Kh36 w/ Kh Schlumpf -- spokes problem

Unicycles and Equipment
1

3 months ago I bought my dream machine ; a Kh36 schlumpf !! After 1 days using it, I broke a shifting pin from my schlumpf and then I had to feel dumb for about 6 weeks having to dismount evrytime I wanted to downshift. :angry: Finaly the new shifting pin arrived and evrything was perfect, except 6 broken spokes over 1500 km done. In the next 1000km (last month) I broke 14 more spokes, feeling dumb evrytime I had to stop and true the wheel again with a new spoke. :angry: At the moment I cant use my 36" anymore, with 4 spokes missing, and my new spokes not received yet.

What can be the problem ? Evry broken spokes lost his head (round part near the hub). Is it about spokes tension too high or too low, or am I only a bad lucked one ? :thinking:

ps: I rode 4 years with some Kh24 and never had I broken spoke! :roll_eyes:

2

Hey. I have a 36 KH/Schlumpf Super Guni and I too break a significant amount of spokes compared to all my other unis. Iā€™ve gone through maybe 8 or so broken spokes in a year, compared to 1 the year before. I think for me my feet are popping the spokes when I ride at high speed and try to brake quickly (I donā€™t use a brake) or when I UPD (sometimes that gets messy). But I have wondered if the hub puts more pressure on the spokes compared to a typical hub. I never broke a spoke in my regular Coker and I rode it many thousands of miles. Now I definitely keep spare Coker spokes handy. I just broke another one yesterday!

3

you could trying using spoke washs. to keep your spoke heads from breaking off so easly. Oh i dont ride a geared you by the way

4

Hey, I have been braking many spokes on my ungeared 36er. They also broke at the hub part. People recommended me to put brass washers on all spokes in order to solve that problem. While it did help I still brake a spoke on the 36er once in a while. Never had this problem on my other unis either. So I donā€™t know but I think maybe the 14G spokes are a bit too weak for 36ers.

5

FWIW (I donā€™t ride a guni - mineā€™s just a normal Nimbus ISIS hub), I donā€™t think the 14g 36er spokes are generally weak. I did have a nipple break just after the wheel was built, but no trouble since so I put that down to a bad nipple. No problems with spoke breakages, even though I ride it mostly xc and hump it up some pretty steep hills on ā€œlongā€ 145 cranks. My wheel was built with spoke washers though, which does help a bit if the flanges are thin.

Rob

6

I suggest paying a decent wheelbuilder to sort the wheel out - they wonā€™t be phased by the unusual wheel and do a proper job on it - even if you provide the spokes heā€™ll be able to supply washers if needed.

7

has anyone tried tying and soldering the spokes on a coker wheel? I know there are some fairly dubious tests that were done which showed no perceptible difference in stiffness over a non tied and soldered wheel, but I also have read many accounts of people who didnā€™t break as many spokes after doing it. While the overall stiffness might not change, I can understand the reasoning behind the apparent gain in strength at the spoke head. One wheelbuilder suspected it was because the stress was distributed over the two spokes at once instead of being solely on the single spoke. Another theory is that there is less ā€œwind upā€ in a tied and soldered wheel. Either way there seems to be pretty good consensus on spokes lasting longer when they are tied and soldered.

It seems like the uni wheel is much more like the penny/farthing wheels that were originally tied and soldered, so it makes sense that this old technique might be applicable. Interestingly, the reason the hi wheelerā€™s were tied and soldered had to do with spokes breaking and not adding strength to the wheel.

8

IF you are going to rebuild your wheel, check that the holes in the hub are deburred properly. They probably are but it wont take long to look. I think that it would also be good if there was a butted 13/14 guage spoke avaliable for 36 inch wheels. The bent end of spokes are always the weakest so this would help a bit. Unfortunately our market is probably too small to have such custom drawn spokes avaliable.

I was recently thinking about doing some research into tying spokes because of the flex in my 36er wheel so i think I will now. If I remember correctly I think Lunicycle had tied spokes on his ā€œ29er Freerideā€ wheel. I will try to find a link.

9

Here is the link. He doesent actually refer to the spoke tying in his review, I just noticed it in the picture. You may be able to contact him for more info.

10

Thanks alot for all the hints !

Iā€™ll try out to add washers, but am I supposed to remove all spokes and rebuild the wheel to do so ? Or can I take out the spokes 1 at a time, add the washer and reinstall them ?

Also Iā€™ll take a look in the holes to be sure they are deburred properly.

Thanks again!

11

Yes, thatā€™s the way I did it. I remembered the pitch of the spoke before removing it, added the washer and retightened it to the right pitch. That way it should keep the rim at the same tension as it is now.
Make sure to get exactly the right washers for your spokes. They should fit perfectly otherwise they wonā€™t fulfill their purpose very well.

