Why are spokes laced so that they rub?
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  1. #1
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    Question Why are spokes laced so that they rub?

    I know the advantage to the 3-cross pattern of lacing spokes, but why weave them so that they rub? Have any of you built a 3-cross wheel without weaving them?

    A lot of Mavic wheels cross spokes, but they don't actually touch, like on the Ksyrium series.

    Any ideas?
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  2. #2

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    WOW! You just got me thinking hard. Then I went to my books.

    At first blush, the answer is easy: As you know, back in the day, they had to figure out how to pre-tension the spokes. Thus, we have the cross pattern we know. So far so good. But why interlace them? Because when rims were made of wood and hubs were less reliable (and spokes, too), they couldn't tension the spokes as much as we can today. In order to counteract this physical limitation, the TIED AND SOLDERED the spokes at the crosses. This was done inorder to effectively extend the hub flange, thereby making it a stiffer wheel. In order to tie and solder spokes, they must touch.

    Now, this is where my own theory comes into play.
    Theory 1: By interlacing the spokes, all the spokes on one side basically come from the hub flange at the same angle (there being a very slight difference because of the diameter of the spokes (actually 1/2 the diameter of the spokes )). If, on the other hand, the spokes came directly from the hub without being interlaced, the ones coming from the inside of the flange would arrive at the rim at a steeper angle than those coming from the outside of the flange. This would do two things: Increase the tension on the inner spokes, and also make them shorter. These two things would then BOTH contribute to making the truing process more difficult since on a rear wheel you would have 4 different tension needs AND necessitate stiffer rims to keep them from wobbling more. That's not to mention the possible need for two different spoke lenghts on the front wheel and 4 on the rear.
    Theory 2: Because good wheelbuilders tend to tension spokes very high, the friction caused where the spokes interlace may have a force similar (although not quite as strong) as that which binds tied and soldered spokes together.

    Now: I am willing to lay odds that
    1: a good wheel could be built without interlacing the spokes GIVEN a good stiff rim and quality double butted spokes (which have some elasticity, thereby protecting their j bend).
    2: a rim with 4 different hole placements (laterally) could be engineered that would provide EXACT angles from the hub flanges for all 4 different spoke configurations (on a front wheel)
    3: given a reasonable rider under normal conditions, a wheel thus configured would work quite well...

    BUT: I personally like to think of my wheels as cohesive, strong, stiff units which flex rather than break. Spokes that don't interlace just feel less cohesive to me.

    I'm curious to know what others think, too.

  3. #3
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    Quote Originally Posted by melamst
    If, on the other hand, the spokes came directly from the hub without being interlaced, the ones coming from the inside of the flange would arrive at the rim at a steeper angle than those coming from the outside of the flange. This would do two things: Increase the tension on the inner spokes, and also make them shorter. These two things would then BOTH contribute to making the truing process more difficult since on a rear wheel you would have 4 different tension needs AND necessitate stiffer rims to keep them from wobbling more. That's not to mention the possible need for two different spoke lenghts on the front wheel and 4 on the rear.
    None of this happens in practice.
    I 've built some front wheels without interlacing the spokes. There was no difference in tension and using the same spoke lenght was just fine.
    The difference of lateral angles is too small to cause noticable different spoke lenghts or tensions.

    Without interlacing the outward spokes on the rear wheel could touch the rear derailleur when riding the biggest sprocket.

    The real thing with interlaced spokes is the then possible interaction between the spokes.
    Two interlaced spokes push against eachother at the last crossing point. So when one of these two spokes looses tension for some reason (f.e. by hitting a pothole) the other spoke takes care of that by pushing against the first spoke preventing it from becoming totally slack.
    That's important especially for flat rims.

  4. #4
    Larry Lackapants
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    Thumbs up

    I tend to agree that 2 spokes touching interact with each other. Let's say we have a lateral hit on the rim in the place where a spoke leaves the rim. The hit tends to stretch out the spoke.

    1) If that spoke doesn't touch any other, it will stretch and then the whole load is transmitted to the spoke J head, one point of the hub flange, and one rim drilling.

    2) If the involved spoke crosses another spoke, then part of the load is distributed on that spoke too. This means that in this case, the load is distributed to 2 rim drillings, and 2 poins on the hub flange. Also the load on each particular spoke is smaller that the load on one spoke in the first case.

