ERD for Mavic Open Pro?
Bill
Help! my trusty LBS can't get me a pair of Mavic Open Sports rims (ERD
608mm) just now; but they can get a pair of Mavic Open Pro.
Spocalc's got an entry for the Pro, ERD = 205mm, but it's dated 2001,
getting a bit old.
Can anyone confirm or deny?
THANKS!!
Helmut Springer
> Help! my trusty LBS can't get me a pair of Mavic Open Sports rims
> (ERD 608mm) just now; but they can get a pair of Mavic Open Pro.
>
> Spocalc's got an entry for the Pro, ERD = 205mm, but it's dated
> 2001, getting a bit old.
I wouldn't assume any change?
--
MfG/Best regards
helmut springer panta rhei
Art Harris
> Help! my trusty LBS can't get me a pair of Mavic Open Sports rims (ERD
> 608mm) just now; but they can get a pair of Mavic Open Pro.
>
> Spocalc's got an entry for the Pro, ERD = 205mm, but it's dated 2001,
> getting a bit old.
>
Not 205mm! It's 605mm (although it is sometimes listed as 602mm which
Mavic calls the "spoke support diameter").
Art Harris
jobst....@stanfordalumni.org
Which of course is the Effective Rim Diameter (ERD) but Mavic doesn't
need to use someone else's terminology, they have their own. 205 is
the number that Spocalc produces from the ERD, spoke cross pattern,
and hub hole circle diameter.
Jobst Brandt
Qui si parla Campagnolo
602mm is the ERD used in the wheelsmith spocalc..for OpenPro and yes
for OpenSport it is 608mm
Ben C
> Art Harris wrote:
>
>>> Help! my trusty LBS can't get me a pair of Mavic Open Sports rims
>>> (ERD 608mm) just now; but they can get a pair of Mavic Open Pro.
>
>>> Spocalc's got an entry for the Pro, ERD = 205mm, but it's dated
>>> 2001, getting a bit old.
>
>> Not 205mm! It's 605mm (although it is sometimes listed as 602mm
>> which Mavic calls the "spoke support diameter").
>
> Which of course is the Effective Rim Diameter (ERD) but Mavic doesn't
> need to use someone else's terminology, they have their own.
ERD is not the same as spoke support diameter. ERD = SSD + 3mm.
jobst....@stanfordalumni.org
>>>> Help! my trusty LBS can't get me a pair of Mavic Open Sports rims
>>>> (ERD 608mm) just now; but they can get a pair of Mavic Open Pro.
>>>> Spocalc's got an entry for the Pro, ERD = 205mm, but it's dated
>>>> 2001, getting a bit old.
>>> Not 205mm! It's 605mm (although it is sometimes listed as 602mm
>>> which Mavic calls the "spoke support diameter").
>> Which of course is the Effective Rim Diameter (ERD) but Mavic doesn't
>> need to use someone else's terminology, they have their own.
> ERD is not the same as spoke support diameter. ERD = SSD + 3mm.
Where do the 3mm come from? Effective Rim Diameter is the effective
diameter at which spoke nipples are supported. Spoke length is
calculated from that and the inputs I mentioned.
Jobst Brandt
Bill
Art, Jobst, Ben & Peter -
Yep, Spocalc notes that the ERD is Mavic's ssd +3mm doesn't it... which
is reasonable.
Of course I meant 605mm, not that typo (205mm, some wheel that'd be!)
Thanks a bunch for the confirm - now I can phone my LBS for the spokes &
rims. (Don't like building on a rim I've not handled...)
Hey, and while I'm thanking: Jobst, thanks for your years of good work,
and especially for THE BOOK - which even in the few places I don't
follow it, is invaluable. It's passing down the generations in this
household - both my daughters now build wheels, though like me they
prefer to drop all the spokes through the hub first, then screw in the
crossing pairs - much the fastest way to lace, I've found :-)
Thanks guys!!
Ben C
Spoke Support Diameter is the distance between opposite nipple seats.
ERD is the distance between the opposite spoke-ends, which is SSD + 3mm
if you want the spokes to come up into the nipple heads a bit.
3mm is about the height of two nipple heads, and is the amount spocalc
uses to convert SSD into ERD.
Bill
I'd take the 3mm to be the height of the nipple head, doubled. Mavic's
602mm is the diameter across the rim; it doesn't include the spoke
heads.
What does Damon Rinard say in his notes on Spocalc? [looking it up]:
"Effective Rim Diameter (ERD) is the diameter on which you want the ends
of the spokes to lie. Most people prefer it near the end of the spoke
nipple" (http://www.sheldonbrown.com/rinard/spocalc.htm).
I prefer mine just below the spoke head, so I knock off the decimal
amount in Spocalc, which usually works fine.
Tom Sherman
> ...
> Of course I meant 605mm, not that typo (205mm, some wheel that'd be!)
The ISO 203-mm bead seat diameter wheels are used on the smallest
children's bicycles, some push scooters, most jogging strollers, etc.
--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful
jobst....@stanfordalumni.org
>>>>>> Help! my trusty LBS can't get me a pair of Mavic Open Sports
>>>>>> rims (ERD 608mm) just now; but they can get a pair of Mavic
>>>>>> Open Pro.
>>>>>> Spocalc's got an entry for the Pro, ERD = 205mm, but it's dated
>>>>>> 2001, getting a bit old.
>>>>> Not 205mm! It's 605mm (although it is sometimes listed as 602mm
>>>>> which Mavic calls the "spoke support diameter").
>>>> Which of course is the Effective Rim Diameter (ERD) but Mavic
>>>> doesn't need to use someone else's terminology, they have their
>>>> own.
>>> ERD is not the same as spoke support diameter. ERD = SSD + 3mm.
>> Where do the 3mm come from? Effective Rim Diameter is the
>> effective diameter at which spoke nipples are supported. Spoke
>> length is calculated from that and the inputs I mentioned.
> Spoke Support Diameter is the distance between opposite nipple
> seats.
> ERD is the distance between the opposite spoke-ends, which is SSD +
> 3mm if you want the spokes to come up into the nipple heads a bit.
Wrong! Effective Rim Diameter (ERD) is exactly that. The diameter on
which spoke niples sit. Spoke length is therefore, such that extend
about 3mm farther to reach the head of the nipple.
Spoke support diameter is also the diameter that supports the spoke
nipples.
> 3mm is about the height of two nipple heads, and is the amount
> spocalc uses to convert SSD into ERD.
Spocalc uses ERD to compute spoke length. SPoke length is NOT ERD.
Jobst Brandt
jobst....@stanfordalumni.org
>>>>>> Help! my trusty LBS can't get me a pair of Mavic Open Sports
>>>>>> rims (ERD 608mm) just now; but they can get a pair of Mavic
>>>>>> Open Pro.
