Why do my spokes keep breaking? - Bike wheel science.

[roubaixtuesday]

I was sat in the dining room when through the sliding door I heard a hissing, went into the conservatory to find the rear wheel slowly deflating. Bike hadn't moved for more than 30 hours (since I'd got home from work the previous morning) maybe another 100 yards of travel and it would have gone but it is weird when just sitting there the tube decides to (audibly) deflate.

That is properly weird! Where was the hole?

 

[raleighnut]

That is properly weird! Where was the hole?

In the innertube

 

[Yellow Saddle]

That is properly weird! Where was the hole?

That's a good question. I can't answer for all self-triggering punctures, but I can for one. I had a similar experience and the hole was the usual valve stem attachment failure. Happened whilst I was in my garage with the bike in there, not used for a week or so. More dramatic, I once did a tubeless conversion, washed the wheel and leaned it against a wall to dry in the sun. An hour later, it spontaneously exploded and shot a couple of meters away from the wall. On inspection (apart from green snot everywhere), the explosion warped the wheel. The lubricious tyre had jumped the hook in the rim. There was a dog sleeping in the sun too. But that story involves more than just green slime.

 

[Dogtrousers]

I was sitting looking cool sipping an espresso at the start of an Audax (The Great Escape from the now closed Look Mum No Hands cafe). There were bikes everywhere as you'd expect.

Suddenly. a tyre on an unattended bike exploded behind me. I looked less cool with espresso all down my jersey.

 

[presta]

I was sat in the dining room when through the sliding door I heard a hissing, went into the conservatory to find the rear wheel slowly deflating. Bike hadn't moved for more than 30 hours (since I'd got home from work the previous morning) maybe another 100 yards of travel and it would have gone but it is weird when just sitting there the tube decides to (audibly) deflate.

Rubber creeps, if it was close enough to the brink of failure when you left the bike, then creep could have tipped it over the edge.

 

[Yellow Saddle]

Rubber creeps, if it was close enough to the brink of failure when you left the bike, then creep could have tipped it over the edge.

I doubt there is creep involved. Thye tube is under compression, not tension. Just thinking aloud. Perhaps there is some tension at the v alve stem base.

 

[Illaveago]

View attachment 446534

Here is the data:
1) The fork is loaded with a force of 60. Ignore units, I've kept all units the same, so it doesn't matter.
2) This wheel has 11 spokes. When the wheel is unloaded, each spoke has a tension of 100.
3) The flat bit at the bottom is the Load Affected Zone (LAZ henceforth). There are three spokes in the load affected zone. Because of the load on the hub, the tension in those thee spokes is reduced. The total reduction equals the load on the hub. Therefore the tension in each one of those is now only 80. 100-80 =20. 3 x 20 = 60, which equals the load.

Ignore the fact that the three bottom spokes are all in equal tension. In reality it the middle one would have the lowest tension and then those straddling it a bit more etc etc. It complicates the basic explanation. We can go into how that varies at a later stage.

The system is in equilibrium and conserves Newton's laws.

I don't know who built that wheel but I certainly wouldn't ride it !

 

[froze]

No. It doesn't work like that. Only the cheap spoke bit is true.

Sorry, but that's not true.

bicycle spokes do undergo microscopic flexing with every pedal stroke regardless of if they are loose or properly adjusted, though it’s subtle and not visible to the naked eye. Here’s what’s happening:

A wheel is essentially a pre‑tensioned structure. Each spoke is pulled tight, and the rim is held in balance by opposing spoke forces.
When you pedal, the torque from the chain and hub transfers to the wheel. The spokes near the contact patch (where the tire meets the ground) experience a drop in tension, while others slightly increase in tension. This change in tension causes tiny elastic deformations in the spokes, they stretch and relax by microns (millionths of a meter). Every rotation repeats this cycle, so each spoke flexes thousands of times during a ride. This is normal and essential to how a tensioned wheel works, the rim carries the load, and the spokes flex just enough to keep everything balanced. Loose, or incorrectly adjusted spokes will flex more.

 

[froze]

Cheap spokes will fatigue quicker, but 3 years is very short period of time, even Walmart bikes the spokes will last a lot longer than just 3 years. If those spokes are breaking due to extremely cheap Chinese made spokes, then the RIM is in the same boat, no one would put cheap spokes on a good rim, thus the rim is also very cheap. Instead of paying for the spokes to get replaced, you should be considering getting a new and better wheel, because all you will be doing is spending money to replace spokes while more break and then the rim will crack at the spoke holes, and now you spent money on spokes and labor only to have a wheel you have to throw away with the new spokes.

Forget about it and buy a new wheel.