wheelbuilding question

On Fri, 09 Jul 2004 22:09:48 -0700, jim beam
wrote:

in addition, as can be seen in damon rinard's experiments, increasing
spoke tension makes absolutely no difference to lateral strength. see:

http://www.sheldonbrown.com/rinard/wheel/tension.gif

original page:
http://www.sheldonbrown.com/rinard/wheel/index.htm

Careful; the info on that page may not have much to do with a wheel's
lateral strength. Here's a quote from that link:

"It must be emphasized that wheel stiffness is not wheel strength, and
in fact may be unrelated to it. I am measuring stiffness, not
strength."

Also, and this statement doesn't appear to be backed up with any
measurements on that page, but he also says (under question #1):

"A wheel whose spokes become slack while riding is a weak wheel,
because slack spokes cannot support the rim. This can be avoided to a
large extent by building wheels with tighter spokes."

However, I wonder if Jobst's "slight taco" method is only one
potential upper limit on spoke tension. Rims cracking in fatigue,
nipples rounding, hub flanges breaking, etc. may be some others.

But I think we agree in practice. Without lots of experimentation,
it's difficult for me to predict the fatigue stuff before I build the
wheel, so I generally follow the manufacturer's specifications when
available.

jim beam wrote:
in addition, as can be seen in damon rinard's experiments, increasing
spoke tension makes absolutely no difference to lateral strength. see:

http://www.sheldonbrown.com/rinard/wheel/tension.gif

original page:
http://www.sheldonbrown.com/rinard/wheel/index.htm

Rinard's wheel test did not test (lateral) strength, as he
stated in his first paragraph: "I am measuring stiffness,
not strength." His test of measuring lateral stiffness at
varying static spoke tension mainly serves to confirm
Hooke's Law.

However, if you take a closer look at the graph, you'll
notice that the deflection increases dramatically when he
backs the tension off below a certain threshold. This
increase in deflection shows a wheel that is more likely to
fail under load. Although Rinard is using a fixed load, it
can be inferred from this data that increased spoke tension
can increase the strength of a wheel. Indeed, you're
supposition that "increasing spoke tension makes absolutely
no difference in lateral strength" is directly contradicted
by Rinard's conclusion from his test. From the web page
referenced above:

"A wheel whose spokes become slack while riding is a weak
wheel, because slack spokes cannot support the rim. This can
be avoided to a large extent by building wheels with tighter
spokes. If spokes are tighter initially, then the sudden
increase in flexibility shown in data points 9 and 10 is
less likely to occur in use because a tighter wheel can bear
a higher load before spokes become slack."



max spoke tension is determined by the rim's manufacturer. something
like a mavic open pro has a recommended max tension of 100-110 kgf.

While one might like to think that rim manufacturers would
recommend maximum tensions for their rims, I have never
actually seen a manufacturer actually publish such data.
Where did you get the value for the Mavic Open Pro?

On the other hand, the concept of excess spoke tension is
often used as a dodge by manufacturers to avoid warranty
replacement for cracked rims. In none of the cases that I
have seen where a manufacturer's rep. denied a warranty by
claiming "the spoke tension must have been too high", no
measurement of actual spoke tension has been made to base
that claim on, nor has the rep. been able to state what the
recommended max. tension should be. The "excess tension"
argument has simply been used as an easy out.


Mark McMaster

jim beam wrote:
in addition, as can be seen in damon rinard's experiments, increasing
spoke tension makes absolutely no difference to lateral strength. see:

http://www.sheldonbrown.com/rinard/wheel/tension.gif

original page:
http://www.sheldonbrown.com/rinard/wheel/index.htm

Rinard's wheel test did not test (lateral) strength, as he
stated in his first paragraph: "I am measuring stiffness,
not strength." His test of measuring lateral stiffness at
varying static spoke tension mainly serves to confirm
Hooke's Law.

