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rickallen124

What causes a spoke to break?

19 posts in this topic

I'm pretty good about keeping my spokes tight but last time I went riding one of them snapped near the rim. I've never broken or damaged a spoke before so I'm curious as to what would cause this. Too tight? Got loose? I usually torque them around 35inch/lbs. I'd like to prevent it from happening again.

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Usually, new spokes stretch a little, once they are a little loose, a severe jump can cause one to fail, then the rest are over worked and a few more can easily break. This is the typical reason.

Though it sounds like you do maintain your wheels, you you should not be a candidate for broken spokes. Other possible explanations would be a spoke hitting a rock and getting a gouge that weakens it, a obstacle caught in them that shears one.

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What is the inch/lb torque recommendations for the stock spokes? Are the aftermarket spokes stronger than oem? The only other possibility I could come up with is another rider brushed against me in a corner and may have gotten it with his footpeg as it broke not too long afterwards. I'll be even more vigilant checking my spokes from here on out. Thanks for the info.

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I dunno about the newer bikes but my 05 came with stainless spokes and aluminum nipples....galvanic reaction i.e. corrosion is probably what got you. When I relaced mine with buchanans stainless nipples and spokes I found several (particularly the ones near the hub loks) that probably got more moisture exposure and were looking grim...well the nipples looked horrible.

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What about using something to prevent the galvanic reaction when using spokes and nipples of two different metals? What about using a little anti-sieze during assembly?

Of course you would have to take the nipple completely off the spoke to do this. Would it even be worth the added work?

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48 inch-pounds is the correct torque for spokes on a dirt bike. The galvanic reaction is insignificant, esp. when a wheel is built right. You must use anti-seize on the spoke threads and on the nipple head or an accurate torque reading is nearly impossible to get. The anti-seize has the added benefit of preventing galling when using stainless spokes.

Your thought on a foot peg in the spokes it a very likely cause. Inspect the broken end. Is it snapped clean, or is there a little bit of bend at the break? Are there any gouges near the break? All signs of a foreign object entangling the spoke.

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The spoke was bent were it broke, so I'm pretty sure the guy clipped it with his peg. I will set the spokes to 46-48 inch/lbs from here on out. Thanks for the info William.

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Yup, sounds like your competitor tried to 'Mad Max' you. Be sure to anti-sieze the spoke threads and nipple head.

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48 inch-pounds is the correct torque for spokes on a dirt bike. The galvanic reaction is insignificant, esp. when a wheel is built right. You must use anti-seize on the spoke threads and on the nipple head or an accurate torque reading is nearly impossible to get.

my service manual for my 426 says 27inlb :eek:

also, william, are you sure about the torque readings? :thumbsup: lubricating the threads of ANY fastener DRAMATICALLY affects the torque. found a good write-up with some math.....

http://www.rockcrawler.com/techreports/fasteners_torque/index.asp

lubricating them will require less torque based on the equations. you just need to find the values of the given lubricant, thread specs, etc... and redo the math to find out what your final torque should be.

***this holds true unless the manuals/mfg'er/specs indicate that the value is for a lubed thread. so i dunno, i guess it depends on the application also.

another good article about bolt failure due to lubricating threads and torquing the bolts to the 'unlubed' spec. http://www.fera.org.uk/cs5.htm

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my service manual for my 426 says 27inlb :eek:

also, william, are you sure about the torque readings? :thumbsup: lubricating the threads of ANY fastener DRAMATICALLY affects the torque. found a good write-up with some math.....

http://www.rockcrawler.com/techreports/fasteners_torque/index.asp

lubricating them will require less torque based on the equations. you just need to find the values of the given lubricant, thread specs, etc... and redo the math to find out what your final torque should be.

another good article about bolt failure due to lubricating threads and torquing the bolts to the 'unlubed' spec. http://www.fera.org.uk/cs5.htm

All quite correct. Unless specified otherwise, all torque specs are given for "clean, dry threads".

Some wheel builders will call for more tension than that. I use paraffin as a thread lube because it is non oily, and I torque by tone of the spokes far more than by nipple torque.

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yep...you can do that when youre older and YZer. hehe.:thumbsup:
As long as you can still hear, that is. IMO, it's a better indication of actual tension than torque is.

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Got one, Thanks. :thumbsup:

In fact, with it cranked up, I can probably hear better that you. :eek::D

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I use the tone method too, on a wheel that has never been apart and has dry, crusty spoke threads. Even with the torque wrench, I follow up with a little 'harp playing' to double check. Now it I had perfect pitch, I would trust my deaf ears more. I also use the tone method to simply check the spokes.

If I was going to build wheels dry, each time I was going to torquethe spokes, I would have remove them, give a good cleaning of the threads and confirm nipple rotation is smooth and no signs of binding.

I just built two sets of wheels, ant-siezing the threads. When completed, all spokes had the classic 'ping'. A 1/4 turn changed it to a dull 'duong', so I am confident they are 'happy wheels'.

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i dont doubt you willie.....if youre doing it by tone, then lubing threads is a non-issue. for the ones who are new to it and using a torque wrench, they should install clean and dry.

:confused:

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On an old, poorly maintained wheel to tighten a few spokes, by tone is the only way.

A new wheel, a torque wrench on dry spokes is fine but, at some point, those nipples are going to get a little rust in them and you will be back to doing it only by tone. Anti-seizing a new build enables use of the torque wrench longer. The other alternative is to remove each spoke, run the correct die on it and the correct tap on the nipple, clean well and re-assemble. On a MX bike, this would a four times a year job.This would leave no time to make a nice sandwich. Instead, every few years, I take a wheel down and do this.

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One of the most important reasons for lubing spokes during a wheel build is to prevent the spokes from "winding up", a condition in which the friction of the threads twists the entire spoke, rather than rotating the nipple on the spoke, which results in unwanted torsional stress stored in the spoke, and misleading torque readings. It's a bigger problem with lighter gauge spokes of course (it's huge in building bicycle wheels).

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