# Problems with Spocalc and Spoke Length?

Discussion in 'Cycling Equipment' started by Snoopy, Apr 16, 2003.

Not open for further replies.
1. ### Snoopy Guest

Or perhaps it's just me?

Whatever, I've been seeing what spoke lengths this calculator (Spocalc.xls) gives me for a wheel I
had built some time ago and it seems that it is giving me the 'wrong' answers (spokes it recommends
are too short, by a couple of mm). I am using DT swaged spokes so went the DT website and tried the
spoke calculator they had there. I got the same result (within measurement error), so I think the
problem is not in the 'spocalc' algorithm, but more in the values I am entering in and/or taking
out of it?

There are a couple of possibilites I have identified.

1/ Have I been measuring spoke length incorrectly?:

According to 'The Bicycle Wheel' by Jobst Brandt, the length of a spoke is measured from the inside
of the elbow to the tip of the threaded end. Exactly what does this mean? According to this website:

http://www.stormpages.com/spokeanwheel/

The spoke length is measured from the edge of the bend closest to the threaded end of the spoke to
the end of the threaded tip. So do I measure to where the bend starts curving, or do I measure to
the apex of the bend? Both I think can be classified as 'the inside of the elbow'. If I measure
right to the apex (which is what I had been doing) a given spoke appears longer by about 2mm.

2/ No allowance is made for the distortion of a spoke when it is mounted with a large anchor angle
and multi weaved into position:

In my case I have a 24 spoke wheel that is 2 crossed and has a 60 degree spoke anchor angle. I have
a wide diameter flange (63mm) linking to a 27" rim. This means that each spoke is in contact with
the hub for about 8mm of its length (near the elbow), and furthermore each spoke is laced under
another spoke before it gets to the rim. Thus the 2X sixty degree spoke is far from straight as
assumed in the Brandt book (Edition 3, Part 3 page 127 'SPOKE LENGTH'- I understand the equations
presented in this book are the basis for 'spocalc').

That distortion may not sound a lot, but I think this lacing arrangement has reduced the effective
length of the spoke by at least 1mm, possibly 2mm.

So could either 1/ or 2/ be the reasons I am having problems matching the results from 'spocalc'
with the spokes actually used in the wheel? Is there something else I have overlooked? TIA

SNOOPY

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2. ### Nigel Grinter Guest

(Snoopy) [email protected]*et.*z.*is'n' wrote in message
news:<[email protected]>...
> Or perhaps it's just me?
>
> Whatever, I've been seeing what spoke lengths this calculator (Spocalc.xls) gives me for a wheel I
> had built some time ago and it seems that it is giving me the 'wrong' answers (spokes it
> recommends are too short, by a couple of mm). I am using DT swaged spokes so went the DT website
> and tried the spoke calculator they had there. I got the same result (within measurement error),
> so I think the problem is not in the 'spocalc' algorithm, but more in the values I am entering in
> and/or taking out of it?
>
> There are a couple of possibilites I have identified.
>
> 1/ Have I been measuring spoke length incorrectly?:
>
> 2/ No allowance is made for the distortion of a spoke when it is mounted with a large anchor angle
> and multi weaved into position:
>
> That distortion may not sound a lot, but I think this lacing arrangement has reduced the effective
> length of the spoke by at least 1mm, possibly 2mm.
>
> So could either 1/ or 2/ be the reasons I am having problems matching the results from 'spocalc'
> with the spokes actually used in the wheel? Is there something else I have overlooked? TIA
>
> SNOOPY

I've used Spocalc for some while and have not yet managed to catch it in an error. In response to

1. Sounds like you are measuring the spokes correctly. I have always assumed the length that
matters is the distance from where the spoke contacts the hub at its elbow to the end of the
threaded portion. I measure the length by hanging the spokes vertically by the elbows from a
thin piece of plastic and measuring from the top edge of the plastic to the end of the spoke.

2. I have never had to make an allowance for deviations from a perfectly straight spoke path
resulting from interweaving spokes. Without doing the math, it seems that these deflections
would cause very minor (i.e., insignificant) differences in path length.

Some questions:

How are you determining that the spokes are too short? Sometimes, particularly if the spokes are
a very snug fit in the hub, it is quite a struggle to wind the hub up enough to get the third
and fourth set of spokes laced. (I am assuming you are building using the methods described in
THE BOOK.)

Are you absolutely sure you are entering the correct hub and rim data into Spocalc? Some
manufacturers change specs on their products without changing the products name - Velocity Aerohead
rims come in at least two flavors, for example.

