Newish bike, broken spokes after wheel truing, whose fault?

[Cambyses]

In November I bought a Whyte Shoreditch (£600 flat-bar disc-brake commuter). After 6 months and maybe 1000 miles largely trouble-free I book it in for a routine service with a local mobile bike mechanic, including wheel-truing. He returns it without mentioning any problems, but 2 days and 20 miles later, it breaks a rear spoke (sheared off at the outer end). Back to the mechanic, who now says the spokes were very loose before truing and it must have been already weakened, assures me that if any more were going to go they'd have done so by now, quotes me £12 to replace it. I give him the benefit of the doubt.

Another week and maybe 50 miles later, another broken rear spoke in exactly the same way.

I assume I'm going to have to get the wheel replaced or rebuilt, which is infuriating as my previous (£300 Decathlon) commuter ran for 3 years before a spoke went! Do I have grounds for complaint to either (i) the mechanic or (ii) the shop? Or is it just bad luck? I fear they will just blame each other: I haven't actually paid the mechanic's bill yet: I'm half-tempted to get the wheel rebuilt elsewhere and deduct the cost of this from the servicing bill. Or would that be unwarranted?

 

[amasidlover]

I have a Whyte Dorset and have had a few rear spokes go - this is not unusual for me as I routinely pull a trailer and have loaded panniers, but its possible that Whyte's wheel building process isn't as good as it should be.

In your case I'd say its very likely that the loose spokes would have been symptomatic of a not-great wheel build and that it would probably have had extra tension on the remaining spokes. That extra tension could well have caused spoke breakage. Its possible that the remaining spokes will be fine, its also possible that you'll end up replacing a significant number of the remainder (I've had both both happen to me on different wheels).

Personally unless you're carrying large amounts of load or are more than averagely heavy I would expect broken spokes within the first year to be covered by Whyte's warranty - I'd be asking the shop to take it up with Whyte on your behalf.

Its also worth considering learning to replace spokes and true the wheel yourself in the longer term; if you're commuting regularly Its not a particularly long or difficult job - the hardest/longest bit is getting the cassette / disc off (and the tyre/tube if the nipple has dropped into the rim) - and it means you're not without your means of transport for however long it takes the bike shop to fit you in. However, in the first year on a typically loaded bike I would expect it to be covered by the warranty.

 

[Deleted member 35268]

I had a series of spokes fail over time and eventually it got to the point where the wheel was deemed knackered. The truing may or may not amplify any weakness, but I wouldn't consider it the mechanics fault at all. When it starts getting exepensive, time to replace it.

 

[Crackle]

Spokes go, especially on factory built wheels. If there's any weakness, then when you adjust them and put more tension in they are more likely to go and not all wheels are equal. You might find a few go now they've been adjusted and then nothing for a good while. Trust you're mechanic or learn to do it yourself, it's not hard to true a wheel.

 

[Rohloff_Brompton_Rider]

Loose spoked wheel builds let the spokes move. This fatigues the material, then they snap, which means their load is transferred onto neighbouring and already fatigued spokes. New spoke fitted, fatigued spokes tensioned, they snap and on goes the viscous circle. Until all the fatigued spokes are eventually removed by either a full rebuild or one by one as they snap.

Question is, do you run the gamble of which is the cheaper more convenient route?

Personally, I've gone down the rebuild route with good quality spokes, but I can rebuild a wheel if I feel like it.

 

[Ajax Bay]

I think if you have one spoke go that's just one of those things but if another goes on a bike which was bought new only 6 months ago and has done only ~1000 miles largely trouble-free, then I think this is definitely to be taken up with the selling shop.
Pay the mechanic's bill - it's not his/her fault.
A word of warning/anecdote regarding the way the spokes are breaking - as you describe "shear[ing] off at the outer end". Normally spokes break at the elbow, by the hub and can do little damage. But on an old (1980 Atom hub on a Weinmann rim) wheel where a number of spokes had broken by the hub, and I'd prophylactically replaced about half on the drive side, I had a spoke which broke just below the nipple, I heard a clicking but could not see where it was coming from. Suddenly the drive train locked up - fortunately when I was going slowly: I managed to stay upright. The spoke, which this time had broken at the nipple, had 'fallen' into the rear derailleur (a Nuovo Record Patent -74, owned almost from new) and generally scrunching occurred. I managed to convert to a single gear large to 19t with a catenary lower chain and limped back to base.
So take care if you carry on cycling on that wheel. After remedial reshaping to return to functionality, the RD has never quite recovered its zest.

