Author Topic: When a spoke breaks...  (Read 1933 times)

Re: When a spoke breaks...
« Reply #25 on: November 21, 2019, 12:17:08 am »

Interestingly, studying the break of the spoke, it's not at the eye, or the bend, but about 30-40mm from the hub. I'm wondering if it got damaged when my rear mech got knocked a couple of months ago when it would accidentally shift into -1 rather than 1st. jamming up, potentially damaging 1 or more spokes. I'm taking the bike to the vet Friday, we'll know more when the wheel is off the bike and we can clearly see both bits of broken spoke.

that's interesting; failures at mid length are pretty rare. I shall be interested to hear what you conclude.

Quote
I carry spare spokes, I even carry a lockring tool. But as I don't have the skill to build a wheel, the thought process was always having the materials for a bike shop to fix it if things went tits up on a tour/race.

The rim is an H+son Archetype. Does that have any bearing on the advice?

that rim is pretty stiff (considering its weight) and the material is quite strong. I think it would take a 'bad set' rather less easily than a lot of other rims.

If you replace the spoke immediately then you can normally bring the wheel back straight by adjusting the tension in that one spoke alone, so no great skill is required. However if the rim 'takes a set' then things can get  a bit more complicated. Even so you should be able to get the wheel pretty good by just adjusting the tension in that one spoke.

BTW if you have to slacken the spokes opposite the break (to make it straight-ish) and then ride on the wheel, try to be methodical about the slackening of the opposing spokes, e.g. exactly one full turn on the two opposing spokes. This way you know you just need to retighten them by this amount to get back to where you started, as it were.

cheers

Cudzoziemiec

  • Dormant but requires tea
Re: When a spoke breaks...
« Reply #26 on: November 21, 2019, 09:58:05 am »
I have a mate who keeps telling me that hub brakes are going to be the Next Big thing in cycling industry marketing hype.
It will come in with nuclear fusion.
The unwilling rider and the one who leaves each control in turn without reluctance, with no desire to come back, obviously cannot be making the same journey, even though their brevets are identical.

Re: When a spoke breaks...
« Reply #27 on: November 21, 2019, 10:39:30 am »
I have a mate who keeps telling me that hub brakes are going to be the Next Big thing in cycling industry marketing hype.
It will come in with nuclear fusion.

so ~25 years away then.

  It has been ~25 years away for at least 50 years now.... ::-)


quixoticgeek

  • Mostly Harmless
Re: When a spoke breaks...
« Reply #28 on: November 22, 2019, 03:43:21 pm »

Got the bike to the vet, stuck it up on the stand, dropped the wheel out, and pulled the cassette off.

Most out the outer Drive Side spokes have some damage from the chain coming off. We're gonna replace all 18 DS spokes just to be sure. Will upload photos of damage in a bit.

J
--
Beer, bikes, and backpacking
http://b.42q.eu/

Kim

  • Timelord
Re: When a spoke breaks...
« Reply #29 on: November 22, 2019, 03:51:20 pm »
Most out the outer Drive Side spokes have some damage from the chain coming off. We're gonna replace all 18 DS spokes just to be sure. Will upload photos of damage in a bit.

That was my approach after the Tesco bag incident.  Of the non-broken spokes, several were visibly damaged, so I replaced the lot.
Careful, Kim. Your sarcasm's showing...

quixoticgeek

  • Mostly Harmless
Re: When a spoke breaks...
« Reply #30 on: November 22, 2019, 07:04:10 pm »

This is the broken spoke. The right hand piece is the short bit that got left on the hub, the left hand bit is the bigger length attached to the rim.



These are 2 other spokes on the same side:





Am starting to think that a dorkdisk isn't such a stupid idea...

J
--
Beer, bikes, and backpacking
http://b.42q.eu/

Re: When a spoke breaks...
« Reply #31 on: November 22, 2019, 07:09:04 pm »
Was about to say looks like they were hit by chain.

