My model of spoke breakage.

zerodish

10 mW
Joined
Nov 9, 2012
Messages
32
The following numbers are from a theoretical wheel with 36 14 gauge spokes. They are number of miles you can expect for the first 6 broken spokes. 10000 11930 13391 14637 15771 16812 Now you can multiply or divide this set of numbers by any other number and get a realistic wheel. If your first spoke broke at 1000 miles simply divide all of them by 10. Also you can change the scale to kilometers or wheel rotations. Pulstar advertised their spokes were 22 percent stronger and lasted 5 times as long. This agrees with fatigue curves for steel with cycles greater than 1000000 that can be found in mechanical engineering books. DT advertised their spokes were 20 percent stronger than regular spokes. So if you switch to top quality spokes such as DT Wheelsmith Sapim or Piller you can expect your spokes to last 5 times as long. If you go to a 13 gauge spoke you can expect your spokes to last 11 times as long. I always get accused of dumping too much information on people at once so tomorrow I will tell you where the numbers come from.
 
Your model doesn't account for enough variables. I have had wheels that accumulated more than 20k miles without spoke breakage. I have had others that began breaking spokes within a couple thousand miles, despite being carefully built from top quality components.

A properly stress-relieved wheel does not operate anywhere close to the yield stress of any part of its spokes.

Poor insertion angle to the rim, steel hub flanges, excessively deep spoke elbows, and exposure to certain kinds of chemicals can all cause spokes to break early, even in painstakingly built wheels.

In the real world, thicker spokes break more often than thinner ones in heavy duty applications. I attribute this to fretting at the elbows due to more frequent slackening in use, but that's conjecture on my part.
 
Chalo said:
Your model doesn't account for enough variables. I have had wheels that accumulated more than 20k miles without spoke breakage. I have had others that began breaking spokes within a couple thousand miles, despite being carefully built from top quality components.

A properly stress-relieved wheel does not operate anywhere close to the yield stress of any part of its spokes.

Poor insertion angle to the rim, steel hub flanges, excessively deep spoke elbows, and exposure to certain kinds of chemicals can all cause spokes to break early, even in painstakingly built wheels.

In the real world, thicker spokes break more often than thinner ones in heavy duty applications. I attribute this to fretting at the elbows due to more frequent slackening in use, but that's conjecture on my part.
Interested in the model zerodish
Fatigue causes failures way below yield as you know from aerospace Chalo, micro fractures from chemical and strain are known causes of fatigue failures
Also interested in why a thicker and so stronger spoke would be more likely to break Chalo
Currently in a "discussion" with the chap who built the wheel but also considering whether 10 Ga are best https://endless-sphere.com/forums/viewtopic.php?f=6&t=110840&start=25#p1649035

I don't understand why, if the rim and hub are matched, a thicker spoke is not stronger and more long lasting. Sure, you need to stretch it the same amound and to do so you need stronger hub and rim but it seems to me that the strenght should scale.

Motorbike wheels work with thicker spokes

My working hypothesis was that people don't tend to have ebikes or thicker spokes so it is poor design & poor quality parts but interested to hear other ideas.

Also my wheel builder is an idiot but don't want to hijack the thread
Solidworks taking the piss:
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BobBob said:
Also interested in why a thicker and so stronger spoke would be more likely to break Chalo

I don't understand why, if the rim and hub are matched, a thicker spoke is not stronger and more long lasting. Sure, you need to stretch it the same amound and to do so you need stronger hub and rim

I think you answered your own question.

My hypothesis is that movement and fretting at the spoke elbows (because thick spokes go slack at lower loads) is the root cause of increased failure rates in thick spokes-- but as I said before, that's my guess. What isn't a guess, but what I've observed firsthand, is that thick spokes in carefully built bicycle and tricycle wheels break more often than thin ones when used in heavily loaded applications.

Thick spokes also loosen far more often and crack rims far more often.