Nigel Grinter

3. ### James Roach Guest

[email protected] (Nigel Grinter) wrote in message news:
>
> Are you absolutely sure you are entering the correct hub and rim data into Spocalc? Some
> manufacturers change specs on their products without changing the products name - Velocity
> Aerohead rims come in at least two flavors, for example.
>
> Nigel Grinter

I agree with checking your hub data. I believe it was a 105 series hub that the data in the
spreadsheet differed from my hub. I assume this to be, as Nigel stated, due to changing specs.
The hub I had was (I believe) a 105sc rear - FH1056 with 130 spacing, the spread sheet just
listed only one 105sc rear hub - FH1055. The hub data was different so I measured the hub and
entered my own data.

James Roach

4. ### G.Daniels Guest

visit the DT spoke site!!

5. ### Ronald Guest

> visit the DT spoke site!!

>> I am using DT swaged spokes so went the DT website and tried the spoke calculator they had there.

He did....

"g.daniels" <[email protected]> wrote in message
news:[email protected]...
> visit the DT spoke site!!

6. ### Snoopy Guest

On 16 Apr 2003 07:26:41 -0700, [email protected] (Nigel Grinter) wrote:

>
>1. Sounds like you are measuring the spokes correctly. I have always assumed the length that
> matters is the distance from where the spoke contacts the hub at its elbow to the end of the
>
>

Yes, but generally a spoke won't take up its final profile until well into the tightening and
truing process. When a wheel is just being laced that elbow curve stands proud of the hub, to the
extent that you can see daylight between the hub and the spoke. I thought that measuring a spoke
just to the start of the bend might be a way of giving the wheel lacers a fraction more length to
work with....

>
>
>I measure length by hanging the spokes vertically by the elbows from a thin piece of plastic and
>measuring from the top edge of the plastic to the end of the spoke.
>
>

The question is exactly from where on the elbows do you hang them? The answer to that question
determines the measurement you will get.

>
>
>2. I have never had to make an allowance for deviations from a perfectly straight spoke path
> resulting from interweaving spokes. Without doing the math, it seems that these deflections
> would cause very minor (i.e., insignificant) differences in path length.
>
>

Sure these deviations aren't large. Probably only a single mm or so with 2X. However, the more
crosses and interweaving you have, and the greater the spoke anchor angle, the worse this effect
gets. I'm not suggesting this would cause problems on its own. But as a cumulative effect with other
measurement errors it could prove significant.

>
>
>Some questions:
>
>How are you determining that the spokes are too short?
>
>

I tried to build an exact duplicate rear wheel to the old one I had. I used 'spocalc' to select the
spoke length and did a quick visual check with the old wheel I had before buying the spokes. The
spokes looked OK for length (silly me for not measuring the old spokes). But when I got everything
home I found there was no way I could build the wheel. The spokes I got were only 2mm or so short
but that was enough to make the wheel unbuildable. I realised I was going to have problems when the
'dish' on the driven side of the wheel disappeared completely!
>
>
>Sometimes, particularly if the spokes are a very snug fit in the hub, it is quite a struggle to
>wind the hub up enough to get the third and fourth set of spokes laced.
>
>

I was able to get one half of the wheel laced (the drive side). That was all! I notice that the
spoke thread has to go some way into the spoke nipple before it engages. I wonder if it is possible
I have mismatched spokes and nipples?

>
>(I am assuming you are building using the methods described in THE BOOK.)
>

Indeed

>
>Are you absolutely sure you are entering the correct hub and rim data into Spocalc?
>
>

No. But I have a pair of vernier calipers so I tried to check all the measurements I loaded in. For
example I am using a Suzue 5A hub. I measured the pitch circle diameter of the spoke holes to be
63mm. The Suzue Hub on the DT website calulator showed 62mm for this measurement. I measured my hub
width as 53mm. The DT website gave
55mm. These are differences but only change the length of the spokes calculated by a few tenths of
millimetres.

Much more critical seems to be the diameter of the rim. It's a Velocity Twin Hollow. I used a tape
measure to determine the outer diameter, then vernier calipers to measure the length down to the
spoke nipple that needs to be taken off the O/D. Yes I did remember to do the subtraction twice! I
came up with an ERD of 622.2mm. I was as careful as I could be, but there does seem to be more
possibility of error with this measurement.

