SAPIM Spoke FAtigue Estimate



J

Johan Bornman

Guest
In my hand I have a SAPIM brochure - Trust in SAPIM Spokes.

On the second-last page of the brochure, SAPIM has a graph showing the
estimated spoke life in wheel revolutions. The company's standard
double-butted spoke, the Race, has an estimated life of just under 1
million revolutions.

Let's say 1 million for argument sake, and that a wheel revolution
translates into two meters on the road. Therefore, the spoke life is
only 2 million meters or, 2000 kms. Not exactly something to brag
about.

Interestingly, but as an aside to this inaccurate estimate by SAPIM,
the company's CD-Ray product, a 2,3mm wide bladed spoke, has an
estimated life of 3,5 million "Wheel Revolutions (in cycles), as SAPIM
puts it.

Why would the company think that it's bladed spoke will last longer
than the round one? Since diameter is a difficult comparison in this
case, perhaps weight is. The bladed spoke has a weight index of 278,
whereas the round one 360. The index btw, is my invention, they weigh
278g per sample length per X number of spokes.

Johan Bornman
 
J

jim beam

Guest
Johan Bornman wrote:
> In my hand I have a SAPIM brochure - Trust in SAPIM Spokes.
>
> On the second-last page of the brochure, SAPIM has a graph showing the
> estimated spoke life in wheel revolutions. The company's standard
> double-butted spoke, the Race, has an estimated life of just under 1
> million revolutions.
>
> Let's say 1 million for argument sake, and that a wheel revolution
> translates into two meters on the road. Therefore, the spoke life is
> only 2 million meters or, 2000 kms. Not exactly something to brag
> about.


that is machine testing, not wheel testing. the machine loads from
0-80kg each cycle. what does a wheel load on each cycle?

>
> Interestingly, but as an aside to this inaccurate estimate by SAPIM,
> the company's CD-Ray product, a 2,3mm wide bladed spoke, has an
> estimated life of 3,5 million "Wheel Revolutions (in cycles), as SAPIM
> puts it.


how much bending moment can a skinny bladed spoke exert compared to a
fat straight gauge spoke?

>
> Why would the company think that it's bladed spoke will last longer
> than the round one?


they don't "think", they test. if tests show one lasts longer than the
other...

> Since diameter is a difficult comparison in this
> case, perhaps weight is. The bladed spoke has a weight index of 278,
> whereas the round one 360. The index btw, is my invention, they weigh
> 278g per sample length per X number of spokes.


what does weight have to do with it other than being a side-effect of
having more material?
 

dabac

Well-Known Member
Sep 16, 2003
2,298
288
83
52
Johan Bornman said:
In my hand I have a SAPIM brochure - Trust in SAPIM Spokes.

On the second-last page of the brochure, SAPIM has a graph showing the
estimated spoke life in wheel revolutions. The company's standard
double-butted spoke, the Race, has an estimated life of just under 1
million revolutions.

Let's say 1 million for argument sake, and that a wheel revolution
translates into two meters on the road. Therefore, the spoke life is
only 2 million meters or, 2000 kms. Not exactly something to brag
about.

Don't you realize that you have just committed a most heinous crime - you dared to question Impressive, Big, Round Numbers Used In Marketing!
 
K

Kinky Cowboy

Guest
On 7 Feb 2007 06:07:53 -0800, "Johan Bornman" <[email protected]>
wrote:

>
>Why would the company think that it's bladed spoke will last longer
>than the round one?


Because the two spokes have different metallurgy. The production
process for the CX-Ray is much more involved than the basic "take a
bit of wire and bang one end into a mushroom" of a cheap straight
guage spoke.

