137 page PhD Thesis on the Bicycle Wheel by Matthew Ford, Dec 2018

Everything about building wheels, glueing tubs, etc.
mattr
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by mattr

Suppose thats the benefit of modelling a wheel, you can "test" theoretically impossible builds.
Don't need to imagine at all. Build a "real" wheel in your software to check boundary conditions. Then start building impossible wheels.

by Weenie


alcatraz
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by alcatraz

Marin wrote: ↑
Fri Jan 18, 2019 11:23 am
bm0p700f wrote: ↑
Thu Jan 17, 2019 3:05 pm
Still not clear why lateralstiffne decreases with spoke tension.
They way I understood it is that with high tension, the wheel gets closer to the "Taco" state.

Regarding symmetrical stiffness, I doubt this has to be symmetrical: Imagine a wheel with the NDS flange really far out and the DS flange under the spoke holes - it obviously will be less stiff if you push the DS towards the NDS.
It must have something to do with the bracing angles.

Ds spokes have less lateral leverage because of their shallow angle. They "prefer" to equalize external forces laterally, more so than nds.

You'd think a good way to counterbalance this is to have more spokes on the DS side (2:1) or thicker spokes. Still it's not that common.

I'm taking shelter now from the experts' fists that will rain down on me. :beerchug:

/struggling amateur :D

bm0p700f
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by bm0p700f

Marin,

I am not sure. I have such a wheel at the shop and both sides move the same ammount when I push. one side does not feel easier to push than the other. You would only get more movement one one side or the other if you could uncouple one side and push. you cant. You should find one side pushes back and the other pulls back when the rim is pushed. the two forces should be indistingiushable and therefore for a given rim load you get a given deflection. I dont see any where in the thesis that the lateral wheel stiffness is handed. I dont think the maths can back that up.

Your assertion assuming that the spoke one one side dont push back there is only the pull back force opposing the load you apply to the rim.

What the author is implying by the maths is lateral stiffness is not just a function of the rim profile and material but deformation state of the rim. Uttery weird. i still dont understand the mechanism./ I can just about follow the maths but not the full derevation. it still does not explain it.

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F45
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by F45

He says the axial compressive loads on the rim decrease stiffness. I cannot put together in my head how that works.

alcatraz
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by alcatraz

Here is my guess...

It means narrow flanges are shit because it increases axial compressive load on the rim.

Maybe the author confuses deflection with decrease in stiffness?

TheKaiser
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by TheKaiser

bm0p700f wrote: ↑
Fri Jan 18, 2019 4:18 pm
What the author is implying by the maths is lateral stiffness is not just a function of the rim profile and material but deformation state of the rim. Uttery weird. i still dont understand the mechanism./ I can just about follow the maths but not the full derevation. it still does not explain it.
I recall Mavic also making the claim that little to no spoke tension lead to a stiffer wheel than the typical tension range we'd use, although that was in reference to their R-Sys with the Tracomp carbon spokes that are supposed to function in both traction/tension and compression. Interestingly, they claim both increased "stiffness" (presumably lateral) as well as increased "vertical compliance", so the old laterally stiff, vertically compliant sales pitch. This is obviously going a little farther afield than the original discussion given the different spoke tech involved, but I thought it was peripherally relevant given that it was the only other source I've seen claiming less tension can be more stiff. This is their marketing blurb on the topic:

"It features Tracomp technology, which stands for Traction/Compression and combines extremely low weight with high lateral stiffness. This innovative design allows the spoke to work both in traction and compression. These spokes are both round and hollow (tubes) so they won’t buckle when compressed. They are clamped on both ends by a nipple that is bonded to the spoke and directly threaded into the rim on one end and into a ring inside the hub on the other.
We use superlight carbon spokes to save weight and bolster stiffness, since carbon fibers don’t stretch as much as steel or aluminum. The result is a wheel that is 30% stiffer laterally than any other wheel in its weight category.
Tracomp also dampens road vibration and adds vertical compliance so you can ride longer with more comfort. "


It is intuitive to me that a spoke that can function in compression as well as tension would build a "stiffer" wheel, at least when loaded beyond the point where wire spokes would lose tension, but, given that carbon generally functions far better in tension than compression, I still don't get how forcing it to work in compression is advantagous. If thats relevant to the topic at hand, please discuss further, but, if it's irrelevant, then...back to your regularly scheduled programming.

Jugi
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by Jugi

bm0p700f wrote: ↑
Fri Jan 18, 2019 4:18 pm
What the author is implying by the maths is lateral stiffness is not just a function of the rim profile and material but deformation state of the rim. Uttery weird. i still dont understand the mechanism./ I can just about follow the maths but not the full derevation. it still does not explain it.
For a non-native English speaker it wasn’t easy to follow (and some things may have gone over my head) but what I took away was:

The thesis mainly discusses the parameters of rims, spokes, hubs (as in lacing dimensions) and their interaction. The main parameter of interest is stiffness - laterally, radially, in the materials themselves and so on.