SNOOPY

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7. ### A Muzi Guest

"Snoopy" <[email protected]*et.*z.*is'n'> wrote in message
news:[email protected]... -snip-
> Have I been measuring spoke length incorrectly? <
>
> According to 'The Bicycle Wheel' by Jobst Brandt, the length of a spoke is measured from the
> inside of the elbow to the tip of the threaded end. Exactly what does this mean? According to this
> website:
>
> http://www.stormpages.com/spokeanwheel/
>
> The spoke length is measured from the edge of the bend closest to the threaded end of the spoke to
> the end of the threaded tip. So do I measure to where the bend starts curving, or do I measure to
> the apex of the bend? Both I think can be classified as 'the inside of the elbow'. If I measure
> right to the apex (which is what I had been doing) a given spoke appears longer by about 2mm.
-snip-

Measure spokes like this: http://www.yellowjersey.org/photosfromthepast/SPOKRULR.JPG

--
Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971

8. ### Snoopy Guest

On Wed, 16 Apr 2003 21:55:55 -0500, "A Muzi" <[email protected]> wrote:

>
>Measure spokes like this: http://www.yellowjersey.org/photosfromthepast/SPOKRULR.JPG
>

Thanks Andrew. That looks like some kind of special spoke measuring tool?

I'm afraid it still doesn't answer my question though. That 'notch' in the LH end of the ruler. Does
it have square edges? Or is it fillet radiused to match the curve at the end of the spoke. The way
the spoke is angled, and the way the light falls on the photo I just cannot tell! I guess it would
be obvious if I was familar with the spoke measuring tool in the photgraph. But I'm not.

SNOOPY

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9. ### Nigel Grinter Guest

(Snoopy) [email protected]*et.*z.*is'n' wrote in message
news:<[email protected]>...
> On 16 Apr 2003 07:26:41 -0700, [email protected] (Nigel Grinter) wrote:
> >
> >
> >Some questions:
> >
> >How are you determining that the spokes are too short?
> >
> >
> I tried to build an exact duplicate rear wheel to the old one I had. I used 'spocalc' to select
> the spoke length and did a quick visual check with the old wheel I had before buying the spokes.
> The spokes looked OK for length (silly me for not measuring the old spokes). But when I got
> everything home I found there was no way I could build the wheel. The spokes I got were only 2mm
> or so short but that was enough to make the wheel unbuildable. I realised I was going to have
> problems when the 'dish' on the driven side of the wheel disappeared completely!
> >

So what do the spokes from the old wheel measure?????

> >
> >Are you absolutely sure you are entering the correct hub and rim data into Spocalc?
> >
> >
> No. But I have a pair of vernier calipers so I tried to check all the measurements I loaded in.
> For example I am using a Suzue 5A hub. I measured the pitch circle diameter of the spoke holes to
> be 63mm. The Suzue Hub on the DT website calulator showed 62mm for this measurement. I measured my
> hub width as 53mm. The DT website gave
> 55mm. These are differences but only change the length of the spokes calculated by a few tenths
> of millimetres.
>
> Much more critical seems to be the diameter of the rim. It's a Velocity Twin Hollow. I used a tape
> measure to determine the outer diameter, then vernier calipers to measure the length down to the
> spoke nipple that needs to be taken off the O/D. Yes I did remember to do the subtraction twice! I
> came up with an ERD of 622.2mm. I was as careful as I could be, but there does seem to be more
> possibility of error with this measurement.
>
> SNOOPY

The Velocity web site lists the ERD for the Twin Hollow as 611 (700c) or 619 (27").

10. ### Hedberg Guest

On Thu, 17 Apr 2003 20:43:01 +1200, (Snoopy) [email protected]*et.*z.*is'n' wrote:

>On Wed, 16 Apr 2003 21:55:55 -0500, "A Muzi" <[email protected]> wrote:
>
>
>>
>>Measure spokes like this: http://www.yellowjersey.org/photosfromthepast/SPOKRULR.JPG
>>
>
>Thanks Andrew. That looks like some kind of special spoke measuring tool?
>
>I'm afraid it still doesn't answer my question though. That 'notch' in the LH end of the ruler.
>Does it have square edges? Or is it fillet radiused to match the curve at the end of the spoke. The
>way the spoke is angled, and the way the light falls on the photo I just cannot tell! I guess it
>would be obvious if I was familar with the spoke measuring tool in the photgraph. But I'm not.
>
>SNOOPY
>

Go to <http://www.dtswiss.com/en/speichen-champion.html> and click where it says "Technical drawing"
and you'll see how DT says to measure the spoke. Depending on the thickness of the gage used to make
the measurement, I suppose there could be some slight variation (because the angle at the end can be
as much as 95 degrees), but I don't think much -- probably within the length tolerance of the spoke.
I think if you measure the length of the spoke properly with a flat rule (as in the yellowjersey
photo) that the spoke may not make contact with the rule over its entire length. That's not
important.