Disregarding the Sapim "hype", the sheer number of boutique wheels
(HED, Corima, Xtreme) which are built with CX-Rays confirms its
position as the uber-spoke

Kinky Cowboy*

*Batteries not included
May contain traces of nuts
Your milage may vary
 
On 7 Feb 2007 06:07:53 -0800, "Johan Bornman" <[email protected]>
wrote:

>In my hand I have a SAPIM brochure - Trust in SAPIM Spokes.
>
>On the second-last page of the brochure, SAPIM has a graph showing the
>estimated spoke life in wheel revolutions. The company's standard
>double-butted spoke, the Race, has an estimated life of just under 1
>million revolutions.
>
>Let's say 1 million for argument sake, and that a wheel revolution
>translates into two meters on the road. Therefore, the spoke life is
>only 2 million meters or, 2000 kms. Not exactly something to brag
>about.
>
>Interestingly, but as an aside to this inaccurate estimate by SAPIM,
>the company's CD-Ray product, a 2,3mm wide bladed spoke, has an
>estimated life of 3,5 million "Wheel Revolutions (in cycles), as SAPIM
>puts it.
>
>Why would the company think that it's bladed spoke will last longer
>than the round one? Since diameter is a difficult comparison in this
>case, perhaps weight is. The bladed spoke has a weight index of 278,
>whereas the round one 360. The index btw, is my invention, they weigh
>278g per sample length per X number of spokes.
>
>Johan Bornman


Dear Johan,

Your question has come up before--it would be nice if Sapim would
include a description of its testing.

The Sapim spoke fatigue tests must use exaggerated stress cycles
because it takes literally years to break spokes in continuous testing
under ordinary low stress cycles--no spoke manufacturer sells spokes
that are expected to fail in only 2,000 km of normal riding.

In the study below, measured road-test spoke-stress ranged from only
20 to 150 MPa. It took months to break 76 test spokes with continuous
10-cycle-per-second testing at 174 to 501 MPa:

"In 1984 and 1985, fatigue tests on stainless steel bicycle spokes
were carried out for Wheelsmith, Inc. at Stanford University. Constant
cycle tests were conducted with pre-tensioning stresses of 174 MPa,
250 MPa, 343 MPa, 347 MPa, 424 MPa, and 501 MPa. . . . In 68 spokes
the failure occurred at the cold-worked elbow; in the remaining 8
spokes the failure occurred at the threads."

"The smallest stress cycle in the fatigue tests was 174 MPa, whereas
the stress range from the road test data was 20 MPa to 150 MPa. Hence,
the fatigue data was extrapolated to the low stress range. (To have
tested a single sample at 40 MPa would have required over a year of
continuous testing at 10 cycles per second, and an unwarranted use of
facilities.)"

http://www.duke.edu/~hpgavin/papers/HPGavin-Wheel-Paper.pdf

Ten stress cycles per second for a spoke on a 700c wheel is roughly 45
mph. It's also 315,360,000 cycles per year, roughly 630,000 km or
380,000 miles.

It's likely that those 1984 spokes were significantly less durable
than modern spokes.

Cheers,

Carl Fogel
 
J

Johan Bornman

Guest
> Dear Johan,
>
> Your question has come up before--it would be nice if Sapim would
> include a description of its testing.
>
> The Sapim spoke fatigue tests must use exaggerated stress cycles
> because it takes literally years to break spokes in continuous testing
> under ordinary low stress cycles--no spoke manufacturer sells spokes
> that are expected to fail in only 2,000 km of normal riding.
>

I have no doubt that it is an exaggerated test cycle. But don't they
know in marketing hype one doesn't cite exaggerated examples, but best
case scenarios. I have SAPIM-built wheels which have done closer to 40
000 kms. Why would a company misrepresent itself so much? I don't
understand and I don't suppose there is a rational answer for this.

JB
 
J

Johan Bornman

Guest
Jim Beam writes:

> what does weight have to do with it other than being a side-effect of
> having more material?


Everything, the more weight for a given length, the more material. I
assume (with confidence) that they use the same material - 18/8
stainless steel, as the brochure states.

