Riding wheel with broken spokes, rebuilding same

[Patrick Lamb]

On Wed, 22 Dec 2004 18:46:43 GMT, [email protected]
wrote:

>David L. Johnson <[email protected]> writes:
>
>>> All breakage on the non-drive side at the head.
>
>> That's fatigue from the spokes becoming completely de-tensioned when
>> they reach the bottom on every revolution. This leads me to think
>> that all those spokes are probably fatigued, so should be replaced.
>
>Becoming slack does not cause fatigue failures but rather cyclic stress
>near the yield stress. Loose spokes that were never tight, can cause
>repeated flexing at the elbow, which causes high stress. As I see it,
>the identity of the spokes is unknown. I'm not sure they are stainless
>or not.

>I'm not familiar with that hub but I don't see throwing out all the
>spokes if they are stainless. Ones that may be cracked should fail on
>stress relieving.

I was thinking along the lines David was, I think. The remaining
spokes have been subjected to whatever stress cycles the broken spokes
experienced, and it's reasonable there are more spokes that are
cracked and will fail soon. Would it be worthwhile cranking the
tension up on the remaining spokes and stress-relieving them to see
how many fail? Keep in mind the OP is a novice, and when I was in his
shoes, the last thing I wanted to do was to have to repeatedly re-true
and re-tension the wheel while the other 16 spokes break, one at a
time.

Pat


Email address works as is.

 

[[email protected]]

Patrick Lamb writes:

>>>> All breakage on the non-drive side at the head.

>>> That's fatigue from the spokes becoming completely de-tensioned
>>> when they reach the bottom on every revolution. This leads me to
>>> think that all those spokes are probably fatigued, so should be
>>> replaced.

>> Becoming slack does not cause fatigue failures but rather cyclic
>> stress near the yield stress. Loose spokes that were never tight,
>> can cause repeated flexing at the elbow, which causes high stress.
>> As I see it, the identity of the spokes is unknown. I'm not sure
>> they are stainless or not.

>> I'm not familiar with that hub but I don't see throwing out all the
>> spokes if they are stainless. Ones that may be cracked should fail
>> on stress relieving.

> I was thinking along the lines David was, I think. The remaining
> spokes have been subjected to whatever stress cycles the broken
> spokes experienced, and it's reasonable there are more spokes that
> are cracked and will fail soon. Would it be worthwhile cranking the
> tension up on the remaining spokes and stress-relieving them to see
> how many fail? Keep in mind the OP is a novice, and when I was in
> his shoes, the last thing I wanted to do was to have to repeatedly
> re-true and re-tension the wheel while the other 16 spokes break,
> one at a time.

Two things make me think otherwise about this. If they are stainless,
then the manufacturer spent some money on relatively expensive wire
and possibly did not waste it by using crude forming tools. That this
is the case, would be evident by malformed spoke heads and tool marks
on the shafts at the elbows.

The other is that not all spokes lie in a threatening position and may
not have suffered any fatigue onset. I am highly aware of that from
my discovery of stress relieving, in which I rode a wheel on a long
tour that previously had frequent spoke failures. I had no freewheel
removal tool and because this required disassembling the freewheel to
replace spokes on the Campagnolo large flange hub, I didn't want to
have any more spokes break after I left the auto shop where I had
borrowed appropriate tools.

After replacing two broken spoke I attempted to break further spokes
that might be ready to break (by what I recognized later as stress
relieving) and succeeded in breaking two more, but failed to noticed
until years later that I had no more spoke failures with that wheel.

Jobst Brandt
[email protected]

 

[jim beam]

[email protected] wrote:
> David L. Johnson <[email protected]> writes:
>
>
>>>>Last weekend I was out on a 200K ride which ended when two spokes
>>>>broke in the rear wheel.
>
>
>>>All breakage on the non-drive side at the head.
>
>
>>That's fatigue from the spokes becoming completely de-tensioned when
>>they reach the bottom on every revolution. This leads me to think
>>that all those spokes are probably fatigued, so should be replaced.
>
>
> Becoming slack does not cause fatigue failures but rather cyclic stress
> near the yield stress. Loose spokes that were never tight, can cause
> repeated flexing at the elbow, which causes high stress. As I see it,
> the identity of the spokes is unknown. I'm not sure they are stainless
> or not.
>
>
>>>Unidentified mfg. spokes. The rim is a Sun CR18 36 hole, the hub a
>>>Shimano BS (86?) Parrallax.
>
>
>>That's a good rim, and an adequate hub. Worth re-building.
>
>
> I'm not familiar with that hub but I don't see throwing out all the
> spokes if they are stainless. Ones that may be cracked should fail on
> stress relieving.

not necessarily. depends on whether any existing the crack length
exceeds critical or not. fracture mechanics. if a crack exists and
doesn't cause fracture on "stress relief", it will continue to grow in
service, particularly with a stainless spoke.

>
> Jobst Brandt
> [email protected]

 

[jim beam]

A Muzi wrote:
> -snip-
>
>> Michael Rasmussen wrote:
>>
>>> All breakage on the non-drive side at the head. The elbows are
>>> still on the unidentified mfg. spokes. The rim is a Sun CR18 36
>>> hole, the hub a Shimano BS (86?) Parrallax.
>
>
> jim beam wrote:
>
>> none of those components are noted for excellence. you can spend $20
>> on good quality spokes, but those hub bearings won't last too long so
>> the benefit of the spoke investment is marginal. unless you want to
>> undertake the rebuilding project for the fun of it, i would consider
>> simply replacing with a better wheel.
>
> -snip-
>
> My experience is that 'cheap' hubs are generally dependable smooth and
> perfectly useful for a good long while _if_ they get proper initial
> setup - clean, plenty of lube, grade 25 bearings, slight preload.
> Shimano 'standard grade' hubs are no worse and better than the average
> 'replacement wheel' hubs (Sovos, Quando, KK, etc). (I'm referring to
> basic aluminum shell models, not stamped steel hubs).
>
> Since he owns the wheel, bearing prep and proper tensioning shouldn't
> require more than an hour. I'd go for it.

"initial setup" is the key. if it's been run for 1000 miles without
such initial prep, the bearing cones are either already starting to
deteriorate or will do so shortly. yes, they can be replaced, but
you're chasing your own tail from that point on.

>
> But taking your comment the other way, yes I think in the future the OP
> would do well to pay a bit more for better equipment - there's better
> value in 'mid-price' than in 'cheap'.

definitely. except for the bb, i'm a big fan of shimano 105.