably flawed in some way, but this assumption of an effectively (for the forces involved) rigid rim seems to me to be potentially game-changing.

 

[Yellow Saddle]

Intuitively, this doesn't sound like a reasonable assumption. I'm fairly confident that a rim without spokes can be compressed into an oval (I have no experience of so doing; it just seems reasonable). More to the point, I'm even more confident that the rim is circumferentially incompressible, at least to the degree where applying radial forces to it will distort it into an oval before inducing circumferential compression.

If those assumptions are correct then won't the wheel try to bow out / become ovoid in the horizontal plane? And if that's true won't the horizontal spokes experience [increased] tension due to resisting the wheel's tendency to become ovoid?

That's just a musing really, and very probably flawed in some way, but this assumption of an effectively (for the forces involved) rigid rim seems to me to be potentially game-changing.

I agree with you. The rim is nothing close to rigid. For instance, you can easily squeeze an aluminium rim into an oval. Although I can sit on a Zipp carbon rim without it breaking, it does still deform. It isn't circumferentially rigid either. Just during building and tensioning the wheel, it loses about 2mm in diameter. With inflation from a tubular tyre, it loses some tension in the spokes, which indicates even more compression. Incidentally, an inflated tyre constricts the rim. A tubular more so because a clincher is just a tubular with a missing piece.


As for the question at the en of your post, the answer is no.

Draw a force diagram as I suggested above and you'll see the deformation.

 

[Yellow Saddle]

@Yellow Saddle

I need to input properties of the sections to satisfy programme requirements, a straight forward plane frame analysis will give some basic results.

I could simulate tyre deformation by inputting springs, but for now I'll consider the rim as rigid.

This is all pretty basic stuff.

Hypothesis............Well, I'm expecting max tension in the upper vertical/ near vertical spokes, gradually reducing to virtually zero on the horizontal, then some minor compression in the vertical / near vertical spokes where the wheel touches the ground.

A simplistic demonstration as to why the top spokes only take tension is how guy ropes and tensile bracing works in structures.

The one variable is the spoke tension.

You can't simulate tyre deformation by substituting it with a spring.

Draw a force diagram and see if you conclude with the same hypothesis.

 

[Salar]

The spring is a deformation, settlement at a support, contact with the ground. This can be input and applied to a seperate element in conjunction with the rim. However with the programmes I use it would require a lot of input.

Just to clarify the rim can be input as "rigid" at node points around the rim, however the input section properties will allow it to deform. It will not remain circular.

Not being a wheelbuilder what type of tensile force is applied to the spokes is it 100Kg?

 

[Yellow Saddle]

The spring is a deformation, settlement at a support, contact with the ground. This can be input and applied to a seperate element in conjunction with the rim. However with the programmes I use it would require a lot of input.

Just to clarify the rim can be input as "rigid" at node points around the rim, however the input section properties will allow it to deform. It will not remain circular.

Not being a wheelbuilder what type of tensile force is applied to the spokes is it 100Kg?

Yes, work at 1000N, that's a good average.

Where's your force diagram?

 

[Salar]

Where's your force diagram?

I've got proper work to do, to pay the bills, clients chasing. If I've time I'll do something over the weekend.