What is ERD...really?



J

John Everett

Guest
Following up on a couple of postings from a few weeks ago, I'm about
to order the spokes for my touring bike's wheel rebuild. I used Damon
Rinard's spocalc.xls to figure the lengths.

I used his hub database, but plugged in the ERD from the Alex Rims web
site for the DM18, 606.4mm.

Since I had the rear hub de-spoked I decided to check the database's
measurements and found that the figures given for a Shimano RSX
FH-A410, 7-speed, 130mm, was off by a few mms. The flange offsets were
wrong, but correcting them only resulted (as one would expect) in
fractional mm changes in spoke length.

Since I was in a measuring mood I decided to check the ERD. I referred
to: http://sheldonbrown.com/rinard/spocalc.htm#MeasureHubAndRim for
the methodology and got an ERD of 612mm. I did check rim roundness
(it's round to within a mm) but I was using a wooden yardstick with a
metric scale on one side so accuracy could be compromised. Still, a
six mm error is pretty far out there.

The method Rinard recommends measures ERD to the top of the nipples.
If I measure to the top of the spoke hole grommets I get 607mm, a lot
closer to the Alex web site figure.

So is ERD measured to the top of the nipple or the top of the spoke
grommet? If I'm using spocalc should I add the height of two nipple
heads to 606.4mm to get the correct answer?

BTW, for the hub mentioned above the left flange offset is 32mm and
the right 19mm.

--
jeverett3<AT>sbcglobal<DOT>net (John V. Everett)
 
Jobst Brandt claims ERD is his idea.

The geometric construction gives a theoretic snapshot.
Actual practice requires examination of the spoke/nipple combo in
hand.
RD requires spoke's threading up to nipple top. If the combo doesn't
do that, adjust for reality. A DT 16mm nipple does not thread a DT
spoke to nipple head.
ERD is effective rim DIAMETER not effective rim RADIUS.
See Andrew Muzi's photo in the ERD posts. Muzi goes short 1.5mm from
base nipple screwdriver slot not head. I try for mileage in HD touring
and short 2.5+ accomadating wear and tear.
Best to build a dishing beam of straight grade 1 tuba4, drill a hole/
basin for the hub, shim up to dish at rim's diameter, right side for
rear and run 8 experimental LBS spokes on that platform.
MEASURE REALITY ON THE BEAM
 
John Everett said:
Following up on a couple of postings from a few weeks ago, I'm about
to order the spokes for my touring bike's wheel rebuild. I used Damon
Rinard's spocalc.xls to figure the lengths.

I used his hub database, but plugged in the ERD from the Alex Rims web
site for the DM18, 606.4mm.

Since I had the rear hub de-spoked I decided to check the database's
measurements and found that the figures given for a Shimano RSX
FH-A410, 7-speed, 130mm, was off by a few mms. The flange offsets were
wrong, but correcting them only resulted (as one would expect) in
fractional mm changes in spoke length.

Since I was in a measuring mood I decided to check the ERD. I referred
to: http://sheldonbrown.com/rinard/spocalc.htm#MeasureHubAndRim for
the methodology and got an ERD of 612mm. I did check rim roundness
(it's round to within a mm) but I was using a wooden yardstick with a
metric scale on one side so accuracy could be compromised. Still, a
six mm error is pretty far out there.

The method Rinard recommends measures ERD to the top of the nipples.
If I measure to the top of the spoke hole grommets I get 607mm, a lot
closer to the Alex web site figure.

So is ERD measured to the top of the nipple or the top of the spoke
grommet? If I'm using spocalc should I add the height of two nipple
heads to 606.4mm to get the correct answer?

BTW, for the hub mentioned above the left flange offset is 32mm and
the right 19mm.

--
jeverett3<AT>sbcglobal<DOT>net (John V. Everett)
Click to expand...

Funny this should come up just a couple of hours after I dealt with something similar. I was using Rinard's to calculate for Mavic open pro rims for which Mavic claims a "spoke support diameter" of 602mm. Rinard's database shows an ERD of 605 with a notation that 3mm have been added to account for spoke nipple heads. I guess what that means is Mavic measures differently, not to mention they have a different terminology.
Dan
 
The entire production smells of irresponsible attitude for the user/
consumer. Right of ask why not announce ERD may be theoretick
according to Brandt then direct an examination of in hand spoke
threading?
Granted, ERD fills the bill for one standard. Without further
direction, ERD is grossly misleading.
To assume ERD is a functional real world spoke measure ask why is
threading wasted into an unthreaded area.
Asking why didn't we see that as the direction to ERD's theoretic
nature is silly oneupmanship practiced by the engine room.
An excuse to beg for one more reorder on top of the returned spokes or
a bad joke when the LBS sez "well, we don't exchange bent used
spokes."
BAH! FUBAR.
 
