Spoke Length: Measurement Methology And Criticality?

jim beam

(PeteCresswell) wrote:
> Per phs123@gmail.com:
>> 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...

A Muzi

>> "(PeteCresswell)" <x...@y.Invalid> 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 <datak...@yahoo.com> 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....03cf91b468b3abc

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

Michael Press

In article
<d4a41fd5-d6f0-48fa-9758-00b1359bf1cf@i7g2000prf.googlegroups.com>,
phs123@gmail.com 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

Clive George

"(PeteCresswell)" <x@y.Invalid> wrote in message
news:4l6ur31mvgahh819q83bok8r21qm4mrs6d@4ax.com...
> Per phs123@gmail.com:
>>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

A Muzi

> Per phs123@gmail.com:
>> 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/photosf...st/SPOKFORM.JPG
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

landotter

On Feb 22, 1:33 pm, A Muzi <a...@yellowjersey.org> wrote:

> Yeah, we knew that already:http://groups.google.com/group/rec....e_thread/thread...
>
> 27 Sep 2002, quite possibly the best r.b.t. post of all time

"(squeeze chicken from bottom to neck several times)"

(PeteCresswell)

Per Clive George:
>mm, sounds quite likely.
>
>So: what hub

Sturmey X-FDD Dynohub.

> what rim?

Ancient and honorable Ayra 26 x 1.75 as supplied with the
original 1982 StumpJumper. I want to stick with it bc it looks
ugly but does the job.

This is my utility/who'd-to-steal-it bike.
http://tinyurl.com/37d4ko

Granted the Dynohub is at odds with that characterization... but
I figure the nastier the rim looks, the more the POS image will
be preserved - especially with sufficient grease/dirt/crud on the
Dynohub.


>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),

That's where it gets sticky. Using calipers and a meter stick,
I get an outside flange width of 61 mm and it *seems* tb
symmetrical. http://tinyurl.com/3a9t2z

But when I double check by measuring inside of flange to a metal
strap bolted to the axle, there is a good 2 mm dif between the
two sides: http://tinyurl.com/3e3r8g


> diameter of >flange.

92 mm outside of spoke-hole-to-outside-of-spoke-hole
http://tinyurl.com/2ofbyz


> Number of spokes

36.

> Dunno... whatever's safe and does the job.

Consensus is that current lacing is 4x.


> ERD of rim.

537 mm inside hole-to-hole, top-of-dimple-to-top-of-dimple.
http://tinyurl.com/36r78k


> Is the rim symmetric or offset?

Not sure what that means, but it's a front wheel and the spoke
holes are about 3mm out from the center of the rim:
http://tinyurl.com/22fm3r


My current guesstimate for spoke length is 244 or 246.
--
PeteCresswell

(PeteCresswell)

Per A Muzi:
>You could just look over at the tattoo of the guy standing next to you:
>http://www.yellowjersey.org/photosf...st/SPOKFORM.JPG

Tattoo? You want to see a tattoo?
http://tinyurl.com/2sp4yb
--
PeteCresswell

(PeteCresswell)

Per (PeteCresswell):
(lacing)
>> Dunno... whatever's safe and does the job.
>
>Consensus is that current lacing is 4x.

OTOH, I observe that on my Rohloff rear wheels, the lacing is
only two across. Justified, IRRC, by the larger flange
diameter. FWIW the Rohloff hub's outside-of-spoke-hole flange
diameter is about 9 mm greater than the Sturmey's.
--
PeteCresswell

Clive George

"(PeteCresswell)" <x@y.Invalid> wrote in message
news:n6bur3tsjtrfcofghdck5j1he29cjlmmqt@4ax.com...
> Per Clive George:
>>mm, sounds quite likely.
>>
>>So: what hub
>
> Sturmey X-FDD Dynohub.
>
>> what rim?
>
> Ancient and honorable Ayra 26 x 1.75 as supplied with the
> original 1982 StumpJumper. I want to stick with it bc it looks
> ugly but does the job.
>
> This is my utility/who'd-to-steal-it bike.
> http://tinyurl.com/37d4ko
>
> Granted the Dynohub is at odds with that characterization... but
> I figure the nastier the rim looks, the more the POS image will
> be preserved - especially with sufficient grease/dirt/crud on the
> Dynohub.
>
>
>>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),
>
> That's where it gets sticky. Using calipers and a meter stick,
> I get an outside flange width of 61 mm and it *seems* tb
> symmetrical. http://tinyurl.com/3a9t2z
>
> But when I double check by measuring inside of flange to a metal
> strap bolted to the axle, there is a good 2 mm dif between the
> two sides: http://tinyurl.com/3e3r8g

You need the centre of the flange. So subtract a bit. The 2mm offset makes
sod all difference - put the numbers into the spreadsheet and see.