However, if you take a closer look at the graph, you'll
notice that the deflection increases dramatically when he
backs the tension off below a certain threshold. This
increase in deflection shows a wheel that is more likely to
fail under load. Although Rinard is using a fixed load, it
can be inferred from this data that increased spoke tension
can increase the strength of a wheel. Indeed, you're
supposition that "increasing spoke tension makes absolutely
no difference in lateral strength" is directly contradicted
by Rinard's conclusion from his test. From the web page
referenced above:

"A wheel whose spokes become slack while riding is a weak
wheel, because slack spokes cannot support the rim. This can
be avoided to a large extent by building wheels with tighter
spokes. If spokes are tighter initially, then the sudden
increase in flexibility shown in data points 9 and 10 is
less likely to occur in use because a tighter wheel can bear
a higher load before spokes become slack."



max spoke tension is determined by the rim's manufacturer. something
like a mavic open pro has a recommended max tension of 100-110 kgf.

While one might like to think that rim manufacturers would
recommend maximum tensions for their rims, I have never
actually seen a manufacturer actually publish such data.
Where did you get the value for the Mavic Open Pro?

On the other hand, the concept of excess spoke tension is
often used as a dodge by manufacturers to avoid warranty
replacement for cracked rims. In none of the cases that I
have seen where a manufacturer's rep. denied a warranty by
claiming "the spoke tension must have been too high", no
measurement of actual spoke tension has been made to base
that claim on, nor has the rep. been able to state what the
recommended max. tension should be. The "excess tension"
argument has simply been used as an easy out.


Mark McMaster

Mark McMaster wrote:
jim beam wrote:

in addition, as can be seen in damon rinard's experiments, increasing
spoke tension makes absolutely no difference to lateral strength. see:

http://www.sheldonbrown.com/rinard/wheel/tension.gif

original page:
http://www.sheldonbrown.com/rinard/wheel/index.htm


Rinard's wheel test did not test (lateral) strength, as he stated in his
first paragraph: "I am measuring stiffness, not strength." His test of
measuring lateral stiffness at varying static spoke tension mainly
serves to confirm Hooke's Law.

hookes law merely states that deformation is directly proportional to
load below yield - the definition of elastic deformation. it's no
predictor of yield or modulus, both of which are measures of "strength".
by that same argument, increasing tension does not increase strength
just the same as it does not increase stiffness.


However, if you take a closer look at the graph, you'll notice that the
deflection increases dramatically when he backs the tension off below a
certain threshold. This increase in deflection shows a wheel that is
more likely to fail under load.

that's an assumption, not a fact. the deflection increases, for slack
spokes /because/ they're slack. if you're towing a car with a slack
rope, the distance between the two cars will increase until the rope
becomes taught. then the distance between the two cars is essentially
fixed and subject only to minor stretching of the rope - many orders of
magnitude less that slack take-up.

Although Rinard is using a fixed load,
it can be inferred from this data that increased spoke tension can
increase the strength of a wheel.

"inferred" how? the material does not change - this material still has
to obey hookes law until it yields. increasing load merely makes it
bend further. if you think about it, pre-tension serves to reduce the
load capacity of a component not increase it.

Indeed, you're supposition that
"increasing spoke tension makes absolutely no difference in lateral
strength" is directly contradicted by Rinard's conclusion from his
test. From the web page referenced above:

"A wheel whose spokes become slack while riding is a weak wheel, because
slack spokes cannot support the rim. This can be avoided to a large
extent by building wheels with tighter spokes. If spokes are tighter
initially, then the sudden increase in flexibility shown in data points
9 and 10 is less likely to occur in use because a tighter wheel can bear
a higher load before spokes become slack."

there's no contradiction. the left part of the graph is essentially a
flat line. leftwards is increasing tension. once you're in the flat
line region, increasing tension is not increasing lateral stiffness.




max spoke tension is determined by the rim's manufacturer. something
like a mavic open pro has a recommended max tension of 100-110 kgf.


