Featured Why do my spokes keep breaking? - Bike wheel science.

Discussion in 'Bicycle Mechanics and Repairs' started by united4ever, 8 Jan 2019.

  1. united4ever

    united4ever Well-Known Member

    3 in 3 months! Ridden for 3 years prior with no broken spokes. I get them fixed by lbs within a few days after each one has gone.

    Shizuoka hoy 1 bike, Commuting down canal towpath 8 miles each way with paneers with clothes and lunch in them. i weigh 87kgs and haven't put on weight recently.

    Anything I should be looking for before just replacing another spoke? is it easy to do for a fairly hands off cyclist who usually uses lbs for much more than puncture or minor tweaks? Should I look at new wheel?
    Tenkaykev likes this.
  2. Yellow Saddle

    Yellow Saddle Veteran

    Loch side.
    Unless someone threw a spear into your wheel whilst you were riding, spokes don't break in tension. They break from fatigue - metal fatigue. Metal fatigue is directly related to the number of cycles the wheel undergoes and, the load the wheel receives whilst doing those cycles.

    Your spokes are fatigued and because it will be highly unlikely for them all to break at the exact same time, they're breaking one after the other.

    Your wheelbuilder has to replace them all, not just the ones that break.
  3. si_c

    si_c Veteran

    My dynamo front wheel is starting to suffer the same problem, I've had two spokes break in the last month or so, both on the left side and both times whilst braking (disc brakes). I've ordered a full set of replacement spokes, I just need to get around to taking the wheel apart and rebuilding. It's the first one I've built, so it was done poorly. A full set of spokes for a wheel should cost around £30 plus the cost of rebuilding it, which around here is around £20 at an LBS, cheaper than just replacing it.
    Illaveago and raleighnut like this.
  4. OP

    united4ever Well-Known Member

    Thanks. Only had the bike a year and only done about 3k miles on it. Would rather it was sorted out once and for all. I bought it from Evans. I may ask the LBS to replace them all then.
  5. OP

    united4ever Well-Known Member

    My LBS have agreed with your consensus...£55 sounds reasonable to me so may go with that:

    "If you keep getting broken spokes there's a few issues that could be causing it. If the wheel is old then the spokes may be reaching the natural end of their lifespan and will continue to break. A poor quality wheel may de-tension with use and put uneven amounts of stress on spokes causes them to break. Or it may be a case of simply overloading the wheels with excess baggage on the bike. It may be time to replace the wheel.

    We could do a similar style hybrid wheel for £55 plus £10 to fit if that's the route you'd like to go down."
  6. Yellow Saddle

    Yellow Saddle Veteran

    Loch side.
    Who's quote is that? That person does not understand the mechanics of wire spoked wheels. Find a real wheelbuilder.
  7. Loose spokes move microscopically with every pedal stroke. Moving spokes fatigue or literally wear out if the movement is between, for example, a steel hub flange and a spoke elbow.

    Cheap spokes tend to die sooner.

    So run tight wheels, or use decent spokes. Or both.
  8. Yellow Saddle

    Yellow Saddle Veteran

    Loch side.
    No. It doesn't work like that. Only the cheap spoke bit is true.
  9. How does a pice of material fatigue if there's no movement?
  10. OP

    united4ever Well-Known Member

    Revolve Manchester


    Anyone know a decent one in Manchester/Trafford/Salford Quays area?
  11. Yellow Saddle

    Yellow Saddle Veteran

    Loch side.
    Where do you propose that movement to happen so that it "literally" wears the spoke? Can you show photos of such wear?
  12. rogerzilla

    rogerzilla Veteran

    They're bad wheels: either built with poor quality spokes or (more likely) badly built - insufficiently tight, not stress-relieved, poor spoke-rim angle or even laced the wrong way round, with spokes from the LH rim holes into the RH flange. Not many bike shops build great wheels; they don't have the time to do the best job for what you'd be willing to pay, probably £25 a wheel labour, so ask around for recommendations. Try to get DT spokes; Sapim are also good but I don't find them quite as easy to build with (consistency in length, probably).

