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Old 2015-09-25, 06:15 PM   #1
janvanhulzen
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KH 26 Inch Spokes snapping

I got a 26 Inch KH muni in April of this year and have been riding on it frequently. Doing muni at the weekends and commuting during the rest of the week. I did not do anything extreme.

Today two of the spokes snapped and the wheel developed a wobble before i noticed.

So i am a bit in doubt. Does this happen often? I never had issues with other unicycles and have been riding for 10 years and never popped a spoke.

What about replacing the spokes? Are there any issues i should be aware off? Can i expect the other spokes to go soon? Do they need to be tightend more than a regular mountain bike wheel?

i would like to know before bringing it in to the bicycle shop...

Jan
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Old 2015-09-25, 07:13 PM   #2
JohnIb
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If it's from April that'd make it less than a year old, wouldn't there be some kind of warranty?
I might be spoilt as I'm from Denmark where customers are reasonably well protected

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Old 2015-09-25, 07:38 PM   #3
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Where did the spokes snap? (Middle, nipple end, or bend)

That can tell you a lot about what is wrong.

In short, no, you shouldn't be having issues in that short about of time unless you're riding really rough drops.

Often the wheels that come with a new cycles are under-tensioned, which can lead to this sort of thing. I doubt it's simply bad spokes, but some of the 36er spokes a few years back had some issues, including my build, where I was breaking spokes in the middle of the spoke every time.

A good strong wheel should be tensioned up to about the same amount whether it's a unicycle or bicycle wheel. You can get more tension if you have a rim with eyelets, which the KH does. You may want to find a handbuilt wheel (or otherwise) and compare the tension on those spokes (make sure it's a 26" wheel you're comparing it to, because the same tension on 2 different sizes feels different) to tension of the spokes on your wheel. A good bike shop can also lend you a spoke tension meter for a few moments, and you can use this chart: http://www.parktool.com/blog/repair-...icle-section-4

In my opinion... and it is an opinion... I wouldn't run a unicycle wheel less than 105 kilograms of force. The site gives some fuzzy ranges so you can gauge for yourself what you think is appropriate given comparisons to other parts. The KH rim is very stout though, and can take the high tension, whereas a single-walled marge lite rim, not so much.
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Old 2015-09-25, 08:24 PM   #4
janvanhulzen
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Both spokes snapped near the hub, probably at the bend. Also the spokes were close to each other with one spoke in between and they both snapped of on the left side. In between the broken spokes is the left pedal. This makes kind of sense since i mount starting with my left foot. So in hindsight i think at least one must have snapped during mounting.

When i got the unicycle i checked the spokes and they appeared to be tight enough. The wheel was straight and the box was in good condition. I did UPD a few months back and the unicycle made a dzoink sound when falling instead of the usual thud.

An interesting read is the following:

http://www.astounding.org.uk/ian/wheel/
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Old 2015-09-25, 08:33 PM   #5
bouin-bouin
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can we get photos to see which hub you are using ?
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Old 2015-09-25, 09:16 PM   #6
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spokes breaking at the elbow are almost always because of fatigue due to movement during riding. Unless you have a loose flange or something odd the usual cause is low spoke tension.

I don't know what tension KH rims are spec'd for, but most modern rims are designed to have tension in the ballpark of 120kgf. The actual number you need is a rim spec, not a spoke or hub spec. As a general rule anything over 100kgf seems to be good enough to keep tension on the spoke during the cyclic loading/unloading of the wheel. The problem arises when the spoke goes slack as the wheel unloads during riding. That leads to the movement that causes the fatigue.

