12

The restaurant I ate at had these wheels with decorative bent spokes.

bent spoke wheel

Understanding that this wheel is decorative and wouldn’t work, could any wheel with bent spokes work?

For this question, I’d like to exclude spokes that are twisted or intertwined to each other - the bend has to be unsupported as the spokes of the wheel in the photo.

  • if they were well insulated electrical conductors, with extraordinarily massively powerful and precisely controlled electric currents passing through them, they could in theory generate a set of magnetic fields that could form a kind of support. For example see those two short parallel pieces coming out from the hub, right before the elbow... imagine both pieces have a magnetic field repelling each other, it could be enough to provide compressive strength. As in, assuming some bizarre technology nobody has actually built yet. – don bright Jun 3 '19 at 0:06
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Spokes bent like that can't take any load (tension), so it would not work. However, bending multiple spokes around each other can produce a feasible wheel with non-straight spokes, like the last photo here. Note that in this particular wheel a single broken spoke will cause multiple others to lose tension, most probably rendering the wheel unrideable. enter image description here

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    Mind boggles where you would even start when truing that wheel..... – mattnz May 31 '19 at 6:33
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    Have seen a couple of this at my local shop back at 2000's. Most people used them as a fashion thing but one crazy guy used one at the front on his ride. Freeride was the haze back then and Josh Bender was a pocket sized god. Dude was dropping from 7ft tall to flat on his chinese hardtail with RST Delta Xl and that wheel was in that bike for years. This are hard to lace, even with a jig, they are hard to true but also hard to untrue by use. If one spoke goes then you need to lace it all over again. – dmb May 31 '19 at 19:43
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    @mattnz Truing should be reasonably normal, as long as spokes go to alternate sides of the hub. However replacing spokes would be more common and harder - look at the exit angles out of the nipples! – Criggie Jun 1 '19 at 7:06
  • Always liked these, and had one built for my MTB years ago but just the one twist on the 3rd cross, if one went, then you'd just lose two consecutive spokes on one side, which would result in a large wobble and rubbing brakes and the end of your ride, which could be bad on the front. The one presented here though, I wouldn't want to ride it anywhere seriously for any duration, sure it'll work, but one day... – Lamar Latrell Jun 2 '19 at 3:50
7

Obviously not with conventional bicycle spokes that are only expected to work in tension. With completely rigid compression spokes, it's possible but pointless (I expect the ones @Chris H links to ("not a recommendation") fall into that category), and a weak point with a sharp bend.

But there is at least one wheel design with curved (not sharply bent) "spokes" that are deliberately intended to flex in a controlled way to provide suspension (for wheelchairs - they did originally advertise a (hub-braked) bicycle version, but seem to have given up on that): https://www.loopwheels.com/technical/characteristics-information-loopwheel/

Picture of a air of loopwheels

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    These wheels could work on a bicycle as long as the bike had disk brakes and enough room in the frame and fork for the wheel to move freely. It would be the equivalent of putting the suspension in the wheels rather than the frame. Depending on how it's tuned and what it's used for a bike like this might be good for something. – David D May 31 '19 at 15:53
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    The problem with the design is that the suspension moves when the wheel rotates. If there is any damping, the rolling resistance will be huge and if not, the suspension will be perfectly bouncy. Both options are awful. It would also be a huge engineering challenge to have any lateral stiffness in the system. – ojs May 31 '19 at 16:11
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    This reminds me of the construction of ancient Egyptian chariot wheels where the spoke are actually two edges of adjacent triangles captured in the wheel. – JimmyJames May 31 '19 at 19:12
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    @ojs there can be no such thing as undamped bicycle suspension, because the rider is the heaviest part of the vehicle and perfectly capable of damping oscillations. The question is whether this burden is less annoying than just playing shock for a rigid bike... For long-travel suspension, the bounce-back of underdamped suspension certainly is annoying, but for short/stiff systems like the Lauf forks this seems to be perfectly ok. – leftaroundabout Jun 1 '19 at 21:45
  • @leftaroundabout I'll believe it is perfectly ok when those forks become common. Now it looks like yet another novelty product. Meanwhile, you can get undamped pogo stick suspension from any BSO but not in serious bikes. – ojs Jun 2 '19 at 6:45
4

The wheel hub will severely displace away from centre as soon as a load is placed on it. The wheel will then come into contact with the bicycle frame, and that point of contact will support most of the load. The wheel rim will likely deform from the load.

If we imagine that the frame is not there (we just have a pure load acting on the wheel hub, with the rim resting on the ground) what happens is that the spokes above the rim will stretch greatly, almost to the point of being straight, and the ones below will compress. The load will essentially be hanging on the upper spokes, supported by nothing but the un-tensioned rim, which will deform.

  • Did you mean "above the hub will stretch greatly" rather than "above the rim will stretch greatly"? – msouth May 31 '19 at 20:39
  • @msouth The rim is the outside of the wheel; the hub is the center bearing where the spokes meet. – Kaz May 31 '19 at 21:41
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    Yes, if you put weight on the hub, the spokes above the hub will stretch. Gravity pulls downward, and when the bike is attached to the wheel it's the spokes above the hub which are being pulled on, right? There are no spokes "above the rim", they are all inside the rim. Above the rim is where the handlebars would be. – msouth Jun 2 '19 at 0:05
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Bends as shown are stress concentrators, so even beefed up massively (enough to take the the riding load at first) they'd soon fail.

Curved "spokes" exist on cast wheels (not a recommendation, and they exist in plastic as well) but I wouldn't say they fit the normal definition of spokes.

You could fake something, at least in the right light, by building an 18 spoke pattern on a 36 hole rim and hub using matte black spokes, and then fit shiny spokes using the remaining holes and shape them creatively. This is perhaps more useful for trolling than a real solution.

  • Note how spokes commonly have a nasty 90° bend right where they are threaded through the hub. And that's where they almost always fail. – Kaz May 31 '19 at 12:58
  • @Kaz yes, even with the bend supported by the hub – Chris H May 31 '19 at 13:05
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    This largely misunderstands the issue; the problem with the idea isn't that the bends weaken the spokes leading to failure, but rather that it requires spokes that can function in compression and not in tension, which a bent piece of wire simply cannot do. It is common to analyze a bicycle wheel as if the lower spokes were in compression, but that's only valid as long as the effective compression is less than the preload tension. If you had a loose spoke in your hands and tried to compress it, it would bow very easily and not support any useful load. – Chris Stratton May 31 '19 at 16:45
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    There's actually not a lot of difference between a wire spoke and a piece of kevlar cable; in fact, such is sold as a field replacement for a broken spoke! – Chris Stratton May 31 '19 at 16:47
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    "beefed up massively" just reads like heavy gauge wire spokes - the whole idea of them being in tension while bent is still nonsense. Only later when you talk about cast spokes (which you argue aren't even spokes) do you start to have a point, but that's after an opening paragraph irrelevant to the unworkable wheel depicted. And cast spokes don't have preload, so they'll be in both tension and compression at different times, increasing their fatigue situation. – Chris Stratton May 31 '19 at 18:13

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