>>>>>> Spocalc's got an entry for the Pro, ERD = 205mm, but it's dated
>>>>>> 2001, getting a bit old.
>>>>> Not 205mm! It's 605mm (although it is sometimes listed as 602mm
>>>>> which Mavic calls the "spoke support diameter").
>>>> Which of course is the Effective Rim Diameter (ERD) but Mavic
>>>> doesn't need to use someone else's terminology, they have their
>>>> own.
>>> ERD is not the same as spoke support diameter. ERD = SSD + 3mm.
>> Where do the 3mm come from? Effective Rim Diameter is the
>> effective diameter at which spoke nipples are supported. Spoke
>> length is calculated from that and the inputs I mentioned.
> I'd take the 3mm to be the height of the nipple head,
> doubled. Mavic's 602mm is the diameter across the rim; it doesn't
> include the spoke heads.
> What does Damon Rinard say in his notes on Spocalc? [looking it up]:
> "Effective Rim Diameter (ERD) is the diameter on which you want the
> ends of the spokes to lie. Most people prefer it near the end of the
> spoke nipple" (http://www.sheldonbrown.com/rinard/spocalc.htm).
I think you should look in "the Bicycle Wheel" where the term ERD was
first used and defined along with the equations. Damon wrote software
that made use of that information and others have ever after tried to
redefine and confuse the term.
> I prefer mine just below the spoke head, so I knock off the decimal
> amount in Spocalc, which usually works fine.
You can do anything you like but don't tell me that it is ERD or SSD.
Jobst Brandt
Ben C
>>>> ERD is not the same as spoke support diameter. ERD = SSD + 3mm.
>
>>> Where do the 3mm come from? Effective Rim Diameter is the
>>> effective diameter at which spoke nipples are supported. Spoke
>>> length is calculated from that and the inputs I mentioned.
>
>> Spoke Support Diameter is the distance between opposite nipple
>> seats.
>
>> ERD is the distance between the opposite spoke-ends, which is SSD +
>> 3mm if you want the spokes to come up into the nipple heads a bit.
>
> Wrong! Effective Rim Diameter (ERD) is exactly that. The diameter on
> which spoke niples sit. Spoke length is therefore, such that extend
> about 3mm farther to reach the head of the nipple.
I don't like to teach my grandmother to suck eggs, and I wish you were
right (today) and ERD were the same as SSD, since I consider that a much
more logical thing to measure, being an actual diameter rather than an
"effective" one.
But it isn't. ERD is slightly longer than the diameter on which spoke
nipples sit, as you have explained yourself previously:
See
http://groups.google.co.uk/group/rec.bicycles.tech/msg/63cea6d0d5a098ae?hl=en
gene> AS SHELDON BROWN'S GLOSSARY: E.R.D. Effective Rim Diameter. This
gene> is the rim diameter measured at the nipple seats in the spoke
gene> holes. The E.R.D. is needed for calculating the correct spoke
gene> length.
jobst.brandt> That's one interpretation but since the term arose first
jobst.brandt> in "the Bicycle Wheel, as did the geometric equations that
jobst.brandt> are commonly used today, I think this is not correct
jobst.brandt> because that diameter is used to calculate the diagonals
jobst.brandt> from sums of squares to give the length to the outer end
jobst.brandt> of spokes. That point being a nipple head farther out.
jobst.brandt> The proper length should reach the end of the nipple when
jobst.brandt> tight, not the bed of the rim, which is as much as 3mm
jobst.brandt> short of that. That is why it is called an "effective rim
jobst.brandt> diameter", because it is not the inner outer or other real
jobst.brandt> diameters.
and as it is explained in Sheldon's glossary:
http://www.sheldonbrown.com/gloss_e-f.html
> Spoke support diameter is also the diameter that supports the spoke
> nipples.
>
>> 3mm is about the height of two nipple heads, and is the amount
>> spocalc uses to convert SSD into ERD.
>
> Spocalc uses ERD to compute spoke length. SPoke length is NOT ERD.
Correct, and that is the main thing to get right or you could end up
ordering spokes for a highwheeler by mistake-- not just a few mm out.
Ben C
[...]
> See
> http://groups.google.co.uk/group/rec.bicycles.tech/msg/63cea6d0d5a098ae?hl=en
>
> gene> AS SHELDON BROWN'S GLOSSARY: E.R.D. Effective Rim Diameter. This
> gene> is the rim diameter measured at the nipple seats in the spoke
> gene> holes. The E.R.D. is needed for calculating the correct spoke
> gene> length.
Now I just noticed that Gene quoted that very badly...
[...]
> and as it is explained in Sheldon's glossary:
> http://www.sheldonbrown.com/gloss_e-f.html
The full text is:
Effective Rim Diameter. This is the rim diameter measured at the
nipple seats in the spoke holes, PLUS THE THICKNESS OF THE TWO
NIPPLE HEADS. The E.R.D. is needed for calculating the correct spoke
length.
My capitals.
Helmut Springer
>> and as it is explained in Sheldon's glossary:
>> http://www.sheldonbrown.com/gloss_e-f.html
>
> The full text is:
>
> Effective Rim Diameter. This is the rim diameter measured at
> the nipple seats in the spoke holes, PLUS THE THICKNESS OF THE
> TWO NIPPLE HEADS. The E.R.D. is needed for calculating the
> correct spoke length.
I never understood why Sheldon insisted on this: ERD is a
characteristic of the rim, and as such independent from whether one
choses to have the spoke inside the nipple head or not. The
calculation can take care of the latter if one does.
Art Harris
> > Effective Rim Diameter. This is the rim diameter measured at
> > the nipple seats in the spoke holes, PLUS THE THICKNESS OF THE
> > TWO NIPPLE HEADS. The E.R.D. is needed for calculating the
> > correct spoke length.
>
> I never understood why Sheldon insisted on this: ERD is a
> characteristic of the rim, and as such independent from whether one
> choses to have the spoke inside the nipple head or not. The
> calculation can take care of the latter if one does.
>
I think Spocalc's definition of ERD is what causes all this grief. A
note in Spocalc says, "ERD is the Effective Rim Diameter. ERD is
measured to the end of the spoke, usually flush with the head of the
nipple."
For the Open Pro, Spocalc shows an "ERD" of 605mm, while Mavic lists
it as 602mm. According to Peter, Wheelsmith also lists it as 602.
Art Harris
Ben C
It's one thing to be clear on the terminology, another how long you want
your spokes. Some people use spoke support diameter (SSD) when
calculating spoke length without adding 3mm, others use SSD+3mm because
they like their spokes a little bit longer.
I believe Sheldon's definition of ERD is correct-- it's consistent with
comments in spocalc.xls (and with Jobst's earlier comments although
there seems to be some confusion about that now).
Although the definition is correct, I think it's a confusing concept.
