Spokes
 

I was wondering which spoke design is preferable for loaded touring. Non-butted or butted? This is assuming using a good quality SS spoke.

The only thing that really matters is that they are tight.... really tight and that there are enough of them to take the loads.

http://sheldonbrown.com/wheelbuild.html#spokes

An expert wheel builder told us in a class I took that the spokes should be so tight that the wheel starts to dish and then backed off just a bit to make it round again.

There are two arguments, the one that seems to have the science of wheelmaking label of approval is that butted spokes are stronger in the wheel, because the load distribution among spokes is broader in the loaded zone. (Not sure how that squares with the idea that net effect on the lower spokes is a positive vertical force, but then that's why I leave all this stuff to the boffins). Anyway the scientific view goes on to say that there isn't any difference in strength between the two kinds of spoke, which I take it means some part of the spoke fails other than the wire, presumably the swaged bitty. So butted are the winners if other than the bitty, you expect your rims to fail, or your hub flange, which does happen too.

The argument for straight spokes is that they are more durable when you get sticks and parts of the paniers or load in the spoke. This kind of midspan trauma has happened to me, while all the sexy spoke, rim, and hub failures never have. Getting junk in the wheels from brush, passing cars, adjascent cyclist, etc... seems pretty comon, and it is nice to just "tear it another one". This seems to be the reason that a number of top drawer makers of custom touring machines spec straight spokes, or maybe they too just can't figure out what the Spokasenti are talking about.

Butted spokes are difficult or impossible (?) to machine build. That probably accounts for a little bit of the prejudice against straight gage spokes. But on the other hand, just because straight gage spokes show up on some prestige wheels, one probably shouldn't let that make one feel any better about the average machine built wheel with SG spokes.

I would take either spokes on the road. My next bike will roll on butted, because they may help baby the Rohloff flange. I think the bigger issues are spoke fit at the hub end, brass nipples, really strong rims that can take maximum spoke pressure, proper build.

The argument that I've heard is that butted spokes will stretch a little in the thinner section when they are stressed(hitting a bump, or just rolling along as part of the bicycle), reducing the impact forces to the spoke nipple and the hub flange. Mkes sense to me.

Instead of tensioning the spokes until the wheel starts to buckle and then backing off, you can use a spoke tensiometer to make sure that all the spokes are at close to the same tension, and tensioned to the rim maker's recommended level.

I have read many accounts of the dreaded "ping" sound as a spoke breaks. Can we make any conclusions as to why this occurs (the spoke breaking that is). Is it usually the swagged end, or the threaded end? This is assuming the break occurs w/o some previous trauma to the spoke, like a crash or an object getting caught in the spokes.
Forgive me as I have no experience with a spoke breaking.

"The argument that I've heard is that butted spokes will stretch a little in the thinner section when they are stressed(hitting a bump, or just rolling along as part of the bicycle), reducing the impact forces to the spoke nipple and the hub flange. Mkes sense to me."

Right, that is the process that spreads the load over a wider area. Because if your main spoke stretches the loads are shouldered by adjacent spokes moreso than otherwise.

"Instead of tensioning the spokes until the wheel starts to buckle and then backing off, you can use a spoke tensiometer to make sure that all the spokes are at close to the same tension, and tensioned to the rim maker's recommended level."

That is said to be a bad process. The claim is that unless you taco, then back off, you don't find the peak performance that your combination of components, and lacing pattern are capable of. Once you have done it for one wheel you can use the spoke gizmo to check future identical combinations, and to check the wheel for an evenly tightened job, but it is claimed you can't find the peak spoke load with gage alone. One might wonder why there isn't (?) a page we could all go to that gives the values for various wheel and spoke combos, presumably there are just far too many. That is without going to the issue of different gages, and their relative accuracy. The amateur may be comforted but is not really helped by having a gage, even the quality issue can be dealt with by listening to spoke pitch. Since most of us don't build many of the same wheels, the gage is of lesser value.

