furballi

I did in post #20. This guy had an older Weinmann concave aluminum rim and ended up ordering spokes that were 2.5-3.0 mm too short. I evaluated the situation and went forward with the build because he was not able to exchange the spokes for the correct size. He probably logged more than 10K miles on that wheel before he sold to his buddy. The wheel has never had a broken nipple.

You don't have to be a rocket scientist to know that motor oil from the 70s is vastly inferior to today's motor oil. The same can be said about automotive tires. Modern automotive intenal components have much better tolerances and metallurgical properties than those built 40 years ago. It's a big joke when people dig up data from 40 years ago and use them as the Gospel!

Airburst

What you did in post #20 is quote one anecdote where the nipples didn't fail. One anecdote isn't proof of anything, unfortunately. Your friend's wheel might not have had trouble, but that doesn't mean all wheels built with spokes too short will be fine.

FBinNY 

Engineering student 1, Engineer 0.

What Furballi is trying to justify is that it's OK to disregard well established practice. He characterizes my rational as being based on 40 year old data (of high quality), saying that maybe materials have improved. Not only does he fail to justify his assumption, which he backs up with anecdotal data consisting of a single non-failure, he also choose to ignore 40 years of anecdotal data that continues to the present document numerous incidents of nipple failure. This is easily researched (I provided links) but Mr. Engineer refuses to look beyond his limited experience.

For these, he prefers to debate what he calls the underlying cause saying it might be corrosion rather than fatigue. I concede that corrosion might be the proximal cause, but the underlying cause remains obvious --- spokes too short and not reaching the nipple head.

I don't say that short spoke wheels will all fail, nor will failure necessarily lead to injury, and someone may choose to take a qualified risk riding such wheels. That's a personal risk assessment, but doesn't change the simple fact that the wheels built with proper length spokes are reliable, and those with short spokes are less so.

furballi

If there is sufficient safety factor built into the design, then the product will not fail. Do you have any knowledge of machine design? This wheel has been exposed to several millions load cycles! A marginal design would fail within a few hundred miles. I don't need to build 1000 wheels in this fashion to know that I have a good product.

Only a fool would cling to 40 year old data knowing that there have been great advances in material science and manufacturing. If all short spoke wheels don't fail, then the shorter spoke is NOT the root cause of the failure.

FBinNY 

This is scary coming from an engineer. It turns logic on it's head. It's patently ridiculous to assume that a marginal design would result in 100% failure, then argue that a no failures in a sample of one proves the design is sound. That's like saying "I've been smoking for 50 years and don't have lung cancer, ergo smoking doesn't cause lung cancer".

We know two things from the cumulative scientific and anecdotal data. BTW- while the scientific data may be old, it trumps no data and wishful thinking about improvements in materials.

1- Nipple failure in wheels with spoke engagement in the heads is extremely low, approaching zero.
2- Nipple failure in wheels where spokes don't engage into the head is relatively common, or for sticklers, much less rare.

Given the simplicity of doing things right, I can't see why we're debating the logic of doing them wrong. But that's just me.

Airburst

Case study, the Viscount death fork. For those not in the know, this nasty little critter had aluminium blades and an aluminium crown, pinned to a steel steerer. Some of the early ones weren't even pinned. These had a very nice habit of suddenly snapping the hell off at the steerer/crown interface, potentially while the bike was moving quite fast, with predictable results for the poor unfortunate so-and-so riding the bike.

At some point, whoever owned Viscount decided that killing people was bad publicity, and decided they'd recall these forks and issue new ones.

Did every fork snap off at the steerer and kill its rider? Hell no!

By the same logic you're using, if all Viscount "death forks" didn't fail at the crown/steerer joint, the bad design of the joint wasn't the root cause of the failure.

Anyway, apologies to everyone else for the off-topic post, it just seemed like a good way to illustrate the bad logic at work here.

furballi

You claimed that option #2 is common, but I've seen many wheels with brass nipples that fall into this category that have logged may thousand miles without nipple failure. Again, most nipple failures posted on the internet are caused by corrosion of the aluminum nipple. Now aluminum nipples have a tendency to corrode and fracture where the head transitions to the body of the nipple. The head snaps off. The solution when using aluminum nipples is to use a longer spoke. This condition does not apply to the OP with brass nipples.

https://www.bikeradar.com/forums/view...004&t=12688519

https://www.bikeradar.com/forums/view...004&t=12842075

https://forums.mtbr.com/wheels-tires/...ld-781325.html

furballi

I'm talking about brass nipples. If the OP was using aluminum nipples, then the proper course of action would be to extend the spoke length into the head of the nipple. A one size fits all approach works well only for simpletons. I will never use aluminum nipples for bicycle wheels. Its mechanical properties are vastly inferior to brass!

