Spoke fatigue & wheel rebuilding

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Gattonero
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Spoke fatigue & wheel rebuilding

Post by Gattonero »

Taping the new rims side to side is much quicker, as you simply move each spoke from the old rim onto the new one. So don't have to tie down then "position" all the spokes at the same time in the new rim.
It's just so simple, each nipple is undone and moved 20mm to the side in the new rim, the spoke goes along and you can't do wrong :)
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...
Brucey
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Re: Wheel rebuild - should I replace the spokes?

Post by Brucey »

re 'the spokes might already be fatigued'; maybe. But the evidence shows that this seems to happen in a very particular way.

Fatigue failures occur in three stages

1) crack initiation
2) crack propagation
3) sudden failure

Once a crack has initiated, that spoke is doomed. If the mechanism of spoke failure were rapid initiation, slow propagation, then failure, there would probably be no point in trying to re-use spokes; in all likelihood, too many would already be cracked, in any wheel that had already broken a few spokes.

However the evidence is that spokes fail quite quickly once cracks initiate. For example I have personally experienced multiple spoke failures after about 700 miles on a set of new wheels that hadn't been stress-relieved. Once I'd stress-relieved the wheels, I broke another spoke shortly afterwards ( and I suppose that that spoke was already cracked) but after than no more spokes broke.

Many riders have similar anecdotes, and Jobst Brandt suggested that if you stress-relieved a used wheel (in which a few spokes had already broken) that 'you might break another couple of spokes shortly after' but after that the wheel might be OK. Again this tallies well with the experience of many riders.

However it doesn't exclude the possibility that in some wheels, (e.g. where spokes are breaking very quickly) that something different might be happening.

I got sufficiently interested in what was going on to do some research into this, starting several years ago. I began to collect used wheels from many LBSs near me. Since replacement spokes are rarely (if ever) identical in manufacture and length, it is easy to tell how many spokes have broken in a wheel, even if they have been replaced. In wheels that had broken a few spokes, I removed all the remaining original spokes, and subjected them to tests that would reveal the presence of any cracks in the elbow.

In summary (having examined many, many wheels) this is what I found;

a) some (a very few) spokes are badly made so that even if the wheel is stress relieved, the spokes will continue to break, because there is a built-in notch in the spoke. For example if worn tooling is used, each and every elbow bend may have a defect in it. Similarly spokes may be built from poor quality steel or suffer damage in service, both of which can create a crack initiation point.

b) some (many...) spokes, mainly in cheap wheels, fit so badly that stress relief is not entirely practical. It would be quicker and easier to rebuild the wheel with new spokes. For example, long elbow bends in thin steel hub flanges.

c) there appears to be a rule for how many remaining spokes might be cracked (assuming a) or b) do not apply). The number of cracked but unbroken spokes can be up to (and including) the number that has already broken, but is very unlikely to exceed it.

d) some spokes break near the nipple (which can be a type b) problem) or at the head itself (which can be a type a) problem). However wheels that suffer such failures (in a non type a) or b) fashion) are much rarer than those in which elbow bends break, and there is no evidence that in such wheels, observation c) does not still apply.

Observation c) appears to hold for wheels that are decades old (and have broken only a few spokes) as well as (very poor quality) wheels that are only a few months old. In extremis I have seen wheels that have (in a few month's use only) broken eight or ten spokes, and amongst the remaining spokes, a similar number are already cracked.

So the implication is that the rate of spoke breakage is primarily related to the rate of crack initiation, rather than the rate of propagation; once you have a crack, it usually propagates to failure relatively quickly.

Thus if you re-use spokes, in a half decent stress relieved wheel, you can expect to break about as many as have broken in that set already, tops.

Arguably if the wheel is re-rimmed (using the rim-lashing method) the spokes ought to be stress relieved already; provided they can be fitted into the new rim without being bent, and they fit in the same way in the new rim, it ought not be necessary to stress-relieve again. However it doesn't seem to hurt to repeat the stress-relief.

If you remove the spokes from the hub entirely, it is best to at least sort them into 'inside' and 'outside' groups, so that they don't need to be re-set when the wheel is rebuilt. However even if this is not done, good quality spokes won't suffer greatly provided the wheel is stress-relieved properly.

BTW in an LBS near me, years ago, they would give unknown spokes an ad-hoc test; using two pairs of pliers, they would grasp a short length of spoke so that there was about a 1/2" length between the pliers. They would then flex the spoke back and forth until it broke. Some poor quality spokes would break after a just a few flexures, whereas better quality spokes would usually survive more flexing before failure occurred.