Better to quote SSD for rims (and call it that) as Mavic do because it's
more obvious what they actually mean and that it's a characteristic of
the rim. Then add 3mm if you want to.
Ben C
> Helmut Springer wrote:
>> > Effective Rim Diameter. This is the rim diameter measured at
>> > the nipple seats in the spoke holes, PLUS THE THICKNESS OF THE
>> > TWO NIPPLE HEADS. The E.R.D. is needed for calculating the
>> > correct spoke length.
>>
>> I never understood why Sheldon insisted on this: ERD is a
>> characteristic of the rim, and as such independent from whether one
>> choses to have the spoke inside the nipple head or not. The
>> calculation can take care of the latter if one does.
>>
>
> I think Spocalc's definition of ERD is what causes all this grief. A
> note in Spocalc says, "ERD is the Effective Rim Diameter. ERD is
> measured to the end of the spoke, usually flush with the head of the
> nipple."
That's consistent with Sheldon's definition. If you could measure the
straight line distance between the ends of two opposite spokes in the
finished wheel, assuming they come up to flush with the heads of the
nipples, that would be the ERD.
> For the Open Pro, Spocalc shows an "ERD" of 605mm, while Mavic lists
> it as 602mm. According to Peter, Wheelsmith also lists it as 602.
Are you sure Mavic aren't quoting an SSD of 602mm? That would make the
ERD 605mm.
jobst....@stanfordalumni.org
ERD := SSD = "Effective Rim Diameter", and has nothing to do with how
far spokes protrude through the rim. Sheldon's two sentences are
about two dimensions, ERD and Spoke length. Only an imprecise reader
will mix the two.
Mavic's coining of a new term is classic for bicycle wheel folks,
their ego preventing them from using a previously well defined term,
like "stress relief" but rather calling it "stabilizing" or
"tensiometer" often called "tensionometer".
http://www.merriam-webster.com/dictionary/tensiometer
http://www.merriam-webster.com/dictionary/tensionometer
Jobst Brandt
Michael Press
Ben C <spam...@spam.eggs> wrote:
Too bad. ERD _should_ mean effective _rim_ diameter without
corrections for spoke extension. Spoke extension should
be simply another parameter to enter into the calculation.
The rim can be measured, and easily too. We can _measure_
the distance between antipodal spoke nipple seats. That
_should_ be ERD.
We now have competing definitions. Feh!
--
Michael Press
Michael Press
Helmut Springer <delta+...@lug-s.org> wrote:
Hear! Hear!
--
Michael Press
Ben C
Yes and those instructions say very clearly that ERD is SSD plus the
thickness of the two nipple heads.
As we know, that dimension (either ERD or SSD, or SSD+3mm, according to
taste) is then used to calculate the spoke length.
You are inadvertently spreading confusion. ERD is NOT the same as
Mavic's SSD, check your own previous posts on the subject.
If someone were to get an ERD quoted for a Mavic rim from spocalc, add
3mm under the mistaken impression that ERD = SSD, then their spokes
would be too long, by enough that it might actually be a problem.
Like others I think SSD is the more sensible measurement to quote, but
whatever you do, don't *redefine* ERD. Instead start using SSD and let
the term ERD die a natural death.
The number of long threads debating what the hell it means on RBT, and
the fact that you-- who invented the term in the first place-- are now
getting it wrong yourself are enough evidence that it's a confusing
idea.
Gene summarized it well here:
http://groups.google.co.uk/group/rec.bicycles.tech/msg/acabf03c04d18297?hl=en
and here
http://groups.google.co.uk/group/rec.bicycles.tech/msg/67ea8bbbbdac11e9?hl=en
jobst....@stanfordalumni.org
I think the concept of an Effective Rim Diameter is a mystery to most
who encounter the concept. Its raison d'etre is that spoke length for
any given lacing pattern is derived from a diameter that is neither
the outside or inside diameter of a rim. That is why I chose ERD as a
determining dimension for spoke length calculation for wheel building
and defined how it is measured.
What others have made of it seems to be some sort of fetish whose
appeal I cannot understand.
> If someone were to get an ERD quoted for a Mavic rim from spocalc,
> add 3mm under the mistaken impression that ERD = SSD, then their
> spokes would be too long, by enough that it might actually be a
> problem.
The height of spoke nipple heads and what to do with it is up to the
practitioner to decide. Whether it is 3mm or greater depends on what
one chooses and what sort of spoke nipples are used after computing
spoke length.
> Like others I think SSD is the more sensible measurement to quote,
> but whatever you do, don't *redefine* ERD. Instead start using SSD
> and let the term ERD die a natural death.
This reminds me of the years of writers from the UK attacking "the
Bicycle Wheel" being all wrong about load distribution in a wire
spokes bicycle wheel and that the wheel hangs from the spokes at the
top of the wheel.
> The number of long threads debating what the hell it means on RBT,
> and the fact that you-- who invented the term in the first place--
> are now getting it wrong yourself are enough evidence that it's a
> confusing idea.
That's your interpretation. As I said, the ERD is neither the ID or
OD of a rim and must be determined for reasonable spoke length
calculation. I find your assessment revisionist.
> Gene summarized it well here:
http://groups.google.co.uk/group/rec.bicycles.tech/msg/acabf03c04d18297?hl=en
> and here
http://groups.google.co.uk/group/rec.bicycles.tech/msg/67ea8bbbbdac11e9?hl=en
That's fine if you want to see it that way but the basis of
determining required spoke length is based on ERD as I defined it and
published the equations that produce the desired result. Your
redefinition is not useful for the process and Damon Rinard knows that
as well.
Jobst Brandt
Art Harris
> Too bad. ERD _should_ mean effective _rim_ diameter without
> corrections for spoke extension. Spoke extension should
> be simply another parameter to enter into the calculation.
> The rim can be measured, and easily too. We can _measure_
> the distance between antipodal spoke nipple seats. That
> _should_ be ERD.
>
> We now have competing definitions. Feh!
>
Feh indeed! So where does that leave us?
1) We know that Mavic measures ERD as you describe (to the nipple
seats), but they insist on calling it SSD.
2) Sheldon and Spocalc add the thickness of two nipple heads (about
3mm) to that easily measureable distance, and call that ERD.
3) Spocalc implies that Mavic is doing something different than other
manufacturers.
4) A different Spoke Calculator defines ERD as the distance between
the bottoms of the slots in opposite spoke nipples!
http://www.mapleflow.com/demo/spoke-calculator-pro/index.php?title=help
This is all academic if you have a rim in hand, and can make the ERD
measurement, and if you know what the spoke calculator is looking for.
But what if you don't? Do other manufacturers specify ERD the same way
as Mavic? I'd like to know the true ERD of a rim before ordering!
Art Harris
Ben C
> Ben C? wrote:
[...]
>> thickness of the two nipple heads.
>
>> As we know, that dimension (either ERD or SSD, or SSD+3mm, according
>> to taste) is then used to calculate the spoke length.