"Can we make any conclusions as to why this occurs"

Depends on whether the wheel was properly built or not. If the wheel was well assembled then it is probably component quality or compatibility. For instance the spoke fit in the hub can lead to early fatigue if not correct. sometimes that fit can be helped with a washer. Or you can have rims without enough strength to allow the spokes to be sufficiently tensioned. You can have the odd spoke that just breaks early. Then you can have a condition like a crash that takes it past the yield point.

If it is properly built using choice components then you may have the odd spoke that quits early or the crash type thing. During the wheel's life, most of the same spokes, and hubs can be laced to new rims repeatedly.

Then you have the situation of poor components, unable to be brought to a high enough tension for the intended use, and it's a race to early component failure. For instance on someone's site I read that some of the normally good components had been negatively altered to make machine building easier. This led to poor fit at the hubs and higher incidence of spoke failure. There are actually a surprisingly small number of the name brand components that will make a first class wheel, we are to some extent just hanging in there to hear some tell it.

Alloy nipples seem to be a bad choice for real strength.

In the touring world, skimping on spokes. In the loaded field less than 32 on 26" or 36 on 700c is skimping, though you can get away with lower numbers. really low number have been successfully built also, but it can be a stunt type of thing requiring a full court approach to the wheel.

There are all kinds of little issues like how the hole is drilled in the hub, or using the same hub for a different lacing pattern.

Almost always at or very near the bend.

Many thanks to all the contributors. The takeaway for me is if getting a wheel built (esp. by hand), go with the best components that you can afford to meet your expectations. This credo also applies I think to many things on a bike. For touring especially, component failure in the middle of nowhere has a high cost. Additionally, butted spokes if given the option would seem the way to go.
Seems like spoke "ping" can happen due to just one spoke falling outside of the quality control parameters and it thus becomes the weakest link. Always wondered at that bend in the spoke, seems like that would be the weakest point.

Remind me to ask you to send me my freebie hub, spokes, and rim so I can use your approach of building the trial wheel, overstress it to the taco point, then ease off and measure the stress with a tensionometer, discard all those overstressed now-junk parts, and build the real wheel that I want with new parts and using the tensionometer. Professional wheelbuilders can afford to do this if they're building a lot of identical wheels, because they can amortize the cost. Us amateurs are usually building up unique wheels every time.

So for those of us with finite incomes, the table that comes with a Wheelsmith tensionometer, showing spoke stress ranges by type of spoke, is good enough for me. I've built about a dozen wheels. Over the years, I've tensioned a couple up too high--though never to the taco-point--and after a few weeks of riding have had the spoke pull out through the rim (Mavic MA2 in both cases), snapping the rim longitudinally at the spoke hole reinforcement. (The first time this happened was before I bought a tensionometer; the second time was using a quarter-century old rim that just couldn't take retensioning.) Anyway, clearly the taco test isn't really a comprehensive test for whether all the parts of the wheel are happy at a given spoke stress.

One thing I will say for sure: Run of the mill machine-built wheels are junk (by this I mean something like an Ultegra hub with DT or Wheelsmith spokes and Mavic Open Pro rim -- maybe those fancy Ksyriums are built better, but I don't think they'd be useful for touring or randonneuring). By "junk" I mean they'll go out of true fast, often losing their tension. Sometimes it is worth it to buy a machine-built wheel if you get a good price, but the first thing you need to do is put it on a truing stand, check that the spokes are all seated and bent-in to their path properly, then use your tensionometer to get all the spokes with the same tension on each side, alternately truing the wheel, stress-relieving, retensioning as needed to get the tension even, stress-relieving, and repeating until the wheel is both true and even. The only hand-built wheel that I've ever bought was built by Peter White using a Schmidt DynoHub, double-butted spokes, and Open Pro rim. It survived a head-on crash that totalled my Reynolds 531 frame, and the wheel didn't even need truing after the crash. I wish I could build wheels quite that good, but my main randonneuring wheels have now gone about 15000 miles and only needed to be trued up slightly once, a few weeks after I built them. The DB spokes are well worth the extra money as they are much more resilient.

Anyway, having built wheels without a spoke guage using the "ping" method and having built them with a spoke guage, I can guarantee you that you get better wheels with the guage. Of course, you need to buy a good guage.