My longest lasting wheels that are still in service (on a pedal bike) use 15-16ga butted spokes. They'll turn 20 years old this year, and they've been on my daily bike for a lot of that time. I think I've trued those wheels once, not because I had to but because I could see that they weren't perfectly true.

My e-bikes use a mix of 13-14, 14-15, and 14-17ga spokes. No breakages yet.
 
Here is an interesting spoke idea.
https://www.youtube.com/watch?v=q_oMh3ehRUE&ab_channel=WorldwideCyclery

I have found in the past, that the quality of the rim seems to play an important part in spoke longevity.
My present set up is 19" motorcycle wheel with QS273 motor with cross pattern 10g stainless steel spokes and front wheel 24" double wall alloy rim with 14g Sapim spokes.
To date no problems at all.

On a previous bike I had a cheap 26" wheel with a 1500w motor and broke spokes almost every 3 days. A PITA to keep changing with a hub motor.
Eventually, I picked up a 2nd hand Mavic rim and fitted that. Same motor, same make of spokes (I was buying bags of 144 spokes) and never had a spoke breakage problem again. So, in my mind, the quality of the wheel rim plays an important part.
Not scientific, just seat of the pants riding.
 
The equation is LOG(stress)=-.3xLOG(cycles)+4.12+.072xZ The Z is the normal distribution. If you only have 1 spoke you put it in the middle of the normal distribution which divides it into 2 parts. So if you have 36 spokes you divide the normal distribution into 37 parts. Take 1/37 and put it into a reverse normal distribution calculator and you get a Z score of 1.926. This is your strongest spoke. Since the normal distribution is symmetrical -1.926 Z score is your weakest spoke. Solve for any stress and you will find your strongest spoke lasts about 8.5 times as long as your weakest spoke. In other words it is between 1.2 and 1.32 times as strong. So that checks. The equation comes from HP Gavin I expect some one can find a link. If you are having problems with a wheel this will tell you how to make a stronger one that meets your needs. I think the model is correct that is spokes break according to a normal distribution after a transform. The HP Gavin paper used higher tension in the spokes that is possible with a practical wheel so we will have to adjust the equation a bit. We have 3 constants we can change. Some one will have to keep precise records of their spoke breakage we can then use curve fitting to adjust those constants.
 
Thing is, thin spokes don't experience the same depth of stress cycles as thick ones. Under the same load, a 12ga spoke can be cycling between (say) 1200 N and zero every time the wheel goes around, where a 14-15ga spoke fluctuates between the same 1200N and maybe 800N. The number of stress cycles is the same, but both the specific stress and the depth of those stress cycles is different.
 
Chalo said:
Thing is, thin spokes don't experience the same depth of stress cycles as thick ones. Under the same load, a 12ga spoke can be cycling between (say) 1200 N and zero every time the wheel goes around, where a 14-15ga spoke fluctuates between the same 1200N and maybe 800N. The number of stress cycles is the same, but both the specific stress and the depth of those stress cycles is different.
I think you mean that with a thicker spoke on an otherwise identical wheel, the load at the bottom of rhe wheel will cause a similar amount of deflection, but as the spoke is thicker, it has been stretched less for the same load and so each spoke, as it reaches the bottom of the wheel, is more fully unloaded.

The immediate answer would seem to be to increase the tension on the thicker spoke so that it is stretched by the same distance/strain as the thinner spoke.
The load will then not deflect the wheel more due to the greater stiffness but less due to it being a smaller proportion of the static tension?

