• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Show us your bicycles!

rdenney

Major Contributor
Forum Donor
Joined
Dec 30, 2020
Messages
2,310
Likes
4,064
All you guys need to do is take a bike with properly tensioned spokes. Have someone sit on it, and start snipping spokes from either the top or bottom. You'll find out soon enough. Destructive testing is the funnest kind. :)
No, you can't do that. That would be like removing the bias from a transistor in operation. Removing it causes the transistor to fall outside its operating range and cease to function, but it is not the bias that constitutes the signal being acted on, or even the bias that is causing the transistor to switch. The bias voltage just moves the junction to a range where a change in the signal can have an effect.

So, another thought experiment: Is a steel-reinforced concrete beam able to carry a bending load on the underside of the beam's center that sees tension? Yes. Is it the concrete or the steel doing the carrying? Most people think the steel carries the load and the concrete is along for the ride. But if it was just the steel carrying the load, the concrete would crack and (eventually) fail. Concrete has negligible tensile strength and will rupture if stretched as much as the steel within it, which has high tensile strength. What keeps that from happening is that the steel is loaded in tension and then the concrete is poured around it. The only reason the concrete can then endure a tensile load (I did NOT say stress) without cracking is that the steel provides sufficient biasing compression to keep the concrete from ever seeing tensile stress. It's the same principle as the spoke, but in reverse. The tension of the steel biases the concrete to only see compressive stress, and giving that up carries a tensile load without cracking.

Rick "the article linked by somebodyelse explains this well with finite-elements analysis" Denney
 
Last edited:

rdenney

Major Contributor
Forum Donor
Joined
Dec 30, 2020
Messages
2,310
Likes
4,064
Sorry right back at you, because you are wrong.


I hope you misquoted Brandt, because that statement (my bold) is wrong too.

View attachment 185678

View attachment 185679

Several more-recent FEAs build on Brandt and say they don't contradict him. This one shows spoke tension changing in every spoke.

And even if only the bottom few changed, my statement would still be 100% correct. "If the tensile stress is never fully relieved, then the axle (and the rider and the bike) must be hanging from the spokes above the axle (or more technically, spokes that connect to the rim higher than where they connect to the hub)."

New-"mythbuster busting is a fool's errand, so I'm just the man for the job"-man
Not that I can read anything important on that blurry mess, but...if I am seeing what I think I'm seeing, the only place where spoke tension increases is immediately on either side of the contact patch. I don't see any significant change in tension at the top of the wheel.

But the change in tension in the spokes around the wheel is negligible compared to the change at the bottom. Furthermore, if the rim were light (weak) enough and there were enough spokes biased to a high enough tension, that change might not occur at all, because the deflection at the bottom might be sufficient to relieve any change in stress elsewhere. The rim carries loads away from the contact patch like a beam, in bending, but if it is really weak in bending, it might not transmit even that little bit of increased tension to the couple of spokes adjacent to the contact patch.

If you are up in your attic and you stand on the edge of a ceiling joist, you might lack the balance to keep from stepping off the joist and poking a hole through the ceiling. So, you might reach up and grab the rafter over your head to steady yourself. You might even grab it hard enough to pull yourself up a bit. That keeps you vertical, within your operating range. But you are still standing on your legs. That's the difference in magnitude we are talking about here.

Rick "cycling civil engineer" Denney
 

antcollinet

Master Contributor
Forum Donor
Joined
Sep 4, 2021
Messages
7,979
Likes
13,550
Location
UK/Cheshire
FFS stop talking about spokes. This thread is for pictures. I WANT MORE PICTURES.

:p

(and no pictures of spokes.... Thankyou :cool: )
 

Dvass13

Member
Joined
Feb 8, 2020
Messages
43
Likes
89
To get this thread back on track... new gravel grinder I picked up last fall.

20211015_130929.jpg
 

NTK

Major Contributor
Forum Donor
Joined
Aug 11, 2019
Messages
2,741
Likes
6,087
Location
US East
So the guy @somebodyelse referenced (in post #300) did the FEA, said "all spokes tensile" in another of his posts, and somehow missed considering the tensile preload in his analysis?

The bottom spokes in the FEA, with no preload, are in compression. That can only mean, in real life when the spokes are always in tension, their tensile loads are reduced. At the same time, the tensile load of the top spokes are increased (by relatively smaller amounts as the load is more evenly spread). I'd concluded that, because the tensile loads for the bottom spokes are reduced whilst the top spokes are increased, the top spokes are the ones doing the job of providing the support, not the bottom ones.
 
D

Deleted member 43441

Guest
Stop clownin around.
 

Attachments

  • 91B51F46-B705-4002-9BBD-663E716D1D66.jpeg
    91B51F46-B705-4002-9BBD-663E716D1D66.jpeg
    44.7 KB · Views: 93

Newman

Major Contributor
Joined
Jan 6, 2017
Messages
3,592
Likes
4,456
Another analysis sensibly starts with a section titled Semantics.
I came across that page yesterday, when I was looking for a plain-English explanation to help clarify the discussion on this page. Its conclusions are so badly wrong that I felt for him and wrote him an email that I hope he pays attention to and fixes it up. But I'm not optimistic, given the "if you think I'm wrong then read my other page here, first" attitude.

The internet is hilarious, really.

