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Why do spokes break?
#1
Why do spokes break?

Spokes can break because they are poor quality.

Spokes can break because the wheel was built poorly, and the spokes are not at the appropriate tension.

Spokes can break because of a narrow rim, which flexes a lot.

Spokes can break because of riding on rough tracks, or going off jumps.

Spokes can break because of heavy riders.

Let's assume for this discussion that, the spokes are good quality, the wheel was built well, and the spokes are at the appropriate tension.

You can have the same rider ride on the same track with one wheel, and the spokes will break, but with another wheel, the spokes will not break. What difference between the wheels, will result in the spokes breaking on one wheel, but not breaking in the other wheel?

Reason one: The bracing angles of the spokes.

Many years ago, most bikes were single speed, and the spokes had a decent bracing angle. Spokes very rarely broke in these wheels.

Then someone invented the 5 speed freewheel. These hubs were often the same width as the single speed hubs, and for them to work, the spokes had a steeper bracing angle. Then there was the 6 speed, the 7 speed, and so on. Some bikes are now 12 speed. The spokes needed to be at a steeper and steeper bracing angle.

As the bracing angle got steeper, more tension was put on the spokes, and breaking spokes became more common.

Following is a diagram of a front hub, showing the bracing angle.

   

Following is a diagram of a back hub designed for several gears, showing the steeper bracing angle.

   

The steep bracing angle results in much more tension on the spokes, and increases the likelihood of spokes breaking.

Reason 2: The stiffness of the rim.

Some modern bikes come with narrow aluminum rims. These can flex a lot. Older bikes had stronger stiffer rims.

Flexing of these narrow aluminum rims, results in more tension on the spokes, and increases the likelihood of spokes breaking.

Conclusions

People wanting strong wheels, should look for wheels with wide hubs, and stiff rims.

I have met a bike tourer who carried spare spokes with him, so he could replace them when they broke. I asked him if they broke often. He said they did. During his trip, he had replaced spokes, hubs, and complete wheels. This can be very inconvenient when cycling in remote places.

I met another bike tourer who had never had a broken spoke, or a broken wheel. He was not a small man, well over 6 feet tall. He also carried a lot of weight on the bike. He had been bike touring for 3 years, and had ridden through over 30 countries. The spokes were the same thickness as the other bike. This bike had a Pinion gearbox, allowing for it to have a wide hub. It also had wide, thick, stiff aluminum rims.

Anyone wanting strong wheels, maybe for bike touring, maybe for rough tracks, maybe because the rider is heavy, get wheels with wide hubs, and stiff rims.

I put together an inexpensive strong wheel using a modified stainless steel rim from an old bike. If I planned to go bike touring for a long distance, I would make a similar wheel with a wider hub. Most likely it would never break.

https://forums.bikeride.com/thread-8529.html
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#2
In my experience, most spokes breaking are from being too loose. But in addition to that, it has to do with the dynamics of machine built wheels. They often use spokes that are longer than needed to hand-build wheels. When the spokes stretch, it causes weak leverage points in the spokes. This leads to microslack at the hub especially, and vibration penetration (instead of transfer) and this is what causes them to break most of all.

For hand-built wheels, the spokes will have some room in the nipple to stretch and be trued up if necessary. The tension on the spokes remains constant, and vibrations are transferred through the rigidity of the wheel instead of being absorbed (and causing vibration).

Other possible ways include over-tension. It is possible, but usually the nipple threads will give out immediately when the spoke is over-tensioned.

I think angle is subjective over the material quality of the spokes. And with any risky angles, the wheel not being tensioned high enough will be the exponential factor of breakage before the angle.

Just from my experience of course.

I absolutely punished my Inferno 27's that I built this summer. Checked them mid-autumn and they were still perfect. This would be a miracle for a machine built wheel. I just got a new GT BMX, and the machine built wheels that came with the bike weren't even true. I had to fine tune them and overhaul the hubs. I can also add that the size of the wheel will play a critical role on the rigidity of the wheel and the spokes. Smaller wheels like 20" come together very tight and stay that way often. The more distance you add on, the more this factor diminishes. For larger wheels, such as 700c, the use of deeper rims helps to add rigidity to the wheel and close the gap on the distance between the hub and the rim for the best possible results.
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#3
There are things wheel manufacturers, and bike manufacturers, sometimes do to make stronger wheels.

1. Use wider hubs. Using hubs a little wider, can result in a significantly stronger wheel.

2. Use an asymmetrical rear end. If the frame is made with the drive side chain stay further from the center line than the non-drive side chain stay, the back wheel can be made with the spokes on both sides of the wheel at the same bracing angle, resulting in maximum strength. Some bike manufacturers make frames like this. The disadvantage is, you can't just buy a standard back wheel and put it on the bike. It needs to be a wheel made with the correct offset.

   
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#4
(02-22-2024, 12:10 PM)ichitan Wrote:  There are things wheel manufacturers, and bike manufacturers, sometimes do to make stronger wheels.

1. Use wider hubs. Using hubs a little wider, can result in a significantly stronger wheel.

2. Use an asymmetrical rear end. If the frame is made with the drive side chain stay further from the center line than the non-drive side chain stay, the back wheel can be made with the spokes on both sides of the wheel at the same bracing angle, resulting in maximum strength. Some bike manufacturers make frames like this. The disadvantage is, you can't just buy a standard back wheel and put it on the bike. It needs to be a wheel made with the correct offset.

this is great stuff, I guess this is why manufacturers introduced boost spacing for mountain bikes since all the wheels are asymmetrical these days, they'll need more width to add more strength to the build and at the same time they can squeeze in wider tires for more traction
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#5
(12-14-2023, 05:58 PM)ReapThaWhirlwind Wrote:  In my experience, most spokes breaking are from being too loose. But in addition to that, it has to do with the dynamics of machine built wheels. They often use spokes that are longer than needed to hand-build wheels. When the spokes stretch, it causes weak leverage points in the spokes. This leads to microslack at the hub especially, and vibration penetration (instead of transfer) and this is what causes them to break most of all.

For hand-built wheels, the spokes will have some room in the nipple to stretch and be trued up if necessary. The tension on the spokes remains constant, and vibrations are transferred through the rigidity of the wheel instead of being absorbed (and causing vibration).

Other possible ways include over-tension. It is possible, but usually the nipple threads will give out immediately when the spoke is over-tensioned.

I think angle is subjective over the material quality of the spokes. And with any risky angles, the wheel not being tensioned high enough will be the exponential factor of breakage before the angle.

Just from my experience of course.

I absolutely punished my Inferno 27's that I built this summer. Checked them mid-autumn and they were still perfect. This would be a miracle for a machine built wheel. I just got a new GT BMX, and the machine built wheels that came with the bike weren't even true. I had to fine tune them and overhaul the hubs. I can also add that the size of the wheel will play a critical role on the rigidity of the wheel and the spokes. Smaller wheels like 20" come together very tight and stay that way often. The more distance you add on, the more this factor diminishes. For larger wheels, such as 700c, the use of deeper rims helps to add rigidity to the wheel and close the gap on the distance between the hub and the rim for the best possible results.

Please excuse me but it is rare to have poor spokes and while I suppose it is possible to have the spokes too loose this would leave the wheel untrue and unround.

99.9% of comme4rcial wheels are machine built and they get it right. The rest are hand built and it takes a VERY skilled workman to get it correct.
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