YEAH YEAH YEAH
HERE WE GO AGAIN BINGO

"Most people prefer it near the end of the spoke nipple." SHELDON
BROWN

now, Sheldon knew better than to say something stupid like this so why
did he write it? is the "most people..." an allusion?

I do not know. I empathize with Beam.

if the spoke goes to the end of the spoke nipple, an impossibility
using 16mm DT nipples and DT Champ spokes, wastes male threading where
no female threading exists, doesn't account for wear and tear
then BINGO
 
On Mar 8, 11:18 am, John Everett
<[email protected]> wrote:

> So is ERD measured to the top of the nipple or the top of the spoke
> grommet? If I'm using spocalc should I add the height of two nipple
> heads to 606.4mm to get the correct answer?

ERD is the diameter of the circle defined by the spoke ends and takes
into account that a spoke must extend into the rim a bit. It is
slightly larger than the inner diameter of a rim. ERD is not actually
"measured" - it is either an estimate or a calculation. On average
the extra length required is about 5 mm per spoke which increases the
ERD to be about 10 mm more than the measured inner diameter of the
rim. But, if you are so inclined, measure the length of a nipple
then insert the nipple into a spoke hole and measure the lenght of the
external nipple portion (which extends towrad the center of the
wheel). The difference between these two measurements is the lenght of
the nipple withn the rim. That value that is doubled and added the the
actual rim inner diameter to get a figure for ERD. This assumes that
spokes are to be flush with the top of the nipple head.

DR
 
DR>

almost. ERD is an hypotenuse not a diameter. That's why we're
suffering thru the grinding interface of language and math here thru
god software and priests.
try using magic tape for defining threading position inside the
nipple. The threading engagment of spoke and nipple related to actual
effective spoke length (AESL) NOT ERD is the measurement we're after
here.
That's a refinment of what you wrote. right?

"This assumes that spokes are to be flush with the top of the nipple
head."

we should not assume that. NADA!
 
On 2008-03-09, datakoll <[email protected]> wrote:
>
> DR>
>
> almost. ERD is an hypotenuse not a diameter. That's why we're
> suffering thru the grinding interface of language and math here thru
> god software and priests.

ERD is a diameter: it's the distance across a circle. The question is
just where is that circle. It is concentric with the rim and about 1.5mm
above where the nipples sit.
 
On Mar 9, 12:36 pm, Ben C <[email protected]> wrote:
> On 2008-03-09, datakoll <[email protected]> wrote:
>
>
>
> > DR>
>
> > almost. ERD is an hypotenuse not a diameter. That's why we're
> > suffering thru the grinding interface of language and math here thru
> > god software and priests.
>
> ERD is a diameter: it's the distance across a circle. The question is
> just where is that circle. It is concentric with the rim and about 1.5mm
> above where the nipples sit.

CHORD is a diameter: it's the distance across a circle.
 
datakoll wrote:
> YEAH YEAH YEAH
> HERE WE GO AGAIN BINGO
> "Most people prefer it near the end of the spoke nipple." SHELDON
> BROWN
> now, Sheldon knew better than to say something stupid like this so why
> did he write it? is the "most people..." an allusion?
> I do not know. I empathize with Beam.
> if the spoke goes to the end of the spoke nipple, an impossibility
> using 16mm DT nipples and DT Champ spokes, wastes male threading where
> no female threading exists, doesn't account for wear and tear
> then BINGO

I have, at one time or another, built wheels with spokes sticking out
the end 2~3mm and also 2~3mm short (threads showing above a 12mm
nipple), neither of which proved to be an actual problem over many years
of use.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971
 
Andrew Muzi wrote:
> datakoll wrote:
>> YEAH YEAH YEAH
>> HERE WE GO AGAIN BINGO
>> "Most people prefer it near the end of the spoke nipple." SHELDON
>> BROWN
>> now, Sheldon knew better than to say something stupid like this so why
>> did he write it? is the "most people..." an allusion?
>> I do not know. I empathize with Beam.
>> if the spoke goes to the end of the spoke nipple, an impossibility
>> using 16mm DT nipples and DT Champ spokes, wastes male threading where
>> no female threading exists, doesn't account for wear and tear
>> then BINGO
>
> I have, at one time or another, built wheels with spokes sticking out
> the end 2~3mm and also 2~3mm short (threads showing above a 12mm
> nipple), neither of which proved to be an actual problem over many years
> of use.

