Spoke Length: Measurement Methology And Criticality?

(PeteCresswell) skrev:

Once the drum brake hub I ordered arrives, my plan is to measure
the spoke-hole-center-to-axle-center distance on the old and new
hubs; pull a spoke from the rim that I'm going to replace the hub
on; measure it; and order new spokes that are shorter by the
diff.

But that depends on my measuring the old spoke properly.

Seems like there's a few mm of wiggle room there depending on
exactly how it's measured.

You measure spoke length from the inside of the spoke elbow from where
the elbow starts to curve upwards.
The sources I know of (Roger Musson http://www.wheelpro.co.uk/wheelbuilding/book.php)
says that spokes elongate by 0,5 mm when tensioned. Not sure whether
this is a permanent elongation. Anyway if the two hubs are identical
just measure a spoke and buy a spoke the same size or 1 mm shorter if
possible. +-1 mm shouldn't be a problem at all. You are better of with
spokes that are somewhat too short so that some thread is visible,
than spokes that are too long, since that means that the necessary
tension may not be achieved.
Just to be sure, check the old wheel for whether any thread is visible
near the spoke nipples (spokes on the short side) or if the spokes
protrude upwards inside the spoke nipple (spokes on the long side).

--
Regards

On Feb 22, 11:37*am, wrote:
(PeteCresswell) skrev:

Once the drum brake hub I ordered arrives, my plan is to measure
the spoke-hole-center-to-axle-center distance on the old and new
hubs; pull a spoke from the rim that I'm going to replace the hub
on; measure it; and order new spokes that are shorter by the
diff.

But that depends on my measuring the old spoke properly.

Seems like there's a few mm of wiggle room there depending on
exactly how it's measured.

You measure spoke length from the inside of the spoke elbow from where
the elbow starts to curve upwards.
The sources I know of (Roger Mussonhttp://www.wheelpro.co.uk/wheelbuilding/book.php)
says that spokes elongate by 0,5 mm when tensioned. Not sure whether
this is a permanent elongation. Anyway if the two hubs are identical
just measure a spoke *and buy a spoke the same size or 1 mm shorter if
possible. +-1 mm shouldn't be a problem at all. You are better of with
spokes that are somewhat too short so that some thread is visible,
than spokes that are too long, since that means that the necessary
tension may not be achieved.
Just to be sure, check the old wheel for whether any thread is visible
near the spoke nipples (spokes on the short side) or if the spokes
protrude upwards inside the spoke nipple (spokes on the long side).

--
Regards

they said: " just to be sure, sacrifice a horned animal"

On 22 Feb., 17:37, wrote:

[snip]
I just realized that you were talking about a new and different hub.
If the hub isn't in the spocalc db, or in DT Swiss online spoke
calculator;
http://www.dtswiss.com/SpokesCalc/We...px?language=en
then you have to measure it yourself. It is quite easy, here are the
instructions and a nice sheet to print out:

http://www.wheelpro.co.uk/spokecalc/
http://www.wheelpro.co.uk/spokecalc/hubmeasure.pdf

You can then use the data to calculate the correct spoke length, using
either spocalc or Mussons or DT Swiss' online calculators.
Always round downwards. If spocalc says 289,8 mm, round it down to 289
mm.
Always prefer slightly shorter spokes eg. Some if not all spoke
manufactures tend to have 1 mm jumps between their spokes, so if
spocalc says 288,6 mm spokes, but you can only get 289 mm or 287 mm
spokes, then get the shorter 287 mm spokes.

Musson's spoke calculator subtracts 0,5 mm from its results because of
spoke elongation:
http://www.wheelpro.co.uk/spokecalc/

I think spocalc gives "raw" values without any correction.

DT Swiss seems to have some kind of correction, but it doesn't says
how much or why.

--
Regards

On Thu, 21 Feb 2008 21:38:28 -0500, "(PeteCresswell)"
wrote:

Anybody know the right way to measure spoke length?