Re: When a spoke breaks...
« Reply #32 on: November 22, 2019, 08:08:38 pm »
In the past I've always replaced spokes  damaged like that fairly promptly but a few years ago it occurred to me that I hadn't seen any such spokes actually break.  If they were going to break it would presumably be by initiating a fatigue crack which meant two things to me

a) it probably wouldn't happen immediately and
b) there ought to be ways of preventing the fatigue crack initiation

  So on training wheels (where a spoke failure is not going to be critical if it does happen) I've tried another approach.  What I've done is to remove the spoke if necessary and then dress the spoke damage with a swiss file and if necessary straighten/ peen the spoke surface with a hammer (which introduces compressive residual stresses into the spoke surface, not dissimilar to those left by the swaging process that is used during manufacture of DB spokes).

It looks dramatic if you file the round part of a 14G spoke into a 'D' shape but the thickness across the short side of the D needs to be a deal less than 1.25mm before you have reduced the cross section to the 64% which is comparable to that of the centre part of a 14/16G DB spoke .  This means that even quite badly damaged spokes can be fettled if you want to do this. The spokes are then stress-relieved in the normal way.

You might ask 'why do this?' And the reason I suppose is twofold

1) it is an interesting experiment (and of some relevance if you are 'doing field repairs' as it were) and
2) in a workshop the correct spokes are not always readily to hand or even available.

On the latter point the spokes could be any length,  14G PG, 14-15G DB, 14-16G DB, 13-14G SB, 13G PG, 15G PG and could have different butt lengths and/or different elbow lengths, or be in silver or black finishes. There is more than one type of black finish too. 

So far, using this approach 'no breakages' is an encouraging sign but in truth I have not put enough miles on such wheels to really conclude if it  is or isn't a really sound repair or not.

In most wheels such damage is confined to a region below the spoke crossings so only half the DS spokes are likely to be damaged anyway. It is worth noting that using certain types of DB spoke on the DS means that the 16G part of the spoke may be damaged by the chain. For example Sapim DB spokes have very short butts. I have built wheels with Sapim on the NDS and DT (with longer butts) on the DS, figuring that the DT spokes might be slightly stiffer, but they are also less likely to be seriously damaged since a chain will most likely contact/mark the longer 14G section.

Maybe others could say what time/mileage intervals have passed between such damage occurring and a spoke breakage that has initiated at the damaged part of the spoke?

Previous (bitter) experiences with duff wheels tells me that if the wheels/spokes are bad then you can start to get fatigue failures between about 700 and 2000 miles or so. But these were not 'damaged spokes' per se, they may behave differently.

cheers

Re: When a spoke breaks...
« Reply #33 on: November 22, 2019, 10:17:58 pm »
But it's got me wondering, when a spoke breaks, what is the thought process on to scratch or not? This was on a 32 spoke wheel.
It goes something like this:
"Oh dear, I've broken a spoke.

Good job I've got another 31 in that wheel."

Gets back on and carries on riding.

One spoke from 32 isn't much of a risk. Last time I broke one it was actually the flange that went, but I did another 150 miles before I had chance to retire that wheel for repair. To be fair, that was on 36s, not 32s.

Re: When a spoke breaks...
« Reply #34 on: November 22, 2019, 10:24:23 pm »

We're gonna replace all 18 DS spokes just to be sure. 

That's a lot of DS spokes for a 32 spoke wheel ;)
If it is a 36, then the comments about it being OK with one broke are even more so. 
Quote
Am starting to think that a dorkdisk isn't such a stupid idea...
They have to become fashionable at some point, may as well get in early, or so I've been telling myself for the last twenty years.  Though I'm not sure I've seen one for a 40T cassette.

zigzag

  • unfuckwithable
Re: When a spoke breaks...
« Reply #35 on: November 22, 2019, 11:23:28 pm »
ideally, chain should not be coming off and spokes should not be breaking. if it's happened it's a lesson for the future.

a fault on a bike can quickly escalate to other undesirable events. many years ago i've put a new chain before a 600k audax and did not check if the cassette was still ok. riding the audax i found it skipping, on one or two cogs. trying to figure out which cogs i was looking down and pressing hard to make them skip. doing so i nearly went into a huge pothole, which i saw at the last moment. swerving to avoid it i went onto a grass verge, which happened to have a perpendicular ditch. off i go over the bars, in the middle of nowhere (aka wales). luckily only minor damages and i could continue and finish the ride - but it could have ended much worse! lesson learned - the bike(s) should be in top condition at all times and touch wood i didn't have any mechanicals on any of my long rides.