Could gene be using some hubs made from an inferior aluminium alloy that
allows the spoke holes to elongate during use? A proper build will not
allow for effective spoke length increase due to the radius of the spoke
elbow changing. The spokes are certainly not elongating from yield or creep.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful
 
In article
<5b3f748e-f6c8-4fb4-bca9-cc396b0d62dc@p73g2000hsd.googlegroups.com>,
DirtRoadie <[email protected]> wrote:

> On Mar 8, 11:18 am, John Everett
> <[email protected]> wrote:
>
> > So is ERD measured to the top of the nipple or the top of the spoke
> > grommet? If I'm using spocalc should I add the height of two nipple
> > heads to 606.4mm to get the correct answer?
>
> ERD is the diameter of the circle defined by the spoke ends and takes
> into account that a spoke must extend into the rim a bit. It is
> slightly larger than the inner diameter of a rim. ERD is not actually
> "measured" - it is either an estimate or a calculation.

It is best measured. A URL for a method is posted in this thread.
It really is measured. Put nipples on a some spokes, measure
some distances on the spoke, put two spokes a pair of antipodal
points, measures some more, add and subtract some measurements.
Do it for three pair of diameters on the rim. If your three
measurements do not rectify, draw a picture, think through
the method, and measure some more.

The great problem is that there are different definitions
of ERD. One needs to be absolutely certain of the definition
used in the calculator and of one's measurements.

--
Michael Press
 
MP,

gnaw. you missed the point. Brandt sez ERD is his idea. ERD
establishes ONE MEASUREMENT STANDRAD for one wheel combination, not 4
standradrs for one wheel combination.

BUTBUTBUT ERD is snot AESL. AESL is the small range of engaged
threading used for ordering spokes and building the wheel. AESL=ERD-
SDR (standard deduction range)

ERD is software's spoke calc standard hypotenuse length as a math
constant. (maybe also a disease)

Its snot the length you use to order spokes. its the length you use to
DEDUCT from to order spokes

Yeah. the dishing beam is essential and a basic wheel building tool.
Insert spokes, seat, gives correct dish. A red oak or better beam
should lean in every shop's corner.
 
On Mar 9, 3:27 pm, Michael Press <[email protected]> wrote:
> > ERD  is the diameter of the circle defined by the spoke ends and takes
> > into account that a spoke must extend into the rim a bit.  It is
> > slightly larger than the inner diameter of a rim. ERD is not actually
> > "measured" - it is either an estimate or a calculation.  
>
> It is best measured. A URL for a method is posted in this thread.
> It really is measured. Put nipples on a some spokes, measure
> some distances on the spoke, put two spokes a pair of antipodal
> points, measures some more, add and subtract some measurements.
> Do it for three pair of diameters on the rim. If your three
> measurements do not rectify, draw a picture, think through
> the method, and measure some more.

You must have a measuring tool that I do not have. I cannot "measure"
ERD on any rim (all being double walled) that I have worked with in
the recent past since the top surface of the nipple heads has always
been recessed below the bed of the rim. That's why I
"calculate" (from some measurements I CAN make) as I described (and
even you describe adding and subtracting some measurements) or
"estimate" it as I also described since many calcualtion have shown
actual rim inner diameter +10 mm to be a usable estimate for
ERD.

> The great problem is that there are different definitions
> of ERD. One needs to be absolutely certain of the definition
> used in the calculator and of one's measurements.
>
True. ERD is really just the innner diameter of the rim with a "fudge
factor" (tied directly to to the configuration of the nipple) factored
in to get us into the ball park. Most nipples are probably similar
enough that a single ballpark "ERD" can be stated by the manufacturer
without creating any significant problems. Years ago I wrote some
software to calculate spoke length taking into account such subtle
factors as the measured and calculated nipple depth within the rim and
hub spoke hole diameter. Such detail is probably overkill, but since
it just applies accurate measurements, it works.

DR
 
On Mar 9, 10:16 am, datakoll <[email protected]> wrote:
> DR>
>
> almost. ERD is an hypotenuse not a diameter.
No, it's a diameter, hence the name "ERD." It is the diameter of a
circle defined by a series of points (spoke ends).
The path of the spoke is irrelevant. The ERD of the rim is the same
regardlees of whether a wheel is radailly or tangentially spoked
(although spoke length will differ).