Spoke length is measured from the inside of the bend at the hub end to
the other end.

Pushing the macro capability of my camera I took a picture of the
modification I made to a plastic metric ruler in order to measure
spokes. It's at:

http://www.flickr.com/photos/sierrajohn/2284349192/

Looking closely I can now see I probably came up about a half
millimeter short when I cut the slot.


--
jeverett3ATsbcglobalDOTnet (John V. Everett)

Per :
Anyway if the two hubs are identical
just measure a spoke and buy a spoke the same size or 1 mm shorter if
possible. +-1 mm shouldn't be a problem at all. You are better of with
spokes that are somewhat too short

I'm kind of boggled by the measurements required for doing it the
right way. Seems like too much chance of error.

SpoCalc seems to come up with different lengths for rite/left
even though the dimensions are entered as being the same. OTOH,
the sheet doesn't document it's terminology and I'm kind of
guessing at the meaning of "OSB Offset spoke bed" - and the
number it comes up with is heavy by at least 15-18 mm...

So I guess it's pretty obvious that I'm making some significant
error.

The hubs are not the same diameter and, as somebody pointed out,
a straight diff in length based on hub diameter diff only works
for radial lacing.

OTOH, when I draw a right triangle with the old spoke on one side
at a length of 270mm, a short side length (the hub radius diff)
of 23.5mm and play with the numbers, it seems like that radius
diff is only good for one or 2 mm.

So I'm back to thinking I'll take the length of an old spoke,
subtract the hub spoke hole radius diff, and then knock off
another 1.5 mm for the diameter diff.
--
PeteCresswell

(PeteCresswell) wrote:
Per :
Anyway if the two hubs are identical
just measure a spoke and buy a spoke the same size or 1 mm shorter if
possible. +-1 mm shouldn't be a problem at all. You are better of with
spokes that are somewhat too short

I'm kind of boggled by the measurements required for doing it the
right way. Seems like too much chance of error.

SpoCalc seems to come up with different lengths for rite/left
even though the dimensions are entered as being the same. OTOH,
the sheet doesn't document it's terminology and I'm kind of
guessing at the meaning of "OSB Offset spoke bed" - and the
number it comes up with is heavy by at least 15-18 mm...

So I guess it's pretty obvious that I'm making some significant
error.

The hubs are not the same diameter and, as somebody pointed out,
a straight diff in length based on hub diameter diff only works
for radial lacing.

OTOH, when I draw a right triangle with the old spoke on one side
at a length of 270mm, a short side length (the hub radius diff)
of 23.5mm and play with the numbers, it seems like that radius
diff is only good for one or 2 mm.

So I'm back to thinking I'll take the length of an old spoke,
subtract the hub spoke hole radius diff, and then knock off
another 1.5 mm for the diameter diff.

but the spokes are not radial - there is more trig involved than that...

"(PeteCresswell)" wrote:
Anybody know the right way to measure spoke length?
Once the drum brake hub I ordered arrives, my plan is to measure
the spoke-hole-center-to-axle-center distance on the old and new
hubs; pull a spoke from the rim that I'm going to replace the hub
on; measure it; and order new spokes that are shorter by the
diff.
But that depends on my measuring the old spoke properly.
Seems like there's a few mm of wiggle room there depending on
exactly how it's measured.
Or am I over-thinking this and there's X mm of slop that can be
taken up by the nipples?

datakoll wrote:
ahhh? the trig from one triangle minus the trig from another? ?????
use the beam and 8 or 12 spoke at equal spacings-4 or 6 one side then
ditto. the complete solution to spoke calc is real time measurement.
measure old spokes v, new spokes? slop? more than enough slop. gotta
spoke rule taped to the countertop with the spoke bend hole over the
side so's the spoke head goes thru? OK, learning how to measure from
this position only gives 2+ mm differences -/+. that is the measurer,
you, needs to learn a method for stabilizing measuring at that point-
with new spokes only. Press down at the bend and pull and press down
at the other end.
Now stabilize with used v. new spokes...probabbbbly enough -/+ mm to
reduce effectiveness for finding a good length.
build a beam, tape measure or stick measure then tape measure stick
(1X2"??), buy 8 trial spokes and urine the correct direction Rinard or
not.