So long as the rim can take it, thicker spokes should then last longer? BTW thanks
 
Chalo said:
BobBob said:
I don't understand why, if the rim and hub are matched, a thicker spoke is not stronger and more long lasting. Sure, you need to stretch it the same amound and to do so you need stronger hub and rim
I think you answered your own question.
Great, hope i'm right, i'll stick with 10 Ga, tightened sufficiently. hope the steel isn't 304ss
I have a 42mm wide double walled rim which seems robust
Chalo said:
My hypothesis is that movement and fretting at the spoke elbows ~ is the root cause of increased failure rates in thick spokes.
Is there a significant thickness reduction from wear in the failed ones when compared to good?
Chalo said:
~ thick spokes in carefully built bicycle and tricycle wheels break more often than thin ones when used in heavily loaded applications.
With stated good build, the null hypothesis is poor design - weak rims
Chalo said:
Thick spokes also loosen far more often and crack rims far more often.
Null hypothesis inssuficient tightening and weak rims
 
zerodish said:
The equation is LOG(stress)=-.3xLOG(cycles)+4.12+.072xZ The Z is the normal distribution. If you only have 1 spoke you put it in the middle of the normal distribution which divides it into 2 parts. So if you have 36 spokes you divide the normal distribution into 37 parts. Take 1/37 and put it into a reverse normal distribution calculator and you get a Z score of 1.926. This is your strongest spoke. Since the normal distribution is symmetrical -1.926 Z score is your weakest spoke. Solve for any stress and you will find your strongest spoke lasts about 8.5 times as long as your weakest spoke. In other words it is between 1.2 and 1.32 times as strong. So that checks. The equation comes from HP Gavin I expect some one can find a link. If you are having problems with a wheel this will tell you how to make a stronger one that meets your needs. I think the model is correct that is spokes break according to a normal distribution after a transform. The HP Gavin paper used higher tension in the spokes that is possible with a practical wheel so we will have to adjust the equation a bit. We have 3 constants we can change. Some one will have to keep precise records of their spoke breakage we can then use curve fitting to adjust those constants.
Cheap, poor quality spokes will have a wider spread of performance than expensive, high quality ones.
The spokes may come from different manufacturing batches or suppliers
The failure modes may not follow a normal distribution - for example if the forming machine sometimes puts a nick in the spoke, you may have two populations or a skew to your curve.
Builders change suppliers of spokes and rims, batches are manufactured from different steel with different heat treatment, riding conditions, skill of wheel builder, salt and corrosion all play a part.
 
I would like to divide the spokes I have broke into 4 catagories. Those that break every 10000 miles. These have an N or a S on the heads. I have broke 7 of those. Those that break every 1000 miles. These have a flat head R on the head which I have been told are an early model Pillar. I have broke around 25 of these. Defective or counterfit DT spokes. Those broke every 200 miles. I broke 24 of those the others did not break and do not seem to be defective. A photo of the defects here. https://flic.kr/p/ffCyCQ Those that broke every 100 miles. Those are generic stainless with no marking on the heads. I broke 3 of those. This was a temporary wheel I used while my main wheel was getting a new rim. Spokes break at even invervals. The problem here is all of my wheel are built with used spokes so I don't know the mileage on them. This is why I think the model is correct.
 
BobBob said:
Great, hope i'm right, i'll stick with 10 Ga, tightened sufficiently. hope the steel isn't 304ss
I have a 42mm wide double walled rim which seems robust

10ga spokes probably won't break, but they'll go slack with every rotation because they have several times too much cross-section/not enough elastic stretch.

The highest recommended maximum tension I have seen for any bicycle rim is 140 kgf. That's not enough to keep 12ga spokes taut under load, let alone 10ga. Either the spokes unscrew constantly, or you glue the nipples in place and they don't unscrew, but the spokes do go slack constantly.

Remember for the purposes of your wheel's structure, a slack spoke is a missing spoke.

Regular 14ga spokes are too thick to allow most bicycle rims to carry the biggest loads they are capable of. They are a compromise that trades off some load capability in return for low cost, ease of building, and resistance to damage from foreign objects.

Using motorcycle spokes with a bicycle rim displays a fundamental misunderstanding about how wheels work. Spokes' are supportive; the strength of the wheel comes from the rim. Spoke tension doesn't increase significantly under normal riding loads. It decreases.