>> diameter of >flange.
>
> 92 mm outside of spoke-hole-to-outside-of-spoke-hole
> http://tinyurl.com/2ofbyz

Again, centre of spoke holes, so substract a bit - this one is more
important, though the numbers suggest you can get a surprisingly large
change in diameter at 3/4x. (ok, not that surprising I suppose).

>> Number of spokes
>
> 36.
>
>> Dunno... whatever's safe and does the job.
>
> Consensus is that current lacing is 4x.
>
>
>> ERD of rim.
>
> 537 mm inside hole-to-hole, top-of-dimple-to-top-of-dimple.
> http://tinyurl.com/36r78k

Ok - to quote spocalc, "ERD is measured to the end of the spoke, usually
flush with the head of the nipple". There are quite a few Araya rims in
there with an ERD of 547mm - TBH I'd guess at that being the answer. Your
rim definitely looks bigger than 537mm on that photo.

>> Is the rim symmetric or offset?
>
> Not sure what that means, but it's a front wheel and the spoke
> holes are about 3mm out from the center of the rim:
> http://tinyurl.com/22fm3r

Symmetric. There are rims both spoke holes offset to one side, intended to
reduce dish in rear wheels. Hence OSB - which will be zero in your case.

> My current guesstimate for spoke length is 244 or 246.

I'm guessing 268 for 4x. Personally I'd use 3x, so 254mm. Spocalc with your
numbers doesn't give 244 or 246 either.

In your situation I'd go through the measurements again. Play with the
flange ones a bit in the spreadsheet to satisfy yourself that they're not
actually that critical, check the ERD, then see what the answer is.

cheers,
clive

jobst.brandt@stanfordalumni.org

Pete Cresswell writes:

>>> Dunno... whatever's safe and does the job.

>> Consensus is that current lacing is 4x.

> OTOH, I observe that on my Rohloff rear wheels, the lacing is only
> two across. Justified, IRRC, by the larger flange diameter. FWIW
> the Rohloff hub's outside-of-spoke-hole flange diameter is about 9
> mm greater than the Sturmey's.

The deciding effect is the angle at which spokes enter the rim. With
large hub flange diameters, fewer crossings should be used to keep
that angle small. If you look at motorcycle wheels, their spokes
emanate from spherical bulges in the rim at fairly large angles from
radial. They being thick and stiff have no options but to go in-line
to the flange from the holes that are drilled by the wheel builder for
custom wheels, that being the cross pattern decider.

Bicycle rims have holes angled left and right but not fore and aft, so
that angle wants to stay near radial to prevent spoke fractures at the
spoke nipple that cannot swivel to larger angles than close to
radial. The Rohloff hub will do well with cross-1 or cross-2.

Jobst Brandt

(PeteCresswell)

Per Clive George:
>In your situation I'd go through the measurements again. Play with the
>flange ones a bit in the spreadsheet to satisfy yourself that they're not
>actually that critical, check the ERD, then see what the answer is.

At my current stage of confusion... I think the logical thing to
do is take the hub and rim down to an LBS that I can deal with
and throw myself on their mercy.... -)

I figure somebody who has it down pat can lace and true a wheel
in about 45 minutes. Dunno what that comes to in shop billing
dollars... but I think I'll explore that tomorrow.
--
PeteCresswell

A Muzi

> Per A Muzi:
>> You could just look over at the tattoo of the guy standing next to you:
>> http://www.yellowjersey.org/photosf...st/SPOKFORM.JPG

(PeteCresswell) wrote:
> Tattoo? You want to see a tattoo?
> http://tinyurl.com/2sp4yb

Yes, cute in its own way.
But it doesn't help with the problem at hand, calculate spoke length.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

datakoll

well, I guess its ok to ask this now.
JB sez the Rohloff takes a 2 cross lacing. Does that mean the Rohloff
isnot indicated for rough over the road long distance riding?