While one might like to think that rim manufacturers would recommend
maximum tensions for their rims, I have never actually seen a
manufacturer actually publish such data. Where did you get the value for
the Mavic Open Pro?

mavic's tech service department - i called them. you can also google
this group - peter chisholm can quote you tensions for a number of rims.


On the other hand, the concept of excess spoke tension is often used as
a dodge by manufacturers to avoid warranty replacement for cracked
rims.

i can see this might be a dodge sometimes, at least at the retail level,
but on a trade basis [the majority of the business] a manufacturer is
entitled to not be second-guessed by a consumer about use in service.
if an diving cylinder manufacturer specified a certain maximum charge
pressure, but a user chose to exceed that manufacturer's limit because
they wanted to extend their dive time, who would be liable for the
resulting cylinder failure? how about a retailer recommending excess
pressure to a consumer because they thought they knew better than the
manufacturer?

In none of the cases that I have seen where a manufacturer's rep.
denied a warranty by claiming "the spoke tension must have been too
high", no measurement of actual spoke tension has been made to base that
claim on,

how are you going to measure original tension once the rim has failed
and slackened the spokes? you /can/ research the s-n fatigue graph for
a component and map out cycles to failure for each load increment. once
you know stress and the curve, you can accurately predict cycles to
failure. likewise, if you can judge cycles to failure from braking
surface wear, you know very closely the load to which the rim has been
subject. and that can also be referenced back to the rim's batch number
and q.c. lab tests. if it's not from a defective batch, then the rim
/has/ to have been subect to use outside of spec.

nor has the rep. been able to state what the recommended max.
tension should be.

as stated above, mavic service dept had no problem telling me
recommended tensions.

The "excess tension" argument has simply been used
as an easy out.

this may be true, but it may not. how many times have you been in a
store and watched other people arguing over something petty like
returning a used garment? 9 times out of 10, the returnee with attitude
will be given a hard time, just because the store personnel hate being
treated like dirt, not because there isn't a valid argument.

Mark McMaster wrote:
jim beam wrote:

in addition, as can be seen in damon rinard's experiments, increasing
spoke tension makes absolutely no difference to lateral strength. see:

http://www.sheldonbrown.com/rinard/wheel/tension.gif

original page:
http://www.sheldonbrown.com/rinard/wheel/index.htm


Rinard's wheel test did not test (lateral) strength, as he stated in his
first paragraph: "I am measuring stiffness, not strength." His test of
measuring lateral stiffness at varying static spoke tension mainly
serves to confirm Hooke's Law.

hookes law merely states that deformation is directly proportional to
load below yield - the definition of elastic deformation. it's no
predictor of yield or modulus, both of which are measures of "strength".
by that same argument, increasing tension does not increase strength
just the same as it does not increase stiffness.


However, if you take a closer look at the graph, you'll notice that the
deflection increases dramatically when he backs the tension off below a
certain threshold. This increase in deflection shows a wheel that is
more likely to fail under load.

that's an assumption, not a fact. the deflection increases, for slack
spokes /because/ they're slack. if you're towing a car with a slack
rope, the distance between the two cars will increase until the rope
becomes taught. then the distance between the two cars is essentially
fixed and subject only to minor stretching of the rope - many orders of
magnitude less that slack take-up.

Although Rinard is using a fixed load,
it can be inferred from this data that increased spoke tension can
increase the strength of a wheel.

"inferred" how? the material does not change - this material still has
to obey hookes law until it yields. increasing load merely makes it
bend further. if you think about it, pre-tension serves to reduce the
load capacity of a component not increase it.