Ideally, spokes and rim are structurally balanced to match each other, but it's much better to have spokes that are too light for a heavy rim than the other way around. Putting too-thick spokes in a bicycle rim makes the wheel weaker and less capable than using the correct gauge or thinner. It also dramatically increases maintenance and risk of damage to the rim and hub.
 
zerodish said:
The problem here is all of my wheel are built with used spokes so I don't know the mileage on them. This is why I think the model is correct.

Spokes that are not adequately stress relieved when first built into a wheel will begin fatigue cracking very quickly. Once this process is initiated, it will continue no matter what you do later. That's why you shouldn't build with previously used spokes unless you did the previous build or otherwise know that stress relieving was done correctly.

Jobst Brandt (who literally wrote the book on wheel building) reused sets of spokes in his own wheels for hundreds of thousands of kilometers, retiring them only when they became deeply notched where they crossed each other. He used normal DT spokes, though I think they were 15-16ga. His personal test results which were meticulously recorded and shared during his lifetime are at odds with your model.
 
Chalo said:
BobBob said:
Great, hope I'm right, I'll stick with 10 Ga, tightened sufficiently. hope the steel isn't 304ss
I have a 42mm wide double walled rim which seems robust

10ga spokes probably won't break, but they'll go slack with every rotation because they have several times too much cross-section/not enough elastic stretch.
10 Ga are 3mm dia instead of 2.6 for 12 Ga or 2mm for 14Ga, so will need 2.25 times the tension of a 14 Ga or 33% more than a 12Ga to stretch by the same amount. This should mean they won't go slack.
This will reduce the cyclic loading on the rim just as it does on the spokes and so reduce the chance of damage around the nipple as well as providing a stronger overall wheel, so long as the rim is capable of taking the additional tension.
I think this agrees with everything you're saying?
Chalo said:
The highest recommended maximum tension I have seen for any bicycle rim is 140 kgf. That's not enough to keep 12ga spokes taut under load, let alone 10ga. Either the spokes unscrew constantly, or you glue the nipples in place and they don't unscrew, but the spokes do go slack constantly.
So you need a rim that can take the additional tension - agreed
Chalo said:
Remember for the purposes of your wheel's structure, a slack spoke is a missing spoke.
Agreed
Chalo said:
Regular 14ga spokes are too thick to allow most bicycle rims to carry the biggest loads they are capable of. They are a compromise that trades off some load capability in return for low cost, ease of building, and resistance to damage from foreign objects.
My Scott Nitrous is built with 2mm 14 Ga spokes. It's a relatively heavy duty wheel fora a feeride full suspension bike.
Scott know a thing or two about bikes and wheels so I am using this as a starting point, hopefully an example of good design.
I agree that thicker spokes with weaker rims is not a good idea
Chalo said:
Using motorcycle spokes with a bicycle rim displays a fundamental misunderstanding about how wheels work. Spokes' are supportive; the strength of the wheel comes from the rim. Spoke tension doesn't increase significantly under normal riding loads. It decreases.
It would, but proportionally thicker spokes with a proportionally stronger rim would seem to be sensible engineering
Chalo said:
Ideally, spokes and rim are structurally balanced to match each other, but it's much better to have spokes that are too light for a heavy rim than the other way around. Putting too-thick spokes in a bicycle rim makes the wheel weaker and less capable than using the correct gauge or thinner. It also dramatically increases maintenance and risk of damage to the rim and hub.
All of this makes perfect sense and I agree, but it all of it assumes that the rim is not strong enough and that the builder has used the same amount of tension for a thick spoke as for a thin spoke, IE poor design and poor build.
If we start from the assumption that the rim is strong enough and the spokes are sufficiently tightened, then what is still wrong with this approach?

