Wheels that might be knackered but don't look knackered
Simontheintrepid
Posts: 128
Hi there
Just had a bit of a challenging ride home. Chain came off twice, then a puncture, then a spoke sheared off, all in the space of 12 miles, resulting in a DNF. Cue much swearing about Italian engineering despite the fact the frame is clearly Taiwanese and the mech Shimano.
(This might be karma for accelerating past another roadie who was clearly cruising so I could award myself an SCR point)
I wanted to ask the collective wisdom of this forum about wheels. This is the second time in a week a spoke on the rear wheel has come off (don't know if the puncture was related, it was my first this year which is a fairly good innings). The rim looks okay to my largely untrained eye. They're the basic Jalco rims that came with the bike (Bianchi Via Nirone) and I've had it about 9 months. It seems a bit soon for a wheel change.
Is there anything on the rim I could be looking out for? Can I be doing anything other than keeping the wheel true to prevent this? Is it time to invest?
If I really need to (don't want to spend the money yet if I can help it), I'm looking at Mavic Ksyriums. I like the look of them but they are radial - would this be a problem given that I have a tendency towards high gear mashing? Any advice on all of the above would be greatly appreciated.
Cheers
Si
Just had a bit of a challenging ride home. Chain came off twice, then a puncture, then a spoke sheared off, all in the space of 12 miles, resulting in a DNF. Cue much swearing about Italian engineering despite the fact the frame is clearly Taiwanese and the mech Shimano.
(This might be karma for accelerating past another roadie who was clearly cruising so I could award myself an SCR point)
I wanted to ask the collective wisdom of this forum about wheels. This is the second time in a week a spoke on the rear wheel has come off (don't know if the puncture was related, it was my first this year which is a fairly good innings). The rim looks okay to my largely untrained eye. They're the basic Jalco rims that came with the bike (Bianchi Via Nirone) and I've had it about 9 months. It seems a bit soon for a wheel change.
Is there anything on the rim I could be looking out for? Can I be doing anything other than keeping the wheel true to prevent this? Is it time to invest?
If I really need to (don't want to spend the money yet if I can help it), I'm looking at Mavic Ksyriums. I like the look of them but they are radial - would this be a problem given that I have a tendency towards high gear mashing? Any advice on all of the above would be greatly appreciated.
Cheers
Si
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Comments
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In my experience, if you break one spoke, then sometimes another one will break in sympathy. I'm not sure why, but the mechanic in the LBS said that it happens sometimes.
As for the Kysriums, strong wheels IMHO you dont need to be worrying about being a grinder with those.
Again all IMHO.0 -
I had the same problem. One spoke went after hitting a pot hole and within a short space of time another two went on separate occasions. Apparently when a spoke goes it can stress the remaining spokes. Had the wheel professionally rethreaded (£50 I believe) and it's been fine ever since.0
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This is a common misdiagnosis. The first spoke failure doesn't cause subsequent failures, in any sense. It was just the first to go, of a few which are already broken by developed fatigue fractures. The fractures are practically invisible – hence ignored. The others follow naturally, soon.mendipmasher wrote:Apparently when a spoke goes it can stress the remaining spokes.
Spokes see their highest tension in a wheel that is at rest, unloaded: in use, spoke tension only decreases. A spoke failure doesn't change that.0 -
Thanks for the advice so far
So I guess I should just get it fixed again and make sure it's trued properly. Only thing is the LBS did do that last time.0 -
Not too sure about that one. Surely as the spokes at the bottom of a loaded wheel decrease in tension then the ones at the top should increase as they are carrying the load. This is why spokes are more prone to breaking or working loose if the wheel is not tensioned enough. Each spoke goes through a bigger stress cycle. Not too sure of the theory but it works that way in practice.Spokes see their highest tension in a wheel that is at rest, unloaded: in use, spoke tension only decreases. A spoke failure doesn't change that.0 -
John.T wrote:
Not too sure about that one. Surely as the spokes at the bottom of a loaded wheel decrease in tension then the ones at the top should increase as they are carrying the load. This is why spokes are more prone to breaking or working loose if the wheel is not tensioned enough. Each spoke goes through a bigger stress cycle. Not too sure of the theory but it works that way in practice.Spokes see their highest tension in a wheel that is at rest, unloaded: in use, spoke tension only decreases. A spoke failure doesn't change that.