> The threading engagment of spoke and nipple related to actual
> effective spoke length (AESL) NOT ERD is the measurement we're after
> here.
> That's a refinment of what you wrote. right?
Not reallly. I wasn't really addressing the issue of thread
engagement ( which needs to be "enough" but not "too much")
But yes. The amount of thread engagement does change where the spoke
ends and the resulting "ERD."

> "This assumes that spokes are to be flush with the top of the nipple
> head."
>
> we should not assume that. NADA!

I was merely describing the underlying assumption of what I was
describing , not "how it should be." Personally I think the ideal
threading for both functionallity and aesthetics would be to have the
spoke end flush with the bottom of the slot in the nipple head. YMMV.

DR
 
On Sun, 9 Mar 2008 21:32:06 -0700 (PDT), DirtRoadie
<[email protected]> wrote:

>You must have a measuring tool that I do not have. I cannot "measure"
>ERD on any rim (all being double walled) that I have worked with in
>the recent past since the top surface of the nipple heads has always
>been recessed below the bed of the rim. That's why I
>"calculate" (from some measurements I CAN make) as I described (and
>even you describe adding and subtracting some measurements) or
>"estimate" it as I also described since many calcualtion have shown
>actual rim inner diameter +10 mm to be a usable estimate for
>ERD.

Dear DR,

I may be misunderstanding you, but have a look at this page:
http://www.sheldonbrown.com/rinard/spocalc.htm#MeasureHubAndRim

Page down once to the diagram of the double-walled rims, and it shows
how to measure the ERD from the top of one spoke nipple inside a
double-walled rim to the other.

Cheers,

Carl Fogel
 
Hi Carl, how was the trip to Goodyear?
measuring for double walls takes NIQ+10 where we arrive at 0
insert spoke into rim, magic tape insertion at rim inside entry hole
for nipple head reach, then for slot base reach, then for 1.5mm short
of slot base reach.
OR tape spoke shaft when spoke reachs inside rim eyelet (the grommet
reinforcement)
WRITE THE NUMBERS DOWN WITH ASSCOCIATED DIAGRAM IN YOUR LOG BOOK.
then insert spoke into nipple to threading: tape insertion on spoke.
measure the short end.
then thread spoke onto nipple until spoke arrives at slot base. tape
spoke shaft and measure short end.
WRITE THE NUMBERS DOWN IN YOUR LOG BOOK.
you now have a spoke length table. Use the table for tilting at ERD.
841

ERD is snot spoke length, spoke length is AESL. Rinard and Brandt,
obviously highly intelligent people continue chanting ERD like mary
had a little lamb is spoke length until people of normal intelligence
believe that, to their error and consternation.
Clearing the problem off the boards using magic tape and AESL is
similar to Gates' ascesnion to world's second richest man, having
soooooo much money he gave it to Africans soooo we can have more
Africans.
 
On Sat, 8 Mar 2008 13:58:54 -0800 (PST), datakoll <[email protected]>
wrote:

>The entire production smells of irresponsible attitude for the user/
>consumer. Right of ask why not announce ERD may be theoretick
>according to Brandt then direct an examination of in hand spoke
>threading?
>Granted, ERD fills the bill for one standard. Without further
>direction, ERD is grossly misleading.
>To assume ERD is a functional real world spoke measure ask why is
>threading wasted into an unthreaded area.
>Asking why didn't we see that as the direction to ERD's theoretic
>nature is silly oneupmanship practiced by the engine room.
>An excuse to beg for one more reorder on top of the returned spokes or
>a bad joke when the LBS sez "well, we don't exchange bent used
>spokes."
>BAH! FUBAR.

As usual Gene is the master of obfuscation. However in this case he's
also wrong on a couple of counts.

He says, "To assume ERD is a functional real world spoke measure"; yet
I don't believe anyone assumes this. ERD is a rim measurement.

Also, he writes about "threading wasted into an unthreaded area". By
this I'm guessing he means the screwdriver slot. I just threaded one
of the spokes I removed from the referenced rear wheel (see OP) and
threaded it backward into one of the nipples. At the point where I
can't pull the nipple from the spoke if I hold the assembly up to a
light I can see light passing through the slot, between the base of
the slot and the end of the spoke. Thus (at least in this case) the
slot is threaded.

But to get back to my original question, should I add twice the height
of one nipple head to Alex's 606.4mm to calculate spoke lengths?


--
jeverett3<AT>sbcglobal<DOT>net (John V. Everett)
 
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