Spoke Breakage Question

[Jan Lindstrom]

Mark wrote:

> Before giving up, I'd suggest finding some way to borrow/use a tension
> gauge to check the overall tension to see if more can reasonably be
> added. Purchase one if needed, but a visit to your friendly LBS may
> make that unnecessary, especially if you are a valued regular customer.
>

Is your view that spokes are braking of lack of tension, not because of
fatigue? I thought the tension doesn't affect spoke life, unless it is
so woefully low that they completely lose their tension. That can be
felt while riding, and since Arthur didn't mention it, I'm assuming that
they're not that loose.

My advice: stress relieve.

Jan

 

[[email protected]]

On Tue, 08 Aug 2006 07:27:40 +0300, Jan Lindstrom
<[email protected]> wrote:

>Mark wrote:
>
>> Before giving up, I'd suggest finding some way to borrow/use a tension
>> gauge to check the overall tension to see if more can reasonably be
>> added. Purchase one if needed, but a visit to your friendly LBS may
>> make that unnecessary, especially if you are a valued regular customer.
>>
>
>Is your view that spokes are braking of lack of tension, not because of
>fatigue? I thought the tension doesn't affect spoke life, unless it is
>so woefully low that they completely lose their tension. That can be
>felt while riding, and since Arthur didn't mention it, I'm assuming that
>they're not that loose.
>
>My advice: stress relieve.
>
>Jan

Dear Jan,

Elsewhere in this thread, the original poster wrote:

"I've done my best to stress-relieve; I've built literally many
hundreds of wheels and seem to have the requisite techniques down
fairly well."

http://groups.google.com/group/rec.bicycles.tech/msg/0cdfa56ea52b5b15

Cheers,

Carl Fogel

 

[Arthur Shapiro]

In article <%[email protected]>, [email protected] wrote:

>Is your view that spokes are braking of lack of tension, not because of
>fatigue

I'm the O.P. Fatigue breaks on the left side of a ten-cog wheel would be
almost unfathomable.

I think I'll grit my teeth and give the right side spokes another quarter or
third of a turn, and tighten the left as necessary to restore the wheel to
centered and true. I generally tighten spokes reasonably snugly, but not to
the point where I want to be wearing Kevlar armor to avoid a career with the
Vienna Boys Choir if they let go.

Art

 

[[email protected]]

On Tue, 08 Aug 2006 05:37:20 GMT, [email protected] (Arthur
Shapiro) wrote:

>In article <%[email protected]>, [email protected] wrote:
>
>>Is your view that spokes are braking of lack of tension, not because of
>>fatigue
>
>I'm the O.P. Fatigue breaks on the left side of a ten-cog wheel would be
>almost unfathomable.
>
>I think I'll grit my teeth and give the right side spokes another quarter or
>third of a turn, and tighten the left as necessary to restore the wheel to
>centered and true. I generally tighten spokes reasonably snugly, but not to
>the point where I want to be wearing Kevlar armor to avoid a career with the
>Vienna Boys Choir if they let go.
>
>Art

Dear Art,

If you measure your spoke tension with a Park gauge before you tighten
all the spokes on one side a mere quarter or third of a turn, you'll
probably be surprised at how moderately the tension increases.

When I was testing the actual tension changes for known spoke
squeezing forces, Joe Riel asked me to measure the tension change on a
2.0 x 1.8 x 2.0mm spoke as I loosened it a quarter turn at a time.

From 54kg to 112kg, quarter turns averaged around 6 kg tension change.
A graph of the tension change was surprisingly linear.

(I had mistakenly expected that the spoke tension would curve
dramatically, rising more and more sharply as I tightened the nipple,
until even a tiny turn would cause the tension to skyrocket.)

The spoke nipple threading is 56 tpi, so a quarter turn tries to pull
the spoke 1/224th of an inch closer to the rim. At ordinary tensions,
there's plenty of elasticity left in the roughly 290mm spoke span.

Of course, a 1/4 turn all the way around amounts to two 1/4 turns on
opposing sides, so you would theoretically expect something closer to
12kg.

But I found during testing that tightening rear spokes on only one
side failed to raise tension nearly as much as I expected, possibly
due to dishing.

