Rim fatigue failure

This was in my overnight email:

https://www.youtube.com/watch?v=qKeeHDuoFq8
--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971

On 4/20/2020 6:18 AM, AMuzi wrote:
This was in my overnight email:

https://www.youtube.com/watch?v=qKeeHDuoFq8

Interesting. I suspect that manufacturers of wheels are not going to be
willing to add the expense of additional materials and labor to each
unit in order to prevent rim cracks that will occur sometime far into
the future.

On 4/20/2020 6:18 AM, AMuzi wrote:
This was in my overnight email:

https://www.youtube.com/watch?v=qKeeHDuoFq8

Thanks, Andy, this was the best thing I've found on R.B.T. in years!

To everybody: IF you haven't watched the video yet, it's rather long
and slow, but worth the time, IMHO. There is actual data obtained by
actual /measurements/ made in a /systematic/ way.

It's admittedly very wonky, but this is a TECH group, yes?

Oh, and it happens to confirm a bunch of my preconceived notions, though
I also learned some new things, e.g. WHY spoke-hole cracks nearly always
start running toward the next spoke hole rather than toward the braking
surface.

In my youth, I ran a lot of tandem wheels at low tension, so I have a
lot of experience with rim cracks. The video makes a very persuasive
case that higher tension would have helped, and why.

It also makes a pretty impressive case (at first glance!) for Sapim
spoke nipples and washers, though maybe DTs have the same noted
features. Good to think about any such claims critically.

Mark J.

On Mon, 20 Apr 2020 08:18:15 -0500, AMuzi wrote:

This was in my overnight email:

https://www.youtube.com/watch?v=qKeeHDuoFq8

One might ask, "Is this a common failure of the bicycle wheel?"
--
cheers,

John B.

On Monday, April 20, 2020 at 8:18:23 AM UTC-5, AMuzi wrote:
This was in my overnight email:

https://www.youtube.com/watch?v=qKeeHDuoFq8

I've met Bill Mould twice, at the Midwest CABDA show near Chicago. He's an interesting guy, and is full of good information about wheels and wheelbuilding. He confirmed that my repeated rim failures on my folding bike (406 Kinetix rims) were the result of excessively wide tires and not, as I had first thought, due to brake-track wear.

On Monday, April 20, 2020 at 3:23:14 PM UTC-7, John B. wrote:
On Mon, 20 Apr 2020 08:18:15 -0500, AMuzi wrote:

This was in my overnight email:

https://www.youtube.com/watch?v=qKeeHDuoFq8

One might ask, "Is this a common failure of the bicycle wheel?"

Yes, very. It was not so much of an issue in the olden days with 120mm rear hubs and 5sp freewheels and stouter, high spoke count rims.

-- Jay Beattie.

On Mon, 20 Apr 2020 15:35:15 -0700 (PDT), jbeattie
wrote:

On Monday, April 20, 2020 at 3:23:14 PM UTC-7, John B. wrote:
On Mon, 20 Apr 2020 08:18:15 -0500, AMuzi wrote:

This was in my overnight email:

https://www.youtube.com/watch?v=qKeeHDuoFq8

One might ask, "Is this a common failure of the bicycle wheel?"

Yes, very. It was not so much of an issue in the olden days with 120mm rear hubs and 5sp freewheels and stouter, high spoke count rims.

-- Jay Beattie.

It would seem that you are saying that with a "properly" built wheel
there was few, if any, problems with wheel cracking but as wheels were
built weaker and more flimsily that cracking became a problem.

One might respond by saying, "well.... yes" :-)
--
cheers,

John B.

On Monday, April 20, 2020 at 12:54:14 PM UTC-7, Mark J. wrote:
On 4/20/2020 6:18 AM, AMuzi wrote:
This was in my overnight email:

https://www.youtube.com/watch?v=qKeeHDuoFq8

Thanks, Andy, this was the best thing I've found on R.B.T. in years!

To everybody: IF you haven't watched the video yet, it's rather long
and slow, but worth the time, IMHO. There is actual data obtained by
actual /measurements/ made in a /systematic/ way.

It's admittedly very wonky, but this is a TECH group, yes?