>
>> You are inadvertently spreading confusion. ERD is NOT the same as
>> Mavic's SSD, check your own previous posts on the subject.
>
> I think the concept of an Effective Rim Diameter is a mystery to most
> who encounter the concept.
Indeed, and I think that's part of the problem.
> Its raison d'etre is that spoke length for any given lacing pattern is
> derived from a diameter that is neither the outside or inside diameter
> of a rim.
Exactly-- it's a diameter that's slightly greater than the nipple-seat
diameter (SSD). ERD is greater than SSD, by about 3mm.
[...]
>> If someone were to get an ERD quoted for a Mavic rim from spocalc,
>> add 3mm under the mistaken impression that ERD = SSD, then their
>> spokes would be too long, by enough that it might actually be a
>> problem.
>
> The height of spoke nipple heads and what to do with it is up to the
> practitioner to decide. Whether it is 3mm or greater depends on what
> one chooses and what sort of spoke nipples are used after computing
> spoke length.
Yes.
>> Like others I think SSD is the more sensible measurement to quote,
>> but whatever you do, don't *redefine* ERD. Instead start using SSD
>> and let the term ERD die a natural death.
>
> This reminds me of the years of writers from the UK attacking "the
> Bicycle Wheel" being all wrong about load distribution in a wire
> spokes bicycle wheel and that the wheel hangs from the spokes at the
> top of the wheel.
All Britishers are fanatic religious fetishists.
>> The number of long threads debating what the hell it means on RBT,
>> and the fact that you-- who invented the term in the first place--
>> are now getting it wrong yourself are enough evidence that it's a
>> confusing idea.
>
> That's your interpretation. As I said, the ERD is neither the ID or
> OD of a rim and must be determined for reasonable spoke length
> calculation. I find your assessment revisionist.
No, I agree with the way you're defining it now. That is consistent with
Sheldon's glossary and comments in Damon Rinard's spreadsheet.
>> Gene summarized it well here:
>
> http://groups.google.co.uk/group/rec.bicycles.tech/msg/acabf03c04d18297?hl=en
>
>> and here
>
> http://groups.google.co.uk/group/rec.bicycles.tech/msg/67ea8bbbbdac11e9?hl=en
>
> That's fine if you want to see it that way but the basis of
> determining required spoke length is based on ERD as I defined it and
> published the equations that produce the desired result. Your
> redefinition is not useful for the process and Damon Rinard knows that
> as well.
I haven't redefined anything! I was a bit worried you were for a minute
there though.
Ben C
> Michael Press wrote:
>> Too bad. ERD _should_ mean effective _rim_ diameter without
>> corrections for spoke extension. Spoke extension should
>> be simply another parameter to enter into the calculation.
>> The rim can be measured, and easily too. We can _measure_
>> the distance between antipodal spoke nipple seats. That
>> _should_ be ERD.
>>
>> We now have competing definitions. Feh!
>>
>
> Feh indeed! So where does that leave us?
>
> 1) We know that Mavic measures ERD as you describe (to the nipple
> seats), but they insist on calling it SSD.
Yes, call that SSD. Don't call it ERD or Gene will subtract 3mm (because
he likes his spokes to come up a bit less high) and end up with spokes
too short.
> 2) Sheldon and Spocalc add the thickness of two nipple heads (about
> 3mm) to that easily measureable distance, and call that ERD.
Yes, that is ERD.
> 3) Spocalc implies that Mavic is doing something different than other
> manufacturers.
>
>
> 4) A different Spoke Calculator defines ERD as the distance between
> the bottoms of the slots in opposite spoke nipples!
> http://www.mapleflow.com/demo/spoke-calculator-pro/index.php?title=help
I think that is effectively the same definition as Jobst's and
Sheldon's. But this is where it gets really subtle...
One definition of ERD is "the diameter between where you want opposite
spoke ends in the finished wheel".
The problem with this definition is that it is subjective-- different
people have different opinions about how high up into the nipples you
want the spokes to come.
They say on that page you want the spoke ends to the bottom of the
screwdriver slots, making ERD (for them) the same as SSD, or as SSD plus
only a small amount.
Some people like them a little higher, making ERD (for them) about 3mm
greater than SSD. I believe Jobst and Sheldon both recommend ERDs a bit
longer than SSDs (and I think it's good advice-- but what do I know).
The only sane way out of this is for everyone to quote SSD and then for
wheelbuilders to add whatever they want to add depending on the nipples
they're using and their preference.
> This is all academic if you have a rim in hand, and can make the ERD
> measurement, and if you know what the spoke calculator is looking for.
The spoke calculator gives you a spoke length that should result in
opposite spoke ends separated by the ERD.
> But what if you don't? Do other manufacturers specify ERD the same way
> as Mavic? I'd like to know the true ERD of a rim before ordering!
That's what I really don't know... I know what Mavic mean, but I've no
idea about the others.
The best advice is just to use the quoted figure. If it's SSD and you
like your spokes a bit longer, tough, they'll still work. If the quoted
figure is greater than SSD because whoever quoted it thought you wanted
your spokes a bit longer, and you don't, never mind, it doesn't matter
much.
But if you add or subtract 3mm to a quoted figure and you guess wrong
what they meant, the error could be as big as 6mm and you might actually
have a problem.
Art Harris
> >> Too bad. ERD _should_ mean effective _rim_ diameter without
> >> corrections for spoke extension. Spoke extension should
> >> be simply another parameter to enter into the calculation.
> >> The rim can be measured, and easily too. We can _measure_
> >> the distance between antipodal spoke nipple seats. That
> >> _should_ be ERD.
>
> >> We now have competing definitions.
>
>
> > 1) We know that Mavic measures ERD as you describe (to the nipple
> > seats), but they insist on calling it SSD.
>
> Yes, call that SSD. Don't call it ERD or Gene will subtract 3mm (because
> he likes his spokes to come up a bit less high) and end up with spokes
> too short.
Most people have never heard of SSD, and anyway it is exactly the same
as ERD was originally defined.
>
> > 2) Sheldon and Spocalc add the thickness of two nipple heads (about
> > 3mm) to that easily measureable distance, and call that ERD.
>
> Yes, that is ERD.
Not to everyone, as you describe below.
>
> > 3) Spocalc implies that Mavic is doing something different than other
> > manufacturers.
>
> > 4) A different Spoke Calculator defines ERD as the distance between
> > the bottoms of the slots in opposite spoke nipples!
> >http://www.mapleflow.com/demo/spoke-calculator-pro/index.php?title=help
>
> I think that is effectively the same definition as Jobst's and
> Sheldon's. But this is where it gets really subtle...
>
I don't think so. I tend to agree with Jobst and Michael Press that
ERD should be strictly based on the rim.