    It's obvious that in the first case, each impacted item is more solicited than each of the impacted items in the second case. Therefore, in case of a strong hit, material failure is more probable.
    I think the most important thing is that in case of spokes touching, all the load is spread on a wider "surface" meaning that the peaks and lows of load on each item are smaller

    br
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  5. #5

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    On some wheels, the spokes don't touch, even in a "cross" pattern. Mavic Ksyriums and Cosmics are common examples.

  6. #6
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    But those aren't traditionally laced wheels in any way. The design doesn't call nor require lacing of spokes as they cross.

  7. #7
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    Spokes are laced to keep the wheel straight (true, from moving sideways). Each spoke that touches another provides lateral support for the wheel. If the spoke was straight, then only the downward tension would be keeping the wheel straight. By lacing the spokes, then there is also sideward support because each spoke is supporting the other that's touching.

  8. #8
    gnauss
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    I think the original question is a good one. I had a pair of custom built wheels that experienced some trauma and needed two spokes to be retightened. Because of this they now rub when I'm climbing in the saddle at low speeds when the spokes are at their load point. The noise drives me crazy.

    Anyone know a good fix for this?

    BTW, I'm planning on having the wheels totally rebuild with a new rim so hopefully that will eliminate the problem.

  9. #9

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    Quote Originally Posted by Spunout
    But those aren't traditionally laced wheels in any way. The design doesn't call nor require lacing of spokes as they cross.
    Good call -- didn't read the original post carefully.

  10. #10
    Larry Lackapants
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    If the low tensioned spokes are on the non-drive side, then turn the rim around (so that the old drive side becomes now the non-drive side). This because the non drive side spokes are already low tensioned, compared to the drive side spokes. That should even out the spoke tension, but i don't know if the noise will disappear. This is what I would try anyway..
    Replacing the rim should solve the problem..

    Good luck
    br
    "There are only 3 motivating factors that change human behavior; pain, fear or ambition. Which button do you want to press?" Steve Hogg

  11. #11
    NeoRetroGrouch
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    Quote Originally Posted by gnauss
    I think the original question is a good one. I had a pair of custom built wheels that experienced some trauma and needed two spokes to be retightened. Because of this they now rub when I'm climbing in the saddle at low speeds when the spokes are at their load point. The noise drives me crazy.

    Anyone know a good fix for this?

    BTW, I'm planning on having the wheels totally rebuild with a new rim so hopefully that will eliminate the problem.
    A drop of oil should cure it. - TF
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    Me, off the back, at my first 50+ road race.

  12. #12

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    I definitely take back my idea about different spoke lengths & tensions.

    There is yet one more piece of the puzzle. The spokes that interlace are all on the same side, AND each pair contains one 'pulling' and one 'following' spoke. This helps to further stiffen the rear wheel because the pulling spokes are supported by the following ones. In pedaling forward, the pulling spokes increase their tension while the following spokes de-tension, but this happens only 1/2 as much as if they were not crossed.


    A drop of oil should cure it. - TF
    That'll cure the squeak, but not the problem. I agree, new rim. Also, make sure to use new nipples!

    And just to make sure the problem disappears, you could use my favorite, and the ever controversial 'tied and soldered' approach.

  13. #13

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    Spoke crossings give no lateral support

    Quote Originally Posted by brblue
    I tend to agree that 2 spokes touching interact with each other. Let's say we have a lateral hit on the rim in the place where a spoke leaves the rim. The hit tends to stretch out the spoke.

    1) If that spoke doesn't touch any other, it will stretch and then the whole load is transmitted to the spoke J head, one point of the hub flange, and one rim drilling.

    2) If the involved spoke crosses another spoke, then part of the load is distributed on that spoke too. This means that in this case, the load is distributed to 2 rim drillings, and 2 poins on the hub flange. Also the load on each particular spoke is smaller that the load on one spoke in the first case.
    Except that spokes can only support loads along their axis - they bend easily to loads perpendicular to their axis. In the case of a lateral load, very, very little of the load can be transmitted to a crossing spoke. This is an insignificant affect.

    Quote Originally Posted by brblue
    It's obvious that in the first case, each impacted item is more solicited than each of the impacted items in the second case. Therefore, in case of a strong hit, material failure is more probable.
    What kind of material failure are imagining here? Spoke tensions never approach their yield or ultimate strength in use. The only way to break a spoke is either through fatigue (which requires many, many load cycles) or to by directly cutting shearing a spokes (as when something goes directly into the spokes, such as a skewer or a pedal in a crash situation).

