Mad Honk 

Scott,
You are correct about that. I went to the LBS and bought 36 straight gauge spokes for my front wheel today. Campy low flange hub with Matrix ISO C rims, and I expect it to last at least a few thousand miles. After that it won't owe me anything. I will likely wear the rim out before the spokes start to give way, but that is just MHO. I have had more destruction of wheels from fire, crashes, and car wrecks in that order, than from spoke failure. I always think that a properly built wheel will last a long time. I don't follow JB's wheel building method and have had thousands of miles on the wheels I build. I built wheels for the guy who was #12 on the USCF professional licence list and all of our riding friends. If they worked for them it is a process that is going to be good enough for me. Argue on folks.... Smiles, MH

pdlamb

I know I'm going to regret asking, but... fire? You riding through campfires, or going so fast they just burn up?

Mad Honk 

pdlamb,
I doubt you will regret it but I really am not much for hanging out in the woods around campfires with the likes of Smokey the Bear and Yogi Bear. But it did make me chuckle! I am attaching a couple of pics of three of the un-restored bikes that were caught in a house fire. Everyone suspected arson but the Fire Inspector could not say conclusively.

63rickert

Schwinn engineers did all the math and all the testing many moons ago. Look at any original Chicago Schwinn and see the .080-.060" spokes. (That's 2.0/1.5 in metric.)Only small wheel kids bikes and some of the trucks had straight gauge. Those guys are all gone now and so are the archives. Suffice it to say Schwinn always did things for reasons.

Andrew R Stewart 

Agreed that Schwinn usually had reasons to do things that generally were valid. But they did miss the ball on mountain bikes in the early 1980s big time. The reasons I have read of had little to do with their customers and more to do with keeping their piece of the pie. Too bad the US market was wanting cake. Andy (who otherwise has found this thread to be interesting in the range of opinions and some speculations)

63rickert

Schwinn missed lots in the final days.

It remains they put millions of bikes on the road with DB spokes at 2.0/1.5mm and there were just no problems. No problems for decades. The wheels were durable.

WizardOfBoz

This thread a bit tldr; but there's a point about "proof" that should be made. If you're looking for causal links between differences in spoke breakage and straight or DB spokes, you have three options:

1) A reasonably comprehensive retrospective analysis of the history of spoke breakage, looking at the type of spoke that broke in each instance. Unless you know the distribution of all spoke types, and the use pattern of each type of spoke, this type of analysis can lead you astray.

2) A reasonably comprehensive prospective study of spoke breakage, in which you create wheels with different spoke diameters and then randomize their use (that is, you try to send proportional amounts of each spoke type to identifiable demographic groups like male/female, light/medium/heavy body weight, MTB/Road, and so forth). Then you look at spoke breakage. This allows you to have an idea of what the different types of spokes do in different situations, and can give you an idea of what the true correlation between spoke type and breakage, having filtered out the differences caused by rider type/usage etc.

3) A model-based engineering approach where we use scientific principles to calculate spoke stress, fatigue, and life under different service conditions.

"Reasonably Comprehensive" means that you have enough subjects so that your results are likely not just the result of random variation. Because spoke breakage is rare, you need an enormous number of subjects (most of whom don't break any spokes) to get sufficient numbers of people who do break spokes so that you can do a statistical analysis. This makes such a "proof" study very expensive. Option 1 is cheapest but only works if you have access to the data and can mislead you if you don't know the population of all spokes that were considered (that is, what fraction of the riding population uses DB spokes vs straight spokes).

Option 2 is gonna be very expensive and likely impractical. A bike company that sells bikes with both types of wheels could likely look at service claims and make some inference. I suspect that's what Schwinn had done in the 70s and 80s, which is why on (for example) my Superior, the spokes were 14/16 guage DB (2mm/1.65mm).

Option 3 requires some pretty good engineering analysis because one has to accurately characterize the geometry and grain structure of the spoke J-bend, where most breakage occurs. For example, "finite element analysis" in which we imagine the spoke chopped up into tens of thousands of little cube-like shapes, and use engineering equations to figure out what is happening in each cubizoid element. Very difficult because the J-Bend is cold-worked and the head is upset, so you have a very complex stress pattern in the bend.

But one can make some inferences and assumptions. As in "Schwinn wasn't a bunch of idiots. They wouldn't have used DB spokes if they had increased breakage service costs and customer problems. Nor would they have spent more gratuitously on DB spokes unless they got practical value." So that's a hint that DB spokes have better fatigue life in service than straight spokes.

And we can to an engineering "mental model". That is: for the same tension, DB spokes are more stretched out. Therefore, they remain in tension over a wider range of displacements than straight spokes. Further, when stretched additionally, a DB spoke adds less additional for to the J-bend for the same displacement. This lowers the maximum stress on the J-bend. So DB spokes decrease the range and the maximum stress on the spoke, and keep the minimum stress above zero. Hence, we expect DB spokes to last longer.

The "I broke a lot of straight spokes but then switched to DB spokes and haven't broken any so far" may be able to tell you that the DB spokes you bought are just better quality spokes, or possibly that there is some improved spoke durability for DB spokes. But it won't allow any statement to be made about the intrinsic superiority of DB or straight spokes. One bike and one user, without controlling who made the spokes and other things, is not generalizable.

So the point is: if you want proof, you're going to be disappointed. Because getting to "proof" in a statistically satisfactory way is not economically or practically feasible.

The closest we're gonna get is probably data that Schwinn had and which may or may not still exist. And, alas, that we wouldn't have access to even if it did.

Trakhak

The issue raised in the opening post is all but irrelevant. Assuming a wheel is built competently and at the correct tension for the type of spoke used, both double-butted and straight-gauge spokes will last indefinitely. As Jobst Brandt once noted, he had gone through countless pairs of rims on his favorite bike, but the spokes were still the originals, with over 200,000 miles of use and no spoke failures.

A better question: why choose double-butted spokes when straight-gauge spokes are almost always less expensive? A hint: back when I was working in bike shops, 35 years ago, DT's catalog referred to their non-butted 14-gauge spokes as "tandem" spokes.

Case in point: back then, a local wheelbuilder used to boast that he always used the lightest rims and the strongest spokes (i.e., DT's tandem spokes) for his builds and then complained about the rim quality, since the rims invariably developed cracks near the spoke holes.

Things have changed since the 1980s, with 16-spoke deep-dish wheels having become all but ubiquitous, but physics is physics. If the rim is light in weight, use double-butted spokes. If the rim is heavier, use either double-butted or straight-gauge spokes.

Worthy of a thread in itself, come to think of it: is there a disadvantage to using double-butted spokes with thick, heavy rims?

Kimmo 

I rebuilt some WH-R540s (those 16/16h paired-spoke Shimano wheels with the lateral cross and elbows at the 560g rim) with CX-Rays, and those spokes stretched about 3mm (spokes replaced one at a time to match the original tension).

Just subjectively, they seemed very robust. Probably closer than usual to the spokes' yield point, but since normal loads only decrease spoke tension, that's no biggie. Rode them for a year or two, stayed perfectly true despite riding like a courier.

IMO this setup is tough as nails.