Re: When a spoke breaks...
« Reply #36 on: November 23, 2019, 12:22:19 am »
I carry spare spokes, I even carry a lockring tool. But as I don't have the skill to build a wheel, the thought process was always having the materials for a bike shop to fix it if things went tits up on a tour/race.
If you replace the spoke as soon as possible, and haven't had to fiddle with other spokes to avoid rim brake rub, there isn't much to the wheel building side of it - just replace the spoke, lacing it to the same pattern as the others, and tighten it up until the rim is straight (this does assume the rim was straight before the spoke broke).
If you want to be thorough, stress relieve the replacement spoke by forcing the middle of it sideways as far as you can with hands and gloves, then re-check that the rim is straight and tighten or loosen the spoke as required.

quixoticgeek

  • Mostly Harmless
Re: When a spoke breaks...
« Reply #37 on: November 23, 2019, 10:38:23 am »
ideally, chain should not be coming off and spokes should not be breaking. if it's happened it's a lesson for the future.

The bike fell over during a storm in Germany, landing drive side down, knocking the rear mech. The rear mech hanger got slightly out of alignment. This resulted in it shifting into -1 rather than 1. Thus the chain falling off.

Quote

a fault on a bike can quickly escalate to other undesirable events. many years ago i've put a new chain before a 600k audax and did not check if the cassette was still ok. riding the audax i found it skipping, on one or two cogs. trying to figure out which cogs i was looking down and pressing hard to make them skip. doing so i nearly went into a huge pothole, which i saw at the last moment. swerving to avoid it i went onto a grass verge, which happened to have a perpendicular ditch. off i go over the bars, in the middle of nowhere (aka wales). luckily only minor damages and i could continue and finish the ride - but it could have ended much worse! lesson learned - the bike(s) should be in top condition at all times and touch wood i didn't have any mechanicals on any of my long rides.

The good ole incident pit.

That's a lot of DS spokes for a 32 spoke wheel ;)
If it is a 36, then the comments about it being OK with one broke are even more so. 
Quote
Am starting to think that a dorkdisk isn't such a stupid idea...
They have to become fashionable at some point, may as well get in early, or so I've been telling myself for the last twenty years.  Though I'm not sure I've seen one for a 40T cassette.

Replace all 16, but ordered 18 spokes so I have a couple of spares. I'm awake, honest.

I was going to try googling for them, but then realised I don't actually know the proper name is.

Given the knock the rear mech+hanger took, and my gravely disposition, I do wonder if I should just ignore the lack of fashionability and add one of those rear mech protector thingies to the dork disk. Reliability trumps all.

J
--
Beer, bikes, and backpacking
http://b.42q.eu/

Re: When a spoke breaks...
« Reply #38 on: November 23, 2019, 11:52:18 am »
how long was it between the -1 incident and the spoke failure?

cheers

quixoticgeek

  • Mostly Harmless
Re: When a spoke breaks...
« Reply #39 on: November 23, 2019, 01:23:18 pm »
how long was it between the -1 incident and the spoke failure?

Early August, but about 2500km or so.

J
--
Beer, bikes, and backpacking
http://b.42q.eu/

Re: When a spoke breaks...
« Reply #40 on: November 23, 2019, 04:24:28 pm »
I think 'spoke protector' or 'spoke guard' are the terms of art; whether anyone makes any suitable for a 40T cassette I don't know.

Regarding mech protectors, IIRC they're a mixed blessing at best: they protect from some knocks, but for more serious crashes you're more likely to bend the frame rather than just the mech hanger, and as they stick out more you're more likely to clip them.

Re: When a spoke breaks...
« Reply #41 on: November 23, 2019, 05:05:25 pm »
This is where the Shimano mtn bike shadow derailleurs may be of benefit . They are designed not to be as proud of the frame as other rear mechs to help protect them.

quixoticgeek

  • Mostly Harmless
Re: When a spoke breaks...
« Reply #42 on: November 23, 2019, 05:07:35 pm »
This is where the Shimano mtn bike shadow derailleurs may be of benefit . They are designed not to be as proud of the frame as other rear mechs to help protect them.

I'm running a Shimano XT di2 rear mech.

