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

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ConnoisseurEquator

Senior Member
Hi
Sorry to revive that thread but I have a problem similar with my 40yo Raleighs.
2 spokes broke on both of them during the last few months.
Both have a hub with a Dyno 3 speed.
I tried to replace 3 of them when I realised that the 4th broke. I don't know when it did actually.
Is it ok to replace them with similar spokes taken from other wheel?
Well one.
They are not the same size by 1-2 mm, so I cut them.

I also notices that the wheel are not perfectly true [? ]. A bit of a spine curved. I noticed it while fixing the brakes pads.
I YouTubed them but the explanation is as clear as a muddy water to me.
If its bend to one side, screw the other side. Not really conclusive.
I tend to do everything on all my 3-4 speed bikes. More recently as I have more time on my hands.
Any ways to understand this jargon a bit more easily?
Thanks
 

Ming the Merciless

There is no mercy
Location
Inside my skull
 

Ajax Bay

Guru
Location
East Devon
My advice would be (and I have tried to keep a rear 1980 wheel alive):
  • If you're getting sequential spoke failure then these are the first few (4!) failing from fatigue and the rest will be on their way, potentially spoiling multiple rides.
  • Bite the bullet and replace all the spokes you haven't already replaced (eg 28?).
  • If you do them one by one, you can tighten each spoke so it 'pings' the same note as its mates and that will get you to a start point for truing the wheel (see the Merciless one's link above).
  • If you know the wheel you're stealing a spoke from has done little mileage you can treat it, for fatigue life, as new.
  • Your LBS (assuming it's good) will have spokes the right length to sell you.
  • Shortening spokes which are bit too long will not result in them being weaker per se, but remember you are reducing the number of engaged threads. A couple of mm: OK.
  • Using spokes which are too short risks the same but also in addition risks the rolled thread showing the hub side of the nipple, and that can result in a stress riser exposed to the elements.
HTH
 

rogerzilla

Legendary Member
Short spokes are especially bad in alloy nipples, as the nipple needs to be full of spoke thread up to the bottom of the screwdriver slot, otherwise it can just snap in half.
 

Ajax Bay

Guru
Location
East Devon
Thought this was a neat image, in the context of wheels standing on the lower spokes or hanging on the upper spokes, or neither.
1644934224440.png
 
Hi,
Let me to ask my question here, suppose it's relevant thread.
Week ago during mountain ride my rear wheel was broken and rim aquired the curvature wich incompatible with further riding.
So, was decided to replace a rim and the spoke set. Appropriate rim an spokes already bought, but when I start lacing the spokes, noticed that effective rim dia ERD in fact a little more, than specified by manufacturer (2-3 mm more).
I confused, and need to replace at least 18 spokes at longer side.
Does anyone have similar experience with misunderstanding between specified ERD and actual one?
Or may be some vendors have alternative way to determine this parameter. Looks like in my case manufacturer determine ERD as imaginary diameter on eylets top sides.
But according to most material found in net ERD is determined as imaginary diameter touches the ends of fully threaded spokes (when the end of spoke located around the bottom of nipple slot).
 

Jameshow

Veteran
Erd from manufacturers are often a stab in the dark tbh.

Usual practice is to measure yourself using 2 spokes or inside the rim +3-4mm

if the spokes are a little short the tensioning if them will normally pull them into a reasonable length.
 
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Rim - Mach1 Road Runner http://www.mach1.fr/en/rims/road-runner-44
ERD 591 according to mfr spec.
Hub - old type Novatec, 50mm both flanges dia.
Spoke length was calculated here https://spokecalculator.qbp.com/spokecalculator/calculate and checked on another sites.
Calculation sheet:


Spoke_calc.png
So, for state-of-the-art 3 cross lacing was decided to use just 1 length set - 283mm DT Swiss Competition (bought from private persone, but looks original with stamp:rolleyes:)
But in fact calculator's ERD is determined according to following picture
1662410709263.png
and mfr ERD obviously specified by another way, may be on the top of eyelets.
As expected, short side spokes still compatible (just 2-3 turns of thread are visible under the nipple skirt, suppose it enough engagement), otherwise longer side have quite poor engagement.
Currently waiting for another 20pcs 286mm spokes for longer side replacement.
And stay confused, why the manufacturers still not have uniform ERD measurement system:cursing:
But for future it will be good lesson to buy rim at first, measure by youself and then buy spokes.
 
I'd be surprised you could use one spoke length normally I'd use 2/3 front, nds and drive side??

When you have calculated lengths difference about 1.5mm for driver side and non driver side, it's possible to use one length for both sides.
But due to real ERD become bigger than mentioned, only driver side have acceptable length.
Speech is only about rear wheel.
 

Ajax Bay

Guru
Location
East Devon
As expected, short side spokes still compatible (just 2-3 turns of thread are visible under the nipple skirt, suppose it enough engagement), otherwise longer side have quite poor engagement.
Currently waiting for another 20pcs 286mm spokes for longer side replacement.
Really annoying to get the 'wrong' ERD for the rim from the supplier.
Allow me to remark that if there is thread visible 'below' the nipple the spoke is not long enough (rule of thumb). Or are they threaded more than 'normal' - in which case you need longer nipples. Threads showing like that are potential stress risers.
 
Last edited:
Actually, the problem was fixed. Non driver side spokes was replaced and all nipples was changed into longer ones.
So, all threads are hidden by nipples.
@Ajax Bay , thanks for advise about visible threads
 

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