ERD...yet another thread

In article ,
John Everett wrote:

I just went around the house and garage and measured the outside
diameter of a bunch of 700C rims. Not surprisingly they all measured
the same, 634mm (at least with my wooden yardstick). Using the
"non-business" end of my dial caliper it's really easy to measure
depths. Measuring an Alex DM18, the depth from the rim edge to the top
of a spoke hole grommet is 13mm, thus one could call the ERD of this
rim 608mm (634 minus twice 13). The Alex web site lists it as 606.4mm.

It helps to have a single definition of ERD. ERD was never
heard of until it was defined in a book on wheel building.
What you measured is not ERD by the first definition. ERD is
measured to the top of a nipple seated in the rim. You
measured to the seat, and that is not the same thing.

Spoke length calculators that use a different definition of
ERD and manufacturers that use a different definition sow
confusion. The confusion is more harmful than varying definitions
of seat tube length and top tube length. The usual variant
definition of ERD will not by itself cause spokes to be
unusable if the original ERD is measured by the user; but
combined with variations in other measurements or with an
attempt to use spokes a little longer than the output of the
spoke calculator will end in tears. Another variation among
spoke calculators is where they mean for the end of the spoke
to be relative to the top of the nipple. Another variation
is allowance for elastic spoke elongation. These variations
can add up to give a calculated spoke length that is unworkable.

--
Michael Press

In article
,
datakoll wrote:

sez Press:
'ERD is measured in the mid-plane of the rim, not along the spokes.'

if ERD is measured thru the rim's mid-plane then why in explketive
deleted would ERD represent spoke length where spokes do not run thru
the mid plane of the rim???

ERD is not spoke length. It is a dimension among others
used to calculate spoke length.

--
Michael Press

In article
,
datakoll wrote:

Mike,

the subject begs refocusing.

Brandt published a book giving the public access to bicycle wheel
engineering. A significant contribution is the math constant ERD,
standardizing an approach to measuring spoke length.

But Brandt then linked ERD, a number, to Brandt's OPINION on spoke
lengths TO WIT: spokes should run to the top of the nipple head.

Brandt, in giving his incorrect opinion on spoke length forever linked
ERD to an incorrect opinion, reducing ERD's math purity to an
confusing obfuscation. Or conversely gave an incorrect opinion math
certainty.

If you read thru the posts herein, that is what you will read: the
effect of Brandt mixing opinion and math certainty. I wasn't seeking
that production but this is the discussion's result if not
clarification.
Surly, rider-mechanics who rattleon about spoke measurements lying in
the diameter are beyong immediate redemption.

ERD must be defined precisely. Likewise the location of
the end of the calculated spoke length must be defined
precisely. Only then can we depend on the calculated
spoke length to be suitable for our purposes. You are
at liberty to do as you please. You are at liberty to
attack a particular definition of ERD and choice of
spoke end position. You are at liberty to construct
your own edifice to predict the length of the spokes to
use with your rim and hub.

--
Michael Press

On Mar 12, 1:02*pm, Michael Press wrote:
In article
,





*datakoll wrote:
Mike,

the subject begs refocusing.

Brandt published a book giving the public access to bicycle wheel
engineering. A significant contribution is the math constant ERD,
standardizing an approach to measuring spoke length.

But Brandt then linked ERD, a number, to Brandt's OPINION on spoke
lengths TO WIT: spokes should run to the top of the nipple head.

Brandt, in giving his incorrect opinion on spoke length forever linked
ERD to an incorrect opinion, reducing ERD's math purity to an
confusing obfuscation. Or conversely gave an incorrect opinion math
certainty.

If you read thru the posts herein, that is what you will read: the
effect of Brandt mixing opinion and math certainty. I wasn't seeking
that production but this is the discussion's result if not
clarification.
Surly, rider-mechanics who rattleon about spoke measurements lying in
the diameter are beyong immediate redemption.

ERD must be defined precisely. Likewise the location of
the end of the calculated spoke length must be defined
precisely. *Only then can we depend on the calculated
spoke length to be suitable for our purposes. You are
at liberty to do as you please. You are at liberty to
attack a particular definition of ERD and choice of
spoke end position. You are at liberty to construct
your own edifice to predict the length of the spokes to
use with your rim and hub.