  14. #14

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    Ksyrium interlacing

    Quote Originally Posted by Spunout
    But those aren't traditionally laced wheels in any way. The design doesn't call nor require lacing of spokes as they cross.
    Of course they're laced in the traditional way. Although Ksyrium spokes use straight heads instead of bent heads, the "pulling" spokes and "pushing" spokes are still laced at different offsets from the hub center, which is equivalent to lacing elbow spokes from different sides of the flange. There is no reason that Ksyrium spokes couldn't be interlaced if they so chose.

  15. #15
    Larry Lackapants
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    Hello Mark McM,

    When doing this discussion I immagine the rim with no lateral stiffness at all, so a hit will be transferred totally to one spoke which is closest and is longitudinally tensioned by the lateral movement of the rim.
    This should come close to the behaviour of old very lightweight rims, or single wall rims, which have less lateral stiffness than modern rims.

    Quote Originally Posted by Mark McM
    Except that spokes can only support loads along their axis - they bend easily to loads perpendicular to their axis. In the case of a lateral load, very, very little of the load can be transmitted to a crossing spoke. This is an insignificant affect.
    Actually, I think lateral movement of the rim is translated to longitudinal force applied to a spoke. I'm saying this because trying to move the rim edit: "on a paralel direction" (parallel) to the axis of the hub, towards the middle of the hub and away from a given flange, will cause the spokes connected to that flange to pull the rim closer to the hub. This is when the spoke is longitudinally solicited, together with the hub flange and the rim drilling.
    Viewed from the "front" of the wheel(perpendicular to the hub axis), a spoke can only perform a circular movement around the spot it is fastened (hub flange)

    I think that lateral movement of the rim, in our specific case, causes the most of the metal fatigue of the spokes, hub flanges and rim drillings.

    Quote Originally Posted by Mark McM
    What kind of material failure are imagining here? Spoke tensions never approach their yield or ultimate strength in use. The only way to break a spoke is either through fatigue (which requires many, many load cycles) or to by directly cutting shearing a spokes (as when something goes directly into the spokes, such as a skewer or a pedal in a crash situation).
    I am immagining metal fatigue. If the max and min force applied to the spoke+hub flange +rim drilling are both closer to a given value(average force calculated over a period of time), then the metal fatigue is reduced (the variations of the force, applied to the components over a given period of time, are smaller).


    In fact, in case of the modern rims, since they are laterally stiff, a lateral blow will cause the whole rim(or at least a great part of it) to move, not just the part around the place of the impact.
    In case of a laterally stiff rim, a greater number of spokes is "holding the rim back", so the force affecting just one spoke is already quite small.
    Therefore, radial spoking can be used, spokes don't have to touch each other any more etc.

    Hope I have answered your questions,
    br
    "There are only 3 motivating factors that change human behavior; pain, fear or ambition. Which button do you want to press?" Steve Hogg

  16. #16

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    lateral loading, lacing and fatigue

    Quote Originally Posted by brblue
    Actually, I think lateral movement of the rim is translated to longitudinal force applied to a spoke. I'm saying this because trying to move the rim edit: "on a paralel direction" (parallel) to the axis of the hub, towards the middle of the hub and away from a given flange, will cause the spokes connected to that flange to pull the rim closer to the hub. This is when the spoke is longitudinally solicited, together with the hub flange and the rim drilling.
    The problem with the theory that interlaced spokes add lateral support to the rim is that there is absolutely no evidence to back it up. In comparisons in lateral stiffness, it has been found that radially laced wheels are stiffer than interlaced wheels. Obviously, radial lacing can not transfer the load from spoke to spoke. The difference in stiffness with radial lacing is minor - only a few percent - and can mostly be accounted for radial lacing using shorter (and therefore stiffer) spokes.

    Quote Originally Posted by brblue
    I think that lateral movement of the rim, in our specific case, causes the most of the metal fatigue of the spokes, hub flanges and rim drillings..
    Why do you believe that? Larger lateral loads occure relatively infrequently, whereas the spokes experience a load cycle from radial loads for each revolution of the wheel. A 700c wheel experiences 800 radial load cycles per mile, so it only takes 1,250 miles to generate a million radial load cycles.