Straightforwardly, John, that's wrong. It might seem that way but it isn't the case. You can prove it to yourself by plucking the spokes of a wheel before and after somebody sits on the bike. You'll notice that the bottom spokes drop in tone, and the upper spokes (and others) are unchanged.
The structure and functional behaviour of a tensioned wire wheel is thoroughly analysed in Jobst Brandt's book, "The Bicycle Wheel". It's not easy to find now, though libraries may have it. You'll enjoy it - many myths (such as the one you describe) are disproved.0 -
Then why do spokes break in slack spoked wheels more than in tight ones. I got some second hand Rolf Sestieres. The previous owner was always breaking spokes. I rebuilt the back one 4 years ago and have done the Tour of Flanders sportive and a local one with 30 mile of off road riding in it. It gets plenty of stick. The wheel has never shifted because I built it correctly with higher tension than it had before. You can quote all the books you like but I have never had a bad wheel and I have been building them for over 50 years. Loose spokes have a bigger stress cycle so fail earlier. Some myths are myths in theory only but are born out in practice.
I do agree that once a wheel starts to brake spokes it should be re-built with new ones. Just replacing as they break is a waste of time and money.0 -
The spokes that are the closest to horizontal are the ones under the greatest tension when the wheel is supporting your weight. They are stopping the rim from flattening. The closer to vertical the spokes are the less tension they are under.
Clearly therefore the stresses are localised. Losing a spoke will increase the tension on the adjacent spokes for a given load.- - - - - - - - - -
On Strava.{/url}0 -
there must be an increase in spoke tension somewhere about the wheel with a rider, as there is more weight on it, it probable spreads itself out around the top half with the arch effect but it must be there because weight cant be suspended with an overall decrease in tension.0
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If you were to slacken all the spokes off then all the load is carried on the ones going verticaly down from the top of the rim. As you increase the tension more spokes come into play until the load is distributed over top half of the wheel. Probably even more as the rim is trying to go oval horizontally. A rolling bike wheel is a dynamic object so these loads are constantly changing. In a well built wheel these changes are small so the stress cycle is smaller and spokes fatigue less. Hence they last longer. Simples.rake wrote:there must be an increase in spoke tension somewhere about the wheel with a rider, as there is more weight on it, it probable spreads itself out around the top half with the arch effect but it must be there because weight cant be suspended with an overall decrease in tension.0 -
That's not the case. Experimental data proves otherwise, and you can prove it to yourself using the method I described.DesWeller wrote:The spokes that are the closest to horizontal are the ones under the greatest tension when the wheel is supporting your weight. They are stopping the rim from flattening. The closer to vertical the spokes are the less tension they are under.
Clearly therefore the stresses are localised. Losing a spoke will increase the tension on the adjacent spokes for a given load.
That's not the case. Experimental data proves otherwise, and you can prove it to yourself using the method I described.rake wrote:there must be an increase in spoke tension somewhere about the wheel with a rider, as there is more weight on it, it probable spreads itself out around the top half with the arch effect but it must be there because weight cant be suspended with an overall decrease in tension.
Why all the armchair theorising?! This stuff is well understood - with data, test procedure, and analysis well documented in a respected text which is publicly available.
@ John.T - I've lost track of the crux of your disagreement with me. Did you try the experiment I explained? That shows that only lower spokes in a loaded wheel change tension. Otherwise, it's certainly true that load cycles partially cause fatigue failure in spokes. A "load cycle" is one revolution, as each spoke loses and regains tension as it passes the "load-affected-zone" (LAZ), which in practice is the bottom of the wheel.
