Broken rear spoke. Caused by rear motor?

John F

Esteemed Pedelecer
Sep 3, 2013
426
54
Just broken my first ebike spoke on my rear hub motor wheel.

It occurs to me that rear wheel spokes must me under greater stress due to the motor effect (as apposed to my previous crank drive bike which did not suffer any spoke issues)

Whilst discussing this with an ebike company owner, he commented, after looking at the bike, that the spokes were not heavy duty enough to cope with the motor (he thought they were standard guage, and the same guage as the front)

Many years ago I rebuilt 2 wheels on my old town bike, which I did well and the spokes remained good and tight for years with no breaks. I think all the spokes on all my subsequent bikes were nowhere near as tightly installed.

I recall reading that one reason that spokes break adjacent to the hub of whatever type (which mine has just done) is that the holes in the flange are not properly drilled out to accomodate the curve in the end of the spoke. I wonder if this contributed to my break?

I weight 94 kgs by the way

Comments/advice anyone? In particular is it worth the trouble of having the wheel respoked?
 

Andy-Mat

Esteemed Pedelecer
Oct 26, 2018
1,861
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Just broken my first ebike spoke on my rear hub motor wheel.

It occurs to me that rear wheel spokes must me under greater stress due to the motor effect (as apposed to my previous crank drive bike which did not suffer any spoke issues)

Whilst discussing this with an ebike company owner, he commented, after looking at the bike, that the spokes were not heavy duty enough to cope with the motor (he thought they were standard guage, and the same guage as the front)

Many years ago I rebuilt 2 wheels on my old town bike, which I did well and the spokes remained good and tight for years with no breaks. I think all the spokes on all my subsequent bikes were nowhere near as tightly installed.

I recall reading that one reason that spokes break adjacent to the hub of whatever type (which mine has just done) is that the holes in the flange are not properly drilled out to accomodate the curve in the end of the spoke. I wonder if this contributed to my break?

I weight 94 kgs by the way

Comments/advice anyone? In particular is it worth the trouble of having the wheel respoked?
I weigh slightly less than you, and I have had two rear hub bikes, one for about 9 years, and the other one for over 3 years now. I have never had a spoke break. Also I ride in the hills on rough unmade paths and roads, as well as normal roads.
I certainly do not think its the "norm" for them to break, but it does happen, but some of the points you mention are to my mind, are certainly possible reasons.
Certainly, you need to identify the thickness of the spokes as a first, and see if the experts here can qualify in any way your thoughts with regard to their strength etc.. Replacing spokes, which I myself have never done, appears to me to be a DIY job, if they are identified as the cause.
And if I was going to do it, I would carefully remove the wheel, mount it in a vice horizontally, and replace each spoke. Followed by an alignment. Many have done it, many are still doing it, so I don't think one needs to be an expert! Just careful and possibly do it slowly at first...
Best of luck
Andy
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
9,822
3,943
Basildon
Just broken my first ebike spoke on my rear hub motor wheel.

It occurs to me that rear wheel spokes must me under greater stress due to the motor effect (as apposed to my previous crank drive bike which did not suffer any spoke issues)

Whilst discussing this with an ebike company owner, he commented, after looking at the bike, that the spokes were not heavy duty enough to cope with the motor (he thought they were standard guage, and the same guage as the front)

Many years ago I rebuilt 2 wheels on my old town bike, which I did well and the spokes remained good and tight for years with no breaks. I think all the spokes on all my subsequent bikes were nowhere near as tightly installed.

I recall reading that one reason that spokes break adjacent to the hub of whatever type (which mine has just done) is that the holes in the flange are not properly drilled out to accomodate the curve in the end of the spoke. I wonder if this contributed to my break?

I weight 94 kgs by the way

Comments/advice anyone? In particular is it worth the trouble of having the wheel respoked?
The ebike company owner doesn't have a clue. I wouldn't buy a bike from them whoever they are. Your crank-drive bike put more stress on the spokes than your hub-motor. Think about it. Which system produces the most torque? The spokes don't know or care where the torque is coming from. They just get it.

