why do my 12 gauge spokes break?

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why do my 12 gauge spokes break?

Postby EdwardNY » Mon Sep 16, 2013 7:39 pm

I thought 12 gauge spokes were overkill for an ebike. Pushing about 3K watts max.

Motor is a yescomusa 1000w hub motor. What I notice is I will break my 12 gauge spokes about 1 per month. They seem to break at the tip of the nipple. Looks like it leaves part of the spoke in the nipple and is broken flush with the nipple.

Is this an error with my wheel lacing, defective spokes, or is my hub motor powerful enough to break 12 gauge spokes? I also ride the bike pretty hard off-road so the wheel does take a beating.

I do not think I can over tighten the spokes because the nipple will strip.
Last edited by EdwardNY on Mon Sep 16, 2013 7:40 pm, edited 1 time in total. View post history.
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Re: why do my 12 gauge spokes break?

Postby kfong » Mon Sep 16, 2013 7:46 pm

Mine was doing the same, but the replacement spokes from John Holmes have been holding up.

DT Swiss or Sapim spokes, 2.0mm straight gauge or 2.0/1.8mm double butted. If the hub flange holes are too big, use washers underneath the spoke heads. Lubricate the spoke threads and nipple seats with something. Tighten to 100kgf minimum on the tighter side of the wheel. Stress-relieve the spokes by squeezing or prying spoke pairs.
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Re: why do my 12 gauge spokes break?

Postby swbluto » Mon Sep 16, 2013 7:50 pm

Lucky stiff! It seems like my spokes are breaking at the rate 4/day! (w/ 120 mile days, anyways.)

The chinese spokes on mine are 5 years old, however, so I'm going to replace them completely and see if the sapim spokes hold up. Many people seem to think they will.
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Re: why do my 12 gauge spokes break?

Postby liveforphysics » Mon Sep 16, 2013 7:59 pm

Thick spokes can't stretch enough while constrained by a bicycle rim to enable a strong wheel. (because to tension them properly to make a strong wheel it pulls the nipple through the rim)
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Re: why do my 12 gauge spokes break?

Postby Drunkskunk » Mon Sep 16, 2013 8:13 pm

Wrong gauge, and poor quality.

There are probably more than a hundred threads on why thick spokes are bad, but the short summery is they need to be able to stretch to function properly. to thick, they can't stretch. 14gauge is about the thickest you want, IIRC Liveforphysics has tried 18 gauge with success.

The other problem is the abysmal quality of the spokes found on most kits. They just aren't strong enough or made of materials with the right properties to even be spokes. As an example, the last wheel I had to re-spoke was lased with cheap 12g, along with several good quality but thinner 14g spokes. I de-laced it with a pair of 6 inch wire cutters and they snipped through the 12g spokes with one hand rather quickly. when i got to the thinner but good quality 14g spokes, I had to use both hands and bare down hard on the cutters to cut through them. They were more than twice as strong.

Best to replace them with a quality 14 straight gauge, or single butted 13/14 gauge if the motor's holes are drilled large. , As Kfong mentioned, John is the man for Ebike spokes. 2.0mm is 14gauge
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Re: why do my 12 gauge spokes break?

Postby el_walto » Mon Sep 16, 2013 9:15 pm

I found that using a standard rim caused my spokes to bust all the time. This may be especially true when running a 2.5" wide tire.

Switch to a thicker downhill rim with thinner spokes.
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Re: why do my 12 gauge spokes break?

Postby MadRhino » Mon Sep 16, 2013 10:02 pm

Spokes are breaking no matter the size, if the wheel is not built tight and/or maintained properly.

Spokes and nipples must be aligned. Drill each nipple hole at an angle to match the lacing pattern.
Spokes must not rub on the motor flange, and spoke heads must be properly seated. If not, use flange washers.
A bicycle rim needs nipple washers to make it able to tension 12 ga spokes, and even then it has to be a good rim.
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Re: why do my 12 gauge spokes break?

Postby wesnewell » Tue Sep 17, 2013 1:49 am

The real problem is they are just crappy spokes. Replace them with some decent ones and you won't have a problem. They also tend to snap easier when they are not tight. And if you're using a wide tire, this would be the time to put a wider rim on it too. Alex DX32 or Weinmann DH39 if you can find one. Both are 32/39mm. I used 166mm 12g Primo ss spokes on a DH39 about a year ago and haven't broken one yet after ~4000 miles.
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Re: why do my 12 gauge spokes break?

Postby Chalo » Tue Sep 17, 2013 2:59 am

kfong wrote:DT Swiss or Sapim spokes, 2.0mm straight gauge or 2.0/1.8mm double butted. If the hub flange holes are too big, use washers underneath the spoke heads. Lubricate the spoke threads and nipple seats with something. Tighten to 100kgf minimum on the tighter side of the wheel. Stress-relieve the spokes by squeezing or prying spoke pairs.


Perfect.

The answer to the OP is that the spokes are bad. Good 12ga spokes will give you all sorts of trouble, but not breakage.

I have a wheel with about 40,000 miles on it that has never broken a spoke. DT Swiss 14-15ga, carefully built. For what it's worth, I doubt any hub motor wheel could match that. But painstaking construction with butted spokes and the optimum lacing pattern could probably come close.
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Re: why do my 12 gauge spokes break?