Beyond that, I suggest you read the book I cited.0 -
I am in total agreement that the spokes unload at the bottom of the revolution. I fail to see that there is no increase towards the top. If you take the 2 extremes of a wheel with spokes that are actualy slack and a wheel with infinite tension then you would have virtualy all the load carried by the top spokes in the slack wheel but in the infinate one this load would be distributed to almost all of the spokes as the tension is infinately greater than any load applied. Obviously infinate tension is impossible and a well built wheel is a lot closer to the slack one so surely the load will be carried on the spokes from the upper quadrent of the wheel. It has to be carried somewhere and for the lower ones to unload there must be a corresponding loading elsewhere in the wheel. It would be quite interesting to build a wheel with strain guages in each spoke and test in real world conditions.
All this, while interesting, is rather irrelevent though as the fact is that slack wheels break more spokes than properly tensioned ones so my suggestion that the OP gets his wheel looked at by someone who knows wheel building still stands.0 -
That's been done (effectively, with FEA), and the results are in. Hence my comments. The net reduction in tension of the spokes in the LAZ is not slightly equivalent to any net increase in the other spokes. The loaded wheel sees a net loss in tension. The data is in the appendix of the book I cited, for your review. Also, there's the experiment I suggested: what were your findings?John.T wrote:It would be quite interesting to build a wheel with strain guages in each spoke and test in real world conditions.
This departure was initiated by you! You chose to report that something I wrote was wrong, which in itself was a correction of a prior analysis (that one spoke failure causes others). Nobody has disagreed with that general diagnosis of the original problem, (that a good wheel-builder should be sought). Perhaps you'd reread the thread to remind yourself of its course.All this, while interesting, is rather irrelevent though as the fact is that slack wheels break more spokes than properly tensioned ones so my suggestion that the OP gets his wheel looked at by someone who knows wheel building still stands.0 -
this is interesting, although i'm reminded of the pedantic architect i have to suffer yet again tomorrow which i dont like so much. Art vs Science is all good fun.0
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Firstly, apologies if I kicked this whole thing off as a result of my obvious complete lack of understanding of the issue. I am more than happy to bow to the superior knowledge and experience of those present.
Having read all of the posts, and without wishing to start it all off again, can I come back with a (probably totally ignorant) comment?
So, we all know that the spokes are under tension and act by pulling the rim in rather than holding it out. If a spoke breaks then the hub will move marginally towards the opposite side of the rim and will therefore slightly decrease the tension in the spokes on this side.
It appears generally acknowledged that slack spokes break more easily than tight spokes. I haven't quite got to grips with this one but assume that this is because there is greater flex in the wheel putting more stress on the spokes (due to a lack of tension, not too much tension). If so, then these opposite spokes could have weakened as a result of the first breakage and subsequently break themselves even if the bike hasn't been ridden far with the broken spoke.
If this is the case, could we all be right?
It was spokes opposite the original one that broke that subsequently broke on my wheel.
....Or perhaps I should just stick to posting in 'Road Beginners'.0 -
Please excuse us pedants banging our heads together. Perhaps me being thick. We do agree on the important thing which is what has probably caused your problem and what to do about it. Basicaly (very) a low tension wheel increases fatigue in the spokes due to more flexing. This flexing of the spokes is caused by load forces and also by lateral forces due to the pedaling action, especialy when out of the saddle. All spokes are affected by this but one has to break first. This one may just have been a 'bad un' so may be worth replacing and retensioning the wheel. If another goes then it is time to replace them all as they have been damaged by the fatigue. The damage is not a result of the first breakage but has taken place before that happened. The one that broke was just the weakest.mendipmasher wrote:It appears generally acknowledged that slack spokes break more easily than tight spokes. I haven't quite got to grips with this one but assume that this is because there is greater flex in the wheel putting more stress on the spokes (due to a lack of tension, not too much tension). If so, then these opposite spokes could have weakened as a result of the first breakage and subsequently break themselves even if the bike hasn't been ridden far with the broken spoke.
