Broken spoke

[alexnharvey]

Is it only high tension that causes flanges to fail and not, for example, fatigue?

[Brucey]

Is it only high tension that causes flanges to fail and not, for example, fatigue?

there is a fatigue element and there is also very often a significant corrosion element. Get the trifecta and you have a 'perfect storm'.

FWIW if you have broken one or two spokes already and are wondering if you should replace them all, bear the following in mind.

1) the spokes almost certainly broke because they weren't 'set' and/or stress-relieved properly.
2) the spokes in a used wheel will either be intact or they will already have cracks in.
3) those spokes with cracks in will definitely break (fairly soon) no matter what you do with them
4) those spokes without cracks in will respond to stress-relief even now and ought to have as good a fatigue life ahead of them as new spokes
5) if you have broken one or two spokes already the chances are that there are another one or two spokes in the wheel which now have cracks in them and will break at some point.

Thus if a broken spoke is a mild inconvenience only, there is no point in replacing all the spokes in a wheel that hasn't been perfectly reliable to date. If stress-relieved now, such a wheel can usually be transformed into one that is pretty good.

cheers

[Mick F]

Wise words.
Thank you.
Both my wheels are 2x Perhaps they should be 1x for better nipple alignment, but that wouldn't be so good for the hub flanges.

The tension you will use on a small wheel is likely to be very low, when compared to bigger wheels, so unlikely to cause issues to the flange, even in 1x constructions

Dunno.
You could be right.

The front wheel I would totally agree with you.
Rear wheel with the dishing issues, I'm not so sure.

My broken spoke was on the non-drive side, so that goes against wot I've just rote.

[Brucey]

FWIW in smaller wheels the temptation is often to use more tension than normal, not less. The reason is that the spokes stretch less and it is more likely that the nipples in less tight spokes will start to back out during moments of temporary spoke slackness.

cheers

[S2L]

In a 16 inch wheel, I wouldn't even be able to measure tension... I don't think the spoke is long enough for a three point gauge to engage in a meaningful manner.

For contrast, my recollection of building a Penny Farthing wheel (60 inch or so) is that even at very high tension, the spokes feel almost slack. I recall breaking a few nipples, before I realised the tension was much higher than I thought.

I've never built anything smaller than a 24 inch, but I kind of assumed the huge bracing angle of a small wheel would not demand high tension

[Cyril Haearn]

Surely small wheels should be built quite differently from normal ones (material, methods, geometry?)

[Mick F]

Different in what way?
I've done a few 20" (406) wheels, and except for them being 2x, the methods are exactly the same as 700c and 27".

[Brucey]

because the spokes are shorter they stretch less (much less) when under tension. Also the rims are stiffer too (some of the 'spoke stretch' comes from the rim deflecting radially). Even if you build with DB spokes the length of the 16G centre portion is not pro-rata with spoke length, because the butted ends are often the same length whether the spoke is long or short. This can mean that a spoke 2/3rds the length is twice as stiff, plus the rim is stiffer too. Thus from full slack to (a given) full tension might only be one turn of the nipple in a small wheel whereas it might be two turns in a 700C wheel. This impacts on both

a) the effects of any settling at the hub end (i.e. the spokes go slack more easily) and
b) the chances of the spokes running momentarily slack (eg under high load) and fretting in the hub or having the nipples back out.

Other things like the bracing angles and the hub torque work in your favour with smaller wheels.

cheers

[Mick F]

I've spent an hour or three today, plus an hour or so yesterday, and maybe an hour or three tomorrow stripping and cleaning the whole machine.
Full transmission including chain, chainset, front and rear mechs, cassette and lubed and adjusted the SA hubgear. Also the headset, brakes and rear suspension pivot.
Still to do the front suspension arms ......... but that's another subject to be discussed some other time.



Back to the subject in hand.
I was looking fairly closely at the rear wheel and how the spokes and nipples look (and feel).
Yet to study VERY closely, but I suspect that some of the spokes and nipples are nicely in line, and others aren't.

It could be, that some nipple seats need "adjusting" and that I'd be better off inspecting very minutely and then loosening off and jiggling the nipples a bit.
.............................. oo er missus!

[Mick F]

I was looking fairly closely at the rear wheel and how the spokes and nipples look (and feel).
Yet to study VERY closely, but I suspect that some of the spokes and nipples are nicely in line, and others aren't.

Looked at them.

It seems to me, that maybe half a dozen or so aren't perfectly aligned. The thing is, I can't see ANY of the drive side wrong, just some of them on the non-drive side. They're not confined to an arc, but seemingly random.

I'm going to leave well enough alone for now, but if another breaks, I'll have to loosen them all off and tweak them individually. The rim is maybe halfway through its life, so if they can hang on, new rim will be on the cards.

[Mick F]

Another one has just gone.
Rear non-drive side again.
820miles since the last one.

Sounds like a good fireside investigation with a glass of beer to hand.

[Brucey]

I'd recommend that you 'tweak' the eyelets in the rim so that the NDS spokes and nipples are better in line. This will at least reduce the ongoing fatigue arising from bending stresses.

However as per an earlier post it is likely that some of the spokes remaining are already cracked. The worst of these will break during stress relief, but the remaining ones will break in service. There is no practical way of inspecting and being 100% sure that there are no small cracks in stainless steel spokes.

Having spokes break at the nipple is more annoying than if they break at the J bend; you need to change the nipple as well as the spoke and that means disturbing the rim tape.

Many people adopt a 'three (or four) strikes' rule; if they break more than a certain number of spokes in a wheel they scrap the lot. In this case since the breakages are confined to NDS spokes you could replace all the NDS spokes and probably achieve a very good level of reliability.

cheers

[Mick F]

Spoke replaced.

I built the wheel originally with plain gauge spokes, but the only spares I have are double butted left over from the previous rear wheel, so the last one and this one are now DB - the only two out of a total of 36.
I have new rims from when these give up the ghost, so it seems a good idea to replace the whole lot. Good advice Brucey.

When the first one went at 3,300miles, the wheel went out of true a tad and I could feel the brake catching.
This one this morning, the wheel stayed true enough, but I could hear a tinkling sound under load or when braking. Freewheeling was fine.

As it happens, the NDS spokes of the original wheel (28h) are the same length as the NDS spokes of this wheel (36h), so I still have another dozen spares that will fit ................. because if I were a betting man, there'll be more to go yet!

[alexnharvey]

Where did you find double butted spokes that are short enough Mick?

[Mick F]

They came on the wheels when the bike was new.
I've replaced both wheels. Made my own with Sun CR18 rims. 28h front 36h rear. Front has a hub dynamo and the existing DB spokes fitted fine.

I bought plain spokes for the rear wheel. With the SA hub, the originals wouldn't fit - but as the original wheel was 28h I needed new spokes anyway. I kept all the original spokes as I said. The NDS would have fitted but I only had fourteen instead of eighteen so I bought the whole lot. The 36 plain gauge spokes came from ............ I actually can't remember!

As for DB that short ........... 174mm?
Looking at Spa and SJS, neither of them do them that short.

Googling, brings up black spokes that short, but not stainless DB from what I can see.
I really don't know where Pashley/Moulton get them from.