JB
 
On 7 Feb 2007 11:48:26 -0800, "Johan Bornman" <[email protected]>
wrote:

>> Dear Johan,
>>
>> Your question has come up before--it would be nice if Sapim would
>> include a description of its testing.
>>
>> The Sapim spoke fatigue tests must use exaggerated stress cycles
>> because it takes literally years to break spokes in continuous testing
>> under ordinary low stress cycles--no spoke manufacturer sells spokes
>> that are expected to fail in only 2,000 km of normal riding.
>>

>I have no doubt that it is an exaggerated test cycle. But don't they
>know in marketing hype one doesn't cite exaggerated examples, but best
>case scenarios. I have SAPIM-built wheels which have done closer to 40
>000 kms. Why would a company misrepresent itself so much? I don't
>understand and I don't suppose there is a rational answer for this.
>
>JB


Dear Johann,

I doubt that Sapim thinks that it's misrepresenting itself.

Sorry that I misunderstood whatever you're complaining about.

Cheers,

Carl Fogel
 
J

jim beam

Guest
Johan Bornman wrote:
> Jim Beam writes:
>
>> what does weight have to do with it other than being a side-effect of
>> having more material?

>
> Everything, the more weight for a given length, the more material.


weight is not known to be a factor in fatigue unless it affects loading
stress in some way.

> I
> assume (with confidence) that they use the same material - 18/8
> stainless steel, as the brochure states.
>
> JB
>
 
J

jim beam

Guest
Johan Bornman wrote:
>> Dear Johan,
>>
>> Your question has come up before--it would be nice if Sapim would
>> include a description of its testing.
>>
>> The Sapim spoke fatigue tests must use exaggerated stress cycles
>> because it takes literally years to break spokes in continuous testing
>> under ordinary low stress cycles--no spoke manufacturer sells spokes
>> that are expected to fail in only 2,000 km of normal riding.
>>

> I have no doubt that it is an exaggerated test cycle. But don't they
> know in marketing hype one doesn't cite exaggerated examples, but best
> case scenarios. I have SAPIM-built wheels which have done closer to 40
> 000 kms. Why would a company misrepresent itself so much? I don't
> understand and I don't suppose there is a rational answer for this.


there /is/ a rational answer for this - almost all fatigue testing is
done on an accelerated basis. since that's standard practice, their
reporting is simply consistent with standard practice.
 
J

Johan Bornman

Guest
On Feb 8, 12:35 am, jim beam <[email protected]> wrote:
>
> > Jim Beam writes:

>
> >> what does weight have to do with it other than being a side-effect of
> >> having more material?

>
> > Johan B wrote: Everything, the more weight for a given length, the more material.

>
> Jim Beam wrote: weight is not known to be a factor in fatigue unless it affects loading
> stress in some way.
>


Johan now says: OK, let me explain why I brought weight into it in the
first place.

1) Sapim Race spokes have a "Wheel Revolutions" limit of 1 000 000
revolutions.
2) Sapim CX-Ray Spokes have a "Wheel Revolutions" limit of 3 500 000
revolutions.
3) They're both made of 18/8 stainless steel.
4) The CX-Ray spoke differs from the Race spoke in that it is a)
flattened and b) has less material for a given length (deducted from
the fact that they WEIGH less than an equivalent length Race spoke).

Thus, all things being equal, a thinner, flattened spoke has a longer
fatigue life than a thicker, round spoke.

We now have two factors that could contribute to the greater fatigue
life - the flattening process or the fact that the shaft is more
flexible (deduced from its relative weight).

There, does that make sense?

JB
 
J

Johan Bornman

Guest
On Feb 8, 12:39 am, jim beam <[email protected]> wrote:
> Johan Bornman wrote:
> >> Dear Johan,

>
> >> Your question has come up before--it would be nice if Sapim would
> >> include a description of its testing.