Thanks for your patience :)

I have a Scott wheel which has 2mm thick spokes and a 26mm wide rim with a 2.6mm thick bead 1.5mm thick rim material
In the photo beside it, I have my ebike rim which is 42mm wide and 3.1 thick bead made from 1.75mm thick material.
It appears to be a much stronger rim. I haven't found a recommended spoke tension on it.
Some quick calculations would indicate that the ebike rim is around twice as strong radially and around 3X as strong for side loading and twist though I don't know what the extrusion profile is internally.
I guess that's the big unknown, the alu thickness is only around 0.25 mm thicker so even if the overall rim is stronger it may not be strong enough locally to the nipple. A washer might be all it needs though?
10 Ga spokes would seem proportional for this stronger rim and I'd guess should be tensioned to around 200-225 Kgf?

Stonking great 42mm rim with offset spoke positions and thicker rim material 3mm dia 10 Ga spokes.
Scott Nitrous factory built 2mm 14Ga spokes and 26mm rim for comparison

Ebike Vs Nitrous rim.jpg
 
BobBob said:
If we start from the assumption that the rim is strong enough and the spokes are sufficiently tightened, then what is still wrong with this approach?

There's nothing wrong with using thick spokes and a rim that can tolerate proportionally high spoke tension. That's what wire wheel motorcycles do.

But a bicycle rim, however strong, is not intended for the high point loads that are imposed by thick spokes dialed up to appropriately high tensions. Alex rims are rated for 140 kgf maximum tension, and some models of Ryde rims are rated for up to 1400 kN, which is about 143 kgf. I have not been able to find any bicycle rims rated for more spoke tension than these.

Even a very large, very heavy bicycle rim will have a spoke bed whose thickness and shape limits how high a spoke tension can be used in practice. Surely there may some outliers, like the out of production Alex Supra E, whose actual spoke tension capacities exceed their ratings. But why violate the manufacturer's rating when you don't have to?

4455.jpg


When you see any amount of distortion (or after a period of use, cracking) at the rim's spoke holes, you can be sure the rim's spoke tension limit has been exceeded. At that point you can be sure that the rim will yield both under peak operating forces and during attempts to true it.

Assuming your rim can tolerate 2250N tension per 3mm spoke (which is 11ga by the way), then yes in that case it would work as well as if it had 2mm spokes at 1000N. But I'm guessing that is an assumption your rim's manufacturer would not agree with. Even if it could in fact tolerate 2250N of per spoke tension, it could carry even more weight and higher peak forces without problems if you used 2mm spokes at 1250N, or 1500N. And it could also do heavier work with 2.0-1.8mm or 1.8-1.6mm spokes at just 1000N.

I don't understand what's the problem with [stronger, more reliable, longer lasting, lighter, easier to service] that you would throw some or all of those qualities away just to have thick spokes instead.
 
Chalo said:
BobBob said:
If we start from the assumption that the rim is strong enough and the spokes are sufficiently tightened, then what is still wrong with this approach?

There's nothing wrong with using thick spokes and a rim that can tolerate proportionally high spoke tension. That's what wire wheel motorcycles do.

But a bicycle rim, however strong, is not intended for the high point loads that are imposed by thick spokes dialed up to appropriately high tensions. Alex rims are rated for 140 kgf maximum tension, and some models of Ryde rims are rated for up to 1400 kN, which is about 143 kgf. I have not been able to find any bicycle rims rated for more spoke tension than these.

Even a very large, very heavy bicycle rim will have a spoke bed whose thickness and shape limits how high a spoke tension can be used in practice. Surely there may some outliers, like the out of production Alex Supra E, whose actual spoke tension capacities exceed their ratings. But why violate the manufacturer's rating when you don't have to?

4455.jpg


When you see any amount of distortion (or after a period of use, cracking) at the rim's spoke holes, you can be sure the rim's spoke tension limit has been exceeded. At that point you can be sure that the rim will yield both under peak operating forces and during attempts to true it.