> One definition of ERD is "the diameter between where you want opposite
> spoke ends in the finished wheel".
>
> The problem with this definition is that it is subjective-- different
> people have different opinions about how high up into the nipples you
> want the spokes to come.
>
> They say on that page you want the spoke ends to the bottom of the
> screwdriver slots, making ERD (for them) the same as SSD, or as SSD plus
> only a small amount.
>
> Some people like them a little higher, making ERD (for them) about 3mm
> greater than SSD. I believe Jobst and Sheldon both recommend ERDs a bit
> longer than SSDs (and I think it's good advice-- but what do I know).
>
Jobst has stated that SSD abd ERD are the same. Note that rim inner
diameter is not the same as nipple seat diameter. I don't think there
is a meeting of the minds yet!
> The only sane way out of this is for everyone to quote SSD and then for
> wheelbuilders to add whatever they want to add depending on the nipples
> they're using and their preference.
>
> > This is all academic if you have a rim in hand, and can make the ERD
> > measurement, and if you know what the spoke calculator is looking for.
>
> The spoke calculator gives you a spoke length that should result in
> opposite spoke ends separated by the ERD.
>
> > But what if you don't? Do other manufacturers specify ERD the same way
> > as Mavic? I'd like to know the true ERD of a rim before ordering!
>
> That's what I really don't know... I know what Mavic mean, but I've no
> idea about the others.
>
And that is the problem! Adding new terminology and definitions just
creates confusion. If you know the rim's ERD (to nipple seats), you
can easily adjust to your desired spoke engagement. I prefer to err on
the side of a slightly shorter spoke.
Art Harris
jobst....@stanfordalumni.org
>>> Yes and those instructions say very clearly that ERD is SSD plus
>>> the thickness of the two nipple heads.
>>> As we know, that dimension (either ERD or SSD, or SSD+3mm,
>>> according to taste) is then used to calculate the spoke length.
>>> You are inadvertently spreading confusion. ERD is NOT the same as
>>> Mavic's SSD, check your own previous posts on the subject.
>> I think the concept of an Effective Rim Diameter is a mystery to
>> most who encounter the concept.
> Indeed, and I think that's part of the problem.
>> Its raison d'etre is that spoke length for any given lacing pattern
>> is derived from a diameter that is neither the outside or inside
>> diameter of a rim.
> Exactly-- it's a diameter that's slightly greater than the nipple-seat
> diameter (SSD). ERD is greater than SSD, by about 3mm.
That is your invention, The two terms are identical and say the same
thing. If you read what the definition of ERD is in the book where it
was first introduced, you'll see that it is the support diameter on
which spoke nipples bear.
> [...]
>>> If someone were to get an ERD quoted for a Mavic rim from spocalc,
>>> add 3mm under the mistaken impression that ERD = SSD, then their
>>> spokes would be too long, by enough that it might actually be a
>>> problem.
>> The height of spoke nipple heads and what to do with it is up to
>> the practitioner to decide. Whether it is 3mm or greater depends
>> on what one chooses and what sort of spoke nipples are used after
>> computing spoke length.
> Yes.
>>> Like others I think SSD is the more sensible measurement to quote,
>>> but whatever you do, don't *redefine* ERD. Instead start using SSD
>>> and let the term ERD die a natural death.
>> This reminds me of the years of writers from the UK attacking "the
>> Bicycle Wheel" being all wrong about load distribution in a wire
>> spoked bicycle wheel and that the wheel hangs from the spokes at
>> the top of the wheel.
> All Britishers are fanatic religious fetishists.
>>> The number of long threads debating what the hell it means on RBT,
>>> and the fact that you-- who invented the term in the first place--
>>> are now getting it wrong yourself are enough evidence that it's a
>>> confusing idea.
>> That's your interpretation. As I said, the ERD is neither the ID
>> or OD of a rim and must be determined for reasonable spoke length
>> calculation. I find your assessment revisionist.
> No, I agree with the way you're defining it now. That is consistent
> with Sheldon's glossary and comments in Damon Rinard's spreadsheet.
>>> Gene summarized it well here:
http://groups.google.co.uk/group/rec.bicycles.tech/msg/acabf03c04d18297?hl=en
>>> and here
http://groups.google.co.uk/group/rec.bicycles.tech/msg/67ea8bbbbdac11e9?hl=en
>> That's fine if you want to see it that way but the basis of
>> determining required spoke length is based on ERD as I defined it
>> and published the equations that produce the desired result. Your
>> redefinition is not useful for the process and Damon Rinard knows
>> that as well.
> I haven't redefined anything! I was a bit worried you were for a minute
> there though.
I can't do that. The book is in print and that portion that defines
ERD has never changed and it won't
Jobst Brandt
Ben C
> Ben C? wrote:
[...]
>> diameter (SSD). ERD is greater than SSD, by about 3mm.
>
> That is your invention, The two terms are identical and say the same
> thing. If you read what the definition of ERD is in the book where it
> was first introduced, you'll see that it is the support diameter on
> which spoke nipples bear.
So why does Sheldon's glossary say, "[ERD] is the rim diameter measured
at the nipple seats in the spoke holes, plus the thickness of the two
nipple heads", and why does Spocalc add 3mm to Mavic's SSDs to get ERDs?
jobst....@stanfordalumni.org
ERD was defined in the days when Fiamme and Mavic, socketed rims were
the norm and the diameter at which the pressure faces of spoke nipples
were supported was not readily measurable. For that a method for
arriving at a dimension (ERD) was needed from which one could derive
spoke lengths to build a wheel.
ERD was determined by measuring the rim OD and then, with a depth
gauge, measure into a socket to a spoke nipple that was resting on the
eyelet retaining the spoke socket in the rim. That depth, together
with the spoke nipple head height, was subtracted twice (for two
diametrally located spoke holes) to give ERD, the diameter that
supports spoke nipples.
I don't see what of this is complicated, but I found everything else
in "the Bicycle Wheel" that I felt was simple and straight forward,
could be given other interpretations by readers in spite of proof
reading by critical reviewers who felt the text was unambiguous.
Jobst Brandt
jobst....@stanfordalumni.org
>>> Exactly-- it's a diameter that's slightly greater than the nipple-seat
>>> diameter (SSD). ERD is greater than SSD, by about 3mm.
>> That is your invention, The two terms are identical and say the same
>> thing. If you read what the definition of ERD is in the book where it
>> was first introduced, you'll see that it is the support diameter on
>> which spoke nipples bear.
> So why does Sheldon's glossary say, "[ERD] is the rim diameter
> measured at the nipple seats in the spoke holes, plus the thickness
> of the two nipple heads", and why does Spocalc add 3mm to Mavic's
> SSDs to get ERDs?
He adds 3mm to the computed spoke length. That is not ERD. You keep
mixing parameters and come op with a mess of imprecision.