PS I am aware of the plea to return to pretty bike pictures: understood. But I contributed my pretty bike pictures yesterday #293, and just above them happened to be a post about spokes, all wrong and misleading to the few who have an interest in bike tech as well as pretty bike pictures. So humour me for another post or two while I finish off the subthread, which topic I didn't start, remember, that was Rick. If he remains stubborn and intransigent then I won't persist, I promise. ;) I'm not this guy:-

duty_calls.png
 

Newman

Major Contributor
Joined
Jan 6, 2017
Messages
3,592
Likes
4,456
Rick "the article linked by somebodyelse explains this well with finite-elements analysis" Denney

He actually got himself into an interpretative tangle. To demonstrate this, let’s look at the final loaded state as a vector force analysis in each spoke individually. A spoke in overall tension can only apply a positive vertical component to the hub when it connects to the rim above where it connects to the hub. None of the spokes “pointing down” to the rim are carrying any of the hub’s vertical load at all: they are dragging the hub towards the ground. No matter how small the real force in them is, it is dragging the hub down to the ground. The hub is carried entirely by spokes that “point up” from the hub to the rim. This is inescapable vector force analysis.

A final proof: take the case where we apply just enough download to the hub so that a few of the lowermost spokes approach zero total force. You seem to agree with the linked article that says, “I conclude that it is perfectly reasonable to say that the hub stands on the(se) lower spokes”, yet I could remove them completely and it would have no effect at all! The hub sure isn’t “standing on them”!

Rick "cycling civil engineer" Denney
New-"actual professional structural civil engineer who knows and can do FEA but doesn't need it to clearly see the first-principles errors in understanding being made here"-man
 

Peafowl

Member
Joined
Sep 24, 2021
Messages
20
Likes
22
Location
Germany
A final proof: take the case where we apply just enough download to the hub so that a few of the lowermost spokes approach zero total force. You seem to agree with the linked article that says, “I conclude that it is perfectly reasonable to say that the hub stands on the(se) lower spokes”, yet I could remove them completely and it would have no effect at all! The hub sure isn’t “standing on them”!
I can't totally agree with that. sorry ^^
I work several years as a downhill Team bike mechanik and also learned a technical job.

If you load a axel up with wight, there is no tension on the lower spokes corect as you said, but also not on the upper ones!
because the rim get and oval and the load - Force is on the spokes the both sides.
This is the point where the spokes geht pulled and snap in worst case.
 

rdenney

Major Contributor
Forum Donor
Joined
Dec 30, 2020
Messages
2,310
Likes
4,064
I came across that page yesterday, when I was looking for a plain-English explanation to help clarify the discussion on this page. Its conclusions are so badly wrong that I felt for him and wrote him an email that I hope he pays attention to and fixes it up. But I'm not optimistic, given the "if you think I'm wrong then read my other page here, first" attitude.

The internet is hilarious, really.

PS I am aware of the plea to return to pretty bike pictures: understood. But I contributed my pretty bike pictures yesterday #293, and just above them happened to be a post about spokes, all wrong and misleading to the few who have an interest in bike tech as well as pretty bike pictures. So humour me for another post or two while I finish off the subthread, which topic I didn't start, remember, that was Rick. If he remains stubborn and intransigent then I won't persist, I promise. ;) I'm not this guy:-

duty_calls.png
Oh, come on. You are absolutely that guy. You posted three times after saying that. I’m out.

Rick “be honest” Denney
 

Newman

Major Contributor
Joined
Jan 6, 2017
Messages
3,592
Likes
4,456
Once, actually. Who's not being honest now?

Wise move, clocking out. Now back to normal programming. Bike pics!

New-"you can tell a sore loser by the way he drops out"-man
 

Dvass13

Member
Joined
Feb 8, 2020
Messages
43
Likes
89
Hey look! It's another picture of a bike... with no more commentary on spokes, FEA, statics, dynamics, free body diagrams, or anything else related to the previous off-topic discussion

14587.jpeg


This was from my first ride with my new bike. Somewhere around 46 miles and 5,500 feet of climbing in Pisgah National Forest outside Asheville, NC.
 

rdenney

Major Contributor
Forum Donor
Joined
Dec 30, 2020
Messages
2,310
Likes
4,064
Once, actually. Who's not being honest now?

Wise move, clocking out. Now back to normal programming. Bike pics!

New-"you can tell a sore loser by the way he drops out"-man
Dude, it’s not about winning and losing. Making it about that ruins the fun. That’s why I dropped out.

Rick “and that’s why you’re that guy” Denney
 

storing

Active Member
Forum Donor
Joined
Aug 27, 2021
Messages
226
Likes
220
Thread needs more small bikes so here it goes; stock picture because mine is on its way still and not quite a complete bike yet. 22" wheels, should be the best of 20" and 24" worlds :)
608ec6243543ac581819d0e2_WTP_Audio_frame_and_fork_set_sideon_white.jpg

On the spokes topic (yeah yeah): I seem to recall this debate was mostly over with recent research? In other words: I find it a bit strange that on this forum particularly people just go on about it and post their own opinions/explanations/links to non-reviewed stuff instead of the real deal. Or perhaps I'm remembering wrong.
 
D

Deleted member 4708

Guest
Moots RSL and Passoni Titanio - my current stable.
 

Attachments

  • IMG_0452.JPG
    IMG_0452.JPG
    237.7 KB · Views: 64
  • IMG_0451.JPG
    IMG_0451.JPG
    377.7 KB · Views: 67
  • IMG_0450.JPG
    IMG_0450.JPG
    270 KB · Views: 58
  • IMG_0446.JPG
    IMG_0446.JPG
    511.7 KB · Views: 63
  • bike4.jpg
    bike4.jpg
    219.6 KB · Views: 69
  • bike3.jpg
    bike3.jpg
    222.3 KB · Views: 59
  • bike2.jpg
    bike2.jpg
    176 KB · Views: 69
  • bike1.jpg
    bike1.jpg
    177.3 KB · Views: 64
  • IMG_0453.JPG
    IMG_0453.JPG
    575.4 KB · Views: 60
Top Bottom