Assuming your rim can tolerate 2250N tension per 3mm spoke (which is 11ga by the way), then yes in that case it would work as well as if it had 2mm spokes at 1000N. But I'm guessing that is an assumption your rim's manufacturer would not agree with. Even if it could in fact tolerate 2250N of per spoke tension, it could carry even more weight and higher peak forces without problems if you used 2mm spokes at 1250N, or 1500N. And it could also do heavier work with 2.0-1.8mm or 1.8-1.6mm spokes at just 1000N.

I don't understand what's the problem with [stronger, more reliable, longer lasting, lighter, easier to service] that you would throw some or all of those qualities away just to have thick spokes instead.
I bought the wheel fully built and with spokes advertised as 10Ga,
i measured a few of them them at between 3.03 and 3.15 mm dia fitted.
The seller was not the builder
My local bike shops have great trouble getting spokes for ebikes they say, so I had little choice other than to either try to buy kits of spokes and a rim and hope they all matched or buy the whole thing.
I took my bike shop's advice and bought the wheel complete.

When the wheel turned up it has alternating long and short spokes
i don't mean it's dished - see thread https://endless-sphere.com/forums/viewtopic.php?f=6&t=110840&start=25#p1649035
The alternating length makes the spoke tension 85% greater on alternating spokes which is not ok in my book

I don't know the rim manufacturer's recommended spoke tension or who the rim manufacturer is and have contacted the seller to say send me the right spokes please. Ebay dispute

There's not much point in getting a bunch of correct length 10 Ga spokes if what I need is 12 Ga.

I am unlikely, however, to get a full set of a different type of spoke on an ebay dispute if I try to change the thickness. They will only change like for like.
They've offered 40 Euros (around $45). The spokes are $55 and lacing at our local bike shop $40
The last bike shop I spoke to said they return whole wheels because they can't get ebike spokes so I'm not likely to get much help there if I can't get the spokes as well

If the rim is strong enough for 10 Ga then I would expect correctly tensioned 10 Ga to be stronger, more reliable and longer lasting. The extra weight is not a consideration and I'm not sure why one is easier to service than the other.
Of course I am not trying to throw away better performance. The key point is not that thicker spokes are weaker or that wheels with thicker spokes are weaker but that bike rims are not designed for thicker spokes so you need a stronger rim or you can't tighten the spokes to the right tension.

The key thing is rim strength and I agree that is an unknown. Thanks for highlighting that point.
Point load on the rim.

I started by assuming the seller / lacer chose a spoke to be suitable for the rim but considering the build quality, I am no longer of that opinion, so I have trying to figure this out for myself from first principles

Thanks for your help, i am going to go back to the seller and try to get a spec for the rim and find out the max spoke tension and work back from there
 
Dang, that's a weird lacing your seller used. I've done some similarly strange stuff when there was no other way, but in this case I think they needed to source the right spokes.

Here's a wheel I worked out with 3 different spoke lengths. I don't love it.
http://www.rideyourbike.com/36hub24rim.shtml
36hub24rimnondrive.jpg

That was many, many wheel builds ago for me. If I had to do that again, the extreme angle spokes on the non-drive wouldn't cross each other. But that would probably mean 5 different spoke lengths.
 
Yours looks kinda cool and a good talking point, mine is just plain wrong.
It's also worse because of the bigger hub.
If they'd skewed it the other way round I could argue that it evened up the stresses under heavy acceleration but they got that the wrong way round as well
I assume they probably just got lazy, had some of the shorter ones and only bought or made the others to suit, thinking they'd get away with it.
 