Indeed, you're supposition that
"increasing spoke tension makes absolutely no difference in lateral
strength" is directly contradicted by Rinard's conclusion from his
test. From the web page referenced above:

"A wheel whose spokes become slack while riding is a weak wheel, because
slack spokes cannot support the rim. This can be avoided to a large
extent by building wheels with tighter spokes. If spokes are tighter
initially, then the sudden increase in flexibility shown in data points
9 and 10 is less likely to occur in use because a tighter wheel can bear
a higher load before spokes become slack."

there's no contradiction. the left part of the graph is essentially a
flat line. leftwards is increasing tension. once you're in the flat
line region, increasing tension is not increasing lateral stiffness.




max spoke tension is determined by the rim's manufacturer. something
like a mavic open pro has a recommended max tension of 100-110 kgf.


While one might like to think that rim manufacturers would recommend
maximum tensions for their rims, I have never actually seen a
manufacturer actually publish such data. Where did you get the value for
the Mavic Open Pro?

mavic's tech service department - i called them. you can also google
this group - peter chisholm can quote you tensions for a number of rims.


On the other hand, the concept of excess spoke tension is often used as
a dodge by manufacturers to avoid warranty replacement for cracked
rims.

i can see this might be a dodge sometimes, at least at the retail level,
but on a trade basis [the majority of the business] a manufacturer is
entitled to not be second-guessed by a consumer about use in service.
if an diving cylinder manufacturer specified a certain maximum charge
pressure, but a user chose to exceed that manufacturer's limit because
they wanted to extend their dive time, who would be liable for the
resulting cylinder failure? how about a retailer recommending excess
pressure to a consumer because they thought they knew better than the
manufacturer?

In none of the cases that I have seen where a manufacturer's rep.
denied a warranty by claiming "the spoke tension must have been too
high", no measurement of actual spoke tension has been made to base that
claim on,

how are you going to measure original tension once the rim has failed
and slackened the spokes? you /can/ research the s-n fatigue graph for
a component and map out cycles to failure for each load increment. once
you know stress and the curve, you can accurately predict cycles to
failure. likewise, if you can judge cycles to failure from braking
surface wear, you know very closely the load to which the rim has been
subject. and that can also be referenced back to the rim's batch number
and q.c. lab tests. if it's not from a defective batch, then the rim
/has/ to have been subect to use outside of spec.

nor has the rep. been able to state what the recommended max.
tension should be.

as stated above, mavic service dept had no problem telling me
recommended tensions.

The "excess tension" argument has simply been used
as an easy out.

this may be true, but it may not. how many times have you been in a
store and watched other people arguing over something petty like
returning a used garment? 9 times out of 10, the returnee with attitude
will be given a hard time, just because the store personnel hate being
treated like dirt, not because there isn't a valid argument.

"jim beam" wrote
Jonesy wrote:

That's true - the more tension you can bring to bear (before
destroying the rim) the better. Read "The Bicycle Wheel" by Jobst
Brandt.

i know that "high tension" recommendation is "in the book" and often
repeated here, but it's a fundamentally flawed piece of advice.

It's also a misquote. The technique Jobst describes is qualified to work only
with lightweight (430 g or less), 36 spoke rims.

the
closer a rim is operated to it's yield point, the less will be its
fatigue life, with the kind of results reported here yesterday:

http://mixednutsband.com/crack4.jpg

just because a rim doesn't fail with static load, doesn't mean it can
take the fatigue load. that's why there are so many reliability
complaint here on r.b.t.

Historically, the dominant wheel problems have been spoke breakage & wheels
coming out of true. Cracking of the spoke bed is strictly a matter of rim
design and spoke tension. For wheels like the one shown, the use of a
tensiometer would seem mandatory.

in addition, as can be seen in damon rinard's experiments, increasing
spoke tension makes absolutely no difference to lateral strength. see:

http://www.sheldonbrown.com/rinard/wheel/tension.gif

original page:
http://www.sheldonbrown.com/rinard/wheel/index.htm

I think you are confusing strength and stiffness. The rationale for high spoke
tension is that radial, not lateral, loads cause the spoke to lose tension, so
the spoke tension (& number of spokes) determines the load carrying capacity
of the wheel. If a wheel is loaded beyond that, the spokes may become
de-tensioned enough to either cause wheel collapse or nipple unscrewing.