J
--
Beer, bikes, and backpacking
http://b.42q.eu/

Re: When a spoke breaks...
« Reply #43 on: November 23, 2019, 05:31:27 pm »
This is where the Shimano mtn bike shadow derailleurs may be of benefit . They are designed not to be as proud of the frame as other rear mechs to help protect them.

I'm running a Shimano XT di2 rear mech.

J

With that electronic gubbins they ought to add a spoke distance sensor to stop it shifting into them  ;D

Re: When a spoke breaks...
« Reply #44 on: November 23, 2019, 06:28:44 pm »
how long was it between the -1 incident and the spoke failure?

Early August, but about 2500km or so.

J

well that is comparable to the time taken for fatigue cracks to initiate for other reasons.

FWIW if the spoke was also  bent when the damage occurred, this might cause cyclic stresses to be higher than they would be otherwise (you get damaging tensile stresses on the ID of a bend, as it sees cyclic tension). Stress concentration from the damage plus cyclic stresses from the spoke being bent = recipe for fatigue crack initiation.

The 'repair' protocol I have outlined above ought to mitigate both things, but if the damage is in the thinner 16G part of a DB spoke, it is almost certainly a question of 'when' not if you replace the spoke .

cheers

Re: When a spoke breaks...
« Reply #45 on: December 06, 2019, 11:19:21 am »
This is where the Shimano mtn bike shadow derailleurs may be of benefit . They are designed not to be as proud of the frame as other rear mechs to help protect them.

I'm running a Shimano XT di2 rear mech.

J

With that electronic gubbins they ought to add a spoke distance sensor to stop it shifting into them  ;D
That's a good idea. I wonder why they haven't?
P.S.
I know nothing about how di2 works.
My view is that it's just another electrical thing (that I don't need) to go wrong/break whilst out on a ride!

FifeingEejit

  • Not Small
Re: When a spoke breaks...
« Reply #46 on: December 06, 2019, 12:01:05 pm »
This is where the Shimano mtn bike shadow derailleurs may be of benefit . They are designed not to be as proud of the frame as other rear mechs to help protect them.

I'm running a Shimano XT di2 rear mech.

J

With that electronic gubbins they ought to add a spoke distance sensor to stop it shifting into them  ;D

That'd have to go into the cage or cassette, adding cost, the Shadow profile is good but not fool proof and the official line is probably "if you think you have a mech hanger don't ride" or as I've noted Shimano regularly put it "the bike may fall over"

All it's really doing is shifting the cage and therefore chain by x mm per click; because the cogs are also x mm apart.
(It actually shifts x+y and then back shifts y)
You can alter the baseline Z by +/- 16 increments.

You could add cage angle, proximity etc. to it, but they're all adjustable depending on cog sizes and b-screw adjustments,
otherwise good mech hanger location is enough to mess up the gear the mech believes it's in on some frames too.

The Limit screws are still mechanical on rear mechs, one of them on front is however electrionic. (I can't remember which)


Re: When a spoke breaks...
« Reply #47 on: December 06, 2019, 12:25:30 pm »
The Limit screws are still mechanical on rear mechs, one of them on front is however electrionic. (I can't remember which)

The front mechs have no H limit screw. The screw labelled "H" is just an adjustment screw that increases the distance between the servo output arm and the mech cage. Since the servo arm only has limited travel that essentially sets how far the mech can move outwards.

The L screw is a normal limit screw.

They can't have limits implemented electronically because as far as I can tell they don't have absolute positioning feedback, only relative from the rotary encoder.

FifeingEejit

  • Not Small
Re: When a spoke breaks...
« Reply #48 on: December 06, 2019, 12:39:23 pm »
The Limit screws are still mechanical on rear mechs, one of them on front is however electrionic. (I can't remember which)

The front mechs have no H limit screw. The screw labelled "H" is just an adjustment screw that increases the distance between the servo output arm and the mech cage. Since the servo arm only has limited travel that essentially sets how far the mech can move outwards.

The L screw is a normal limit screw.

They can't have limits implemented electronically because as far as I can tell they don't have absolute positioning feedback, only relative from the rotary encoder.

Just checked, the latest Di2 mechs only have a high limit screw; the lower limit is electronic.