If this test is repeated using spokes that are deliberately damaged in some way, the spokes almost invariably fail more quickly; you can gauge from this what kind of damage is (or isn't) likely to be significant in any given type of spoke.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
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Phil_Chadwick
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Re: Wheel rebuild - should I replace the spokes?

Post by Phil_Chadwick »

Taping the new rim alongside is dead quick, just as Brucey said. It makes the job quite manageable too.
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Gattonero
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Re: Wheel rebuild - should I replace the spokes?

Post by Gattonero »

Brucey wrote:re 'the spokes might already be fatigued'; maybe. But the evidence shows that this seems to happen in a very particular way.

....


Again, if one has the time to do all this... my opinion is that once you're set to replace a rim, you may as well do a good job and stay happy in the future if this means to spend £10 in new spokes.
Is a tenner worth the chance of wasting time in future and/or suffering a spoke failure when far from home?
Also, replacing the spokes will give a good insight of how well they fit on the hub (not being loose) and to check all the old spokes.

But as said, this does often apply to cheap spokes, and less on quality ones. The latter are unlikely to be found in industrial-high volume built wheels for off-the-shelf medium/low priced bicycles (no offence)
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...
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Phil_Chadwick
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Re: Wheel rebuild - should I replace the spokes?

Post by Phil_Chadwick »

I tend to re-use spokes through 3 or 4 rim replacements. Never had one fail yet.
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Gattonero
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Re: Wheel rebuild - should I replace the spokes?

Post by Gattonero »

Talk to me, I cannot remember having ever broken a spoke :mrgreen:
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...
Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Wheel rebuild - should I replace the spokes?

Post by Brucey »

there's more than one way to skin a cat, obviously, but you could argue that replacing spokes that hadn't yet given any trouble 'because they might start breaking and they are surely worse than new spokes' is an entirely flawed argument:

a) The wheel rebuild will definitely take longer,
b) the new wheel will definitely be no good at all (and certainly no better than the old wheel) unless it is thoroughly stress-relieved
c) you leave yourself open to the new spokes being flawed e.g. in material or manufacture.

So I would suggest that in many cases you would definitely be better off re-rimming a wheel using the old spokes rather than having a full rebuild.

It isn't as if it is 'just ten quid's worth of spokes' either; in LBSs most folk are being asked to pay between 50p and £1 for a medium quality stainless steel spoke these days, so it is more like £20 or £30 for a set of spokes if you use your local wheelbuilder. If you use certain aero spokes then these can be about £4 each, retail, and Mr Shimano thinks his spokes (even if they are just round straight pull ones with funny nipple) are worth up to about £5 each... :shock: . Thus if you can't rebuild using the old spokes, you can be looking at a high cost (£120 per wheel in some cases) just in spokes.

On the other side of the coin if you build wheels for other people you can't sensibly give a warranty on a wheel built with used spokes, and this will affect the choice that people make.

My advice to folk who have a (thus far reliable) wheel that needs re-rimming is to either

a) do it yourself, or
b) at least lace the new rim on, and let a wheel builder finish the wheel off.

cheers
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531colin
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Re: Wheel rebuild - should I replace the spokes?

Post by 531colin »

Its really simple.
If you are a wheelbuilder in a shop posting wheels out all over the country, you don't want your wheelbuilding to be judged on the condition of your customer's old spokes, so you recommend new spokes.
If you are happy to repair your own bike in the shed, and you have a pair of wheels with one broken spoke (that you didn't even notice) spend 5 minutes stress-relieving your old spokes in your new rim, and expect to replace another spoke or maybe two in the future. (The hardest bit will be finding a rim thats a "straight swap".)
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NATURAL ANKLING
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Re: Wheel rebuild - should I replace the spokes?

Post by NATURAL ANKLING »

Hi,
Gattonero wrote:Talk to me, I cannot remember having ever broken a spoke :mrgreen:

Never say never, you'll get a flat next ride :mrgreen:

You must be a pretty good wheel builder, Brucey's had tons (his own admission) :)

I have learnt more about building wheels in the last year than I ever thought possible in over 40 years of doing my own wheel repairs / building, in these posts.
And until a couple of years ago never hardly ever broke spokes.
If you never fallen off a bike you will never learn how to stay on.

As per usual, Bruceys explanations are pretty good, I thought also that a wheel that had never given a problems would be more or at least as good as a new wheel if just re-rimming.