12

If youā€™ve not done it already, it may be easier to do a few spokes at a time: detension the whole wheel first and you can see that the spokes are in groups which will make the re-lacing easierā€¦

13

It is really important to detension the whole wheel first as Mike pointed out. If you are doing more than one spoke at a time you can put serious stress on the hub flanges if you donā€™t detension the wheel first. I went to a Campagnolo training a long time ago where they insisted that clipping spokes would weaken the hub flanges. I donā€™t see a lot of difference from a stress point of view.

I would detension the wheel either way, as you will have to tension and true it anyway once you are finished putting the washers in.

14

So whatā€™s wrong with doing them one by one and tuning them back to the same pitch as before? Thatā€™s what I did, no detensioning or truing needed at all.

15

There is probably nothing wrong with it. I can only assume that you have logged many miles with your wheel tensioned this way and that your wheel is still holding strong.

I have built hundreds of wheels, and for me it is very little work and time to build a wheel. I canā€™t say that I have any data to support my ideas, but I think that if you are going to replace the spokes in a wheel, or in this case add washers, it will be a stronger more reliable build if you tension it and true it at once rather than spoke by spoke.

Unless you have ā€œperfect pitchā€ it is somewhat unreliable to gauge tension by the sound that the spokes make. Itā€™s hard to say if that technique is better or worse than squeezing the spokes together. I wonder how sharp or flat the sound needs to before there is enough tension variance to make a difference. It might be possible that the tension could be dramatically different with only a subtle, imperceptible, change in the pitch.

16

As a musician I do have very close to perfect pitch and I really tuned the spokes back as precisely as I could. The idea of disassembling and reassembling the whole wheel just scared me too much to give it a go. And it stayed true that way, so it worked alright for me.

17

Broken spokes on 36er GUNI

Here are my 2 centsā€¦

The loads on the spokes of a 36er are substantially higher than smaller wheels, simple function of the lever. And when you increase the speed due to the geared hub, the loads multiply to the point where the spokes are continuously over stressed until they unlimately break.

Now here are a list of actions that can be taken to reduce breakage:

First, you need to start with quality spokesā€¦chinese spokes use junk steelā€¦I do not trust any spokes without a reputation for proven quality. If I start getting spoke breakage on my 36er, I am going to have DT Swiss cut me custom spokesā€¦

Second, once the wheel is built, spoke tension becomes absolutely critical. The longer the spoke the more often it will need to be retensioned, because as the spoke is ridden, it will continuously stretch, get longer. Find a bike shop with a tensiometer, and monitor the spoke tension every 250, 500, 750 etc. kilometers. At the beginning, the spokes will stretch more and will need to be retensioned more often. In my experience, after you build a wheel, especially a 36er, the wheel will need to be retensioned (retrued) after every few rides, until fully stress relieved.

Third, washers between the spoke heads and hub is a solution that has been discussed in previous posts. However, one detail that was missed is counter sinking the spoke holes in the hub to match the head of the spoke. The reason for brass washers is the friction between the spoke head and hub is substantially reduced. The washer serves as a bearing.

Fourth, wrapping the spoke intersections with wire and soldering the wire wrap has also been discussed in a previous post.

Items, three and four would be considered old school wheel building. These methods were common for race bikes, road, mountain and particularly track bikes up until the late 90ā€™s. In 2009, the materials and hub, spoke and rim designs for race bikes have substantially improved to the point where these methods are not needed or cannot work anymore.

There is a great book The Art of Wheelbuilding: A Bench Reference for Neophytes, Pros & Wheelaholics (Spiral-bound)
by Gerd Schraner. I consider this the best refernence on wheel buildingā€¦

18

Iā€™m not convinced by that theory. Putting washers under the spoke heads pulls the spoke closer to the hub flange, making for a stronger interface (less likely to snap the spoke elbow). Itā€™s a compensation for when the spoke elbow is too long for the thickness of the flange. It does reduce spoke breakages, but IMO not because of a ā€œbearing for the spoke headā€ - that is implying that the spoke head rotates in the flange hole and eventually sheers the head off, which I canā€™t imagine happening. Spokes usually break at the elbow bend.

Rob

19

I have > 600 miles on my KH/Schlumpf 36er and I havenā€™t had any problems with breaking spokes. I used brass washers (recommended by Corbin) and had the spokes cut by UDC USA and the wheel built by a bike shop.

FWIW I have never broken a spoke on a 36er. I havenā€™t taken the geared 36 offroad much, but my ungeared 36er I use only for muni now and I have had no issues with the spokes at all.

Find a good wheelbuilder (ask bicyclists in your area who they would recommend) and I am sure the wheelbuilder will be thrilled to work on building a 36" wheel. My LBS was more than happy to build a custom truing stand and work on building the 36" wheel up. He said he was glad to work on something different and only charged about $30 for the work he put into it.