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 !