>
> >> The Sapim spoke fatigue tests must use exaggerated stress cycles
> >> because it takes literally years to break spokes in continuous testing
> >> under ordinary low stress cycles--no spoke manufacturer sells spokes
> >> that are expected to fail in only 2,000 km of normal riding.

>
> > I have no doubt that it is an exaggerated test cycle. But don't they
> > know in marketing hype one doesn't cite exaggerated examples, but best
> > case scenarios. I have SAPIM-built wheels which have done closer to 40
> > 000 kms. Why would a company misrepresent itself so much? I don't
> > understand and I don't suppose there is a rational answer for this.

>
> there /is/ a rational answer for this - almost all fatigue testing is
> done on an accelerated basis. since that's standard practice, their
> reporting is simply consistent with standard practice.- Hide quoted text -
>
> - Show quoted text -


You miss the point, being scientifically rational doesn't make sense
in this brochure. It is intended for consumers who can quickly do the
sums and discover that SAPIM kind of suggests a useful life of 1 000
kms for wheels built with its spokes. A good copywriter with the
company's interest at heart would have phrased the exercise completely
differently.

Johan Bornman
 
R

Ron Ruff

Guest
On Feb 7, 11:02 pm, "Johan Bornman" <[email protected]et> wrote:
> Thus, all things being equal, a thinner, flattened spoke has a longer
> fatigue life than a thicker, round spoke.
>
> We now have two factors that could contribute to the greater fatigue
> life - the flattening process or the fact that the shaft is more
> flexible (deduced from its relative weight).


The ends of the spoke have the same shape and size so it isn't
surprising that spoke with the thinner center section (cross sectional
area) outlasts the thicker one. In practice the thinner spoke will see
a lower stress cycle on the ends, because the center will stretch more
easily.

I don't agree with the way Sapim presented the data... with too little
explaination. But then I never like ads... there are always so many
claims made and so much left out.
 
On Feb 7, 12:38 pm, [email protected] wrote:

> "In 1984 and 1985, fatigue tests on stainless steel bicycle spokes
> were carried out for Wheelsmith, Inc. at Stanford University. Constant
> cycle tests were conducted with pre-tensioning stresses of 174 MPa,
> 250 MPa, 343 MPa, 347 MPa, 424 MPa, and 501 MPa. . . . In 68 spokes
> the failure occurred at the cold-worked elbow; in the remaining 8
> spokes the failure occurred at the threads."
>
> "The smallest stress cycle in the fatigue tests was 174 MPa, whereas
> the stress range from the road test data was 20 MPa to 150 MPa. Hence,
> the fatigue data was extrapolated to the low stress range. (To have
> tested a single sample at 40 MPa would have required over a year of
> continuous testing at 10 cycles per second, and an unwarranted use of
> facilities.)"
>
> http://www.duke.edu/~hpgavin/papers/HPGavin-Wheel-Paper.pdf
>
> Ten stress cycles per second for a spoke on a 700c wheel is roughly 45
> mph. It's also 315,360,000 cycles per year, roughly 630,000 km or
> 380,000 miles.
>
> It's likely that those 1984 spokes were significantly less durable
> than modern spokes.


FWIW, Jobst is often quoted disparaging the durability
of older spokes, I think he meant spokes a lot older than
1984. Like 1960s or 1970s spokes. Once upon a time
stainless spokes were pretty rare (and I don't know if they
were all good either). By the mid 80s people might likely
have been building with DT (or Wheelsmith?) stainless
spokes fairly similar to today's. I would guess that a couple
of the grotty old Mavic wheels in the picture I posted to
the Finite Element thread are from the 80s, (red/gold Mavic
sticker era) and they have nice DT stainless spokes.
Time has not been as kind to the spoke eyelets.

