9 spokes exploded out building a wheel.

[Offroader]

Had really bad luck building wheels. Decided to use a dirtbike prowheel rim. Used 13 gauge sapim spokes and dirtbike steel nipples.
First wheel build I didn't tension the spokes enough as I noticed a couple of loose spokes after my first ride, I tightened those up when I should have re tensioned the whole rim. This wasn't my first wheel build and I really thought I had a lot of tension on those spokes.

During my next ride, I was practicing riding stairs and was beating the rim badly, noticed instability of the bike and it felt like my motor axle was broke on my cromotor as I noticed play when grabbing the rear wheel and pushing it side to side.

When I got back home I noticed a whopping 11 spokes were broke at the elbow, at least 9 of them were all together so I had a big chunk of the rim without spokes. I am surprised I was able to drive home over 25MPH with that many broke. I think they may have gotten wedged into the cromotor a bit as they were not loose and maybe that offered some support.

anyway, ordered some new 13 gauge spokes and decided to retention the wheel tighter this time. I was really tensioning them down, but many spokes turned fairly easily with the spoke wrench so I didn't think I was over doing it. The spoke wrench was a dirt bike spoke wrench so it is very big and easy to apply torque unlike those park tool bicycle spoke wrenches.

Anyway, when I went to true the wheel vertically, I noticed that tensioning down the spokes above a high point didn't cause that high point to lower. Then I just decided to true horizontally. While tightening down one spoke to true horizontally I heard a big explosion and shattering noises all around my garage. 9 spokes at the same time broke off at the elbow and shot out of the rim with the nipple attached. Still can't find 2 of them.

luckily they blew out towards the floor and not towards my face. Next time I will be wearing safety goggles, who would ever think you needed to wear safety goggles when building a wheel.

I just ordered 11/12 gauge spokes, which are a lot thicker at the elbows. Hopefully I won't over tension these things.

 

[biohazardman]

Up and down stairs with a Cromotor and a bicycle rim? Lots of torque lots of weight and huge stress on the wheel. Yes, I would expect some sort of damage. Sounds like you may have way to much tension on the spokes if they break while building the wheel as you describe. Might want to do some more research on wheel building as well to see if your spoke fit is proper at the hub and how tight things need to be. If you tension spokes on one side of the wheel you need to loosen them on the other to get your desired outcome. If you get stronger spokes you may be able to tighten them enough to pull the nipples through the rim? Maybe check out what others with similar builds are doing for wheels. If all else fails you can always do a moped rim build. Several here have done so with good results. I wish you luck with your build.

 

[dogman dan]

Surprised that you didn't just pinch flat a tire.

Hardtail? Lot of broken spokes for a good FS. I'd rather have lower power, than run a hubmotor that weighs more than 15 pounds on my local rock staircases.

 

[MadRhino]

Uneven tension kills the spokes, and sometimes the rim too. I ride the stairs (and worse) frequently with a cromotor in a 24" Halo SAS bicycle rim laced with 12ga Sapim spokes, rim and flange brass washers, big brass nipples, 3" Duro tire. My wheel had seen 2 complete summer season, riding almost 1000 Km a week, about 20 tires and tubes, riding hard and fast.

Buy the good components, build it perfect, maintain it often, and it will last. Riding hard requires proper tuning and maintenance, not only for the wheels.

 

[cal3thousand]

Sounds like the other spokes that weren't fully broken during the ride home developed some stress failures. Then, when (over) tightening, the compromised spokes gave out.

Here's some things to think about during wheel build:

• When truing, it's not always a tightening adjustment. Sometimes, you need to loosen other spokes on the opposite side instead.
• You should have a tension gauge when building wheels unless your manual tension reading skills are amazingly well tuned (That only comes with building dozens and dozens of solid wheels, and I definitely don't have that skill yet, but my wheels are still bulletproof)
• 11/12 Gauge spokes won't be necessarily stronger than 13G spokes since they won't stretch as much.
• Those spokes failed not due to overtension, but first fatigue, THEN overtension
• Make sure to stress the spokes after building the wheel and before giving final true, otherwise you may end up with the same situation

 

[fechter]

How do you go about stressing the spokes?

