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Spokes in a wheel are (shall) be loaded always in tension. Seems like a simple rope of steel strings would do.

Furthermore, uneven spoke tension can lead to lots of problems (among which loose spokes, broken spokes, cracked rim holes). A single strand of thread, passing through all spoke holes in a star-like fashion would eliminate uneven tension.

And even if such a wheel isn't technically superior to current designs, it would be interesting. People throw thousands at purchasing 3-spoke wheels, grouped spoke wheels and whatnot.

  • 1
    Check out Tioga Tension Disk wheels. They were manufactured in the end of 1990s but they used to break so quickly that te idea soon died. – Slovakov Feb 12 '15 at 10:55
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    I gather you mean a steel cable, "laced" back and forth between hub and rim. A big problem with such a scheme is that it would be impossible to properly adjust, to "true" the wheel. (You are mistaken that the cable would automatically "equalize" tension. Friction at the anchor points would prevent the cable from moving in a way that would equalize -- though it would still retain the unfortunate characteristic of moving unexpectedly on bumps.) – Daniel R Hicks Feb 12 '15 at 12:28
  • @DanielRHicks is correct. Assuming you could perfectly manufacture rims with no defects and overcome the friction issue at the bends, you'd still be left with a wheel that would go out of true the first time any damage/irregularity occurred with the rim, and you wouldn't be able to adjust it. – Deleted User Feb 12 '15 at 17:23
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    Once upon a time you could get steel cable emergency spokes. The problem with a cable is that they are wound and under tension they will unwind. To avoid that you'd need straight cables like climbers' ropes where the filaments are parallel and held together by a kind of spun tube. Plain spokes will then be lighter. – Carel Feb 12 '15 at 18:20
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    You can get replacement spokes made with a high tech fiber similar to kevlar. peterwhitecycles.com/fiberfix.asp – Fred the Magic Wonder Dog Feb 14 '15 at 4:37
11

Mavic has made some wheels like you describe, more or less. They're called "R-Sys" and they have aramid (Kevlar) spokes surrounded by carbon fiber sheaths. Here's an exploded view:

Mavic R-Sys exploded view

For more details about that, see the page the image is from: http://www.pardo.net/bike/pic/fail-001/FAIL-105.html

More seriously, yes, you could make wheels with "rope" spokes only. Why do the Mavic ones have the carbon sheaths then? I would speculate that the carbon acts as armor for the aramid fibers, which must never be nicked or they will fail. The carbon also stabilizes the whole arrangement, reducing lateral flex.

As for your notion that spoke tension would always be even if continuous fibers were used, I'm not so sure. The problem is that to achieve self-evening tension you would need to allow the fibers to run freely through some turning points. And if they run freely they will abrade rather quickly if they actually move at all. So you're at an impasse: either the fibers move and wear out prematurely (and perhaps lead to collapse of the wheel even sooner because of unstable geometry), or the fibers in fact do not move and you have the same tensioning concerns as with conventional wheels.

Finally, consider that spokes are thin and behave not like rods or struts so much as wire. So in a way we are already riding your wheels of the future today.

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    Haha, "exploded" view! 1. A possible solution to the catastrophic failure shall the string break is have 2 continuous strings - now there are be different tensions, but the single point of failure is eliminated. 2. Concerning movement of the strings: not sure if this can be engineered, but what if friction is enough to allow the string to move only when being tightened (adjusted) and not during normal riding (excluding hard jumps - there the movement of the string could add to the strength of the wheel). – Vorac Feb 12 '15 at 11:17
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Getting the tension equal on all of the spokes made from a single length of a flexible string would be very difficult due to friction. And because no rim is perfect, spokes have to be adjusted to moderately different tensions to bring a wheel into true. Threaded spoke nipples work amazingly well on single-strand steel spokes. A spoke material or construction which cannot be threaded requires fittings on one end which can, or unusual and complicated construction as with the helicopter spool in a photo in another comment -- also can't be re-trued like a wheel with threaded spokes.

  • Gidday and welcome to SE Bicycles. Great first answer - I look forward to your future contributions. – Criggie Mar 11 '16 at 21:05
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A single cable as you suggest would mean bad things happening for a single failure. Although lightweight bikes will always push the spoke count as low as possible they can still handle a broken spoke without automatically crashing. You also don't have enough degrees of freedom to dish a rear wheel even if you assume the wheel is self truing.

If instead you consider replacing each spoke of a conventional setup with a cable you add the weight and part count of the fasteners (offsetting any saving in the spokes themselves). You still need the same tensile strength and there's no need for them to be flexible so a single thick strand is no worse than a cable of thinner strands so you're back to the same weight assuming steel. Plus fasteners. You might shave a little weight off in total using something like spectra rope but you would have to ensure no risk of fraying at the fixing points. To overcome all this optimally you'd need to redesign the hub and rim. That's expensive and reduces your market.

There are always titanium spokes for those worried about weight. These would retrofit easily on a standard wheel.

It would be nice to see an old set of wheels rebuilt with cable for demonstration purposes -- you wouldn't want to go fast but you could probably ride on strong fishing line with one piece for each side of the wheel.

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You could argue that some carbon fibre disk wheels meet that description...

Disk wheel under construction

Compare this, the drive spool for a human powered helicopter with Kevlar "spokes":

Drive spool

0

Spinergy has something like that - though not with a single rope.

http://www.spinergy.com/catalog/product_info.php?cPath=20&products_id=84

Actually it's not extra light.

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