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spoke length problem



 
 
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  #11  
Old November 30th 17, 10:56 PM posted to rec.bicycles.tech
Frank Krygowski[_4_]
external usenet poster
 
Posts: 6,161
Default spoke length problem

On 11/30/2017 4:53 PM, wrote:
Why yawl refuse real time measurement with a simply made device is intolerably STUPID


I did not have the rims when I ordered the spokes. Why is that not clear?

--
- Frank Krygowski
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  #12  
Old November 30th 17, 11:07 PM posted to rec.bicycles.tech
AMuzi
external usenet poster
 
Posts: 9,635
Default spoke length problem

On 11/30/2017 3:23 PM, Frank Krygowski wrote:
On 11/29/2017 11:22 PM, jbeattie wrote:
On Wednesday, November 29, 2017 at 7:58:57 PM UTC-8, Frank
Krygowski wrote:
Warning: Actual bike tech content below.

I'm building up an antique bike for a kid. After a false
start with the
original rims (very light, but in a very obscure size) I
ended up
replacing the wheels with 20" Sun rims on hubs that I had
lying around:
a Campy front hub, and a Shimano 3CC 3 speed rear hub
with coaster brake.

I measured both hubs and used Sun's online ERD value of
396mm for the
rim. I plugged dimensions into three different online
spoke calculators.
It looked like I could use the same spoke length front
and rear if I
went 2x front and 3x rear.

Here were the calculator results:
Sapim said front 189mm, rear 188mm.
DT said 186 front, 186 rear.
United Bicycle Institute said 185.6 front, 185.1 rear.
So I ordered 14 gauge Sapim spokes, 186 front and rear.

The front wheel built up perfectly, as usual. But the
rear wheel won't
tension up. The spoke threads are bottoming.

I just double checked my hub dimensions. They seem to be
spot on. And
again, everything was perfect in front. The spokes
measure 186 with 10mm
of thread. The nipples are 16mm long with an unthreaded
5mm deep hole at
the end that slides over the spoke.

I can think of several possible solutions:

1) buy shorter spokes.

2) sacrifice a few nipple threads by drilling into the
end of the nipple
to counterbore another 2mm or so. It's for a little kid,
and I doubt
he'll be stressing the wheel very much.

3) acquire a die and extend the spoke threads. The cut
threads won't
have a full thread form, but there should be plenty of
strength in the
existing threads.

4) put washers under the spoke heads. It's a double wall
rim so there's
room in there.

5) and next time, maybe go 2mm shorter than the
calculators say? But
why? These spokes aren't stretching. I can't get any
tension at all.

I'm curious if anyone's had a similar problem. If so, did
you determine
what caused the error? I'm prepared to smack my forehead
if necessary.



They're too long, obviously. Is lacing 4X a possibility?
Otherwise, you buy new spokes. You could also find a shop
with a Phil or other spoke cutter.


4x won't work. That would require roughly 195mm spokes. I
happen to have a set of 170mm spokes (intended for the
original odd rims) and the calculators tell me x2 would need
177mm. So I'm assuming 170 is too short.

I'll see if some shorter nipples might work. If not, I'll
probably go with washers under the spoke nipple heads.

I'm more interested in knowing what might have gone wrong.
I've never had this problem occur before.

I just tried measuring the ERD myself, using a tape measure
to get circumference of the rim tape's surface (1260mm) and
a metric vernier caliper to get the "drop" from that surface
to the face of the hollow rivets on which the spoke head
rests (3.8mm). Circumference divided by pi minus (drop x 2)
gives me 393.5mm. From
https://www.sheldonbrown.com/spoke-length.html I get the
advice to add a couple millimeter for the thickness of each
nipple head, which gives me ERD = 397.5mm. That compares
well with the online catalog value of 396, so I'm still
baffled.


Our calculator gives 185 left & right for that rear wheel.
Sorry but I didn't see any obvious error.

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


  #13  
Old November 30th 17, 11:14 PM posted to rec.bicycles.tech
Frank Krygowski[_4_]
external usenet poster
 
Posts: 6,161
Default spoke length problem

On 11/30/2017 5:17 PM, jbeattie wrote:
On Thursday, November 30, 2017 at 11:37:28 AM UTC-8, wrote:
All my experience is with buying too short spokes. I use the calculators to figure the right length. Then always buy a spoke 2-3-4 mm shorter figuring the calculators are over generous and the spokes will stretch when tightened. Went a bit overboard on this on one set of wheel and ended up with lots of threads showing below the nipple. In your situation the other suggestions of new spokes or cutting longer threads on the existing spokes is the best method. But just using washers under the nipples inside the rim would be the easiest fix and still be fine and dandy.


