Wheel deflection

On 2008-10-31, steve wrote:
On Oct 30, 12:57*pm, Ben C wrote:
On 2008-10-30, wrote:

Ben C? wrote:
[...]
But you may be right that in practice plastic deformation of the rim
does not occur until after the spokes have gone slack. The purpose of
the experiment I was proposing to Steve was to investigate this.

When staying in the elastic range of spokes (not going slack)
deflections are in one or two tenths of millimeters, less than is
required to flatten a rim permanently.

That may well be the case.

My testing has shown that any wheel that has a shallow (19mm) to
medium (25mm) depth and is tensioned to 110kg will have spokes going
slack well before the rim starts to permanantly deform. Obviously the
shallower the rim the more it will bend before permanently deforming.
On an average depth rim (21mm) I would say that the rim can deflect at
least another .5mm in the radial direction before you start to
plasticly deform.

Interesting, thanks for doing that test and letting us know.

On Thu, 30 Oct 2008 10:58:52 -0500, Ben C wrote:

On 2008-10-30,
wrote:
Ben C? wrote:
[...]
While the spokes are borrowing more strength from the rim as there
tension increases, they should give it right back to the rim as the
rim starts to deform from an outside force. Therefore, unless the
spokes overcome the strength of the rim in a static state I don't see
how the rim would permanently deform more easily than if the spoke
tensions were lower and a radial load was applied.

They will go a bit slacker as you apply the outside force, but the
total load on the rim still goes up, unless they go completely slack.

Here's a simpler example: suppose you have a rod with a rubber band
wrapped tightly around it lengthwise, compressing the rod.

Now squeeze the two ends of the rod together. The rod compresses a
bit more and the rubber band loses some tension. Although the rubber
band is now applying a bit less force to the rod, the total load on
the road is still higher: it's whatever you're applying plus the force
from the rubber band.

Note that the rod is under more load than if you applied the same
squeeze without the rubber band there, and it's also under more load
than if you didn't squeeze it at all. It must be or you wouldn't be
able to compress the rod until the rubber band had gone slack.

The total load is always preload + applied load. If the effect of
applying a load is to reduce the preload a bit, then it does reduce
the total a bit. But the total load is still going up.

I don't think your example has a parallel in bicycle wheels. Total
load (what stress are you visualizing?). Compressive load in the rim,
caused by spoke tension, does not change with radial load (weight on
the axle).

I don't see how that's possible. Sit on your bike and the rim flattens a
bit at the bottom and some spokes lose a bit of tension. The rim has
deformed therefore there must be more load on it.

of course - jobst's blatherings are just underinformed misconjecture.




That is apparent from FEA evaluation.

ah, the "fea" that calculates load, not strength - one of your most
spectacular mistakes jobst!!!


Radial loads are supported by
slackening downward spokes in "the load affected zone".

The load is supported both by the spokes and by the rim. Both deform--
the spokes lose tension and the rim flattens.

of course - you cannot have stress without strain.




With current, un-socketed rims, high spoke tension, varying between
static tension (the highest) to loaded tension (the lowest) in the load
affected zone, causes local fatigue and cracking around spoke holes.
This was formerly not a problem with quality rims used at the time "the
Bicycle Wheel" was written. Tubular rims from Fiamme, Mavic, and
others, performed well for long use with tension as high as the rim
could bear without warping (in compression).

You may wonder why many riders who build their own wheels are yearning
for a Mavic MA-2, or Torelli socketed rim. I believe it is
dissatisfaction with rims that cannot be tensioned high enough to not
have rattling spokes under heavy loading.

The high dish on rear wheels these days is also a big part of the
problem-- you have to make the right side very tight (and risk cracking)
or use glue on the left side.

Low spoke tension came to the business from machine built wheels that
could not deliver higher tension because at higher tensions, spoke
twist from thread friction was as large as the adjustments required to
try wheels. Therefore, truing robots went into infinite loops of
tightening and loosening spoke nipples with no progress. By setting
tension to levels where spoke twist was no longer a problem, various
glues such as SpokePrep (R) and linseed oil came into play to cover for
slack spokes that would otherwise unscrew in use.