If this is the case, could we all be right?
It was spokes opposite the original one that broke that subsequently broke on my wheel.
....Or perhaps I should just stick to posting in 'Road Beginners'.
If you follow this advice you will not go far wrong.
Balthazar. I did not 'choose to report' that what you said was wrong. I said I was not sure about it which has a different emphasis. You have obviously studied the theory of this much more than me so are almost certainly right. I am just a technician and have only looked at how it works in the real world which has served me well for many years. I will see if I can get a copy of Jobst's book to look at and see if he can get it into my head.
I did try the test and there was no noticable change in note. But really I did not expect there to be as the load applied when distributed among most of the spokes is such a small proportion of the total of spoke tension plus load as to have so little affect that a human ear could not detect it.0 -
Simontheintrepid.
I have just gone back and read your original post. I see you have a Bianchi Via Nirone. A freind has one of these that he got second hand. He was breaking spokes in the front wheel and took it to Caygills in Richmond. They found all the spokes were brittle and could be broken just by bending them once off the wheel. Rebuilt with new spokes and no more trouble. His rear one seems fine. This would be your cheapest option.0 -
@ John: That's fine. It's just a technical disagreement, no more. That is the lifeblood of conversation. Get the book, you'll enjoy it.
@mendipmasher: there's nothing wrong at all with asking questions around these subjects. It's only uninformed statements that are trouble.
Nobody really understood how tensioned wire wheels work before Jobst Brandt's scientific study. Everybody thought they did, and tied themselves in knots with tortuous "thought experiments", like those we've heard in this thread. In a tensioned wheel, stresses are highly unlike our expectation.
Apart from the fact of that, I think there's a lesson - that the straightforward collection of data can reveal much more than the musings of a collection of "elders", which is the usual way of things in cycling. Mendipmasher, if you're interested in this, get "The Bicycle Wheel" from the library.0 -
Hi Chaps
Thanks for all your comments which right or wrong were all very interesting and a good bit of debate. I tried the experiment (although I was on my own and could only reach the top of the wheel and indeed the tension was lower). The LBS pointed out the spokes are pretty basic (not even butted) and for the standard issue stuff I'm not that surprised.
The rim looks okay so I'll have to put it down to fatigue cycles, I'm a bit of an uncompromising rider and a little too oblivious of potholes sometimes. The damage was probably done over a period of time and there may be a few more weakened ones in there. If I break one or two more soon I'll replace the lot.
I've decided to repair it myself this time and apart from the massive caveat I haven't had the chance to ride it yet I'm pleased with the results (expect me to post back about my latest adventure to the tarmac very soon). John. T - I know you told me to get it looked at professionally and the advice is good, I'm just a stubborn bugger. I will do if I have any more problems.
Laterally at least it's dead straight now and I'm quite chuffed I've learnt how to true a wheel. Although, I am aware of the fact that the 'tone' of the rear spokes (the problem wheel) when I pluck them is now higher than the front ones. Nothing seems untoward or too rigid though.
So I'll just say it..
What's the worst that can happen!!!0 -
John.T:I am not going to argue further but I can not get my head round the idea that sticking an extra 12 stone on top of a wheel does not increase loadings. Confused
(Hopefully without getting caught up in the middle of this "technical discussion"...)
Maybe the above quote indicates part of the reason for your confusion. The external forces on the front wheel on a stationary bike with rider are applied at (around) the middle of the wheel--by the forks--and at the bottom of the wheel by the ground. There is no external force applied at the top.
(unless that was just casual wording for increasing the load on the wheel!)
Cheers0 -
It was. I am well aware that the load is applied to the hub and the reaction is from the ground. The spokes must carry this load or the whole thing will collapse. The spokes at the bottom will slacken due to rim deflection. I am still trying to satisfy myself about how the load is distributed among the rest but am not going to start this again. 8)(unless that was just casual wording for increasing the load on the wheel!)0