Jobst Brandt
Ben C
>
> ERD was defined in the days when Fiamme and Mavic, socketed rims were
> the norm and the diameter at which the pressure faces of spoke nipples
> were supported was not readily measurable. For that a method for
> arriving at a dimension (ERD) was needed from which one could derive
> spoke lengths to build a wheel.
>
> ERD was determined by measuring the rim OD and then, with a depth
> gauge, measure into a socket to a spoke nipple that was resting on the
> eyelet retaining the spoke socket in the rim. That depth, together
> with the spoke nipple head height, was subtracted twice (for two
> diametrally located spoke holes) to give ERD, the diameter that
> supports spoke nipples.
If you don't subtract 2x the spoke nipple head height, you have the SSD.
That is why Rinard adds 2x the spoke nipple head height to convert
Mavic's quoted SSDs (that's what they call them-- "Spoke Support
Diameter"s, they don't abbreviate it) into ERDs.
Ben C
>
>>>> Exactly-- it's a diameter that's slightly greater than the nipple-seat
>>>> diameter (SSD). ERD is greater than SSD, by about 3mm.
>
>>> That is your invention, The two terms are identical and say the same
>>> thing. If you read what the definition of ERD is in the book where it
>>> was first introduced, you'll see that it is the support diameter on
>>> which spoke nipples bear.
>
>> So why does Sheldon's glossary say, "[ERD] is the rim diameter
>> measured at the nipple seats in the spoke holes, plus the thickness
>> of the two nipple heads", and why does Spocalc add 3mm to Mavic's
>> SSDs to get ERDs?
>
> He adds 3mm to the computed spoke length.
No, he adds it to the SSD quoted by Mavic. Here is an example, from
spocalc.xls:
ERD: 587 Mavic CXP30 (ERD is Mavic's Nipple Seat Dia + 3mm for nipples)
Adding 3mm to the SSD results in spokes about 1.4mm longer. If you added
3mm to the computed spoke length, that would be too much.
3mm is about two nipple head thicknesses, not one.
Art Harris
> > ERD was determined by measuring the rim OD and then, with a depth
> > gauge, measure into a socket to a spoke nipple that was resting on the
> > eyelet retaining the spoke socket in the rim. That depth, together
>
> ^^^^^^^> with the spoke nipple head height, was subtracted twice (for two
>
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> > diametrally located spoke holes) to give ERD, the diameter that
> > supports spoke nipples.
>
> If you don't subtract 2x the spoke nipple head height, you have the SSD.
>
No! Jobst is starting with the rim's OUTER diameter. Then measuring
depth to a nipple. Then subtracting twice that depth and twice the
nipple head thickness. That gets you the nipple seat diameter (a.k.a.
ERD, a.k.a. SSD).
Art Harris
Ben C
Ah now I see what you mean! I should have read that more carefully.
Thank you. Well that does make SSD and ERD the same according to that
definition of ERD.
But then why does Rinard add 3mm, and how do we explain Sheldon's
glossary entry?
Ben C
And how also to explain this earlier explanation by Jobst:
jobst.brandt> That's one interpretation but since the term arose first
jobst.brandt> in "the Bicycle Wheel, as did the geometric equations that
jobst.brandt> are commonly used today, I think this is not correct
jobst.brandt> because that diameter is used to calculate the diagonals
jobst.brandt> from sums of squares to give the length to the outer end
jobst.brandt> of spokes. That point being a nipple head farther out.
A nipple head farther out from what? I thought he meant a nipple head
farther out from the point on the rim upon which the nipple sits, which
is consistent with the idea that the spoke should come up to the top of
the nipple, and with Sheldon's definition of ERD in his glossary.
It is of course a nipple head farther in from the measurement made with
a depth gauge, so perhaps he was obliquely referring to that... but
that's stretching things.
In any case, the definition he just gave (at the top of this message)
sounds more like the definitive one, and according to that, ERD = SSD.
But that makes Sheldon's glossary wrong, which seems unlikely, although
this is a highly confusing subject.
Art Harris
> And how also to explain this earlier explanation by Jobst:
>
> jobst.brandt> That's one interpretation but since the term arose first
> jobst.brandt> in "the Bicycle Wheel, as did the geometric equations that
> jobst.brandt> are commonly used today, I think this is not correct
> jobst.brandt> because that diameter is used to calculate the diagonals
> jobst.brandt> from sums of squares to give the length to the outer end
> jobst.brandt> of spokes. That point being a nipple head farther out.
>
You left out the part where Gene quoted :
# AS SHELDON BROWN'S GLOSSARY:
# E.R.D.
# Effective Rim Diameter. This is the rim diameter measured at the
# nipple seats in the spoke holes. The E.R.D. is needed for
# calculating the correct spoke length.
So at that time, Sheldon was defining ERD at the nipple seats.
His website now says:
"E.R.D.
Effective Rim Diameter. This is the rim diameter measured at the
nipple seats in the spoke holes, plus the thickness of the two nipple
heads. The E.R.D. is needed for calculating the correct spoke length."
Why the change? I don't know.
But even more interesting, I dug out my first edition copy of The
Bicycle Wheel (1981). On page 132, under Equations, Jobst writes:
"To compute spoke lengths it is necessary to determine the effective
rim diameter "D" to within one millimeter. This is the diameter to
which the end of the fully tensioned spokes extend."
So clearly, "D" wasn't nipple seat diameter. It sounds more like what
you quoted above: "That point being a nipple head further out."
I think we all understand the basic principles at work here. We're
just getting twisted up in definitions.
>
> In any case, the definition he just gave (at the top of this message)
> sounds more like the definitive one, and according to that, ERD = SSD.
> But that makes Sheldon's glossary wrong, which seems unlikely, although
> this is a highly confusing subject.
>
> jobst.brandt> The proper length should reach the end of the nipple when
> jobst.brandt> tight, not the bed of the rim, which is as much as 3mm
> jobst.brandt> short of that. That is why it is called an "effective rim
> jobst.brandt> diameter", because it is not the inner outer or other real
> jobst.brandt> diameters.-
Amen to that.
Art Harris
Ben C
>> And how also to explain this earlier explanation by Jobst:
>>
>> jobst.brandt> That's one interpretation but since the term arose first
>> jobst.brandt> in "the Bicycle Wheel, as did the geometric equations that
>> jobst.brandt> are commonly used today, I think this is not correct
>> jobst.brandt> because that diameter is used to calculate the diagonals
>> jobst.brandt> from sums of squares to give the length to the outer end
>> jobst.brandt> of spokes. That point being a nipple head farther out.
>>
>
> You left out the part where Gene quoted :
>
> # AS SHELDON BROWN'S GLOSSARY:
> # E.R.D.
> # Effective Rim Diameter. This is the rim diameter measured at the
> # nipple seats in the spoke holes. The E.R.D. is needed for
> # calculating the correct spoke length.