As this trend spread through the wheel business, rim manufacturers
began making rims that were strong enough for loose tensioning and away
went the socketed rim. Sockets add cost and weight, and what better
advertising quality that these two parameters?

You can still get socketed rims-- the Mavic Open Pro for example.

On Thu, 30 Oct 2008 11:57:55 -0500, Ben C wrote:

On 2008-10-30,
wrote:
Ben C? wrote:
[...]
The load is supported both by the spokes and by the rim. Both
deform-- the spokes lose tension and the rim flattens.

Bot so. The load is supported by the spokes. Only after spokes have
gone significantly slack does bending of the rim become a problem.

The rim has to bend for the spokes to become slack.

That is why a strong wheel must have high tension, so the rim does not
go out of round to the point of plastic deformation.

When the spokes go slack, the wheel becomes much less stiff. But the
rim's strength is not affected.

"available" strength is affected. in this case, available strength is /
negatively/ affected by increasing spoke tension.




The load required to deform it
plastically can only be reduced by high spoke tension.

indeed.



High spoke tension does not make anything stronger. It just increases
the threshold at which spokes go slack and the wheel suddenly becomes
less stiff.

indeed.




But you may be right that in practice plastic deformation of the rim
does not occur until after the spokes have gone slack. The purpose of
the experiment I was proposing to Steve was to investigate this.

When staying in the elastic range of spokes (not going slack)
deflections are in one or two tenths of millimeters, less than is
required to flatten a rim permanently.

That may well be the case.

why? if a rim is at 99.9% of yield, how much strain is it going to take
to effect yield? and for bonus points, as a test of your materials
theory, how straight is the "hookes law" stress/strain line for aluminum?

On Thu, 30 Oct 2008 15:58:26 +0000, jobst.brandt wrote:

Frank Krygowski wrote:

Second, it sounds like your framework and bottle jack will be
preventing any lateral movement of the rim. Â*But one of the common
forms of wheel failure is by the wheel assuming a potato chip shape,
which involves lateral movement of the rim. Â*It sounds like you're
reinforcing against a failure you're trying to measure. Â*Also, I
think such impact loads may have a lateral component, and it sounds
like your setup duplicates only an ideal radial load.

You are right, I do not allow for lateral movement when I am applying
a radial load. In fact I have an indicator to ensure that the lateral
deflection is kept to a minimum. Â*The reason for this was that if you
put a perfectly radial load on a wheel there shouldn't be any lateral
movement of the rim. The reason most wheels fail the way you described
is because there is inevitably a lateral component to the force being
applied that would taco the wheel. Â*Most of my testing is non-
destructive in order to get an idea of how stiff the wheel is and at
what point the spokes loose tension.

If you're trying to be realistic, you need to allow for lateral
buckling.

It sounds like what you're doing is analogous to measuring the
compressive strength of a yardstick while preventing the yardstick's
buckling. Buckling is the most likely mode of failure, so it can't be
ignored.

I could be wrong, because it may be you're after some more limited,
theoretical piece of data. But in real life, wheels buckle into potato
chips. I doubt there's a lot of value in finding how strong a wheel
would be if only it didn't buckle.

BTW, on another matter: If you're interested in the effect of an
inflated tire, it seems you should take some data with and without an
inflated tire in place, and compare. Have you done that?

Let's get practical. If you ride bike much, you must have flattened a
rim and also damaged rim beads from rough terrain. Both occur long
before a wheel is in buckling mode as is evident from years of riding
that caused such failures. I have a stack of cast off rims that have
flat spots (about 200mm long)

that's because you ride ancient, shallow section ma2's. you need to
update to a modern rim with deeper profile.



from a hard landing on flat ground as well
as rims that landed on a "knob" and dinged the bead hook.

When spokes go slack the rim is on its own, trying to bridge the
unsupported gap and readily yields a flat spot.

so? you think rims are made of putty like this?
http://www.flickr.com/photos/38636024@N00/417157612/



I can recall racing
down steep meadows full of gopher holes that would male spokes twang
when they regained tension.

good for you jobst. good for you.


