Do broken spokes indicate a flawed wheel design?

Question

My gravel bike is less than 2 years old and somehow I've broken all 7 of the rear-wheel, right-side, even-numbered spokes (the ones that see high tension on braking). None have broken twice and no others have broken. I have an 11 speed cassette so the wheel is dished quite a bit even with a disc brake.

I just discovered that the original spokes are stainless steel and my replacements are normal/plated/carbon steel. The gauge and length do match. Normal steel is slightly stronger than stainless.

It appears that I may have fixed the wheel accidentally by using normal steel replacement spokes but I'm wondering if this indicates a problem with the design of the wheel.

Does mixing spoke types have any negative consequenses?

(UPDATE May 8: I guess I should clarify some things. The wheel is nicely trued with fairly even spoke tension on all 28 straight spokes. I weigh about 185 lbs. It's been 5-6 months since the last spoke broke and I consider the wheel fixed and don't expect any more breakage. I follow Sheldon Brown's advice for stress relieving and truing. The replacement spokes are Bavel brand and were the cheapest on Amazon. The bike is the State Bicycle Company, 4130 All-Road with drop bars.

I know I broke two spokes on one ride but other than that they've broken and been replaced one at a time. I made an effort to replace and re-tension the broken spokes without altering any others to keep the wheel trued as it came from the factory but after the last break or two I did re-true the whole wheel. It's definitely rideable with one broken spoke so I just carry a zip tie to secure the flapping spoke and then fix it at home.

Someone suggested that these broken spokes are due to a manufacturing problem, not a design problem. That does seem more likely to me.)

Answer 1

I would rephrase some of what juhist wrote.

If I broke more than one spoke on a wheel while riding (i.e. you didn't break them in some sort of accident), I would consider having the wheel re-laced completely, as this could indicate a poor build. For example, the spoke tension may have been uneven, perhaps exacerbated if the rim was not flat, or not properly stress relieving, or some other thing. OEM wheels tend to be built by machine (albeit with human assistance), and they are not always well built. There is probably some systematic problem with this particular wheel, and it would be better for you not to break yet another spoke in the middle of a ride. I would just match the original spoke type, unless it were straight gauge. If it were, then most people would suggest going to a butted spoke, most likely a 14/15/14 gauge spoke (2.0 butted to 1.8mm).

juhist has a thing about 32 spoke wheels.¹ He is a heavier rider. For the rest of us, it depends on the rim, the quality of the build, the total load, and what we're doing to the bike. The triple butted spokes he referenced are extra thick around the hub flange. They're good in MTBs and e-bikes. They are likely not necessary for most drop bar bike riders provided the wheel was built well and the rim is adequate for the loads it sees.

The hub flange gets indented regardless of spoke type. A wheelbuilder would know to re-lace it as originally built. There are more than one credible brand of spoke manufacturers. As far as I know, DT and Sapim are widely available in bike stores. As far as I know, Pillar is regarded as credible, but I think it's more of an OEM brand (supplied to people building stock wheels). It is possible to buy them, but I'd just get your store to help you and they'll probably have DT or Sapim.

If you are a heavier rider, then yes, the design could be at fault - particularly the rim type and spoke count.

Footnotes 1: In the 2000s and earlier, light aluminum rims typical on road bikes wouldn't be strong enough. MTB wheels would have had stouter rims that also were smaller. Manufacturing expertise and possibly materials quality have improved since then, plus rims have got heavier.

Answer 2

They might indicate a manufacturing flaw rather than a design flaw. Some factory-built wheels aren't very good. Hopefully you've caught yours in time and the failure mode was such that a total rebuild wasn't necessary.

Personally, I always use stainless spokes (usually Sapim Race). I've had more issues with rusted spokes than broken ones. In fact, I've never broken a spoke on a wheel I've built, but I haven't broken many without an obvious cause overall.

Answer 3

Stainless steel spokes are the preferred type of spoke, and work extremely well in wheels that withstand huge loads. I wouldn't claim that those wanting greater strength should use carbon steel. Maybe in bolts carbon steel could be stronger as long as it doesn't corrode (example: 12.9 bolts), but the high quality of stainless steel used in spokes and the work hardening when drawing and butting makes the situation in spokes maybe not comparable to bolts. The highest quality stainless steels used by name brand manufacturers have been work hardened by drawing them into a wire and then work hardened even more by butting the spokes with a hammer, so the ultimate tensile strength and yield strength of those high-quality spokes will be huge, and in typical builds, they should be able to resist fatigue failure as well (but they do that better if you stress relieve the wheel).