  17. #17
    Larry Lackapants
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    Talking

    Quote Originally Posted by Mark McM
    The problem with the theory that interlaced spokes add lateral support to the rim is that there is absolutely no evidence to back it up. In comparisons in lateral stiffness, it has been found that radially laced wheels are stiffer than interlaced wheels. Obviously, radial lacing can not transfer the load from spoke to spoke. The difference in stiffness with radial lacing is minor - only a few percent - and can mostly be accounted for radial lacing using shorter (and therefore stiffer) spokes.
    I said in the beginning, that the model I described applied to rims with very low lateral stiffness. Therefore I'm quite convinced that wheels with single wall rims are stiffer when interlaced. Therefore, the first wheels were interlaced ; in my opinion anyway. Nowadays, since rims are very stiff lateral stress is already distributed on a larger number of spokes, so lacing to share the load between two intersecting spokes would have little sense. Probably the advantage of lacing is compensated by the longer and therefore longitudinally more elastic spokes.

    Quote Originally Posted by Mark McM
    Why do you believe that? Larger lateral loads occure relatively infrequently, whereas the spokes experience a load cycle from radial loads for each revolution of the wheel. A 700c wheel experiences 800 radial load cycles per mile, so it only takes 1,250 miles to generate a million radial load cycles.
    In case of a single walled rim, since the rim isn't vertically stiff either, vertical load is not distributed by the rim to the spokes very well, so vertical hits will deffinately be supported more by the rim and less by the spokes, compared to lateral hits that go directly to the spokes. Therefore, you'll see a lot of single walled, and double walled box section rims having "hops" generated vertical hits (aka "potholes"), the spokes still intact after such a hit.

    I think that this answer would support best, in kind of a historical way, the laced wheels.
    If there is anyone out there to give us facts to support either theory, please don't hesitate
    In the meanwhile, I'm still convinced it's best to lace spokes it you're building up a lightweight box section or shallow and lightweight V rim.
    And regarding the rest of them, I think it makes no difference, if the hub is strong enough to support radial lacing (and most of the hubs usually are)

    Have fun riding,
    br
    "There are only 3 motivating factors that change human behavior; pain, fear or ambition. Which button do you want to press?" Steve Hogg

  18. #18

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    History - radial spokes came first

    Quote Originally Posted by brblue
    I said in the beginning, that the model I described applied to rims with very low lateral stiffness. Therefore I'm quite convinced that wheels with single wall rims are stiffer when interlaced. Therefore, the first wheels were interlaced ;
    Actually, if you go back into the history of the bicycle, you'll find that the first first wire spoke wheels (which did not have stiff rims) in fact were not interlaced. They were all laced radially. Crossed spoking came later. Here's a picture of the Starley and Hillman Arial, from about 1870, which featured some of the first wire tension spoke wheels:



    (You'll notice that this wheel also has paired spokes - all these "new-fangled paired spokes wheels" like Rolf, Bontrager, etc. are really a step backward, not forward).


    Quote Originally Posted by brblue
    In case of a single walled rim, since the rim isn't vertically stiff either, vertical load is not distributed by the rim to the spokes very well, so vertical hits will deffinately be supported more by the rim and less by the spokes, compared to lateral hits that go directly to the spokes.
    Actually, just the opposite is true. Although vertical loads are not supported by a flexible rim as well, the affect is to concentrate the load on just a few spokes near the load point. In other words, a flexible rim means higher spoke loads, not lower. In the case of lateral loads, the steep angle of the spokes means that they provide a lower lateral stiffness, so the stiffness of the rim becomes more dominant, and lateral loads are distributed to more spokes than for vertical loads. This is basic elastic theory for structural members of varying elasticities. (By the way, I'm not making this up. Just do a we search for FEA or stress/strain analyses of spoked bicycle wheels.)

    Quote Originally Posted by brblue
    Therefore, you'll see a lot of single walled, and double walled box section rims having "hops" generated vertical hits (aka "potholes"), the spokes still intact after such a hit.
    As mentioned before, potholes do not break spokes. The main affect of a pothole is to decrease tension on the spokes nearest the hit (with virtually no changes in tension anywhere else), so there is no reason for the spokes not to be intact.

  19. #19

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    Quote Originally Posted by Mark McM
    (By the way, I'm not making this up. Just do a we search for FEA or stress/strain analyses of spoked bicycle wheels.)
    YOU are so full of CRAP, Mr McM. It's a "wee" search, not a "we" search. Jeez!!

    I'm amazed at how crackpot science has taken hold in modern society. If someone needs proof that American students aren't getting the science and math they need in school, all that someone needs to do is read a cycling BBS to get all the whacko stuff: bikes that don't bounce as high because their tires are filled with nitrogen instead of air; carbon fiber that explodes under the pressure of someone's penetrating gaze; inner tubes that increase someone's averae speed by 3 mph.......

    When exactly did critical thought and deductive reasoning die?

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