el forestero

On my rear Bontrager AT-750 rim, the DS spoke tension range is 107 to 120 kgf. NDS is 70 to 81. I've read the recommended tension is at least 60 for NDS rear spokes and 110 for DS rear spokes, with 120 sometimes being recommended for a rider weighing about 250 lbs.

Though I just weigh about 170 lbs, I dialed it up to the higher end of that tension range because I've had issues with NDS spokes unscrewing themselves over time, and because I sometimes ride weighed down with a lot of camping gear. (I couldn't find a manufacturer's recommendation for spoke tension on those rims, so just went with what I read here: https://www.cyclingforums.com/thread...spokes.462265/)

I recently rode about 350 km with a lot of camping gear weighing down the rear end of the bike. Since then I've broken 2 spokes on rides without any camping gear on the bike. In light of this, I'm wondering if I may have the tension dialed up too high. Or maybe I just overstressed the spokes from that recent ride with all the weight on the bike. Or maybe both are likely causes of the spokes breaking. I don't have enough experience with spoke tension or riding with heavy gear to know what's going on.

Is 120 DS too high, such that I should dial tension on all the spokes down a bit? Or does this case sound more like I've done the spokes in by recently overloading the bike with heavy gear?

Bill Kapaun

I think your spokes were over fatigued before you dialed up the tension.
The fact they were "unscrewing themselves" meant they were LOOSE. That over bends the J bend. Kind of a running start for the tension to peak.

speedevil 

Did you build the wheels? Just prior to lacing and threading on the nipple, I always dip the spoke threads in linseed oil which turns "gummy" over time and helps to prevent spokes loosening, especially NDS spokes on the rear wheel. There are commercial preps available for spoke threads, but linseed oil is much cheaper and has been used for this purpose for a very long time.

Also, don't forget a tiny bit of grease on the nipple itself where it contacts the seat in the rim. It will make it much easier to bring the tension up, with little risk of galling. It's more important on rims without eyelets, but I use grease for all of my wheel builds.

UPDATE: I don't think that 120 is too high for DS rear wheel spokes, but it read that you were basically already there, or close to it.

ThermionicScott 

I agree with Bill, sounds like the spokes were already toast, and you just happened to bring out the failures by tightening them up and riding a little more. If you like the wheels, it's probably time to respoke them and make sure they are at a decent tension and stress-relieved thoroughly before you ride a mile on them. I don't know what spokes those wheels come with, but double-butted spokes would be a good idea.

BTW, there isn't really a specific minimum DS tension that you need to shoot for. It's always the NDS spokes that are at risk of coming loose. People throw out figures like 120 kgf DS only because that means the NDS spokes will probably have enough to stay put at that point.

berner

In my limited experience, more spoke troubles are due to low spoke tension than from too high. For all things relating to bikes, Sheldon Brown's website has a wealth of information. On spokes and without a spoke meter, using sound by plucking works very well. All that is needed is a pitch pipe. I also think the main requirement is for all spokes to have the same tension so that they all do equal work. I also put a drop of thread lock on spokes. https://www.sheldonbrown.com/spoke-pitch.html

fietsbob

it was the riding them loose that caused the flex cycles bending the spokes as the wheel rolled .

maintaining balanced tension, the whole wheel acts together.. as one..

davidad

With a 36 spoked wheel you would normally run about 100 to 110Kg of tension. I never worry about the NDS because it should be up to at least 60.
When the spokes loosened that may have raised the fatigue factor and caused breakage.

cpach

Excessive spoke tension rarely causes spoke failure; the rim failing is the risk there.

The tension ranges you mentioned are pretty good for a factory wheel. You are clearly exceeding the load limits of the wheel—touring is very rough on wheels because the luggage is completely unsprung- the rider takes up some shocks in the arms and legs.

You'd be well served by skillfully hand built wheels made with a touring rim and 36 or more butted spokes. A touring rim will be more rigid, butted spokes will flex in the center rather than the spoke head or threads which are more likely to break, more spokes means less spoke fatigue, and good hand built wheels will have more even tension, will be stress relieved, and will have much less spoke windup.

el forestero

Thanks for the super helpful input, all!

Kimmo 

How do you figure that, given that low tension is what leads to spoke fatigue?

Low spoke count wheels aren't prone to spoke fatigue, because if they don't have high tension, they don't work. I've seen a far higher proportion of traditional wheels with spoke fatigue - they can roll out the door without adequate tension.

cpach

This hasn't been my experience. The issue is the amount of total tension on the wheel. A 36 spoke wheel tensioned to 110kgf DS is still going to have more tension in total than a 24h wheel at 160kgf DS, and more spokes will be re tensioned at a time as the wheel rolls. When I have seen people tour with panniers over the rear wheel of a bike with a 24 spoke wheel, I've seen a lot of broken spokes! You may be seeing higher failure rates of economy wheels with high spoke counts, which often have very low average tension and extremely uneven tension, compared to mid to high end system wheels, which tend to have very high and relatively even spoke tension.

pdlamb

Problem isn't low tension, it's spokes going slack and then being re-tensioned. That repeated cycling (sorry, it's precise technical language as well as a pun) is what causes spoke fatigue and cracking.