 

[johnrobholmes]

The wheel in question is using a moped rim. The failure was indeed set into motion with loose spokes and stair riding. I would assume the spokes were not cold set during building, and so came loose. After the first break, the wheel becomes unstable and more spokes break. In this case, 11/12ga swaged spokes will be a good match for the cromotor and dirtbike rim as proper tension can be used.


Cold setting = stressing the spokes. While building the wheel and increasing tension, the spokes need to be forced into place. It is done so the rebounded position has no bending forces within the spoke. Spokes that have not been set look "fluffy". There are many methods. Sheldon Brown's website goes over it.


I don't use a tension gauge (deflection gauge) for building wheels. I have before, but it doesn't give me useful information. Not a single deflection gauge on the market is calibrated for what I typically build, nor do some even fit inside cromotor wheels. I do want to build one for my needs though, I would like to have an increased accuracy. Along with the meter would have to be a calibration stand too, so it would be a nice project.

 

[johnrobholmes]

Here is a "fluffy" wheel. Pic was taken for the customer mid build. The outer spokes have not been set yet, and curve from flange to rim. A wheel ridden like this would lose tension quickly.

This wheel has been set. The pattern is a bit different, but the concept is the same. Straight lines, tight bends, no curvy flexy sections.

The closer radial spokes were trying to bow into place just like the blue wheel. I had to wrench the spokes slightly past the nipple hole, so when they bounced back it was on center. Tight bends at the flange, straight shot to the nipple hole after.

On a steel flange I will use a small rubber mallet if a wrench can't be used. On alloy flanges it is best not to hammer, but they are also typically paired with smaller spokes so bending is easier.

 

[cal3thousand]

^^^ Excellent info from a Master wheel builder ^^^

Put it in Evernote fellas :wink:

 

[friendly1uk]

I have never had a wheel that could make use of a tension gauge. I treat each spoke differently, guided by what the rim is telling me. I do find that going for perfectly round leaves some spokes looser than I would like, but I don't like to compromise how true it sits. Even if it does lack a little integrity as a result.

So far I have never snapped a spoke. I keep waiting for the learning experience, but no, nothing. Why do I even carry a spoke spanner everywhere. Maybe if I leave it at home they will all bust lol


Really can't fathom how peeps bust them. You would have to fit a cromotor and bounce it down stairs or something.

Oh.. wait up.... lol

 

[spinningmagnets]

Did you take any pics of the broken spokes? Please post them, it may be helpful to future researchers...

 

[Gregory]

Maybe a dumb question JRH. If radial lacing the drive side of this wheel why not run the spokes through the inside of the flange so you don't have to bend them over it to get a nice line to the nipple? Or does bending over the outside of the flange give a stronger wheel?

 

[Tench]

I recently laced a Crystalyte motor and found that one way the spoke had the right length between bend and head, inserted from the other side they would have required washers so I did mine all one way. the difference was created partly by the spoke angle and partly by the depth of countersink being different on the inside and outside of the flange. A different set of spokes may have fit better the other way round. It depends on many factors. Small rims on big hubs give you the least number of options.

 

[johnrobholmes]

The half radial wheel is on a 4 wheel h2 race car. Radial for side loads, and laced outbound to increase brace angle which reduces lateral rim movement for a given load.

 

[Gregory]

Thanks mate. Its those subtle secrets that make wheel building so mysterious to me. I thought it may be the increase in angle but wasn't sure how much that few degrees would help.

 

[zombiess]

And this is why I pay volt riders to do my custom rim builds. There is some art too it and the further you stray from the norm... Ebike hub motor builds, the more you have to really know what you are doing.

Warp9 rim with a Cromotor looks sexy.