[jacquesm]

Spokes can and do stretch differently over time due to manufacturing variance. Checking your wheel periodically by strumming the spokes can help identify spokes that have stretched unevenly compared to the rest. Typically you'll find the opposing spoke to also have lost some tension and probably one or two spokes earlier and later.

[jimnotgym]

Spokes coming loose over time can be caused by lack of stress relieving. This is where there is some twist in the spoke due to friction between the nipple and rim. This is where handbuilt wheels have an advantage

[wiredfool]

To be a little more specific, you're conflating two things here.

1) Stress relieving is tensioning the spokes by grabbing pairs and squeezing them. This takes a elastic bending moment in the j-bend and over-stresses it into plastic deformation, permanently changing the shape of the spoke. When relaxed from the stress relieving, the spoke is bent differently, and the stress in the spoke is more uniform with less of a bending moment. (bending moments lead to a compressive stress on one side and tension on the other, superimposed over the tension of the spoke. If the compressive side of the spoke winds up with an actual stress reversal on every wheel revolution, it will start to crack and fail in O(1e6) cycles, or 2000km). Due to the overstress here, this also beds the spoke into the hub.

2) Windup comes from the spoke being a long torsional spring. There's friction between the spoke threads and the nipple, and if the threads aren't lubricated, the friction is enough to twist the spoke instead of tightening the thread. You'll still see some of this with thinner spokes and higher tension, but you can back off a bit on each adjustment and make sure that the spoke isn't twisted before going on. This windup causes the pinging when a new wheel is used for the first time, and each spoke is somewhat unloaded when it's at the bottom of the rotation. This reduces the friction in the threads, and the spoke springs back, changing it's total length.

Incidentally, the highest compression in the rim and highest tension ever in the spokes is in the stress relieving step of wheel building. This is where a super tensioned wheel will potato chip buckle if it's going to. Adding a tire and air pressure reduces the spoke tension. When riding, the bottom ~4ish spokes detension somewhat (depends on the spoke count, numbers are for old school 32ish/ 700c not terribly deep rims).

[jimnotgym]

I wasn't conflating two things, it appears my stress relieval procedure has more steps than yours. For your part 2 (in addition to what you said for part 1) I also used to grab the wheel with one side against my belly, forarms across the rim edge, so elbows at 3 and 9 oclock and hands at 12. Then I would push my elbows down to get the pinging sound you described, and then rotate a quarter turn and repeat. Then turn over and do the same. When it stopped I would retrue the wheel and do it again. If you don't do this you get the pinging you described on your first ride and a therefore a wonky wheel.

I believe this is one of the important steps in making a wheel stay true and not need trueing after one ride. This is described better in the Art of Wheelbuilding if you want to try it.

[jacquesm]

All good stuff this, thank you! Some of it I knew intuitively but not good enough to really understand, let alone explain it to others.

The tire and air pressure thing is perfectly logical and anybody can demonstrate this, as you pump up the tire the spoke pitch goes down.

[jacquesm]

Yes, as well as the spoke end becoming embedded, stretch and the spoke nipple becoming embedded (typically: harder spoke nipples vs aluminum wheels). So make sure when you get a new bike to check this after your first couple of rides and then again after 6 weeks or so when more subtle effects start to kick in.

[wiredfool]

What (specific) type of deformation are you seeing? Elastic deformation, plastic deformation, or creep?

Elastic deformation is not a time dependent property, and should be the regime in which the wheel is operating.

Plastic deformation is (also not time dependent) where you have gone beyond the yield point of the material, and have permanently changed the shape, even after unloading the part. All of the plastic deformation of wheel components should happen at build time.

Creep is when a constant load causes additional time dependent strain. There shouldn't be anything in a wheel that creeps, but it's possible that some plastics or epoxy/composites could creep.

[jacquesm]

> All of the plastic deformation of wheel components should happen at build time.

I suspect this is true, except that parts being what they are (always with small inconsistencies) and the spoke nipples riding inside the rim and j bends in the spokes riding inside the holes in the hub tend to 'find their spot' after being exercised for a while. I've made it a pretty hard rule to re-check after 6 weeks and invariably something has shifted. This probably indicates that my wheel building technique could be better, then again, I've never had a wheel that I built fail - so far - and over the years have done between 100 and 200, some of them for very heavily loaded bikes (tandem trekking bikes).

Most recent wheel was actually this weekend, I'll be sure to give it another really good look to see if I missed something that might cause this which I can catch at an earlier stage.

My typical wheels: double walled aluminum rims, quality spokes and nipples (and the latter seem to be hit-and-miss, I've had bad batches of nipples more than once in spite of re-ordering the exact same kind, but I noticed it immediately during assembly), typically Shimano hubs.

[analog31]

I have to admit that my stress relieving method is pretty much ad hoc. I take the wheel off the stand a couple times and press the axle against the floor. I grab the spokes and squeeze. I pluck the spokes and listen.

Usually I put the wheel back on the stand after a week or two of riding. A really good builder shouldn't need to do this, but part of this whole exercise is to evaluate and improve my skills as I build more wheels. And I'm not building racing wheels, but trying to do the best possible job is part of the learning process.

[jacquesm]

Pretty similar here. And I trust my own wheel building skills more than the kid at the bikestore (and once upon a time I was that kid... respoking wheels and patching tires for pocket money).

[jimnotgym]

I have never had these kind of problems with dtswiss spokes and nipples and quality rims. Handbuilding is so labour intensive why would you compromise on materials like this?

[jacquesm]

Interesting. I've had this happen even with good materials and I totally agree that compromising on materials makes no sense. Even so, it doesn't hurt to check things periodically so they don't sneak up on you.

I recently re-spoked my s-pedelec because I didn't like the spoke brand and nipples used, that thing is too heavy and too fast to take any chances with.