A rims resistance to spoke pull through is simply proportional to it's thickness. Bontrager figured this out with his BCX series. You have to determine where your spokes are breaking. Most stainless steel spokes break at the elbow. Spokes are made with 2.2 2.3 2.4 2.5 and 2.6mm at the elbow with a 14 gauge nipple. If you are using a large flange with out a directional drilling on the rim then you will be breaking spokes at the threads. There is nothing to do here but go with a thicker spoke. A spokes diameter at the threads if you grind down the threads is 1.8mm for a 14 gauge spoke. Threads impose a 3.3 stress riser on the spoke. This means you can make the shaft of the spoke 1 mm thick. That will solve breaking flanges and cracking rims but will not be stiff enough for most applications. Right now I think the best proportions for an ebike spoke are 2.6 2.0 2.3 Pillar will make such a spoke if there enough interest.
 
zerodish said:
A rims resistance to spoke pull through is simply proportional to it's thickness.
It's a little more complex than that:
  • A stiffer rim will flex less and distribute the load at the bottom of the wheel more. This in turn will mean that the reduction in load is distributed across more spokes. It's a little tenuous but one might argue that resistance to pull through might include avoidance :)
  • The material (steel or aluminium will certainly affect the resistance to pull through as well as the specific grade used, heat treatment etc
  • The shape of the rim profile will make a difference. If you look at the aluminium section in Chale's post above, there is a concave arch shape on the inner side of the rim and supporting struts either side toward the outer part of the rim
  • The failure of the rim on a wider flatter rim is likely to me largely due to bending causing fracturing of the material near the nipple.
  • The span / distance from the sides of the rim to the spoke hole make a difference to whether the rim experiences more bending, compressive or tensile loading.
  • The lacing pattern wlil affect whether the loading is more radial or at more of an angle and this in turn will load one side of the hole more than the other
  • Washers may spread the load and apply it to a wider area around the spoke hole
  • Too small a hole between the rim and the nipple will add a bending force to the spoke hole which may increase loading
I'm not saying that all of the above will be significant but they might be. For my rim, the old Nitrous has steep walls next to the nipple which mean the rim material is largely under tension whereas on the wider wheel it is largely bending and so despite being of thicker material (unknownd aluminium alloy of unknown quality, consistancy and treatment) it may be weaker locally but flex less and so be less prone to pull out because of that
zerodish said:
Bontrager figured this out with his BCX series. You have to determine where your spokes are breaking.
It is a brand new, unused wheel but I need to know whether I can tighten the spokes as much as they need
zerodish said:
Most stainless steel spokes break at the elbow. Spokes are made with 2.2 2.3 2.4 2.5 and 2.6mm at the elbow with a 14 gauge nipple.
They are 10 Ga
zerodish said:
If you are using a large flange with out a directional drilling on the rim then you will be breaking spokes at the threads. There is nothing to do here but go with a thicker spoke.
I was thinking that a machined insert with an angled hole might spread the local load better than a washer but was also condidering belvue conical washers with a matched spring force or bonding a strip with a hole in it to the outside face of the spoke bed
zerodish said:
A spokes diameter at the threads if you grind down the threads is 1.8mm for a 14 gauge spoke.
But you don't grind down the threads, or cut them, they are roll threaded rather than cut is to maintain the original cross section, IE the cross section is the same for the threaded bit as the plain part
zerodish said:
Threads impose a 3.3 stress riser on the spoke.
Bending or axial load have different effects, the local work hardening and lead in of the thread rolling machine have an effect as does the shape of the female thread in the nipple. Real world fatigue is a combination of multiple cyclic loads
zerodish said:
This means you can make the shaft of the spoke 1 mm thick.
If this were true then wheel designers would make the spoke 1mm thick to reduce air resistance.
Find me one
As you note above, they normally fail at the elbow rather than at the thread
zerodish said:
That will solve breaking flanges and cracking rims but will not be stiff enough for most applications.
Why do they need to be stiff? - they are under tension, they would work if made from chain link, there are some floppy plastic ones made from HDPE available that work well. They would not be strong enough, failure due to exceeding yield
zerodish said:
Right now I think the best proportions for an ebike spoke are 2.6 2.0 2.3 Pillar will make such a spoke if there enough interest.
I would suggest that starting with the overall system use / load one should work out how strong the wheel must be in various loading scenarios and then design depending on things like the sprung and unsprung weight, whether it is to be raced down mountains with a big heavy hub moior (needs motorbike type wheels) or only used as a city commuter (can get away with standard bike wheels).
2.6 2.0 2.3 looks pretty good but I'm no expert - see what Chalo thinks - I reckon he'll say thinner
 