Oh, and it happens to confirm a bunch of my preconceived notions, though
I also learned some new things, e.g. WHY spoke-hole cracks nearly always
start running toward the next spoke hole rather than toward the braking
surface.

In my youth, I ran a lot of tandem wheels at low tension, so I have a
lot of experience with rim cracks. The video makes a very persuasive
case that higher tension would have helped, and why.

It also makes a pretty impressive case (at first glance!) for Sapim
spoke nipples and washers, though maybe DTs have the same noted
features. Good to think about any such claims critically.

Mark J.

Boy, if ever a thread cried out for a good old Jobst and Sheldon commentary. Sigh.

I wore out a Specialized front rim one time in my life as the metal began to bulge. (brake wear).

Since I'm a 27" curmudgeon I hope my Mavic Mod 4's hold up for the next decade or two, I have not found spares. (Should have bought the Velocity Dyad while Peter White had them.)
I have a Wolber in the basement just in case.
I run 48H in back and 40H in front since I am a Clydesdale....I think Chalo said he is, too, and Ron Wallenfang might be one besides.

Thanks for the link.
pH in Aptos

On 4/20/2020 6:23 PM, John B. wrote:
On Mon, 20 Apr 2020 08:18:15 -0500, AMuzi wrote:

This was in my overnight email:

https://www.youtube.com/watch?v=qKeeHDuoFq8

One might ask, "Is this a common failure of the bicycle wheel?"

These days? Yes. At least for the trendiest, lightest, "highest
performance" bike wheels. Not for more conservative choices.

Who was it that said "Light, reliable, inexpensive - pick two"?

ISTM that a lot of bicycling's "high performance" design choices amount
to removing more and more material, to see how light parts can be made
before too many customers complain about too many failures. And it's a
trial and error process, because unlike a lot of industrial machinery,
the loading conditions aren't well defined or well known.

Note the "too many" phrases. The "high performance" guys often expect
that their parts are going to fail. Some hope they last a year, some
hope for three or five. Nobody in that group cares about anything
lasting ten years, because they will be using some new and flashier
gizmo long before then.

We just got back from a short ride on our 34 year old bikes. I rebuilt
or replaced the wheels once (and re-used the parts on other bikes). Rims
are still perfectly fine. Total broken spoke count in 34 years is one,
and I suspect it was caused by the guy who borrowed my bike, fell and
stepped on the spokes.


--
- Frank Krygowski

On 4/20/2020 3:54 PM, Mark J. wrote:
On 4/20/2020 6:18 AM, AMuzi wrote:
This was in my overnight email:

https://www.youtube.com/watch?v=qKeeHDuoFq8

Thanks, Andy, this was the best thing I've found on R.B.T. in years!

To everybody:Â* IF you haven't watched the video yet, it's rather long
and slow, but worth the time, IMHO.Â* There is actual data obtained by
actual /measurements/ made in a /systematic/ way.

It's admittedly very wonky, but this is a TECH group, yes?


If you want to get even wonkier: It's interesting and relevant that the
higher tension wheels in that test had less variation in tension during
loading. And it reminds me that the design of a tension spoke wheel has
a similarity to the design of a bolted joint subject to fatigue loading.

As an example, think of the cylinder head bolts on an engine or piston
compressor. As cylinder pressure varies, the force in the bolts varies.
It turns out that for that sort of bolted connection, a bolt with a
thinner central section (between the head and the threads) torqued to a
higher preload stress can be much more resistant to fatigue than a
thicker bolt at a lower stress. The strongest bolt is something like the
third one in figure 12 at
https://www.fastenal.com/en/3289/fastener-fatigue

This jibes with Jobst's frequent statement that butted spokes at high
tension were most resistant to fatigue failures.The key is the thinner
one sees less percentage-wise variation in stress, and that variation is
the main driver of fatigue.

A common design strategy for those bolted joints is to use either
Soderberg's or Goodman's equations. This article
https://web.njit.edu/~sengupta/met%2...indefinite.pdf
gives an idea of the math behind it, although it doesn't do a good job
of describing the test data that lead to Soderberg's or Goodman's formulas.

--
- Frank Krygowski