>
> So at that time, Sheldon was defining ERD at the nipple seats.
>
>
> His website now says:
>
> "E.R.D.
> Effective Rim Diameter. This is the rim diameter measured at the
> nipple seats in the spoke holes, plus the thickness of the two nipple
> heads. The E.R.D. is needed for calculating the correct spoke length."
>
> Why the change? I don't know.
That did just occur to me. At first I thought Gene misquoted for some
reason (and that's what I said in the next post).
But perhaps Sheldon did change the glossary. Even more worryingly, he
might have changed it because he was reading that very thread.
You see I thought, during that thread, that Sheldon had defined it as
Gene quoted (ERD = SSD), but that everyone else, including Jobst, was
saying ERD = SSD + a bit.
Then I checked the glossary again and thought I'd missed something
because there was that extra bit about two nipple head heights. I
assumed I'd misremembered, but perhaps Sheldon did make a change during
that thread, because he thought (as I did) everyone was saying ERD = SSD
+ a bit.
> But even more interesting, I dug out my first edition copy of The
> Bicycle Wheel (1981). On page 132, under Equations, Jobst writes:
> "To compute spoke lengths it is necessary to determine the effective
> rim diameter "D" to within one millimeter. This is the diameter to
> which the end of the fully tensioned spokes extend."
>
> So clearly, "D" wasn't nipple seat diameter. It sounds more like what
> you quoted above: "That point being a nipple head further out."
Good point.
> I think we all understand the basic principles at work here. We're
> just getting twisted up in definitions.
Yes. As many others have said, the measurement should, in an ideal
world, be a property only of the rim, and have nothing to do with how
high up into the nipple you want the spokes to come.
Where it gets really confusing is that for many people the SSD is the
ideal spoke end position, so to them the definitions (spoke end diameter
and nipple seat diameter) are equivalent. If it never occurred to you to
want the spokes longer than that you wouldn't see a problem defining it
that way.
I had Jobst down as someone who did recommend the spokes coming up into
the nipples a bit, but it's abundantly possible I misunderstood that. He
may want the spoke ends at SSD, which makes that 1981 definition
consistent.
That would also make Gene happy as he can't understand why anyone would
want spokes longer than SSD.
Art Harris
>
> > But even more interesting, I dug out my first edition copy of The
> > Bicycle Wheel (1981). On page 132, under Equations, Jobst writes:
> > "To compute spoke lengths it is necessary to determine the effective
> > rim diameter "D" to within one millimeter. This is the diameter to
> > which the end of the fully tensioned spokes extend."
>
> > So clearly, "D" wasn't nipple seat diameter.
> Good point.
>
>
> Where it gets really confusing is that for many people the SSD is the
> ideal spoke end position, so to them the definitions (spoke end diameter
> and nipple seat diameter) are equivalent.
>
> I had Jobst down as someone who did recommend the spokes coming up into
> the nipples a bit,
>
Back in January,Jobst wrote:
"The ERD is the diameter to which the threaded ends of spokes are to
reach, and that is the top of spoke nipples inserted in the rim.
This
can be assessed by measuring the outside rim diameter and subtracting
twice the distance measured down to the spoke nipple head from this
outer diameter... meaning Effective Rim Diameter for spoking. "
That definition of ERD is consistent with what appears in my copy of
The Bicycle wheel. It is not consistent with what Jobst wrote in this
current thread.
The method above starts with the rim's OD and subtracts twice the
depth from the outer edge of the rim to the top of the nipple. That is
not nipple seat diameter (a.k.a. Spoke Support Diameter). It is nipple
seat diameter plus twice the nipple head thickness.
Therefore, since Mavic only provides SSD, approximately 3mm needs to
be added to that to get ERD. It makes sense for Mavic to provide SSD
rather than SSD because spoke nipples can have different thicknesses.
Spocalc needs ERD not SSD to make its calculations.
I think other rim manufacturers provide ERD, but I'm not sure of that.
Jobst recommends that spokes come flush with the top of the nipple.
Some folks prefer the spokes at the bottom of the slot. Your reference
to the bottom of the nipple head sounds a little short to me, but not
a disaster.
Art Harris
Ben C
> Ben C wrote:
>
>>
>> > But even more interesting, I dug out my first edition copy of The
>> > Bicycle Wheel (1981). On page 132, under Equations, Jobst writes:
>> > "To compute spoke lengths it is necessary to determine the effective
>> > rim diameter "D" to within one millimeter. This is the diameter to
>> > which the end of the fully tensioned spokes extend."
>>
>> > So clearly, "D" wasn't nipple seat diameter.
>
>> Good point.
>>
>>
>> Where it gets really confusing is that for many people the SSD is the
>> ideal spoke end position, so to them the definitions (spoke end diameter
>> and nipple seat diameter) are equivalent.
>>
>> I had Jobst down as someone who did recommend the spokes coming up into
>> the nipples a bit,
>>
>
> Back in January,Jobst wrote:
>
> "The ERD is the diameter to which the threaded ends of spokes are to
> reach, and that is the top of spoke nipples inserted in the rim.
> This
> can be assessed by measuring the outside rim diameter and subtracting
> twice the distance measured down to the spoke nipple head from this
> outer diameter... meaning Effective Rim Diameter for spoking. "
>
> http://tinyurl.com/6eeqzk
>
> That definition of ERD is consistent with what appears in my copy of
> The Bicycle wheel.
And also with Sheldon's glossary (as it is today) and Damon Rinard's
comments in spocalc.xls.
> It is not consistent with what Jobst wrote in this current thread.
I agree, it would seem not.
> The method above starts with the rim's OD and subtracts twice the
> depth from the outer edge of the rim to the top of the nipple. That is
> not nipple seat diameter (a.k.a. Spoke Support Diameter). It is nipple
> seat diameter plus twice the nipple head thickness.
Yes.
> Therefore, since Mavic only provides SSD, approximately 3mm needs to
> be added to that to get ERD. It makes sense for Mavic to provide SSD
> rather than SSD because spoke nipples can have different thicknesses.
Yes. I wish everyone just provided SSD.
> Spocalc needs ERD not SSD to make its calculations.
Exactly-- so you add a bit to SSD before putting it into the calculator
if you want to.
> I think other rim manufacturers provide ERD, but I'm not sure of that.
And if they do, how to be sure they mean ERD as defined in The Bicycle
Wheel and by the January version of Jobst, or if they mean SSD, or if
they mean the diameter to the bottom of the screwdriver slots (which is
between the two) like the link you posted earlier:
http://www.mapleflow.com/demo/spoke-calculator-pro/index.php?title=help
> Jobst recommends that spokes come flush with the top of the nipple.
> Some folks prefer the spokes at the bottom of the slot. Your reference
> to the bottom of the nipple head sounds a little short to me, but not
> a disaster.