Washers are so trailer.

It is odd that the length was fine for the front but not the rear. The obvious explanation would be a mistaken flange height/spoke hole measurement. The ERD was correct for the front so it should be correct for the rear, assuming the as-manufactured rim is not out of spec. I assume Frank put the right number of spoke holes into the calculator. The only variable in the equation is the hub. No?


Yes, everything was double checked, then double checked again when
things didn't fit. I'm using both dial calipers and vernier calipers on
the hub dimensions.

It occurs to me that the front wheel barely tensioned up. I don't think
I could have gotten another millimeter worth of turns out of those nipples.

I suspect that the rim ERD is a bit undersized. That's the most
difficult measurement to make, and I know from stories of super-tight
tires that rim diameters are not super precise. (The front tire was
certainly easy to mount, no tire levers required.) The most exact way of
measuring the ERD directly would require stripping all the spokes out
again, then precisely measuring the diameter using a couple spokes and a
caliper. But I don't plan on going through that trouble.

It's also interesting to me that the various spoke length calculators
don't precisely agree. Four different calculators gave 188, 186, 185.1
and 185.3. At its heart, the calculation is just three dimensional
Pythagorean theorem. The variations indicate some assumptions that are
hidden and different.

For kicks, I used Sketchup (a three dimensional drafting program) to
draw a simple model of the hub and rim. (Details on request. It's
overkill for standard spoking patterns, but could be handy for spoking
oddball wheels.) I drew in a couple spokes with the proper number of
crosses and measured a spoke length of 186.1mm. That's straight line
point-to-point geometry, and it certainly confirms the 186mm spokes I
bought. Too bad they don't fit.

This afternoon I dug in my junk piles and found some shorter spoke
nipples that thread a millimeter further onto the 186 spokes. I think
those plus washers should fix things.

At least washers in a rim are less visible than hose clamps on a stem! ;-)


--
- Frank Krygowski
  #14  
Old November 30th 17, 11:15 PM posted to rec.bicycles.tech
Frank Krygowski[_4_]
external usenet poster
 
Posts: 6,161
Default spoke length problem

On 11/30/2017 6:07 PM, AMuzi wrote:
On 11/30/2017 3:23 PM, Frank Krygowski wrote:
On 11/29/2017 11:22 PM, jbeattie wrote:
On Wednesday, November 29, 2017 at 7:58:57 PM UTC-8, Frank
Krygowski wrote:
Warning: Actual bike tech content below.

I'm building up an antique bike for a kid. After a false
start with the
original rims (very light, but in a very obscure size) I
ended up
replacing the wheels with 20" Sun rims on hubs that I had
lying around:
a Campy front hub, and a Shimano 3CC 3 speed rear hub
with coaster brake.

I measured both hubs and used Sun's online ERD value of
396mm for the
rim. I plugged dimensions into three different online
spoke calculators.
It looked like I could use the same spoke length front
and rear if I
went 2x front and 3x rear.

Here were the calculator results:
Sapim said front 189mm, rear 188mm.
DT said 186 front, 186 rear.
United Bicycle Institute said 185.6 front, 185.1 rear.
So I ordered 14 gauge Sapim spokes, 186 front and rear.

The front wheel built up perfectly, as usual. But the
rear wheel won't
tension up. The spoke threads are bottoming.

I just double checked my hub dimensions. They seem to be
spot on. And
again, everything was perfect in front. The spokes
measure 186 with 10mm
of thread. The nipples are 16mm long with an unthreaded
5mm deep hole at
the end that slides over the spoke.

I can think of several possible solutions:

1) buy shorter spokes.

2) sacrifice a few nipple threads by drilling into the
end of the nipple
to counterbore another 2mm or so. It's for a little kid,
and I doubt
he'll be stressing the wheel very much.

3) acquire a die and extend the spoke threads. The cut
threads won't
have a full thread form, but there should be plenty of
strength in the
existing threads.

4) put washers under the spoke heads. It's a double wall
rim so there's
room in there.

5) and next time, maybe go 2mm shorter than the
calculators say? But
why? These spokes aren't stretching. I can't get any
tension at all.

I'm curious if anyone's had a similar problem. If so, did
you determine
what caused the error? I'm prepared to smack my forehead
if necessary.


They're too long, obviously. Is lacing 4X a possibility?
Otherwise, you buy new spokes.* You could also find a shop
with a Phil or other spoke cutter.


4x won't work. That would require roughly 195mm spokes. I
happen to have a set of 170mm spokes (intended for the
original odd rims) and the calculators tell me x2 would need
177mm. So I'm assuming 170 is too short.

I'll see if some shorter nipples might work. If not, I'll
probably go with washers under the spoke nipple heads.