Ben
 
J

jim beam

Guest
Johan Bornman wrote:
> On Feb 8, 12:39 am, jim beam <[email protected]> wrote:
>> Johan Bornman wrote:
>>>> Dear Johan,
>>>> Your question has come up before--it would be nice if Sapim would
>>>> include a description of its testing.
>>>> The Sapim spoke fatigue tests must use exaggerated stress cycles
>>>> because it takes literally years to break spokes in continuous testing
>>>> under ordinary low stress cycles--no spoke manufacturer sells spokes
>>>> that are expected to fail in only 2,000 km of normal riding.
>>> I have no doubt that it is an exaggerated test cycle. But don't they
>>> know in marketing hype one doesn't cite exaggerated examples, but best
>>> case scenarios. I have SAPIM-built wheels which have done closer to 40
>>> 000 kms. Why would a company misrepresent itself so much? I don't
>>> understand and I don't suppose there is a rational answer for this.

>> there /is/ a rational answer for this - almost all fatigue testing is
>> done on an accelerated basis. since that's standard practice, their
>> reporting is simply consistent with standard practice.- Hide quoted text -
>>
>> - Show quoted text -

>
> You miss the point, being scientifically rational doesn't make sense
> in this brochure.


it makes more sense than being scientifically irrational or making
claims like "our spokes last forever if you don't use them", which is
basically where you end up if you exclude presentation of normal data.

> It is intended for consumers who can quickly do the
> sums and discover that SAPIM kind of suggests a useful life of 1 000
> kms for wheels built with its spokes.


see above.

> A good copywriter with the
> company's interest at heart would have phrased the exercise completely
> differently.


bottom line, while /you/ may not appreciate the format, the fact is,
sapim are the only ones that dare to present fatigue data. that should
tell you more than anything else.
 
J

jim beam

Guest
Ron Ruff wrote:
> On Feb 7, 11:02 pm, "Johan Bornman" <[email protected]> wrote:
>> Thus, all things being equal, a thinner, flattened spoke has a longer
>> fatigue life than a thicker, round spoke.
>>
>> We now have two factors that could contribute to the greater fatigue
>> life - the flattening process or the fact that the shaft is more
>> flexible (deduced from its relative weight).

>
> The ends of the spoke have the same shape and size so it isn't
> surprising that spoke with the thinner center section (cross sectional
> area) outlasts the thicker one. In practice the thinner spoke will see
> a lower stress cycle on the ends, because the center will stretch more
> easily.


but they don't fatigue in the center. skinnier section however does
produce a much lower bending moment on the elbow - the point where it
does break.

>
> I don't agree with the way Sapim presented the data... with too little
> explaination. But then I never like ads... there are always so many
> claims made and so much left out.
>

yes, there's a good deal left out - but in this case, it's good stuff
about longevity, not bad. if criticism is due, it's for not being bold
enough, not for daring to present data when no one else will.
 
A

A Muzi

Guest
>>>>> Dear Johan,
>>>>> Your question has come up before--it would be nice if Sapim would
>>>>> include a description of its testing.
>>>>> The Sapim spoke fatigue tests must use exaggerated stress cycles
>>>>> because it takes literally years to break spokes in continuous testing
>>>>> under ordinary low stress cycles--no spoke manufacturer sells spokes
>>>>> that are expected to fail in only 2,000 km of normal riding.


>>>> I have no doubt that it is an exaggerated test cycle. But don't they
>>>> know in marketing hype one doesn't cite exaggerated examples, but best
>>>> case scenarios. I have SAPIM-built wheels which have done closer to 40
>>>> 000 kms. Why would a company misrepresent itself so much? I don't
>>>> understand and I don't suppose there is a rational answer for this.


jim beam wrote:
>>> there /is/ a rational answer for this - almost all fatigue testing is
>>> done on an accelerated basis. since that's standard practice, their
>>> reporting is simply consistent with standard practice.-


> Johan Bornman wrote:
>> You miss the point, being scientifically rational doesn't make sense
>> in this brochure.