Harold

11. ### G.Daniels Guest

wheel building for spring. yep. i have a deore hub sitting idle while i develop an general idea of
spoke lengths for mail order without lacing up before hand with local spokes new or used from the
flea market boys. this goes on for some time now on my second temp wheel/huib combo. this oddesssy
began with a circumference measurement very carefully done- i carpenter to 128"-the circumference
measure compared with the DT measuring suggestion? a 6-7 mm difference. holy lufkin batman!!!
that'll let the air out on delivery day-plus \$8! add to this conundram are the facts:rims are not
round. the DT man emailed back with the specs i needed taken from a rim catalog. outasight!!!thanks,
DT!! yeah, but my measurment is 4mm off the catalog's. is there a moral? experience.LBS. \$8. a spoke
collection... buy the whey, the excel calcs work well here at the publib and if the gizmo works here
breau it'll work anywhere.

12. ### Hedberg Guest

On Thu, 17 Apr 2003 13:52:48 +1200, (Snoopy) [email protected]*et.*z.*is'n' wrote:

[...]
>
>Sure these deviations aren't large. Probably only a single mm or so with 2X. However, the more
>crosses and interweaving you have, and the greater the spoke anchor angle, the worse this effect
>gets. I'm not suggesting this would cause problems on its own. But as a cumulative effect with
>other measurement errors it could prove significant. [...]

Deviations from straight caused by spoke crossings can be safely ignored in calculating the spoke
length. If you have a 300mm spoke length and the path between ends deviates by 2mm at the middle
(150mm from either end) the angle that the spoke makes with the straight path is about .75 degrees.
The difference between the straight line length and the path length with this 2mm deviation is less
than .02mm. That's less than .001", for the SI challenged. If you're familiar with some basic math
you recognize this as the fact that the sine and tangent of a very small angle are essentially
equal. If you have a scientific calculator, you can see this by asking it to give you the sine and
tangent of 1 degree (about .175 radian). Maybe you need to worry about such small amounts when
traveling to the moon, but not when you're building a wheel.

Harold

13. ### G.Daniels Guest

IDEA! Why not place the rim list with diameters into bike.tech as specd by the factory and a well
done technical drawing of DT's spoke measurement suggestion as in what is that nipple surface really
doing resting on the ferrule, where does the measurement begin at that point and other added ideas
place able herein. An animation of the wheel truing process? Ya know with the little man ect. Or
maybe a squid! Visualize the axle centering as in Sheldon Brown's truing guide as the builder cranks
in torque from the opposite side and cranks out torque from the benth . Off to the scifair!!

14. ### A Muzi Guest

> On Wed, 16 Apr 2003 21:55:55 -0500, "A Muzi" <[email protected]> wrote:
> >Measure spokes like this: http://www.yellowjersey.org/photosfromthepast/SPOKRULR.JPG

"Snoopy" <[email protected]*et.*z.*is'n'> wrote in message
news:[email protected]...
> Thanks Andrew. That looks like some kind of special spoke measuring tool?
>
> I'm afraid it still doesn't answer my question though. That 'notch' in the LH end of the ruler.
> Does it have square edges? Or is it fillet radiused to match the curve at the end of the spoke.
> The way the spoke is angled, and the way the light falls on the photo I just cannot tell! I guess
> it would be obvious if I was familar with the spoke measuring tool in the photgraph. But I'm not.

It's just a flat plate of aluminum, and all brands of spoke ruler are similar. You want to measure
from the inside radius, about where a 2mm flat plate would fall inside the curve, to the end of the
threads. There does seem to be a slight variance across brands ( 0.5mm) but it's negligible. Yes,
the edge is a simple edge.

--
Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971

15. ### kh6zv9 Guest

A Muzi <[email protected]> wrote:

: It's just a flat plate of aluminum, and all brands of spoke ruler are similar. You want to measure
: from the inside radius, about where a 2mm flat plate would fall inside the curve, to the end of
: the threads. There does seem to be a slight variance across brands ( 0.5mm) but it's negligible.
: Yes, the edge is a simple edge.

: --
: Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971

My Park Spoke Length Gauge has a egg shape hole to hang the spoke in for measuring.

--------------------------------
Bob Masse' [email protected]
--------------------------------

16. ### A Muzi Guest

> A Muzi <[email protected]> wrote:
>
> : It's just a flat plate of aluminum, and all brands of spoke ruler are similar. You want to
> : measure from the inside radius, about where a 2mm
flat
> : plate would fall inside the curve, to the end of the threads. There
does
> : seem to be a slight variance across brands ( 0.5mm) but it's negligible. Yes, the edge is a
> : simple edge.