Postby d8veh » Tue Sep 17, 2013 5:14 am

Don't they use 12g spokes on motorcycles that run much higher stresses and rarely break?
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Re: why do my 12 gauge spokes break?

Postby MadRhino » Tue Sep 17, 2013 8:43 am

12 ga is very small in the motorcycle world. I've had 9 ga spokes break on my first Trial bike, some 40 years ago. I didn't know better then, wasn't servicing the wheels until they fail. Even a cheap 12 ga spoke can take a very hard beating if it has to support only its equal share of the load. When a wheel is loose, out of true, one single spoke can suddenly support many times the load that it is made for, because the hit is not spread equally so its little brothers are not doing their part of the job.
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Re: why do my 12 gauge spokes break?

Postby spinningmagnets » Tue Sep 17, 2013 9:51 am

I also ride the bike pretty hard off-road so the wheel does take a beating


You need to come over to the dark side...and try a mid-drive...
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Re: why do my 12 gauge spokes break?

Postby dogman dan » Tue Sep 17, 2013 10:05 am

But learn to tune your wheel.

You just can't ride around romping on the bike with motors on unturned wheels. It won't matter if you gear drive it, you still gotta tune spoked wheels.

Back when I was all young and pedaled hard, I serviced the back, powered wheel weekly. Lots of curb hopping.
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Re: why do my 12 gauge spokes break?

Postby liveforphysics » Tue Sep 17, 2013 11:16 am

The extra money for butted spokes over straight spokes will also result in a stronger wheel. That gives you a shaft with more compliance, while both ends where failures can happen remain beefy.
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Re: why do my 12 gauge spokes break?

Postby wesnewell » Tue Sep 17, 2013 12:37 pm

Spoke stress is completely different on a hub motor spoke than it is on a standard bike hub because of the diameter of the hub and where the spokes attach to it. On a bike hub most of the pressure is applied to the entire length of the spoke with close to a 90 degree angle to the rim even when there's huge torque on the wheel. Not so with a large hub motor hub. That's why you'll see motorcycle rims with angled spoke holes, to get the same type of 90 degree stress. With a hub motor and standard rim the stress on the spokes is greatly angled. This causes metal fatigue from the constant angled application and release of pressure. Basically like bending metal back and forth to break it. Better spokes will last longer, but will still fail eventually from this pressure. What they need is a rim with angled spoke holes.
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Re: why do my 12 gauge spokes break?

Postby John Bozi » Mon Nov 18, 2013 6:06 am

awesome info here thanks a lot, I busted a rim a few months ago and just a few days ago my first spoke.

next question is what's a decent rim with angled spoke holes and would 11/12 butted spokes be better than my 12 gauge spokes. It seems the holes are bigger but maybe the extra width of the spoke would push more against the flange.

btw the spoke that broke was where the rim joins which was the hardest part to true. kind of sticks out more than the rest of the wheel. Maybe I over tightened it to try to get the wheel more round....
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Re: why do my 12 gauge spokes break?

Postby cal3thousand » Mon Nov 18, 2013 12:16 pm

John Bozi wrote:awesome info here thanks a lot, I busted a rim a few months ago and just a few days ago my first spoke.

next question is what's a decent rim with angled spoke holes and would 11/12 butted spokes be better than my 12 gauge spokes. It seems the holes are bigger but maybe the extra width of the spoke would push more against the flange.

btw the spoke that broke was where the rim joins which was the hardest part to true. kind of sticks out more than the rest of the wheel. Maybe I over tightened it to try to get the wheel more round....


You don't want to go with thicker spokes. Which 11/12 would be thicker than 12G.

As suggested 14/15 butted spokes make very strong wheels for bicycle rims. If you insist on going to a larger spoke, be prepared to drill out the bicycle rim so that an acceptable angle will be acheived. Otherwise, step up to a Moped rim. There are some people running 17 to 19" moped rims with DOT tires using larger spokes on here.
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Re: why do my 12 gauge spokes break?

Postby liveforphysics » Mon Nov 18, 2013 1:50 pm

d8veh wrote:Don't they use 12g spokes on motorcycles that run much higher stresses and rarely break?



If you run a spoke with double or triple the cross-section, then you need double or triple the tension to still get enough stretch displacement in the spoke system to make a wheel the distributes stress. Bicycle rim's simply pull the nipples clean through them before you can get the tension you require on bigger spokes.

Why do they break? When you don't have properly stretched spokes, load on the wheel is distributed over a very narrow area. You could view it like landing a big jump with your wheel being actually supported by 1-2spokes over a just a few eyelets on the rim. Of course they break frequently, or bulge the rim nipple area, or pull the nipple through, or best case just constantly loosen up and make an unreliable wheel.

A strong wheel is a wheel that distributes load. That means as the rim deforms a bit, it doesn't cause most of the spokes to become loose and carry no load, and cause a few places to carry all the load (which is what a stiff thick spoked low-stretch wheel does when loaded). If you want the strongest wheel, you want a wheel that has the most spokes constructively sharing load at a given moment, that means you need the spokes able to stretch or contract as the rim inevitably deforms but still carry something from each of them.

Likewise, you want your spoke butted, it's an absolute no brainer that a butted spoke is a stronger spoke, and a better performer at keeping a wheel together.
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