    The well-known specialist builders insist on choosing the components as they know they can get good results in an acceptable time when all the unknowns are eliminated.
  13. OP

    united4ever Well-Known Member

    This makes sense...I had the identical bike (until it got wrecked in an accident) which seemed to have been built better somehow.....the replacement fells less harmonious somehow and I had no broken spokes with last bike....though that was the same quality parts so maybe just got lucky and was unlucky to get a badly put together one this time. Suppose you get what you pay for.
  14. DCBassman

    DCBassman Basses or Bikes? Hmmm...

    "How does a pice of material fatigue if there's no movement?"

    I'm no expert, but repeated tension/compression cycles? That doesn't imply movement.
    C R, Yellow Saddle and si_c like this.
  15. Yellow Saddle

    Yellow Saddle Veteran

    Loch side.
    "Loose spokes move microscopically with every pedal stroke."

    There is no relative movement between spokes and spokes, or spokes and other wheel parts during a wheel's use that's enough to cause any sort of wear in a spoke. Wear implies loss of material, of which there is none.

    Spokes do flex during wheel revolutions and they flex at the bottom of the wheel in the load affected zone, which is an area between the road and rim. Even then, they only flex by becoming SHORTER. This change in length is indeed microscopic and it is taken up evenly along the entire length of the spoke. Therefore the change in length per mm of spoke length is indeed microscopic. For all intends and purposes the relative movement between hub and spoke, where the spoke touches the hub flange is thus zero. We know this because there is no visible rouge in that area when you disassemble a wheel, nor is there ever any signs of material loss on the spoke itself. The hub flexes with the spoke, reducing relative movement between the two.

    Steel hubs with sharp edges do indeed cause more spoke breakages but this is not because of wear, but because of conditions that exacerbates metal fatigue. An aluminium hub, being softer than the spoke, changes shape to accommodate the spoke elbow. This smearing creates a larger contact area and softer bend in the spoke, which reduces work hardening and subsequently, metal fatigue in the spoke. Steel hubs don't, causing a very sharp transition at the spoke elbow.

    Flex is not movement.

    Spokes flex when just rolling along and additionally with each pedal stroke. Flex from the latter is confided to rear wheels and mostly the right hand spokes only and, only every second one on the right hand side. This flex is small since even a strong launch to sprint only increases the spoke tension in those spokes by less than 5% It is less than the flex induced by mere rolling.

    "Moving spokes fatigue or literally wear out if the movement is between, for example, a steel hub flange and a spoke elbow"

    Movement is not flex. A spoke that's moving is one that's rattling away in the wheel because it has no tension. Such a spoke experiences no forces which cause metal fatigue. As soon as a spoke has some modicum of tension, it will flex as described above and start to fatigue. The rate of fatigue is irrelevant whether the spokes are high tensioned or just-just tensioned enough to keep the wheel together.

    I've dealt with the topic of wear. It implies relative movement, abrasion and loss of material. That doesn't happen.

    "Cheap spokes tend to die sooner."

    Price is not a reliable indicated of poor spokes, but it has bearing. It costs more to make a double-butted spoke than a straight-gauge spoke and therefore it should cost more. But a double-butted spoke from a SAPIM box or a double-butted spoke from a Campagnolo catalogue are exactly the same spoke, although the price is hugely different. I'm sure you know this but someone else may not.

    Good spokes are made from de-gassed, 18/8, cold-forged stainless steel. Rubbish spokes are made from high-tensile steel and then galvanised.
    Budget spokes are made from the same material as above, but not butted (drawn) and thus don't receive as much of the benefitical cold forging. But non-butted bit of the spoke, i.e. the thin shank, flexes more than the thick bits at either end. This reduces the strain on those bits and hence, inputs less metal fatigue in those critical parts. Metal fatigue is not as prevalent in the thin, flexible central shank even though it flexes more than the thicker parts.

    However, an expensive spoke still needs one bit of material treatment to make it long-lasting and that treatment is stress relieving. It is done by the builder after the build. Unfortunately the spoke company can't build it in, it has to be done after the wheel is finished. Most builders don't have a clue about this, hence the poor wheels we see.

    "So run tight wheels, or use decent spokes. Or both."

    For long spoke life the wheels don't have to be tight. I explained why in the text above. Tight is good however, because it prevents nipples coming loose and wheels losing trueness. Very tight is even better, but it has nothing to do with spoke life. Uneven tension also has nothing to do with spoke life but you don't want such a wheel 'cause it wobbles.
    raleighnut, FishFright and mickle like this.
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