 

[mickle]

Loose spoked wheel builds let the spokes move. This fatigues the material, then they snap, which means their load is transferred onto neighbouring and already fatigued spokes. New spoke fitted, fatigued spokes tensioned, they snap and on goes the viscous circle. Until all the fatigued spokes are eventually removed by either a full rebuild or one by one as they snap.

Question is, do you run the gamble of which is the cheaper more convenient route?

Personally, I've gone down the rebuild route with good quality spokes, but I can rebuild a wheel if I feel like it.

This. 100%.

In future, take your new bike back to the shop after 100 miles to have the wheels (and everything else) checked and tensioned. All reputable retailers offer this for free. Why didn't yours?

 

[Cambyses]

In future, take your new bike back to the shop after 100 miles to have the wheels (and everything else) checked and tensioned. All reputable retailers offer this for free. Why didn't yours?

They did and I did. Or at least, I took it back as recommended - I can't tell you what they did or didn't actually check as I left it with them to do it....

 

[Cambyses]

Thanks for the thoughts and recommendations, everyone. I'll pay the mechanic for work done, and try taking it back to the shop to get it sorted.

One more elementary question: I've heard it said that disc (and hub) brakes apply unusual forces to the wheel, due transfer of backwards rotational force from hub to rim when braking the centre of the wheel. Is this true, and does it significantly shorten the lifespan of the spokes, or change the frequency with which truing is needed, or even the process of truing?

 

[mrandmrspoves]

Certainly, disc and to some degree hub brakes can exert increased forces on the spokes and forks too. Not really a problem on a heavy gauge wheelset as you would get on a mountain bike or roadster - but the uptake on light weight road bikes may create problems where the spoke count or gauge is simply too low for the increased forces exerted. Spoke pattern may also play a part in the final wheel strength so I would want to see a 3x pattern on the front wheel as well as the rear, and a spoke count of 36 or thereabouts.

 

[Rohloff_Brompton_Rider]

Thanks for the thoughts and recommendations, everyone. I'll pay the mechanic for work done, and try taking it back to the shop to get it sorted.

One more elementary question: I've heard it said that disc (and hub) brakes apply unusual forces to the wheel, due transfer of backwards rotational force from hub to rim when braking the centre of the wheel. Is this true, and does it significantly shorten the lifespan of the spokes, or change the frequency with which truing is needed, or even the process of truing?

True on poorly built wheels, but well built wheels take this into consideration. TBH discs have been around for so long it's pretty uncommon to find this not included in the design.

Loose spoke builds are done even by the best manufacturers. I've had a few sets of Hope Hoops and I've always had to tension the spokes to get them in to tune.

 

[Yellow Saddle]

In November I bought a Whyte Shoreditch (£600 flat-bar disc-brake commuter). After 6 months and maybe 1000 miles largely trouble-free I book it in for a routine service with a local mobile bike mechanic, including wheel-truing. He returns it without mentioning any problems, but 2 days and 20 miles later, it breaks a rear spoke (sheared off at the outer end). Back to the mechanic, who now says the spokes were very loose before truing and it must have been already weakened, assures me that if any more were going to go they'd have done so by now, quotes me £12 to replace it. I give him the benefit of the doubt.

He deserves more than benefit of doubt. It is in no way his fault. Spokes break by a mode called metal fatigue, not shear. Shear is a very particular type of break that can be envisaged by holding a peeled banana in front of you clutched in both hands with your thumbs touching. Now move the one hand forward and the other backwards. This will break the banana in the mode called shear. Spokes don't break like that. They break because of metal fatigue caused by cyclical stresses as the spokes lengthen and shorten once every cycle of the wheel. A mechanic doesn't have the time or the equipment to do that other than to ride the bike with a heavy load for hundreds and thousands of miles. It is not his fault.

Another week and maybe 50 miles later, another broken rear spoke in exactly the same way.