>

jim beam wrote:
> it makes more sense than being scientifically irrational or making
> claims like "our spokes last forever if you don't use them", which is
> basically where you end up if you exclude presentation of normal data.


> Johan Bornman wrote:
>> It is intended for consumers who can quickly do the
>> sums and discover that SAPIM kind of suggests a useful life of 1 000
>> kms for wheels built with its spokes.


> Johan Bornman wrote:
>> A good copywriter with the
>> company's interest at heart would have phrased the exercise completely
>> differently.


jim beam wrote:
> bottom line, while /you/ may not appreciate the format, the fact is,
> sapim are the only ones that dare to present fatigue data. that should
> tell you more than anything else.


Maybe.
Or were those numbers pulled out of the air? "2000k lifetime" is
nonsensical to anyone with familiarity. But any ad writer would eagerly
write "one million cycles" for any product - especially if he weren't
burdened by knowledge of bikes or spokes.

If they meant 1MM cycles at an extreme load, why no mention of that? If
that was intended, it's simple in English:
"Our product will bear up to 1MM cycles of extreme load"
"Our product sustained 1MM cycles of industry standard fatigue testing"
"Our competitor's product failed at merely 985,00 cycles"

That is not what they wrote.

I was also curious about the smaller-section aero spoke showing 2.3x
longevity. That does not make any sense at all as _less_ material just
couldn't bear _2.3x_ the load cycles. And the values are nice and round,
too, 1,000,000 and 2,300,000. Convenient numbers, those, as they just
happen to fit the price curve but do they relate to the actual product?

It is not at all clear to me.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971
 
J

jim beam

Guest
A Muzi wrote:
>>>>>> Dear Johan,
>>>>>> Your question has come up before--it would be nice if Sapim would
>>>>>> include a description of its testing.
>>>>>> The Sapim spoke fatigue tests must use exaggerated stress cycles
>>>>>> because it takes literally years to break spokes in continuous
>>>>>> testing
>>>>>> under ordinary low stress cycles--no spoke manufacturer sells spokes
>>>>>> that are expected to fail in only 2,000 km of normal riding.

>
>>>>> I have no doubt that it is an exaggerated test cycle. But don't they
>>>>> know in marketing hype one doesn't cite exaggerated examples, but best
>>>>> case scenarios. I have SAPIM-built wheels which have done closer to 40
>>>>> 000 kms. Why would a company misrepresent itself so much? I don't
>>>>> understand and I don't suppose there is a rational answer for this.

>
> jim beam wrote:
>>>> there /is/ a rational answer for this - almost all fatigue testing is
>>>> done on an accelerated basis. since that's standard practice, their
>>>> reporting is simply consistent with standard practice.-

>
>> Johan Bornman wrote:
>>> You miss the point, being scientifically rational doesn't make sense
>>> in this brochure.

>>

> jim beam wrote:
>> it makes more sense than being scientifically irrational or making
>> claims like "our spokes last forever if you don't use them", which is
>> basically where you end up if you exclude presentation of normal data.

>
>> Johan Bornman wrote:
>>> It is intended for consumers who can quickly do the
>>> sums and discover that SAPIM kind of suggests a useful life of 1 000
>>> kms for wheels built with its spokes.

>
>> Johan Bornman wrote:
>>> A good copywriter with the
>>> company's interest at heart would have phrased the exercise completely
>>> differently.

>
> jim beam wrote:
>> bottom line, while /you/ may not appreciate the format, the fact is,
>> sapim are the only ones that dare to present fatigue data. that
>> should tell you more than anything else.

>
> Maybe.
> Or were those numbers pulled out of the air? "2000k lifetime" is
> nonsensical to anyone with familiarity. But any ad writer would eagerly
> write "one million cycles" for any product - especially if he weren't
> burdened by knowledge of bikes or spokes.


no, it's standard practice engineering notation. and it's orders of
magnitude that are of interest - 1,519,341 cycles is indistinguishable
from 1,544,982 in engineering terms.