The greatest single factor that causes spokes to break, apart from the weight on them, is the use of ones which are too strong (stiff), so putting heavier ones on is worse. Your higher torque crank-drive bike most likely had 14g spokes, while as most hub-motor bikes wrongly use the thicker 13g ones.

If you want to rebuild your wheel, you should do it with 14g spokes, then you will never get another problem.

I know you're going to think I'm nuts, but there is a logical reason, and that's that thick spokes are not elastic enough to absorb and cushion the load like thinner ones do. It's a bit like riding a bike with 22mm tyres pumped up to 60 pdi compared with 2.2" MTB tyres pumped up to 32 psi. How long can you ride each until your bum breaks?

Thinner spokes also give the advantage of a slightly more comfortable ride and they're lighter.
 

Scorpio

Esteemed Pedelecer
Apr 13, 2020
303
126
Portugal Algarve (temporary)
I bought an older 27"/700C ladies shopping bike last year, very good quality but it had several broken spokes in the rear wheel and another one has just snapped.
Odd that there are no broken spokes in the front wheel, even though that's where the hub motor is. For info the spokes in both wheels are same diameter.
 

Nealh

Esteemed Pedelecer
Aug 7, 2014
15,061
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West Sx RH
14g spokes on all my hubs.
 

Benjahmin

Esteemed Pedelecer
Nov 10, 2014
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West Wales
I have 3 hub powered bikes and never broken a spoke yet, riding the poorly surfaced back lanes of Wales.
Break is more likely caused by a badly tensioned wheel, have you tried the 'ping'test? I check mine whenever the bikes on the stand, probably about once a year.
 

sjpt

Esteemed Pedelecer
Jun 8, 2018
2,792
2,158
I bought an older 27"/700C ladies shopping bike last year, very good quality but it had several broken spokes in the rear wheel and another one has just snapped.
Odd that there are no broken spokes in the front wheel, even though that's where the hub motor is. For info the spokes in both wheels are same diameter.
Rear wheels (derailleur ones anyway) are often weaker because of the asymmetry between the left and right spokes, and the higher tension needed on the right.

The largest contributor to spoke breakage is probably a poorly built wheel. Weight and the way you ride are also important. The difference between 13g and 14g spokes is less important.
 

mike killay

Esteemed Pedelecer
Feb 17, 2011
3,010
1,627
There are spokes and spokes.
Some OEM spokes are very poor quality and break easily.
Also, no-one mentions the fact that stainless steel unlike the older mild steel spokes suffers from crevice corrosion and can snap suddenly.
 

Danidl

Esteemed Pedelecer
Sep 29, 2016
8,278
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Ireland
There is another reason, which feeds into Vfrs response. The length of the spoke. The hub motor is always larger than a standard hub, and the spokes shorter, hence less flexibility. A thinner but higher quality steel restores the flexibility.
 
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Ocsid

Esteemed Pedelecer
Aug 2, 2017
320
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Hampshire
There is another reason, which feeds into Vfrs response. The length of the spoke. The hub motor is always larger than a standard hub, and the spokes shorter, hence less flexibility. A thinner but higher quality steel restores the flexibility.
Agreed, and that vital flexibility allows the load to be shared with adjacent spokes, not all being at one point. Not only does it save spokes it saves the hub flange too, if the spokes spread the load over a few holes.
It does not stop there the wheel's increased flexibility, compliance, in itself reduces the magnitude of suddenly applied loads, encountered hitting the multitude of bumps we can't avoid.
 

John F

Esteemed Pedelecer
Sep 3, 2013
426
54
Interesting info thanks. A few more observations that come to mind which might help the debate:-

1. All the spoke breaks I've ever had have been at the back and where the spoke laces into the flange. This leads me to conclude that some flanges are made more precisely to alleviate the issue. It's a stress point where the outside edge of the flange hole butts against the curve of the spoke leading to failure.