Low spoke count wheels share the load among fewer spokes. If you've tensioned the low spoke count wheels much higher than the low spoke wheels, you can prevent them from de-tensioning as the wheel rolls (depending on spoke count, spacing, and rim stiffness). It's also possible to tension wheels with more spokes a bit more to prevent de-tensioning as those wheels roll.

Kimmo 

Every system wheel I can think of is 27h or less...

mynewnchome

So I just tried an experiment. I have a front that needed minor tweaking, one slight wiggle. I took my Snark mandolin tuner and clipped it in a couple spokes, one at the time, and tapped with a wrench near rim with tuner on axle end.

I tuned them to F# by tightening and loosening as I went around. That wheel is DEAD STRAIGHT now. There is something to this theory.

Marcus_Ti

Problem being...spokes on a bicycle wheel are not pitched--they don't have a fundamental. Even if they were the frequency is a matter of mass, tension, and length.

Kimmo 

Sure, but get a front with a decent rim to ring all spokes at the same pitch, and it should be true.

28 spokes or more, and the window between not enough tension and too much should be pretty large, depending on the strength of the nipple bed in the rim.

63rickert

Baggage on a bike is pure unsuspended weight. Baggage weight is just brutal on wheels. If you overload your wheels the two choices are to not expect much or to have extremely overbuilt wheels for when you carry the big loads. Touring/trekking/e-bike rims that are plain heavy will not flex so much, will not lead to spoke fatigue so readily. Take a look at something like Ryde Andra rims. Over 800 grams for a reason.

A well built wheel doesn't really de-tension much under static load or when just rolling along. Have a friend sit on the bike while you check with a tension meter. Take same wheel and overload it, then hit a pothole, and yeah the spokes lose tension. If you do kitchen sink camping you just need heavy wheels.

If you break one spoke it is reasonable to replace it. Could be a fluke. Break two spokes in same wheel in a short period and you may assume all spokes are fatigued. Time to replace them. All of them. Full tension will always reduce fatigue. Stout rims reduce fatigue too.

el forestero

Very helpful info. Thanks!

cpach

Now I need to do some frequency analysis of a plucked spoke. Sort of joking?
But seriously, I have very good relative pitch, and certainly perceive a definite pitch when plucking spokes and certainly use this when evening tension (but not for setting absolute tension--I rely on a meter for that). An approximate semitone seems to be a relatively good tolerance. On some excellent builds I've gotten them to within a sixth tone, which is basically unmeasurable on a park tension meter.

Perceived pitch also doesn't necessarily have to do with the presence of a true fundamental. Basically if there are three or more partials of a composite sound that form part of an approximate harmonic series, a fundamental at the root of that harmonic series is perceived.

Kimmo 

Hmm...

Marcus_Ti

In physics terms...."unpitched" in this context means you put a tuning needle next to it--and the machine will see chaos. There's no absolute overtone series that is consistent. You can only hear any kind of pitch comparatively with a human ear.


Well, strictly speaking if you've trued by sound you've done a frequency analysis--albeit not a true FFT. Lots of percussion class instruments aren't pitched--the difference between a tam-tam and a gong is that the former is unpitched. Church bells are, as it turns out, another problematic instrument WRT absolute pitch--and as such can only really be heard comparatively. Similar to say a spoke or other (proper) instruments.

WRT tolerance... a properly pitched string instrument, a violin for example. The open string length is nominally about 325mm. So you do some math, and TL;DR, the first fingered whole-step is 36mm up the strings.....however the physical spacing of adjacent one ET cent is about 0.2mm. a 1/6th tone is ~17cents or on a violin string is a couple millimeters. And, ofc, that spacing gets narrower the short you stop the string. That is the difference between a pitched instrument with ideal (sometimes) strings....and bicycle spokes on a wheel that are not pitched or ideal.


The Park Tool tension meter is just above useless in precision, FWIW. You can build your own digital scale spoke tension gauge for the cost of their spring-scale dealio.

cpach

A equally tempered sixth tone is 33.3c. You're dividing the ~200c wholetone, not the semitone. Intonation control among excellent performers is within a handful of cents of just in slow passages. My subspecialty musically is microtonality and tuning theory. Believe me, if there is a perceivable pitch (regardless of actual harmonic content of the sound source) hearing an approximately 30c deviation is easy. It's trivial to to tune a perfect fifth on a stringed instrument within a cent of just by ear.

A calibrated park meter should be reasonably accurate for setting average tension if you're targetting, say, 110-120kgf. It's also accurate enough to show inequality of tension on nearly every factory wheel, including some fairly expensive ones. I don't really use mine to check for evenness of tension--it pretty much only comes out at final tensioning (or setting final tension on the DS of a dished rear wheel if I'm tensioning that before the NDS).