Some of those wheels didn't come away
unscathed but none of us folded a wheel as you suggest.

really? can we take your word for this? like we can take your word that
rims unsupported by spokes and spoke tension "as high as the rim can bear"
collapse?

http://www.flickr.com/photos/38636024@N00/417157612/

On 2008-10-31, jim beam wrote:
On Thu, 30 Oct 2008 11:57:55 -0500, Ben C wrote:
[...]
The load required to deform it
plastically can only be reduced by high spoke tension.

indeed.
[...]
But you may be right that in practice plastic deformation of the rim
does not occur until after the spokes have gone slack. The purpose of
the experiment I was proposing to Steve was to investigate this.

When staying in the elastic range of spokes (not going slack)
deflections are in one or two tenths of millimeters, less than is
required to flatten a rim permanently.

That may well be the case.

why? if a rim is at 99.9% of yield, how much strain is it going to take
to effect yield?

Not much, but can you get it to 99.9% of yield without stripping the
nipple threads or tacoing? See also Steve's test:

"My testing has shown that any wheel that has a shallow (19mm) to
medium (25mm) depth and is tensioned to 110kg will have spokes going
slack well before the rim starts to permanantly deform. Obviously
the shallower the rim the more it will bend before permanently
deforming. On an average depth rim (21mm) I would say that the rim
can deflect at least another .5mm in the radial direction before you
start to plasticly deform."

Still I think you might be able to get the tension a bit higher than
110kgf (on say an Open Pro or CXP 33, both of which are deeper section
than an MA2) but I don't know how high.

and for bonus points, as a test of your materials theory, how straight
is the "hookes law" stress/strain line for aluminum?

http://gmiller.ce.washington.edu/cee...rainCurves.pdf

It's straight for a bit, and then it gradually starts to wander, without
(unlike steel) any sudden discontinuity at which it turns to toffee.
Yield for aluminium is defined arbitrarily as the stress at which
permanent deformation after you relax it back down is = 0.2%.

On Sat, 01 Nov 2008 05:43:18 -0500, Ben C wrote:

On 2008-10-31, jim beam wrote:
On Thu, 30 Oct 2008 11:57:55 -0500, Ben C wrote:
[...]
The load required to deform it
plastically can only be reduced by high spoke tension.

indeed.
[...]
But you may be right that in practice plastic deformation of the rim
does not occur until after the spokes have gone slack. The purpose of
the experiment I was proposing to Steve was to investigate this.

When staying in the elastic range of spokes (not going slack)
deflections are in one or two tenths of millimeters, less than is
required to flatten a rim permanently.

That may well be the case.

why? if a rim is at 99.9% of yield, how much strain is it going to
take to effect yield?

Not much, but can you get it to 99.9% of yield without stripping the
nipple threads or tacoing? See also Steve's test:

"My testing has shown that any wheel that has a shallow (19mm) to
medium (25mm) depth and is tensioned to 110kg will have spokes going
slack well before the rim starts to permanantly deform. Obviously
the shallower the rim the more it will bend before permanently
deforming. On an average depth rim (21mm) I would say that the rim
can deflect at least another .5mm in the radial direction before you
start to plasticly deform."

Still I think you might be able to get the tension a bit higher than
110kgf (on say an Open Pro or CXP 33, both of which are deeper section
than an MA2) but I don't know how high.

it will go quite a bit higher -

http://www.flickr.com/photos/38636024@N00/1498602218/

that is a mavic x517 rim - similar profile to open pro, single eyelet.



and for bonus points, as a test of your materials theory, how straight
is the "hookes law" stress/strain line for aluminum?

http://gmiller.ce.washington.edu/cee...rainCurves.pdf

It's straight for a bit, and then it gradually starts to wander, without
(unlike steel) any sudden discontinuity at which it turns to toffee.
Yield for aluminium is defined arbitrarily as the stress at which
permanent deformation after you relax it back down is = 0.2%.

correct. the pertinent point for aluminum though is that unlike "mild"
steel, dislocations start to move about well below the defined "yield"
point and thus the "straight" part of the line is in fact slightly
curved. it's a point people argue about, but it explains fatigue onset.