datakoll wrote:
before using your method or Rinard
build an altar with a white floor, sacrifice an animal . get a big
animal. larger the better. cut the animals throat at the carotid or
juglar. more blood the better. see alt.sacrifice for nuance. sell
tickets.

Yeah, we knew that already:
http://groups.google.com/group/rec.b...f91b4 68b3abc

27 Sep 2002, quite possibly the best r.b.t. post of all time

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

In article
,
wrote:

(PeteCresswell) skrev:

Once the drum brake hub I ordered arrives, my plan is to measure
the spoke-hole-center-to-axle-center distance on the old and new
hubs; pull a spoke from the rim that I'm going to replace the hub
on; measure it; and order new spokes that are shorter by the
diff.

But that depends on my measuring the old spoke properly.

Seems like there's a few mm of wiggle room there depending on
exactly how it's measured.

You measure spoke length from the inside of the spoke elbow from where
the elbow starts to curve upwards.
The sources I know of (Roger Musson http://www.wheelpro.co.uk/wheelbuilding/book.php)
says that spokes elongate by 0,5 mm when tensioned. Not sure whether
this is a permanent elongation.

If it were permanent, what restrains it from further elongation?

--
Michael Press

"(PeteCresswell)" wrote in message
...
Per :
Anyway if the two hubs are identical
just measure a spoke and buy a spoke the same size or 1 mm shorter if
possible. +-1 mm shouldn't be a problem at all. You are better of with
spokes that are somewhat too short

I'm kind of boggled by the measurements required for doing it the
right way. Seems like too much chance of error.

SpoCalc seems to come up with different lengths for rite/left
even though the dimensions are entered as being the same. OTOH,
the sheet doesn't document it's terminology and I'm kind of
guessing at the meaning of "OSB Offset spoke bed" - and the
number it comes up with is heavy by at least 15-18 mm...

So I guess it's pretty obvious that I'm making some significant
error.

Mmm, sounds quite likely.

So: what hub, what rim?

Are they in the database?

If not, what are their dimensions? Need distance between centre and flange
for both sides (would be the same for a normal front hub), diameter of
flange. Number of spokes, how many cross you want to do. And ERD of rim. Is
the rim symmetric or offset?

cheers,
clive

Per :
Anyway if the two hubs are identical
just measure a spoke and buy a spoke the same size or 1 mm shorter if
possible. +-1 mm shouldn't be a problem at all. You are better of with
spokes that are somewhat too short

(PeteCresswell) wrote:
I'm kind of boggled by the measurements required for doing it the
right way. Seems like too much chance of error.

SpoCalc seems to come up with different lengths for rite/left
even though the dimensions are entered as being the same. OTOH,
the sheet doesn't document it's terminology and I'm kind of
guessing at the meaning of "OSB Offset spoke bed" - and the
number it comes up with is heavy by at least 15-18 mm...

So I guess it's pretty obvious that I'm making some significant
error.

The hubs are not the same diameter and, as somebody pointed out,
a straight diff in length based on hub diameter diff only works
for radial lacing.

OTOH, when I draw a right triangle with the old spoke on one side
at a length of 270mm, a short side length (the hub radius diff)
of 23.5mm and play with the numbers, it seems like that radius
diff is only good for one or 2 mm.

So I'm back to thinking I'll take the length of an old spoke,
subtract the hub spoke hole radius diff, and then knock off
another 1.5 mm for the diameter diff.

You could just look over at the tattoo of the guy standing next to you:
http://www.yellowjersey.org/photosfr...t/SPOKFORM.JPG
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971