That happened because all spokes fatigue at exactly the same rate. But they don't all break at once, that would be a massive co-incidence. The fact that it happened again is a sure sign of fatigue and all spokes need to be replaced or you'll have it happen again and again.

I assume I'm going to have to get the wheel replaced or rebuilt, which is infuriating as my previous (£300 Decathlon) commuter ran for 3 years before a spoke went! Do I have grounds for complaint to either (i) the mechanic or (ii) the shop? Or is it just bad luck? I fear they will just blame each other: I haven't actually paid the mechanic's bill yet: I'm half-tempted to get the wheel rebuilt elsewhere and deduct the cost of this from the servicing bill. Or would that be unwarranted?

You are correct. The wheel has to be rebuilt by a competent wheelbuilder who understands how to prevent metal fatigue in the first place. This is unfortunately not taught at bicycle mechanic school and the very simple procedure is apparently a secret. Factory built wheels are generally not stress-relieved (the process that delays metal fatigue) unless they are top end wheels. A stress-relieving machine is expensive but the process can be done very effectively by hand.

You have grounds of complaint to the manufacturer, but good luck with that. It probably doesn't understand stress-relieving either.

 

[Yellow Saddle]

In your case I'd say its very likely that the loose spokes would have been symptomatic of a not-great wheel build and that it would probably have had extra tension on the remaining spokes. That extra tension could well have caused spoke breakage. Its possible that the remaining spokes will be fine, its also possible that you'll end up replacing a significant number of the remainder (I've had both both happen to me on different wheels).

No. Spokes don't break from tension. Steel and stainless steel is a Hookean material that responds linearly to stress. It is only the difference in stress between the loaded and unloaded positions in the wheel that happens once per revolution that has an effect on the spoke through metal fatigue. In other words, a spoke under high tension and a spoke under low tension will both break after exactly the same number of cycles of the wheel.

Further, a wheel with some spokes in high tension and others in low tension is not a true wheel and will not clear the brake pads.

 

[Yellow Saddle]

Thanks for the thoughts and recommendations, everyone. I'll pay the mechanic for work done, and try taking it back to the shop to get it sorted.

One more elementary question: I've heard it said that disc (and hub) brakes apply unusual forces to the wheel, due transfer of backwards rotational force from hub to rim when braking the centre of the wheel. Is this true, and does it significantly shorten the lifespan of the spokes, or change the frequency with which truing is needed, or even the process of truing?

There is no need for concern wether the wheel is hub or rim-braked. A good wheel will take either in its stride. On rim brakes under breaking forces, the entire set of spokes at the front of the wheel bisected by the top and bottom spokes in the 112 and 6 o clock positions increase a bit in tension and the opposite set decrease a bit in tension. Under maximum braking (absolute maximum on the front wheel only) the difference in tension is less than 5%. Therefore braking has no effect on spoke life. Under the same conditions with a hub brake every alternate spoke increases a bit in tension and the other set decreases a bit, again about 5% maximum. This again has no effect on spoke life.

Spokes are mostly fatigue just by riding. Your weight loads and unloads the spokes by up to 50% with each revolution. This fatigues the metal in two particular spots - the first thread at the nipple or, the elbow at the hub end. Where it happens is a function of spoke design. Spokes should be double-butted to minimize this problem.

 

[Yellow Saddle]

Certainly, disc and to some degree hub brakes can exert increased forces on the spokes and forks too. Not really a problem on a heavy gauge wheelset as you would get on a mountain bike or roadster - but the uptake on light weight road bikes may create problems where the spoke count or gauge is simply too low for the increased forces exerted. Spoke pattern may also play a part in the final wheel strength so I would want to see a 3x pattern on the front wheel as well as the rear, and a spoke count of 36 or thereabouts.

Not quite. I don't know what you mean by "heavy gauge wheelset" but I'll assume that you mean thicker and thinner spokes as in gauge being wire thickness?

In that case, the gauge itself has nothing to do with durability. In fact, thinner double-butted spokes last longer than thicker double-butted spokes.

Spoke pattern has no effect on wheel strength at all. Strength being the ability to carry a load. Durability being the ability to carry a load over long distances without fatigue.