My problems started not after rebuilding a wheel with new spokes but by reusing spokes, even tho I Identified the (I thought by visual inspection) correct 1 of 4 set of each spoke in the wheel (maybe an after removing inspection was a bad move).
I was naïve / not experienced enough in stress relieving, you live and learn.
NA Thinks Just End 2 End Return + Bivvy - Some day Soon I hope
You'll Still Find Me At The Top Of A Hill
Please forgive the poor Grammar I blame it on my mobile and phat thinkers.
Brucey
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Re: Wheel rebuild - should I replace the spokes?

Post by Brucey »

NATURAL ANKLING wrote:
You must be a pretty good wheel builder, Brucey's had tons (his own admission) :)
.


To clarify; not in wheels I have built myself.

I have not broken spoke in any wheel I've built (for myself or others, which is several hundred pairs) since 1980-something. Back then I broke several spokes in one wheel; when I carried out an investigation into the failures, I found the spokes had a manufacturing defect in them.

Once every few years I try a set of 'off the shelf' wheels, without stress-relieving them first. I have broken spokes in every single set of such wheels I have tried, regardless of cost or materials used. By contrast if I take a set of machine built wheels, then (provided the spokes fit well etc) once they are stress-relieved, they are almost invariably pretty reliable.

A good example of this is a set I prepped for a neighbour of mine, for him to commute on; nothing special, 32 spoke wheels built radial PG (except for rear DS) onto a ~480g rim, using joytech hubs (with cup and cone bearings) and inexpensive stainless spokes. These are pretty average wheels that you might find on a mid-price Giant road bike. I stress-relieved them, made the tensions a bit more uniform, and serviced the hubs. Those wheels have done about 25000 miles now, and in that time the bearings didn't need adjustment, only one NDS spoke in the rear wheel needed half a turn on it, and about five sets of tyres have been consumed.

cheers
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Gattonero
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Re: Wheel rebuild - should I replace the spokes?

Post by Gattonero »

NATURAL ANKLING wrote:Hi,
Gattonero wrote:Talk to me, I cannot remember having ever broken a spoke :mrgreen:

Never say never, you'll get a flat next ride :mrgreen:

You must be a pretty good wheel builder, Brucey's had tons (his own admission) :)
....


It would be the first broken spoke in over 20 years? I still have the original Crossride with yellow hubs that I raced a few times with, and a set of 28h Dt Swiss rims&hubs that too had races. Both have had several bad crashes, one I broke the saddle rails (!), another one I ended up with one foot jammed in between the spokes and the forks, had to remove the shoe as it won't get out. None of those times the spokes broke.
Luck? Perhaps, but I like to think that it was good quality stuff to begin with.
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...
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531colin
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Re: Wheel rebuild - should I replace the spokes?

Post by 531colin »

Gattonero wrote:............
It would be the first broken spoke in over 20 years? I still have the original Crossride with yellow hubs that I raced a few times with, and a set of 28h Dt Swiss rims&hubs that too had races. Both have had several bad crashes, one I broke the saddle rails (!), another one I ended up with one foot jammed in between the spokes and the forks, had to remove the shoe as it won't get out. None of those times the spokes broke.
Luck? Perhaps, but I like to think that it was good quality stuff to begin with.


So the saddle rails were fatigued, and the spokes were not.
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Gattonero
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Re: Wheel rebuild - should I replace the spokes?

Post by Gattonero »

The saddle hit a rock, the spokes didn't! It was a San Marco Aspide, with tubular titanium rails. Although I was only 69kg at that time, it had a few seasons so it had done its job.
It broke right after the clamp, which does suggest a pressure point that induced fatigue, the big hit killed it. There was no crack before.

The saddle clamp works with the saddle rails a bit different from what the spokes do in the hub. I'm not sure is worth elaborating why and what, I'm ok with replacing stuff when it has done its job, no bike parts would really last forever (Chris King bearings could be the exception)
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...
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531colin
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Re: Wheel rebuild - should I replace the spokes?

Post by 531colin »

If the saddle rails broke, they were fatigued. If they are not fatigued and you impose a big load, they bend, they don't break.
Similarly with the spokes.....put a big enough load on a new spoke, it will pull through the rim before it breaks. A spoke that breaks in a crash (or hitting a pothole, or sprinting) was already fatigued.
MikeF
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Re: Wheel rebuild - should I replace the spokes?

Post by MikeF »

Brucey wrote: If you remove the spokes from the hub entirely, it is best to at least sort them into 'inside' and 'outside' groups, so that they don't need to be re-set when the wheel is rebuilt. However even if this is not done, good quality spokes won't suffer greatly provided the wheel is stress-relieved properly.

cheers
You can reset/reduce the angle at the elbow by putting the spoke through a hub hole and pushing on the spoke, but how do you increase the angle?
"It takes a genius to spot the obvious" - my old physics master.
I don't peddle bikes.
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