On 2008-11-01, jim beam wrote:
On Sat, 01 Nov 2008 05:43:18 -0500, Ben C wrote:

On 2008-10-31, jim beam wrote:
On Thu, 30 Oct 2008 11:57:55 -0500, Ben C wrote:
[...]
When staying in the elastic range of spokes (not going slack)
deflections are in one or two tenths of millimeters, less than is
required to flatten a rim permanently.

That may well be the case.

why? if a rim is at 99.9% of yield, how much strain is it going to
take to effect yield?

Not much, but can you get it to 99.9% of yield without stripping the
nipple threads or tacoing? See also Steve's test:

"My testing has shown that any wheel that has a shallow (19mm) to
medium (25mm) depth and is tensioned to 110kg will have spokes going
slack well before the rim starts to permanantly deform. Obviously
the shallower the rim the more it will bend before permanently
deforming. On an average depth rim (21mm) I would say that the rim
can deflect at least another .5mm in the radial direction before you
start to plasticly deform."

Still I think you might be able to get the tension a bit higher than
110kgf (on say an Open Pro or CXP 33, both of which are deeper section
than an MA2) but I don't know how high.

it will go quite a bit higher -

http://www.flickr.com/photos/38636024@N00/1498602218/

that is a mavic x517 rim - similar profile to open pro, single eyelet.

The gauge says about 26.5. What's that in Newtons?

and for bonus points, as a test of your materials theory, how straight
is the "hookes law" stress/strain line for aluminum?

http://gmiller.ce.washington.edu/cee...rainCurves.pdf

It's straight for a bit, and then it gradually starts to wander, without
(unlike steel) any sudden discontinuity at which it turns to toffee.
Yield for aluminium is defined arbitrarily as the stress at which
permanent deformation after you relax it back down is = 0.2%.

correct. the pertinent point for aluminum though is that unlike "mild"
steel, dislocations start to move about well below the defined "yield"
point and thus the "straight" part of the line is in fact slightly
curved. it's a point people argue about, but it explains fatigue onset.

Where is the fatigue limit for mild steel? Presumably quite a bit lower
than yield stress, so there's also a region where dislocations are
moving around without any noticeable plasticity.

On Sat, 01 Nov 2008 09:25:24 -0500, Ben C wrote:

On 2008-11-01, jim beam wrote:
On Sat, 01 Nov 2008 05:43:18 -0500, Ben C wrote:

On 2008-10-31, jim beam wrote:
On Thu, 30 Oct 2008 11:57:55 -0500, Ben C wrote:
[...]
When staying in the elastic range of spokes (not going slack)
deflections are in one or two tenths of millimeters, less than is
required to flatten a rim permanently.

That may well be the case.

why? if a rim is at 99.9% of yield, how much strain is it going to
take to effect yield?

Not much, but can you get it to 99.9% of yield without stripping the
nipple threads or tacoing? See also Steve's test:

"My testing has shown that any wheel that has a shallow (19mm) to
medium (25mm) depth and is tensioned to 110kg will have spokes
going slack well before the rim starts to permanantly deform.
Obviously the shallower the rim the more it will bend before
permanently deforming. On an average depth rim (21mm) I would say
that the rim can deflect at least another .5mm in the radial
direction before you start to plasticly deform."

Still I think you might be able to get the tension a bit higher than
110kgf (on say an Open Pro or CXP 33, both of which are deeper section
than an MA2) but I don't know how high.

it will go quite a bit higher -

http://www.flickr.com/photos/38636024@N00/1498602218/

that is a mavic x517 rim - similar profile to open pro, single eyelet.