--
Michael Press- Hide quoted text -

- Show quoted text -

Mike Rules,

right. I agree more or less.

Rinard/Brandt/Brown/harris is a preeminent spoke calc.
The RBRh calc produces "wrong" spoke lengths from an outdated approach
to the CLASS ERD where point B, the nipple heads., are wrongly defined
as WHERE THE SPOKE ENDS SHOULD BE.
Jesus.
A simple instruction at RBRh for examining real time spoke threading
before choosing the nipple head as point B is what I was lobbying for.

Itsnot a big deal really, a simple instruction is all that's
YYYOOOOOOOOHOOOOOOOO! called for...

Now I did it, again with correction in caps, not changing ERD but
suggesting an after calculation deduction may be in order after
examination of nipple and spoke in real time


Mike Rules,

right. I agree more or less.

Rinard/Brandt/Brown/harris is a preeminent spoke calc.
The RBRh calc produces "wrong" spoke lengths from an outdated approach
to the CLASS ERD where point B, the nipple heads., are wrongly defined
as WHERE THE SPOKE ENDS SHOULD BE.
Jesus.
A simple instruction at RBRh for examining real time spoke threading
before choosing the nipple head as point B as WHERE THE SPOKE ENDS SHOULD BE. is what I was lobbying for.

Itsnot a big deal really, a simple instruction is all that's
YYYOOOOOOOOHOOOOOOOO! called for...- Hide quoted text -

- Show quoted text -

John Everett wrote:
Even though I've now ordered the spokes I was writing about when I
started the ERD thread, I still never received a clear answer to my
original question. Let me rephrase:
Should ERD actually be the diameter of the circle defined by the ends
of the spokes in the built wheel?

Michael Press wrote:
It is the diameter of the circle defined by the outermost
surface of the nipples. Many spoke calculators aim to get
the end of the spoke to or almost to that circle, even taking
into account the elastic elongation of the spoke.

John Everett wrote:
If so, should the end of the spokes
theoretically be even with the top of the nipple, or buried somewhere
inside the nipple? If buried, should they be even with the outside
surface of the rim holes, or even with the bottom of the screwdriver
slot?
Note that we're talking about millimeter differences here, which
strikes me as a bit like discussing the number of angels the can dance
on the head of a pin. ;-)

Michael Press wrote:
Do not ignore small corrections. They can add up
and leave you with a situation that will take
you far longer to remedy than the initial time
investment in getting it right. People who know,
know what can be ignored because the have calculated
the error bounds far closer than one millimeter.

John Everett wrote:
I've re-rimmed wheels with rims that were
5mm larger in published ERD than the originals without problems. Makes
me wonder how many nipple threads actually need to be engaged to build
a safe wheel.

Michael Press wrote:
Asking me? All of them.

John Everett wrote:
I'm guessing from Jobst's response in my OP's thread that ERD is
precisely defined in "The Bicycle Wheel", but I've managed to build a
number of wheels without ever reading it.

Michael Press wrote:
Are you asking for our advice?

datakoll wrote:
See here's another one.
YO MATH WHIZ ? if ERD is a diameter then why are rear spokes in two
lengths ?

Uh, because they are the hypotenuses of two triangles to the same (ERD)
altitude with different (flange offset) bases.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

datakoll wrote:
sez Press:
'ERD is measured in the mid-plane of the rim, not along the spokes.'

if ERD is measured thru the rim's mid-plane then why in explketive
deleted would ERD represent spoke length where spokes do not run thru
the mid plane of the rim???

See if this helps:
http://www.grc.nasa.gov/WWW/K-12/airplane/pythag.html


--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

what's REALLY happening here is correct measurements in all areas
asked for are then distorted by Brandt's authority ndefining ERD as
spokes end at spoke heads.
ERD then determines spoke length on Brandt's authority.
For the unaware, novice, people in a rush...mail odor personnel... DIY
types not reading RBT...

John Everett wrote:
[...]
Anyway I now have my spokes. With this my participation in these
threads ends.

Well spoken.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

On Mar 12, 9:24*pm, Tom Sherman
wrote:
John Everett wrote:
[...]
Anyway I now have my spokes. With this my participation in these
threads ends.

Well spoken.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

my day was ruined