Since I started this several interesting things have happened. My last defective DT broke and went into the gears locking them up. I was fortunate I was going slow and was able to pedal to a stop. Spokes must never be allowed to break in the middle. I'm going to repeat this often. I have used DT Alpine 3 spokes 2.3 1.8 2.0. These felt stiffer than a plain 2.0 mm spoke. The reason for this is the elbow flexes. A thicker spoke at the elbow flexes less and there is less room for it to move in the spoke hole. Dont go too far with this. If you force an elbow into the flange the flange will fail. I think a spoke can only be swaged .3 mm at a time. Each time you do this it costs 25 cents. Spokes can be made thinner in the middle if you are willing to pay the price. Also spokes thinner than 1.6 mm tend to twist making them harder to work with. It is easier to blade a spoke than swage it. This also make it easier to see if it is twisting. Im willing to test a bladed spoke that has been swaged and bladed so the larger diameter is no more than 2.0 mm. Also I have built a wheel with a Rhyno Lite rim. The brass ferule on this rim allow for a tighter spoke. I have put 3000 miles of heavy touring on this and it is dead true.
 
You want the rim to flex, thats why you dont go with to thick a spoke.

Look no further then Grintech, they only sell 12-13, 13 and 13-14 gauge spokes.

I would love to send my rear hub motor to Grintech, get their wheel man to lace it for me and see how long it will last.
I never had success with rear hub motor when I was 380lbs. Things are different now at 291lbs soon to be 250-260lbs.
I might be able to get into a full suspension bike now :lol:

I like DM Alexrims, I just dont like that the cavity isnt much not like the spacious Crystalyte rim.
https://ebikes.ca/shop/electric-bicycle-parts/rims.html?rim_nom_size=60
 
Santacruz said:
Here is an interesting spoke idea.
https://www.youtube.com/watch?v=q_oMh3ehRUE&ab_channel=WorldwideCyclery
....
H'mmm, I think I have a couple of hanks of paracord around somewhere :wink:

As a very young teenager I had a paper route (delivering 300 newspapers to residences for those too young to know what that is) all loaded down on an old double triangle steel frame 27" inch bike with an 3 speed SA IGH hub (the old british version). I delivered those papers on that bike until I saved up enough money to purchase a used Honda 50 Cub (wish I still had it).

In over 6 decades the only time I have ever broken a spoke is when I hit a pothole at 25+MPH (my first e-bike ... equipped with a front hub motor and three SLA batteries). In that case the wheel collapsed, the bike stopped and I took flight. What are you people doing to your poor bicycles ?
 
Reminds me of The Flyer Force, people delivering flyers. News papers are going away, its rare to see now as its all online but theres still newspaper hardcopies still for sale.

Flyers should really be outlawed, its a waste of pulp. If they are outlawing straws and bags then the first thing to outlaw are mail flyers but to much money to be made for delivering them from the post office to the mail man. Someone should really dump a pile at the sorting centers.

Another random thought
Do you remember the Columbia Records deal?
Where you buy cd's and you get free cd's, Bryan Adams was talking about that with Dan Rather.

I mowed lawns myself, it rained and the mower got bogged down but I kept trying until parents came by to tell me to come home.

How all this relates to broken spokes I dunno but bicycles are designed for normal sized, normal weight people.
I busted countless saddles, countless spokes broken being fat and obese.
 
markz said:
I mowed lawns myself, it rained and the mower got bogged down but I kept trying until parents came by to tell me to come home.

Did that as well. In Birmingham, Alabama ... had to have two mowers. The second one had a rope rather than a metal handles. Place it at the top of a steep slope and let out the rope. Then pull it up, move it over about two feet and repeat. :)
 
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