I'm more interested in knowing what might have gone wrong.
I've never had this problem occur before.

I just tried measuring the ERD myself, using a tape measure
to get circumference of the rim tape's surface (1260mm) and
a metric vernier caliper to get the "drop" from that surface
to the face of the hollow rivets on which the spoke head
rests (3.8mm). Circumference divided by pi minus (drop x 2)
gives me 393.5mm. From
https://www.sheldonbrown.com/spoke-length.html I get the
advice to add a couple millimeter for the thickness of each
nipple head, which gives me ERD = 397.5mm. That compares
well with the online catalog value of 396, so I'm still
baffled.


Our calculator gives 185 left & right for that rear wheel.
Sorry but I didn't see any obvious error.

Thanks for checking. At least I don't have to slap my forehead just yet.

--
- Frank Krygowski
  #15  
Old December 1st 17, 01:45 AM posted to rec.bicycles.tech
AMuzi
external usenet poster
 
Posts: 9,635
Default spoke length problem

On 11/30/2017 5:15 PM, Frank Krygowski wrote:
On 11/30/2017 6:07 PM, AMuzi wrote:
On 11/30/2017 3:23 PM, Frank Krygowski wrote:
On 11/29/2017 11:22 PM, jbeattie wrote:
On Wednesday, November 29, 2017 at 7:58:57 PM UTC-8, Frank
Krygowski wrote:
Warning: Actual bike tech content below.

I'm building up an antique bike for a kid. After a false
start with the
original rims (very light, but in a very obscure size) I
ended up
replacing the wheels with 20" Sun rims on hubs that I had
lying around:
a Campy front hub, and a Shimano 3CC 3 speed rear hub
with coaster brake.

I measured both hubs and used Sun's online ERD value of
396mm for the
rim. I plugged dimensions into three different online
spoke calculators.
It looked like I could use the same spoke length front
and rear if I
went 2x front and 3x rear.

Here were the calculator results:
Sapim said front 189mm, rear 188mm.
DT said 186 front, 186 rear.
United Bicycle Institute said 185.6 front, 185.1 rear.
So I ordered 14 gauge Sapim spokes, 186 front and rear.

The front wheel built up perfectly, as usual. But the
rear wheel won't
tension up. The spoke threads are bottoming.

I just double checked my hub dimensions. They seem to be
spot on. And
again, everything was perfect in front. The spokes
measure 186 with 10mm
of thread. The nipples are 16mm long with an unthreaded
5mm deep hole at
the end that slides over the spoke.

I can think of several possible solutions:

1) buy shorter spokes.

2) sacrifice a few nipple threads by drilling into the
end of the nipple
to counterbore another 2mm or so. It's for a little kid,
and I doubt
he'll be stressing the wheel very much.

3) acquire a die and extend the spoke threads. The cut
threads won't
have a full thread form, but there should be plenty of
strength in the
existing threads.

4) put washers under the spoke heads. It's a double wall
rim so there's
room in there.

5) and next time, maybe go 2mm shorter than the
calculators say? But
why? These spokes aren't stretching. I can't get any
tension at all.

I'm curious if anyone's had a similar problem. If so, did
you determine
what caused the error? I'm prepared to smack my forehead
if necessary.


They're too long, obviously. Is lacing 4X a possibility?
Otherwise, you buy new spokes. You could also find a shop
with a Phil or other spoke cutter.

4x won't work. That would require roughly 195mm spokes. I
happen to have a set of 170mm spokes (intended for the
original odd rims) and the calculators tell me x2 would need
177mm. So I'm assuming 170 is too short.

I'll see if some shorter nipples might work. If not, I'll
probably go with washers under the spoke nipple heads.

I'm more interested in knowing what might have gone wrong.
I've never had this problem occur before.

I just tried measuring the ERD myself, using a tape measure
to get circumference of the rim tape's surface (1260mm) and
a metric vernier caliper to get the "drop" from that surface
to the face of the hollow rivets on which the spoke head
rests (3.8mm). Circumference divided by pi minus (drop x 2)
gives me 393.5mm. From
https://www.sheldonbrown.com/spoke-length.html I get the
advice to add a couple millimeter for the thickness of each
nipple head, which gives me ERD = 397.5mm. That compares
well with the online catalog value of 396, so I'm still
baffled.


Our calculator gives 185 left & right for that rear wheel.
Sorry but I didn't see any obvious error.

Thanks for checking. At least I don't have to slap my
forehead just yet.


Because Shimano tricoaster and the trig are well known, I
suspect the actual ERD is not what we assume. There are
several rims whose dies were changed over the years with
various retoolings.

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


 




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