The gauge says about 26.5. What's that in Newtons?

for 1.8mm spokes, what that one is, my handy park tension meter conversion
table tops out at 26 = 175kgf.




and for bonus points, as a test of your materials theory, how
straight is the "hookes law" stress/strain line for aluminum?

http://gmiller.ce.washington.edu/cee...rainCurves.pdf

It's straight for a bit, and then it gradually starts to wander,
without (unlike steel) any sudden discontinuity at which it turns to
toffee. Yield for aluminium is defined arbitrarily as the stress at
which permanent deformation after you relax it back down is = 0.2%.

correct. the pertinent point for aluminum though is that unlike "mild"
steel, dislocations start to move about well below the defined "yield"
point and thus the "straight" part of the line is in fact slightly
curved. it's a point people argue about, but it explains fatigue
onset.

Where is the fatigue limit for mild steel? Presumably quite a bit lower
than yield stress, so there's also a region where dislocations are
moving around without any noticeable plasticity.

check this out:
http://garfield.library.upenn.edu/cl...EH31000001.pdf

On Nov 1, 8:12*am, jim beam wrote:
On Sat, 01 Nov 2008 09:25:24 -0500, Ben C wrote:
On 2008-11-01, jim beam wrote:
On Sat, 01 Nov 2008 05:43:18 -0500, Ben C wrote:

On 2008-10-31, jim beam wrote:
On Thu, 30 Oct 2008 11:57:55 -0500, Ben C wrote:
[...]
When staying in the elastic range of spokes (not going slack)
deflections are in one or two tenths of millimeters, less than is
required to flatten a rim permanently.

That may well be the case.

why? *if a rim is at 99.9% of yield, how much strain is it going to
take to effect yield?

Not much, but can you get it to 99.9% of yield without stripping the
nipple threads or tacoing? See also Steve's test:

* * "My testing has shown that any wheel that has a shallow (19mm) to
* * medium (25mm) depth and is tensioned to 110kg will have spokes
* * going slack well before the rim starts to permanantly deform.
* * Obviously the shallower the rim the more it will bend before
* * permanently deforming. On an average depth rim (21mm) I would say
* * that the rim can deflect at least another .5mm in the radial
* * direction before you start to plasticly deform."

Still I think you might be able to get the tension a bit higher than
110kgf (on say an Open Pro or CXP 33, both of which are deeper section
than an MA2) but I don't know how high.

it will go quite a bit higher -

http://www.flickr.com/photos/38636024@N00/1498602218/

that is a mavic x517 rim - similar profile to open pro, single eyelet.

The gauge says about 26.5. What's that in Newtons?

for 1.8mm spokes, what that one is, my handy park tension meter conversion
table tops out at 26 = 175kgf.

I wonder if there is a problem with the tensiometer (inaccure at
higher readings) -- because when you get high tensions on an Open Pro
(1.8/2.0), you start start getting serious nipple binding -- even if
there is lubrication, and you can get eyelet pull out. Also, tension
above about 125kgf leads to cracking around the spoke holes after not
too many miles. It has also been my experience that really high
tension makes for an untrueable wheel -- not to create myth and lore,
but I think the rim gathers or puckers (don't take that to the bank),
but the bottom line, is that it gets very twitchy to work on and side
loads (twist relieving) turns it in to taco time. Maybe you have some
super mutant rim.

In fact, not to make myself look too stupid, I was playing with a
Velocity Aerohead rear wheel the other day (in a fit of time wasting)
doing some tension balancing by tone and tensiometer -- just to see
how good my pitch was or how accurate the tensiometer was. Well, I
was only working the right side which was at a final tension of about
100kgf. (I built this wheel in a hurry at my brother's house using a
brake caliper -- really pretty close, all things considered). I made
some pretty big adjustments (tightening and loosening), working my way
around the wheel, and then it developed a big wobble -- a permanent
one. I can see that sort of thing happening at really high tensions,
but this wheel was not that tight anywhere -- no nipple binding. I
felt like a real dork -- I have built a lot of these wheels with no
problems, and now I have to buy a new rim, because I don't want to
beat this one in to true with wild, out of balance spoke tensions. --
Jay Beattie.