The whole ”laterall stiffness decreases when spoke tension rises” thing was rather vaguely depicted (in my opinion), but on page 119 he clearly concludes ”increasing tension prevents the spokes from going slack under load, but decreases the lateral stiffness of the rim.” For the most part through reading I wondered how higher spoke tension would decrease the wheel’s stiffness, but what he is concluding is the rim’s structural stiffness (as a component in the whole equation) is compromised when critical spoke tension is achieved. Carbon as a rim material is not mentioned at all in the paper, making the findings a bit hard to relate to the typical wheel builds described on this forum.

The conclusion reminded me of a short experiment I did back when I wanted to learn wheel building. I had a couple of old 36 spoke wheels which were essentially going to the recycle bin, so I decided to use them to learn all things one shouldn’t do when truing or building wheels. The rims were very ”soft” traditional box sections, and when tightening them I could produce a systematic wave pattern on them before the nipples gave out or the rim’s spoke holes cracked. I suspect that was clearly beyond the ”critical” spoke tension, where the pulling force of the spokes overcame the rim’s structural stiffness, resulting in sharp bends between spoke holes before buckling completely.

Karvalo
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by Karvalo

Marin wrote: ↑
Fri Jan 18, 2019 11:23 am
Regarding symmetrical stiffness, I doubt this has to be symmetrical: Imagine a wheel with the NDS flange really far out and the DS flange under the spoke holes - it obviously will be less stiff if you push the DS towards the NDS.
So how come your wheel is stable in that configuration before you pushed on it? :wink:

The spokes on both sides are under tension, right? So if the spokes on one side are better at pulling the rim sideways than the spokes on the other side then that's what they'll do - your wheel will spontaneously re-dish itself until it reaches equilibrium and the spokes on each side have the same lateral pull as the spokes on the other side.

Or to put it the other way, the only way you have managed to build your wheel with uneven flange spacing in the first place is by playing with the spoke tensions until they cancel out the spoke angle differences and lateral force is equal on either side.

Marin
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by Marin

Karvalo wrote: ↑
Mon Jan 28, 2019 1:33 pm
:wink:
Hmm. Another thought experiment:

If I were to build a symmetrical, centered front wheel with 1.8 - 1.4 - 1.8 Sapim Superspokes on the left, and 2.3mm straight gauge spokes on the right.

Would it still deflect by the same amount for the same load pulling to the left or right?

Karvalo
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by Karvalo

Absolutely no idea - I'm just making it up as I go along :lol:

alcatraz
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by alcatraz

Marin wrote: ↑
Mon Jan 28, 2019 2:04 pm
Karvalo wrote: ↑
Mon Jan 28, 2019 1:33 pm
:wink:
Hmm. Another thought experiment:

If I were to build a symmetrical, centered front wheel with 1.8 - 1.4 - 1.8 Sapim Superspokes on the left, and 2.3mm straight gauge spokes on the right.

Would it still deflect by the same amount for the same load pulling to the left or right?
I think you would move in that direction, assuming your build is unequal to begin with. (Maybe there are designs that are more or less equal from the beginning with the same spokes, like possibly a combination of following properties: an asymetric rim, laced 2:1, certain flange design)

alcatraz
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by alcatraz

I think the stable while stationary is not a very solid argument to prove that lateral travel is equal.

To be stable the opposing lateral forces have to be equal - yes.

That doesn't mean the rim travel is equal for a given force in both directions.

Because of the bracing angles DS and NDS's "tension vs lateral force" graphs are different. DS spokes will have a shallower graph, and NDS spokes will have a steeper graph.

Thats why pushing results in different travel because DS spokes are less affected when pushing the rim laterally. That's also why nds only needs a fraction of ds spoke tension to produce the same lateral pull = increased lateral leverage because of a shallower bracing angle.

I'd draw an example but I'm on my phone. :)

(Also the argument that the same side spokes 180 degrees from eachother would cancel eachother out, I don't think applies. I don't think the rim rotates as much as it travels laterally. It moves less at the 180 degree point.)

I know I'm missing tons of proof.

MikeD
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by MikeD

Why are we so concerned about wheel stiffness? Jobst Brandt didn't consider it very important and stiffness does not equal strength (read the thread on Berk spokes that have half the stiffness of an equivalent thickness steel spoke, yet they build functional wheels). This paper is flawed in that it focuses on the spokes but in real life, it's the rim that fails and the spokes are plenty strong enough.

Marin
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Location: Vienna Austria

by Marin

- I've had more spokes fail than rims.
- Stiffess feels good, and brake rub sucks. Also, a stiffer wheel will last longer.

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Hellgate
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by Hellgate

Marin wrote:- I've had more spokes fail than rims.
- Stiffess feels good, and brake rub sucks. Also, a stiffer wheel will last longer.
Yup...

by Weenie


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