Cheers,

Carl Fogel

 

[suzyj]

One other data point is that the 15/16 gauge spoke on the left side aren't a close fit in the hub, like 14/15s...

I usually use 14/15's on both sides, and have no problems. It seems self evident that your spoke tension is low. However now that the left side spokes are fatigued, you'll probably find that tnnsioning the wheel properly will simply see more of them fail.

When you replace the left side spokes, it might be a good idea to use DT revs, as at least then you can use ones with 14 gauge ends.

Cheers,

Suzy

 

[daveornee]

One other data point is that the 15/16 gauge spoke on the left side aren't a close fit in the hub, like 14/15s...

I usually use 14/15's on both sides, and have no problems. It seems self evident that your spoke tension is low. However now that the left side spokes are fatigued, you'll probably find that tnnsioning the wheel properly will simply see more of them fail.

When you replace the left side spokes, it might be a good idea to use DT revs, as at least then you can use ones with 14 gauge ends.

Cheers,

Suzy

I agree. The more loose fitting the spoke at the hub spoke hole the more chances are for fatigue at either the head or the elbow.

 

[Mark]

Jan Lindstrom wrote:
> Mark wrote:
>
>> Before giving up, I'd suggest finding some way to borrow/use a tension
>> gauge to check the overall tension to see if more can reasonably be
>> added. Purchase one if needed, but a visit to your friendly LBS may
>> make that unnecessary, especially if you are a valued regular customer.
>>
>
> Is your view that spokes are braking of lack of tension, not because of
> fatigue?

"Both"

> I thought the tension doesn't affect spoke life, unless it is
> so woefully low that they completely lose their tension.

Yes, that's why I said "both". On 9/10 speed wheels, the dishing is so
pronounced that unless the right/drive side is very tight, the left side
spokes can slacken, leading to fatigue through flexion (is that a
word?). So added tension can solve the problem, if that's what the
problem is.

> That can be felt while riding,

I don't think I agree with that claim.

> My advice: stress relieve.

Probably good advice. I always do.

Mark J.

 

[Art Harris]

D'ohBoy wrote:
> Some recommend radial lacing on the NDS as a solution to this problem
> (NDS spoke breakage).

What is the rationale for that? Using a crossed pattern tends to
minimize spokes going slack because of the force exerted at the cross
points. Why would radial lacing be better?

Art Harris

 

[[email protected]]

Art Harris wrote:
> D'ohBoy wrote:
> > Some recommend radial lacing on the NDS as a solution to this problem
> > (NDS spoke breakage).
>
> What is the rationale for that?

http://www.sheldonbrown.com/wheelbuild.html#half-radial

I don't have any personal experience with it, however.

 

[daveornee]

D'ohBoy wrote:
> Some recommend radial lacing on the NDS as a solution to this problem
> (NDS spoke breakage).

What is the rationale for that? Using a crossed pattern tends to
minimize spokes going slack because of the force exerted at the cross
points. Why would radial lacing be better?

Art Harris

Radial lacing with heads out makes for a smaller spoke support angle.
The result is closer spoke tension matching from right to left. See:
http://sheldonbrown.com/wheelbuild.html#half-radial

 

[Paul Kopit]

On Mon, 07 Aug 2006 17:42:40 GMT, [email protected] (Arthur
Shapiro) wrote:

>I'm breaking 2 - 3 spokes per year on the non-driven side of my rear (Campy 10
>speed 3x to an Ambrosia Excellence.) Saturday was typical - powering into a
>turn with the bike consequently leaning to one side, and PING. I'm using DT
>15/16 on the left and 14/15 on the right. So in my case we're talking a
>failure every 2-3K miles.
>
[snip]
>
>Do other folks have this same issue? I'm reluctant to deliberately underdish
>the wheel, but that's one obvious action that could be taken. A broken spoke
>on the left isn't a particularly big deal in that the wheel doesn't go grossly
>out of true, but one shouldn't have to worry about it in the first place.
>
I build my wheels with the same spoke configuration and weigh ~200
lbs. I don't break spokes. You need more tension on each side of the
wheel. On a 14/15 ga spoke, the spoke wrench will be difficult to
turn with 2 fingers, assuming that the spokes and spoke holes are
lubricated.