I was involved in a discussion recently related to tension loads on wire wheel spokes. I thought that spokes carried tension loads exclusively, and that stranded steel wire could work, but someone mentioned that it’s been tried already and they found that it didn’t work well at low speeds.
Is the stiffness of a solid-wire spoke necessary for practical use in wire wheels? Can someone provide a link relating to the use of stranded wire as spokes?
Not sure if it is what you are looking for but a company called Spinergy makes bicycle and wheelchair wheels that use flexible PBO fibers as spokes.
Are you talking about bicycle or automobile wheels?
On a bicycle wheel, the spokes are not rigidly attached to the hub. The bent end of the spoke is hooked on the hole in the hub flange. The only force it can withstand is tension.
In any case, bicycle spokes are thick steel wires. There’s no real difference between a rod and a wire except the thickness.
There may be some benefits to the slight stiffness of bicycle spokes – certainly having stiff spokes (as opposed to floppy cables) makes it far easier to build a wheel. There may be some other dynamic benefits, too that make stiffness more suitable.
But maybe not. I imagine it’s cheaper to make a solid wire spoke than a flexible cable, so pure economics (and ease of assembly) may be the reason for solid spokes.
Remember bicycle spokes are only sort of stiff. Get a hold of one and push the ends together. It doesn’ take much pressure at all to bend it. When you’re talking about the kind of forces that bicycle wheels deal with, spokes are much more like cables than beams or struts.
Spokes handle tension loads, not compression loads. Bicycle wheel spokes have a ferrule at one end that nestles into a hole in the rim, preventing the spoke from pulling out of the rim and allowing tension to be applied. The ferrule is free to drop out the other direction into the rim cavity. And seating of the other end into the hub is likewise designed only to resist a pull, not a push.
Stranded wire brings unnecessary complexity to the problem, while offering less material to do the job for a given outer diameter, due to air spaces between the strands. Where a large degree of flexibility is needed, stranded wire is called for. Where the piece in question will remain essentially straight, solid wire is preferred.
Something like this?
There used to be a bicycle wheel where all the spokes had been replaced with a single kevlar(?) thread, but that was a long time ago and I can’t find a reference yet.
Stranded wire would also be just insanely hard to assemble - you can thread a solid spoke, or bend a hook at the end for attaching it to the hub, but stranded wire would need some sort of nipple or ferrule crimped on the ends so it can be attached to the hub and rim. The crimp would be a prime failure point - a bad crimp may pull apart entirely.
Also, stranded wire has a good bit more stretch than a solid wire - the “lay” of the stranding, and the air space, between individual wires, and the end-crimps “settling in” will make things slightly unpredictable WRT how much the wire will stretch before it’s tight, and you’ll need more adjustment range to handle this. Pre-stretching the spokes before assembly would help somewhat, much like some fabrics are pre-shrunk before being cut and sewn into clothes.
All that aside, I can’t see why stranded wire wouldn’t work. It’d just be a major pain to set up and get all the spokes tensioned properly.
-
-
- I remember the mountain bike wheel that used kevlar cord too (or some kind of cord). You could only get the rear wheel–not a front one. It was called something like “Powerdrive” or [something]-drive. It was pretty expensive and wasn’t popular, it was sold as an alternative to rear-wheel suspension just as rear-wheel suspension began to show up on high-end mtb’s, which (I doubt) it was.
-
- There is also a company somewhere that sold stranded-wire “emergency” replacement spokes for mountain bikes. I guess they’d work for a regular road bike also, but they were sold in mtb magazines. The reason was that you could coil it up and fit it into a small under-seat pack or a pocket.
~
After doing some searching (asking the guys in the bike shop), the rear wheel was made by Tioga in '91 or '92. Apparently, it was worse than useless.
The emergency spoke can be found by clicking on the link in my first post.