<[email protected]> wrote in message news:[email protected]...
> My Park Spoke Length Gauge has a egg shape hole to hang the spoke in for measuring.

Right you are. In cross section, the spoke sits on a simple edge. i.e., the oval hole is just
punched out of the aluminum plate.

--
Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971

17. ### Snoopy Guest

On 17 Apr 2003 05:06:49 -0700, [email protected]ega.com (Nigel Grinter) wrote:

>
>So what do the spokes from the old wheel measure?????
>
>
As an example I pulled a spoke out of the off-side on the wheel that someone else built for me that
has been 'proved' to work. The spoke I measured is no longer a 'virgin' spoke of course as stress
relieving it has moulded the bend at the elbow to the hub, so that there is no longer any gap
between the elbow end of the spoke and the hub. This means that I have an obvious line on the spoke
elbow to measure to.

The length of the spoke from the plastic bend line at the elbow to the end of the threads is 300mm.
When tightened, these 300mm spoke threads come right up inside the head of spoke nipple into the
slotted area where it would be possible to insert a screwdriver if the spoke was not there. The end
of the spoke does not protrude beyond this slotted head in the nipple however.

By contrast 'Spocalc' gives a 2X spoke length of 297.4mm, based on a spoke hole diameter (S) of
2.5mm, flange diameter (d) of 63mm, Width from Center to Offside flange (W) of 35mm and effective
rim diameter of 622.2mm

>
>
>The Velocity web site lists the ERD for the Twin Hollow as 611 (700c) or 619 (27").
>
>

Huh? How can they publish an ERD without knowing how far above the seating face on the perimeter of
the rim, the heads of the spoke nipples rise up? My vernier calipers tell me that the spoke nipple
heads rise up 2.8mm above the seating base of the head. The thread in the nipple isn't complete all
the way to the top of the head though. I measure that it ends 1.5mm from the top of the spoke head.
So I calculate the ERD of the rim as:

619 + 2(2.8-1.5) = 621.6

Putting that figure into 'Spocalc' gives a 2X spoke length of 297.2mm, and that is even shorter than
the assumptions I used (from my own direct measurement of the rim).

SNOOPY

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18. ### Snoopy Guest

On Thu, 17 Apr 2003 23:30:56 -0500, "A Muzi" <[email protected]> wrote:

>
>You want to measure from the inside radius, about where a 2mm flat plate would fall inside the
>curve, to the end of the threads. There does seem to be a slight variance across brands ( 0.5mm)
>but it's negligible.
>

Right, so on a virgin spoke I measure from the tips of the thread right up to where the spoke just
starts to bend. If I measure any plasticly deformed material then I have measured too much length. I
am glad that is settled!

SNOOPY

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19. ### A Muzi Guest

"Snoopy" <[email protected]*et.*z.*is'n'> wrote in message
news:[email protected]...
> On Thu, 17 Apr 2003 23:30:56 -0500, "A Muzi" <[email protected]> wrote:
>
> >
> >You want to measure from the inside radius, about where a 2mm flat plate would fall inside the
> >curve, to the end of the threads. There does seem to be a slight variance across brands ( 0.5mm)
> >but it's negligible.
> >
>
> Right, so on a virgin spoke I measure from the tips of the thread right up to where the spoke just
> starts to bend. If I measure any plasticly deformed material then I have measured too much length.
> I am glad that is settled!

Measure to a point the inside of the curve where the edge of the plate shown touches the spoke. That
will indeed be within the curved area. http://www.yellowjersey.org/photosfromthepast/SPOKRULR.JPG

--
Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971

20. ### Almost Fast Guest

Maybe it's not settled.

DT seems to indicate their spokes are measured from the tip of the threaded end to the crook of the
bend (all the way to the near edge of the base of the head).

Have a look at www.dtswiss.com, choose yer language (on the bottom), choose Spokes (on the left),
choose any spoke model (on the right), then click on "Technical Drawing".

(Snoopy) [email protected]*et.*z.*is'n' wrote in message
news:<[email protected]>...
> On Thu, 17 Apr 2003 23:30:56 -0500, "A Muzi" <[email protected]> wrote:
>
> >
> >You want to measure from the inside radius, about where a 2mm flat plate would fall inside the
> >curve, to the end of the threads. There does seem to be a slight variance across brands ( 0.5mm)
> >but it's negligible.
> >
>
> Right, so on a virgin spoke I measure from the tips of the thread right up to where the spoke just
> starts to bend. If I measure any plasticly deformed material then I have measured too much length.
> I am glad that is settled!
>
> SNOOPY
>
>
>
>
> --
> Join the fight against aggressive, unrepentant spammers 'china-netcom'. E-mail me for more details