2 My break this time was on the gears side

3 I do the ping test every time the bike is on the stand. None of the spokes are as tight as I think they should be, but they are all roughly equal. I also had recently had a very loos spoke. Conclusion? poor wheel building?

4 Years ago there used to be "double butted spokes" Are these available and relavent to ebikes?

5 I ride on Marathon Plus tyres, well inflated and fairly often on farm tracks etc, but nothing to demanding

6 See attached photo. This shows that my spokes are painted black. The broken spoke is replaced by the narrower unpainted one. Does this help establishing the guage ? (related to the size of the nipple?)spokeWEB-162730.jpg
 

Sturmey

Pedelecer
Jan 26, 2018
242
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Ireland
1. All the spoke breaks I've ever had have been at the back and where the spoke laces into the flange. This leads me to conclude that some flanges are made more precisely to alleviate the issue. It's a stress point where the outside edge of the flange hole butts against the curve of the spoke leading to failure.
I partially agree with you here (at least in my case and after many spoke breakages). If you look at the photo below, you will see a gap at the place marked (red) X caused by the 13g stainless steel spokes been too hard/rigid to wrap tight against the flange properly. This does not happen with the milder steel or 14g spokes which wrap better, so I agree with others above. This gap allows unwanted movement at the flange and therefore metal fatigue to take place.
Its not a problem with front wheels as less weight on wheels.42187
 
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John F

Esteemed Pedelecer
Sep 3, 2013
426
54
Spokes from Ryan do all sorts of spokes, including variable thickness:

Interesting web site. Just measured my spokes. They are 2.3 mm D throughout the length, and seem to be identical to this one from Ryan:
...................................................................
Best for: Low to mid-power eBike wheels or for anywhere that a stiff, utility build is required such as cargo bikes.

The Sapim Leader 13g/2.3mm J-Bend Spoke is strong, reliable and great value. If you want the strongest and lowest cost wheel going, the 13g is the way to go.

As a heavy-duty spoke it’s perfect for eBike wheels
. We’d also recommend if for smaller wheels where weight isn’t your main issue, such as trailers, Bromptons or anything with a shorter spoke.

The Sapim Leader 13g Spoke is available in 1mm increments from 50mm to 310mm.
Technical Specifications:

  • Weight: 13G 2,3 mm (64 pcs x 260 mm lg) 431 g
  • Quality: Stainless
  • Strength on middle section: 1080 – 1180 N/mm2
  • Diameter 13g – 2.3 mm
  • .........................................................
So Ryan's advice contradicts many of the previous posters opinions?
 

Sturmey

Pedelecer
Jan 26, 2018
242
115
65
Ireland
So Ryan's advice contradicts many of the previous posters opinions?
Read article below which should clarify things for you.

As regards getting your wheel fixed for now, getting identical replacement spokes to replace the broken spoke is probably the best way to go. Its often possibly to bend or curve the replacement spoke and slip it in and fix to existing nipple without removing the wheel or even deflating the tyre if you are lucky and there is nothing in the way. I use to be able to replace the spokes on my old bike ( 'v' braked) in about 15 minutes. Put some tape on the nipple so it doesn't fall into the wheel cavity if doing this.
 
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vfr400

Esteemed Pedelecer
Jun 12, 2011
9,822
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Read article below which should clarify things for you.

As regards getting your wheel fixed for now, getting identical replacement spokes to replace the broken spoke is probably the best way to go.
If one spoke breaks, replace it. If a second one goes, replace it. If a third one goes, rebuild the wheel with 14g spokes.

Spokes can break for any reason, but when three in the same wheel break, there must be something wrong with the spokes, or the way the wheel has been built, or failure to maintain them with the correct tension. In each case, the wheel is compromised, so no point in carrying on with it.
 

John F

Esteemed Pedelecer
Sep 3, 2013
426
54
Only one break and one loose spoke so far, and that was a while ago. I do the ping test weekly and apart from still thinking they could perhaps benefit from being a bit tighter (as my home laced wheels were years ago) they seem ok. Never thought of trying to replace the broken one without wheel removal so good tip!