It is unfortunately not uncommon for wheels on new unicycles/bicycles to have low spoke tension. These wheels are almost always built on a machine, and hardly ever finished by hand. This oversight cuts a lot of cost, and is normally not discovered due to lack of use by the end buyer. If you replace the two broken ones and have the wheel brought up to the appropriate tension you should be okay. If you then continue to break spokes you should go ahead and get a whole new set and a new wheel build. You may want to see if you can get the wheel serviced/replaced under warranty (and have the new one checked for tension before you take delivery ).
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Old 2015-09-26, 12:13 AM   #7
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Quote:
Originally Posted by jtrops View Post
spokes breaking at the elbow are almost always because of fatigue due to movement during riding. Unless you have a loose flange or something odd the usual cause is low spoke tension.
It's also possible that they just weren't stress relieved at all, but just doing that is going to drop the tension that's already on the spokes significantly.

(to stress relieve spokes, take a wrench or crank arm and put them between crossing spokes and twist them around each other, bringing the tension up and setting the spoke, usually done while building the wheel a few times. I also used a hammer to flatten the spoke bend so that it meets the hub flange on the one build I did. Overall this makes for less movement, and thus no breaking at the bend. . . at least from what I've read.

A more experienced builder may have more insight.
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Old 2015-09-26, 02:06 AM   #8
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jtrops = experienced builder.
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Last edited by Killian; 2015-09-26 at 02:07 AM.
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Old 2015-09-26, 02:29 AM   #9
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Good suggestions above. I'll add that I've had spokes break because of a one-time event, maybe something that happened while storing or transporting the unicycle, or something jammed between them during a muni session perhaps. Unless there's an obvious problem with the wheel, you might just replace the broken ones, true and check tension on the wheel, and see how it goes before trying a more drastic remedy.
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Old 2015-09-26, 07:00 PM   #10
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Quote:
Originally Posted by juggleaddict View Post
It's also possible that they just weren't stress relieved at all, but just doing that is going to drop the tension that's already on the spokes significantly.

(to stress relieve spokes, take a wrench or crank arm and put them between crossing spokes and twist them around each other, bringing the tension up and setting the spoke, usually done while building the wheel a few times. I also used a hammer to flatten the spoke bend so that it meets the hub flange on the one build I did. Overall this makes for less movement, and thus no breaking at the bend. . . at least from what I've read.

A more experienced builder may have more insight.
What you are describing as "stress relieving" is the one factor that I think leads to machine built wheels failing more than anything else because it gives a false impression of adequate tension. I prefer to think of it as "setting" the spokes so that the spokes run true between the hub and the rim. Also it helps bed the nipple, and the spoke head. if this isn't done, and the wheel is relying on tension alone to straighten the path of the spokes it leads to problems because the spokes are constantly wanting to spring back to their rest position. So, by setting the spokes it makes a new rest postion that is aligned to the direction of pull that the wheel exerts on the spoke. As a result the spoke will stay aligned even when the tension is reduced during cyclic stress. As long as there is enough tension to keep the spoke from going slack it won't move.
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Old 2015-10-15, 12:13 AM   #11
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My spokes have been snapping at the elbow ever since I did my first wheel rebuild, and the one that broke today was next to some others that have been getting very loose, although my (20") wheel does not appear to be much out of true, even with a missing spoke. Side hopping is generally what I am doing (or have just done) at the instant when a spoke breaks. Longer sidehops than those used to just climb the stairs seem to be especially problematic.

I have been marking each replacement spoke with a tiny piece of Scotch tape just to "keep tabs" on them, but there haven't been any repeat offenders, and now I have 7 marked spokes! I have a stash of 20 more replacement spokes, so I guess I could order 20 more and rebuild my wheel, but now that Jtrops' post (above) has informed me that loose spokes are the problem, I am tempted to just replace the one that broke today and then crank all those bastards til they're nice and tight...
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Old 2015-10-15, 02:29 AM   #12
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My 29" needed serious help

When I got my 29" KH last year, I constantly heard clicking from the wheels. I took it to a dedicated wheelbuilder and she said that not only was the tension low, but that it was "all over the place". She tensioned the wheel and it has not made a peep since, not have I broken any spokes. It is worth taking the wheel to someone who knows what they are doing to tension and true before spokes start breaking.
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Old 2015-10-15, 03:03 AM   #13
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Spokes are over-rated. Just remove them all.
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