"jim beam" wrote
Jonesy wrote:

That's true - the more tension you can bring to bear (before
destroying the rim) the better. Read "The Bicycle Wheel" by Jobst
Brandt.

i know that "high tension" recommendation is "in the book" and often
repeated here, but it's a fundamentally flawed piece of advice.

It's also a misquote. The technique Jobst describes is qualified to work only
with lightweight (430 g or less), 36 spoke rims.

the
closer a rim is operated to it's yield point, the less will be its
fatigue life, with the kind of results reported here yesterday:

http://mixednutsband.com/crack4.jpg

just because a rim doesn't fail with static load, doesn't mean it can
take the fatigue load. that's why there are so many reliability
complaint here on r.b.t.

Historically, the dominant wheel problems have been spoke breakage & wheels
coming out of true. Cracking of the spoke bed is strictly a matter of rim
design and spoke tension. For wheels like the one shown, the use of a
tensiometer would seem mandatory.

in addition, as can be seen in damon rinard's experiments, increasing
spoke tension makes absolutely no difference to lateral strength. see:

http://www.sheldonbrown.com/rinard/wheel/tension.gif

original page:
http://www.sheldonbrown.com/rinard/wheel/index.htm

I think you are confusing strength and stiffness. The rationale for high spoke
tension is that radial, not lateral, loads cause the spoke to lose tension, so
the spoke tension (& number of spokes) determines the load carrying capacity
of the wheel. If a wheel is loaded beyond that, the spokes may become
de-tensioned enough to either cause wheel collapse or nipple unscrewing.

Peter Cole wrote:
"jim beam" wrote

Jonesy wrote:


That's true - the more tension you can bring to bear (before
destroying the rim) the better. Read "The Bicycle Wheel" by Jobst
Brandt.

i know that "high tension" recommendation is "in the book" and often
repeated here, but it's a fundamentally flawed piece of advice.


It's also a misquote. The technique Jobst describes is qualified to work only
with lightweight (430 g or less), 36 spoke rims.

has he ever said that? i don't have his book in front of me; i can't
recall such a qualification, but i've seen jonsey's kind of statement
here many times.



the
closer a rim is operated to it's yield point, the less will be its
fatigue life, with the kind of results reported here yesterday:

http://mixednutsband.com/crack4.jpg

just because a rim doesn't fail with static load, doesn't mean it can
take the fatigue load. that's why there are so many reliability
complaint here on r.b.t.


Historically, the dominant wheel problems have been spoke breakage & wheels
coming out of true. Cracking of the spoke bed is strictly a matter of rim
design and spoke tension. For wheels like the one shown, the use of a
tensiometer would seem mandatory.

good observations.



in addition, as can be seen in damon rinard's experiments, increasing
spoke tension makes absolutely no difference to lateral strength. see:

http://www.sheldonbrown.com/rinard/wheel/tension.gif

original page:
http://www.sheldonbrown.com/rinard/wheel/index.htm


I think you are confusing strength and stiffness. The rationale for high spoke
tension is that radial, not lateral, loads cause the spoke to lose tension, so
the spoke tension (& number of spokes) determines the load carrying capacity
of the wheel. If a wheel is loaded beyond that, the spokes may become
de-tensioned enough to either cause wheel collapse or nipple unscrewing.

i've read the radial loading argument of high tension [and i know the
difference between strength & stiffness!]. regarding lateral loading,
this adds to the spoke pre tension on one side and subtracts from the
other. radial loads subtract only. if a spoke has a yield strength of
say 300kg, preloading it to 200kg only gives 100kg of lateral load
before yield. if the spokes have 100kg preload, it means they can take
twice as much lateral.

i want to be clear - i'm not advocating "too low tension" - i'm saying
that tension needs to be within spec, not this nebulous unscientific
concept of "as high as the rim can bear". agreed, too low tension can
lead to nipple unscrewing, but i guess that's why spoke manufacturers
sell threadlock & self-locking nipples.

