Problems with Spocalc and Spoke Length?



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"almost fast" <[email protected]> wrote in message
news:[email protected]...
> 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".

Yes, I've seen that. There are other manufactirer's differences and they are similarly minor.

Most wheelbuilders use a ruler similar to the one shown. We then correct to the brand of spoke we
commonly use. That means we know whether to choose a millimeter up or a millimeter down from
whatever calculator we use or from a measured spoke out of a repair wheel.

The variance, while real, is never a full milllimeter, in my experience and is therefore negligible
for purposes of bicycle wheel spoke selection.

--
Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971
 
On Wed, 16 Apr 2003 22:23:58 +1200, (Snoopy) tennyson@caverock.*et.*z.*is'n' wrote:

>
>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?
>
>
Well it's been a while. After re-reading all the suggestions I decided that measuring the length of
the spoke into the curvature of the bend was the way to go. Although really it didn't make much
difference. I could accommodate the 1mm or so error of measuring the wrong way.

After rethreading the DS spokes through the correct hub holes (I was using a hub with more holes
than I needed, so it was possible to mount the spoke relative positions just in the wrong place),
then loosening the opposite side spokes, and with a bit of push and pull I have managed to get the
spoke lengths as recommended by 'spocalc' to work!

IOW the problem was 'just me' after all! Don't give up on Spocalc!

SNOOPY

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and i went over to the equipped LBS and used that in-house program and that program said 288mm- DT
and Spokclac wuz 10mm off!or were they at 288mm? the LBS said "all" shim rear hubs had the same
dimensions and the LBS program had a actual rim diamter readout to simplify understanding. same
diamtere as suggested by the DT man! But the DT program was 10mm short. this is unnerving. program
had a try lacing it tomorrow.
 
On 7 Jun 2003 12:23:37 -0700, [email protected] (g.daniels) wrote:
>
>
>and i went over to the equipped LBS and used that in-house program and that program said 288mm- DT
>and Spokclac wuz 10mm off!or were they at 288mm? the LBS said "all" shim rear hubs had the same
>dimensions and the LBS program had a actual rim diamter readout to simplify understanding. same
>diamter as suggested by the DT man! But the DT program was 10mm short. this is unnerving. program
>had a try lacing it tomorrow.
>

I can't vouch for the DT web spoke calculator, but Spocalc just uses the same trigonometry as found
in Jobst's book.

Of course, like all computer programs the principal of 'GIGO' applies. If you feed the wrong values
into the program you will get the wrong answer. And if you can't translate the answer you get into
the right physical component (in this case a spoke), you might have trouble building the wheel.

Perhaps all rear hub diameters for cartridge spokes are the same, or near enough to being so. I have
never run cartridge hubs so have no experience in this area. However, even if this is true it is
only a 'fact' until some hub maker decides to make a hub that is not the same!

Furthermore, measuring to the complete outside of the rim and then taking off 10mm will only work if
the end of the spoke is always 10mm below the surface of the outer rim diameter measured. This is
definitely not always the case.

All in all, it sounds like your LBS is to be applauded for using a spoke calculator. However, to me
it seems like their simplifications are foolish rules of thumb that remove the user one step away
from the true geometery of what is happening for no reason.

I am puzzled by the phrasing of your words "g. daniels", because it sounds like you are using the
spocalc program to select a rim, rather than select spokes. You can do that, but I would have
thought the easier thing to do would be to take the whole old wheel in to the LBS and just eye up
your new rim to see that it fits.

SNOOPY

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the problem seems to be in data transmission not data entry. re checking measurements verifying what
the system tries to suggest is inorder. taking a machines word for reality while the work is at hand
is not inorder. Or so it seems. Even the DT man said that.
 
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