I think that's about the minimum. I guess it also depends what kind of
rim: if you've got a double-skinned rim like the typical Mavic there's a
bit more room for the spoke to come up a bit higher. The slightly longer
spoke makes lacing easier and makes sure you've got plenty of threads
engaged. But on something like a cheap MTB rim there's more of a risk of
the spoke sticking into the inner tube if it's a bit too long.
The spoke does elongate a little bit when it's tensioned so using SSD
directly works out OK. I used Mavic's SSD for the last two kinds of
wheels I built and the spokes ended up at least as far as the
screwdriver slot. YMMV (your millimeterage may vary).
Art Harris
[Regarding spoke engagment to the bottom of the nipple head]
> I think that's about the minimum. I guess it also depends what kind of
> rim: if you've got a double-skinned rim like the typical Mavic there's a
> bit more room for the spoke to come up a bit higher.
I just did a test with a DT spoke and nipple. The spoke thread bottoms
out when the end of the spoke is about 1mm beyond the top of the
nipple head. That's one rerason why I usually round down when ordering
spokes.
Art Harris
jobst....@stanfordalumni.org
>>> But even more interesting, I dug out my first edition copy of The
>>> Bicycle Wheel (1981). On page 132, under Equations, Jobst writes:
>>> "To compute spoke lengths it is necessary to determine the
>>> effective rim diameter "D" to within one millimeter. This is the
>>> diameter to which the end of the fully tensioned spokes extend."
>>> >> So clearly, "D" wasn't nipple seat diameter.
>> Good point.
>> Where it gets really confusing is that for many people the SSD is
>> the ideal spoke end position, so to them the definitions (spoke end
>> diameter and nipple seat diameter) are equivalent.
>> I had Jobst down as someone who did recommend the spokes coming up
>> into the nipples a bit,
> Back in January,Jobst wrote:
> "The ERD is the diameter to which the threaded ends of spokes are to
> reach, and that is the top of spoke nipples inserted in the rim.
> This can be assessed by measuring the outside rim diameter and
> subtracting twice the distance measured down to the spoke nipple
> head from this outer diameter... meaning Effective Rim Diameter for
> spoking."
I was wrong about that because nipple height and other personal
preferences should not be a part of ERD as I mentioned more recently.
Nipple height and whether the spoke should lie below that or above can
readily be added by the user.
> That definition of ERD is consistent with what appears in my copy of
> The Bicycle wheel. It is not consistent with what Jobst wrote in
> this current thread.
You are right and I was remiss in not following my precepts in that
discussion in the book.
> The method above starts with the rim's OD and subtracts twice the
> depth from the outer edge of the rim to the top of the nipple. That
> is not nipple seat diameter (a.k.a. Spoke Support Diameter). It is
> nipple seat diameter plus twice the nipple head thickness.
The problem is that many different spoke nipple types have +-1mm
differences in head thickness and for instance some hex head spoke
nipples have heads that are 4mm high
> Therefore, since Mavic only provides SSD, approximately 3mm needs to
> be added to that to get ERD. It makes sense for Mavic to provide
> SSD rather than SSD because spoke nipples can have different
> thicknesses.
I'm in favo of that and I see why Mavic decided on their own term SSD
for this dimension, to not get caught up in that which has swirled
aroun in this thread.
> Spocalc needs ERD not SSD to make its calculations.
> I think other rim manufacturers provide ERD, but I'm not sure of
> that.
> Jobst recommends that spokes come flush with the top of the nipple.
> Some folks prefer the spokes at the bottom of the slot. Your
> reference to the bottom of the nipple head sounds a little short to
> me, but not a disaster.
Thanks,
Jobst Brandt
Ben C
I get "500 - Internal Server Error" for that link.
Thank you for clearing this up.
Unfortunately this means your book and Sheldon's glossary (the two most
definitive sources for many people) both have the wrong definition :(
What's the solution? Leave ERD as SSD + about 3mm, and steer towards
using the less confusing term SSD instead; or try to redefine ERD as it
should have been defined in the first place? I think the former since
it's hard to undo a definition.
Art Harris
> > Back in January,Jobst wrote:
> > "The ERD is the diameter to which the threaded ends of spokes are to
> > reach, and that is the top of spoke nipples inserted in the rim.
> > This can be assessed by measuring the outside rim diameter and
> > subtracting twice the distance measured down to the spoke nipple
> > head from this outer diameter... meaning Effective Rim Diameter for
> > spoking."
>
> I was wrong about that because nipple height and other personal
> preferences should not be a part of ERD as I mentioned more recently.
> Nipple height and whether the spoke should lie below that or above can
> readily be added by the user.
>
> differences in head thickness and for instance some hex head spoke
> nipples have heads that are 4mm high
>
> > Therefore, since Mavic only provides SSD, approximately 3mm needs to
> > be added to that to get ERD. It makes sense for Mavic to provide
> > thicknesses.
>
> I'm in favor of that and I see why Mavic decided on their own term SSD
> for this dimension, to not get caught up in that which has swirled
> aroun in this thread.
>
Thanks, I think we're all in sync now.
The only problem is that the "ERD" numbers in Spocalc and most
published ERD specs (except for Mavic) include the extra 3mm for
nipple head thickness. That's not a problem as long it's clearly
defined that way. If someone is using thicker nipples, or prefers
shorter/longer spokes, they can easily add or subtract a millimeter or
two from the Spocalc result.
I agree with Ben that since The Bicycle Wheel, Sheldon Brown's
glossary, and Spocalc all define ERD as the diameter to the nipple
tops, it's probably best to leave it that way. SSD should be adopted
as a separate manufacturers spec.
Art Harris
A Muzi
>>> correct spoke length.
> Helmut Springer wrote:
>> I never understood why Sheldon insisted on this: ERD is a
>> characteristic of the rim, and as such independent from whether one
>> choses to have the spoke inside the nipple head or not. The
>> calculation can take care of the latter if one does.
Art Harris wrote:
> I think Spocalc's definition of ERD is what causes all this grief. A
> note in Spocalc says, "ERD is the Effective Rim Diameter. ERD is
> measured to the end of the spoke, usually flush with the head of the
> nipple."
>
> For the Open Pro, Spocalc shows an "ERD" of 605mm, while Mavic lists
> it as 602mm. According to Peter, Wheelsmith also lists it as 602.
>
> Art Harris
I have been called philistine and worse but what the heck is wrong with
a spoke length to the bottom of the slot in the nipple? We find that
optimal. Longer if one uses some weaker alternate material nipple maybe.
In a normal bicycle wheel, it saves grief all over to not maximize
spoke length.
The experience of being at the end of a build only to find the nipples
cannot thread through the end is frustrating. A build with single wall
rims raises stakes on spoke length calculation as well. I assume people
who build with aluminum nipples in hollow rims would just correct for
that independently. It need not affect common usage of "ERD".
--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971
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