Peter Cole wrote:
"jim beam" wrote

Jonesy wrote:


That's true - the more tension you can bring to bear (before
destroying the rim) the better. Read "The Bicycle Wheel" by Jobst
Brandt.

i know that "high tension" recommendation is "in the book" and often
repeated here, but it's a fundamentally flawed piece of advice.


It's also a misquote. The technique Jobst describes is qualified to work only
with lightweight (430 g or less), 36 spoke rims.

has he ever said that? i don't have his book in front of me; i can't
recall such a qualification, but i've seen jonsey's kind of statement
here many times.



the
closer a rim is operated to it's yield point, the less will be its
fatigue life, with the kind of results reported here yesterday:

http://mixednutsband.com/crack4.jpg

just because a rim doesn't fail with static load, doesn't mean it can
take the fatigue load. that's why there are so many reliability
complaint here on r.b.t.


Historically, the dominant wheel problems have been spoke breakage & wheels
coming out of true. Cracking of the spoke bed is strictly a matter of rim
design and spoke tension. For wheels like the one shown, the use of a
tensiometer would seem mandatory.

good observations.



in addition, as can be seen in damon rinard's experiments, increasing
spoke tension makes absolutely no difference to lateral strength. see:

http://www.sheldonbrown.com/rinard/wheel/tension.gif

original page:
http://www.sheldonbrown.com/rinard/wheel/index.htm


I think you are confusing strength and stiffness. The rationale for high spoke
tension is that radial, not lateral, loads cause the spoke to lose tension, so
the spoke tension (& number of spokes) determines the load carrying capacity
of the wheel. If a wheel is loaded beyond that, the spokes may become
de-tensioned enough to either cause wheel collapse or nipple unscrewing.

i've read the radial loading argument of high tension [and i know the
difference between strength & stiffness!]. regarding lateral loading,
this adds to the spoke pre tension on one side and subtracts from the
other. radial loads subtract only. if a spoke has a yield strength of
say 300kg, preloading it to 200kg only gives 100kg of lateral load
before yield. if the spokes have 100kg preload, it means they can take
twice as much lateral.

i want to be clear - i'm not advocating "too low tension" - i'm saying
that tension needs to be within spec, not this nebulous unscientific
concept of "as high as the rim can bear". agreed, too low tension can
lead to nipple unscrewing, but i guess that's why spoke manufacturers
sell threadlock & self-locking nipples.

"jim beam" wrote
Peter Cole wrote:

It's also a misquote. The technique Jobst describes is qualified to work
only
with lightweight (430 g or less), 36 spoke rims.

has he ever said that? i don't have his book in front of me; i can't
recall such a qualification, but i've seen jonsey's kind of statement
here many times.

I wrote that with the book in front of me, it's stated very clearly.


i've read the radial loading argument of high tension [and i know the
difference between strength & stiffness!].

OK, it's really the only argument Jobst makes.

regarding lateral loading,
this adds to the spoke pre tension on one side and subtracts from the
other. radial loads subtract only. if a spoke has a yield strength of
say 300kg, preloading it to 200kg only gives 100kg of lateral load
before yield. if the spokes have 100kg preload, it means they can take
twice as much lateral.

This lateral load argument doesn't really have any practical considerations.

i want to be clear - i'm not advocating "too low tension" - i'm saying
that tension needs to be within spec, not this nebulous unscientific
concept of "as high as the rim can bear". agreed, too low tension can
lead to nipple unscrewing, but i guess that's why spoke manufacturers
sell threadlock & self-locking nipples.

The more serious consequence is that the wheel can become unstable and buckle.