FBinNY 

While short spoke failure is more common with aluminum nipples, though many wheels log thousands of miles without failure, brass nipples also fail the same way.

So, proper spoke length is more critical with aluminum nipples vs. brass, but brass nipples aren't immune to this kind of failure.

However your assumption that the fact that wheels going thousands of miles without failure proves anything, could also be said of aluminum nipples, because even with aluminum nipples, the majority hold up pretty well.

Dan Burkhart 

: Just when I thought I was in for a boring evening.

Airburst

The point of that "case study" was not to demonstrate how dangerous aluminium is, it was to point out the flaw in your logic where you said that one wheel not failing with the spokes too short meant that wheels with spokes too short didn't fail because of it.

If I'd known you were going to misinterpret it like that, I'd have thought of a different way to make the point...

mrrabbit 

Kinda glad I'm in the middle of replacing all house windows, painting, base board trimming, base board painting, picture hanging, building wheels, starting this season's garden, meeting up with various groups in support of 2nd Amendment rights, upgrading and rebuilding my server, wiping a dozen 250G and 750G SATA drives, etc...

...cause I don't have time to argue with anyone.

Ain't that grand?

=8-)

reddog3

But of those many wheels with brass nipples, that have logged thousands of miles without failure, how do you know the spokes weren't the proper length. Are you saying it doesn't matter? If you haven't witnessed nipple failure (brass) with too short a spoke, you just haven't been around long enough.

furballi

High cycle fatigue is not the root cause if the wheel does not fail after the first 1500 miles. The most likely suspect is corrosion. Brass is more corrosion resistant than aluminum. This is why there is more failure seen with older aluminum nipples.

furballi

A good designer always take into account all variables before making the appropriate recommendation. The OP has a steel wheel with brass nipple. The chance of nipple failure in this setup is virtually non-existent if the spokes were properly tensioned and stress relieved.

Airburst

What does spoke tension and stress relief have to do with it? Spokes break if they're not stress-relieved because they're at or close to yield at the points where they're interlaced, which greatly reduces their fatigue life, and they break if they're not tight enough because they go slack and flex, causing excessive fatigue. Neither of those affects the spoke nipples.

You're still basing your assumption that the nipples won't fail if the spokes are too short on your personal experience with one wheel. I know it can happen - I messed up measuring a broken spoke for a BMX wheel once and put in a replacement one that was a few mm too short, with a new nipple. Sure enough, a few days later, the same bike turned up at the co-op with a broken nipple on the spoke I replaced (I know it was the same one, it was a black nipple where all the others were silver). Metaphorical egg on metaphorical face.

FB has also seen instances of it happening, as have most of the other people who've weighed in. Even if we disregard theory and simply make deductions based on what we've all seen, lacing wheels with spokes that aren't quite long enough isn't a good idea, not because it'll definitely cause failure, but because it can cause failure.

furballi

Excessive spoke tension may cause pre-mature nipple failure due to higher stress/strain at the point where the head transitions to the body of the nipple. We bought many cheap steel wheels in the early 80s where the spokes can fall short of the head of the nipples. One only need to spend a few minutes to true and stress relieve the spokes. Have not seen a single returned wheel due to nipple breakage.

Having shorter brass spokes can contribute to nipple failure, but it is not the MAJOR contributor. Excessive spoke tension, corrosion, and the shape of the spoke hole are ranked higher. The recommended practice has built-in safety factor because one cannot expect an average bike mechanic to understand machine design. When a component does not meet specs, it is sent to the material review board, where it is often bought-off by structural engineers to use as-is. Why? Because the engineer analyses the problem and determines that there is still sufficient safety factor remaining for safe operation.

FBinNY 

bobotech

For what its worth, my son has a factory cheaper Schwinn rear wheel that kept on breaking spokes at the bend. This was with less than 200 miles on the wheel. I rebuilt the wheel with new DT Swiss spokes however they were about 1 or 2mm too short but I said screw it. My son is large, 300 pounds and a masher.

The wheel and spokes have held up just fine for the last 8 months or more however two weeks ago, 1 nipple head broke off. He and I thought that the spoke has snapped but it was fine, the head of the nipple popped off.

I replaced it and the wheel has been fine since but I know that the heads might be popping off on other spokes.

reddog3

You've been doing this since the early 80's and you still haven't figured it out? Maybe you entered the wrong field? I'm an engineer too- on a model railroad!

Airburst

Then you haven't seen enough wheels....

I'm with FB at this point, I have more sensible things to do than argue with you about a point you're not going to concede because of some preconcieved notion of how engineers know more than wheelsmiths about wheelbuilding. It's that kind of arrogance that ends up giving engineers a bad name.