>
> If they meant 1MM


"MM" is financial, not engineering.

> cycles at an extreme load, why no mention of that? If
> that was intended, it's simple in English:
> "Our product will bear up to 1MM cycles of extreme load"


it's not "extreme", it's simply full cycle as opposed to indeterminate
partial cycle that you have in service. guaranteed to give shortest
life which make testing more practical too - that's why it's standard
practice.

> "Our product sustained 1MM


1M, not 1MM. unless you mean $.

http://en.wikipedia.org/wiki/Engineering_notation

> cycles of industry standard fatigue testing"
> "Our competitor's product failed at merely 985,00 cycles"


then if they didn't name the other manufacturer, r.b.t people would
complain about lack of specificity there too! no manufacturer is
sensibly going to directly target a competitor like that unless they're
run by lawyers or like large legal expenses.

>
> That is not what they wrote.


so they're underselling themselves! how refreshing.

>
> I was also curious about the smaller-section aero spoke showing 2.3x
> longevity. That does not make any sense at all as _less_ material just
> couldn't bear _2.3x_ the load cycles.


it makes absolute sense for the reasons i've stated before. spokes fail
because of elbow bending. consider what exerts the most bending force.

> And the values are nice and round,
> too, 1,000,000 and 2,300,000. Convenient numbers, those, as they just
> happen to fit the price curve but do they relate to the actual product?


actual product. it's standard engineering practice to use round
numbers. first, it's because these are not single spoke results, it's
for multiple samples. second, it's a log scale on the s-n graph.

>
> It is not at all clear to me.
 
G

Gary Young

Guest
On Wed, 07 Feb 2007 07:33:25 -0800, jim beam wrote:

> Johan Bornman wrote:
>> In my hand I have a SAPIM brochure - Trust in SAPIM Spokes.
>>
>> On the second-last page of the brochure, SAPIM has a graph showing the
>> estimated spoke life in wheel revolutions. The company's standard
>> double-butted spoke, the Race, has an estimated life of just under 1
>> million revolutions.
>>
>> Let's say 1 million for argument sake, and that a wheel revolution
>> translates into two meters on the road. Therefore, the spoke life is
>> only 2 million meters or, 2000 kms. Not exactly something to brag
>> about.

>
> that is machine testing, not wheel testing. the machine loads from
> 0-80kg each cycle. what does a wheel load on each cycle?
>
>>
>> Interestingly, but as an aside to this inaccurate estimate by SAPIM,
>> the company's CD-Ray product, a 2,3mm wide bladed spoke, has an
>> estimated life of 3,5 million "Wheel Revolutions (in cycles), as SAPIM
>> puts it.

>
> how much bending moment can a skinny bladed spoke exert compared to a
> fat straight gauge spoke?
>


Except that the spoke that does second best on the test, while not
straight gauge, is a very fat spoke. The "Strong" is 2.3/2.0 and is said
to have a middle-section strength of 1400 N/mm2 and a fatigue life of
1,600,000 revolutions.

Furthermore, bending moment doesn't seem to explain why the Laser
(1.5mm center & 1,250,000 revolutions) does better than the CX (1.3mm
center along one dimension & 1,250,000 revolutions) -- unless the
bending moment is exerted by the 2.8mm dimension of the CX.

>> Why would the company think that it's bladed spoke will last longer
>> than the round one?

>
> they don't "think", they test. if tests show one lasts longer than the
> other...
>
>> Since diameter is a difficult comparison in this case, perhaps weight
>> is. The bladed spoke has a weight index of 278, whereas the round one
>> 360. The index btw, is my invention, they weigh 278g per sample length
>> per X number of spokes.

>
> what does weight have to do with it other than being a side-effect of
> having more material?
 