Besides, in typical wheels, the limit of the load the wheel can withstand is caused by nipples self-loosening due to momentarily slack spokes. If the spokes are breaking but not self-loosening, it is most likely a combination of two factors, (1) you used no-name spokes as opposed to name brand (DT Swiss) spokes, (2) the spokes have not been stress relieved, as described in "The Bicycle Wheel" by Jobst Brandt. By using the best spokes you can find (DT Swiss triple butted stainless), you may be able to omit stress relieving. Jobst Brandt has said that the importance of stress relieving for durable wheels was discovered by using low quality spokes, and as materials improved, it became possible to build adequately durable wheels without stress relieving (but you should still stress relieve since it provides a margin of safety). Note that Jobst Brandt used 1.6mm midsection butted spokes and when stress relieved they didn't break in his wheels. If you use thicker butted spokes, the likelihood of spokes breaking is even lower.

You didn't mention using butted spokes in your question. This may also add to the likelihood of breaking spokes in addition to (1) and (2).

I would throw all your spokes away, replace them with DT Swiss Alpine III triple butted stainless steel 2.34mm/1.8mm/2.0mm spokes or maybe double butted 2.0mm/1.8mm/2.0mm spokes and build the wheel to a high and even spoke tension and then stress relieve.

My gravel bike is less than 2 years old and somehow I've broken all 7 of the rear-wheel, right-side, even-numbered spokes (the ones that see high tension on braking)

7*4 = 28. That is not an adequate number of spokes. The wheel may be able to be salvaged if you only use it for low loads. If you are overweight or carry lots of cargo on your bike, then I recommend replacing it with a 36-spoke wheel.

It appears that I may have fixed the wheel accidentally by using normal steel replacement spokes but I'm wondering if this indicates a problem with the design of the wheel.

Could have been a bad batch of spokes, or spokes from a no-name manufacturer, or lack of stress relieving or most likely a combination of all of these factors. 28 spokes is a problem in the design of the wheel, but still, a wheel that has so many spoke failures should be rebuilt entirely, with all spokes being replaced. Nipples can be reused if their threads are not damaged, rim can be reused, hub maybe can be reused but please make sure to lace it the same way if the hub flanges have been indented by high spoke tension. Actually, it might make sense to replace all spokes one by one, not all at once, to ensure it's laced the same way so the hub flange indentations will match the new spoking.

Since 28 spokes is marginal, triple butted stainless steel spokes from a name brand manufacturer are recommended, although your hub flanges may have been indented by non triple butted spokes so using normal butted spokes (example: by replacing 2.0mm/2.0mm/2.0mm spokes with 2.0mm/1.8mm/2.0mm spokes) might have benefits in this very special case of respoking an old hub. For new builds, always prefer triple butted.

Then, when all spokes have been replaced, remember to true and tension the wheel to a high and even spoke tension and then stress relieve the wheel.

Does mixing spoke types have any negative consequenses?

Not any major issues, but by mixing poor and good spokes the weakest spoke is the weakest link of the chain. Besides, if the old spokes have failed so much, all of them should ideally be replaced.

Answer 4

Not necessarily per spoke mix... while almost all 11s have wide left side dish, uniform spoke tension per side should off set a spoke mix.

I question your assertion stainless vs "normal" steel... latter being superior which more a function of spoke Q rather than stated metallurgy... which who knows per quality. Sapim stainless are some of the best made... there're cheaper imitators which are just that.

MAIN ISSUE: most likely, note your rt breaking spokes are INBOUND... meaning likely w the original spoke the elbows make no flange contact... are unsupported. 'hanging in the wind' I call that. LEFT side braking spokes being trailing OUTBOUND most often are supported by the flange making less elbow strain.

Your steel replacements rt inbound likely produce some flange support.. hence more durable.

Answer 5

"I would throw all your spokes away, replace them with DT Swiss Alpine III triple butted stainless steel 2.34mm/1.8mm/2.0mm spokes or maybe double butted 2.0mm/1.8mm/2.0mm spokes and build the wheel to a high and even spoke tension and then stress relieve"

1. stress relieve AS you build... grabbing spokes AND lateral force on hub ea side on floor.
2. I call it the 'sergeant spoke' ... one carry highest tension usually breaks. Machine made wheels good for this w lower Q spokes and poor elbow flange fit.
3. get DS rear very uniform KGF and then dish LS lubing spoke rim interface.
4. I calculate NDS slightly long... just enough to add a drop of finger nail polish to lock the spoke