On Sat, 01 Nov 2008 12:43:10 -0700, Jay Beattie wrote:

On Nov 1, 8:12Â*am, jim beam wrote:
On Sat, 01 Nov 2008 09:25:24 -0500, Ben C wrote:
On 2008-11-01, jim beam wrote:
On Sat, 01 Nov 2008 05:43:18 -0500, Ben C wrote:

On 2008-10-31, jim beam wrote:
On Thu, 30 Oct 2008 11:57:55 -0500, Ben C wrote:
[...]
When staying in the elastic range of spokes (not going slack)
deflections are in one or two tenths of millimeters, less than
is required to flatten a rim permanently.

That may well be the case.

why? Â*if a rim is at 99.9% of yield, how much strain is it going
to take to effect yield?

Not much, but can you get it to 99.9% of yield without stripping
the nipple threads or tacoing? See also Steve's test:

Â* Â* "My testing has shown that any wheel that has a shallow
Â* Â* (19mm) to medium (25mm) depth and is tensioned to 110kg will
Â* Â* have spokes going slack well before the rim starts to
Â* Â* permanantly deform. Obviously the shallower the rim the more
Â* Â* it will bend before permanently deforming. On an average
Â* Â* depth rim (21mm) I would say that the rim can deflect at
Â* Â* least another .5mm in the radial direction before you start
Â* Â* to plasticly deform."

Still I think you might be able to get the tension a bit higher
than 110kgf (on say an Open Pro or CXP 33, both of which are deeper
section than an MA2) but I don't know how high.

it will go quite a bit higher -

http://www.flickr.com/photos/38636024@N00/1498602218/

that is a mavic x517 rim - similar profile to open pro, single
eyelet.

The gauge says about 26.5. What's that in Newtons?

for 1.8mm spokes, what that one is, my handy park tension meter
conversion table tops out at 26 = 175kgf.

I wonder if there is a problem with the tensiometer (inaccure at higher
readings) -- because when you get high tensions on an Open Pro
(1.8/2.0), you start start getting serious nipple binding -- even if
there is lubrication, and you can get eyelet pull out.

there's nothing wrong, or as some idiot accused at the time, rigged with
that tensiometer. i did however build that wheel with grease on the spoke
nipples, and d.t. swiss spoke wrench that doesn't burr. indeed, the
eyelets have pulled very slightly.



Also, tension
above about 125kgf leads to cracking around the spoke holes after not
too many miles.

indeed - as you would expect with a highly anisotropic material on its
yield limit like this.



It has also been my experience that really high tension
makes for an untrueable wheel -- not to create myth and lore, but I
think the rim gathers or puckers (don't take that to the bank), but the
bottom line, is that it gets very twitchy to work on and side loads
(twist relieving) turns it in to taco time. Maybe you have some super
mutant rim.

maybe, but the bottom line is that modern deeper profile rims can take a
fearsome tension before onset of buckling, so all this twaddle about spoke
tension "as high as the rim can bear" is just underinformed guesswork - no
better than a car mechanic telling you he doesn't need a torque wrench to
fix your head gasket. sure, he may get it on, and sure, it work "ok" for
a while, but at best it's a kludge, at worst, it causes expensive [and
stupidly avoidable] damage. cracking in the case of rims.





In fact, not to make myself look too stupid, I was playing with a
Velocity Aerohead rear wheel the other day (in a fit of time wasting)
doing some tension balancing by tone and tensiometer -- just to see how
good my pitch was or how accurate the tensiometer was. Well, I was only
working the right side which was at a final tension of about 100kgf. (I
built this wheel in a hurry at my brother's house using a brake caliper
-- really pretty close, all things considered). I made some pretty big
adjustments (tightening and loosening), working my way around the wheel,
and then it developed a big wobble -- a permanent one. I can see that
sort of thing happening at really high tensions, but this wheel was not
that tight anywhere -- no nipple binding. I felt like a real dork -- I
have built a lot of these wheels with no problems, and now I have to buy
a new rim, because I don't want to beat this one in to true with wild,
out of balance spoke tensions. -- Jay Beattie.