G

Gary Young

Guest
On Thu, 08 Feb 2007 11:50:03 -0600, A Muzi wrote:

>>>>>> Dear Johan,
>>>>>> Your question has come up before--it would be nice if Sapim would
>>>>>> include a description of its testing. The Sapim spoke fatigue tests
>>>>>> must use exaggerated stress cycles because it takes literally years
>>>>>> to break spokes in continuous testing under ordinary low stress
>>>>>> cycles--no spoke manufacturer sells spokes that are expected to
>>>>>> fail in only 2,000 km of normal riding.

>
>>>>> I have no doubt that it is an exaggerated test cycle. But don't they
>>>>> know in marketing hype one doesn't cite exaggerated examples, but
>>>>> best case scenarios. I have SAPIM-built wheels which have done
>>>>> closer to 40 000 kms. Why would a company misrepresent itself so
>>>>> much? I don't understand and I don't suppose there is a rational
>>>>> answer for this.

>
> jim beam wrote:
>>>> there /is/ a rational answer for this - almost all fatigue testing is
>>>> done on an accelerated basis. since that's standard practice, their
>>>> reporting is simply consistent with standard practice.-

>
>> Johan Bornman wrote:
>>> You miss the point, being scientifically rational doesn't make sense
>>> in this brochure.

>>

> jim beam wrote:
>> it makes more sense than being scientifically irrational or making
>> claims like "our spokes last forever if you don't use them", which is
>> basically where you end up if you exclude presentation of normal data.

>
>> Johan Bornman wrote:
>>> It is intended for consumers who can quickly do the sums and discover
>>> that SAPIM kind of suggests a useful life of 1 000 kms for wheels
>>> built with its spokes.

>
>> Johan Bornman wrote:
>>> A good copywriter with the
>>> company's interest at heart would have phrased the exercise completely
>>> differently.

>
> jim beam wrote:
>> bottom line, while /you/ may not appreciate the format, the fact is,
>> sapim are the only ones that dare to present fatigue data. that should
>> tell you more than anything else.

>
> Maybe.
> Or were those numbers pulled out of the air? "2000k lifetime" is
> nonsensical to anyone with familiarity. But any ad writer would eagerly
> write "one million cycles" for any product - especially if he weren't
> burdened by knowledge of bikes or spokes.
>
> If they meant 1MM cycles at an extreme load, why no mention of that? If
> that was intended, it's simple in English: "Our product will bear up to
> 1MM cycles of extreme load" "Our product sustained 1MM cycles of
> industry standard fatigue testing"
> "Our competitor's product failed at merely 985,00 cycles"
>
> That is not what they wrote.
>
> I was also curious about the smaller-section aero spoke showing 2.3x
> longevity. That does not make any sense at all as _less_ material just
> couldn't bear _2.3x_ the load cycles. And the values are nice and round,
> too, 1,000,000 and 2,300,000. Convenient numbers, those, as they just
> happen to fit the price curve but do they relate to the actual product?
>
> It is not at all clear to me.


Also, the Strong spoke -- a 2.3/2.0mm -- does better than all of the
thin-section spokes except the CX-Ray.

I noticed that Sapim has a new technical document on its website:

www.sapim.be/index.php?st=checklist&taal=uk

This repeats some of the oddities of the old FAQ -- e.g., throw out the
hub if a few spokes break -- and adds some new ones (CX-Ray and Race are
"more resistant to vibrations" than their other spokes?). The old FAQ is
at www.sapim.be/index.php?st=faq.

What I find interesting is that they seem to acknowledge that spoke
alignment is a problem -- see the references to a gap between spoke and
flange and between spoke and nipple (yes, they refer to a "gap" between
spoke and nipple). But instead of recommending that one correct the spoke
line, they suggest getting a new hub or using a different crossing
pattern. Since I've encountered these "gaps" even when using fairly
high-end Shimano hubs (XT and Ultegra), I'd like to know what they suggest
instead (maybe they hope that I'll buy from their marketing partner edco).