Unique hub failure
 

A bike came into the co-op last week with a rear wheel issue.... Rim is 559 SunRim CR-18, 32 hole, laced 3x w/14 gauge straight spokes on a Ringle hub. There is no evidence of stress at the rim eyelets or visible rounding of nipples from excessive tension during the build.

I've seen broken flanges but never like this. 6 pair of spokes on NDS and 4 pair of spokes on DS all fractured themselves to freedom. The failures, on both sides of the hub, were in 2 separate locations? Sorry, I could not get the NDS picture to load-it's similar but has more damage.

Spoke tension for the remaining spokes on the DS measured from an average of 117 KGF to (185KGF?) two blank boxes above the numbers on the Park Tensionometer conversion chart. NDS averaged 117KGF as well w/a couple hitting 131KGF. Spokes all end very close to the slot in the nipple.

I've built low spoke count wheels and understand higher tension for low spoke counts.

Are the high loads on this hub the cause of the failure or did the tensions rise with the release of the spokes that broke out of the flanges?

What else can I learn from this gem?
Thank you.

Attachment 594082

Well, Ringle wasn't really known for their durable parts. Light weight yes, super long lasting, no. If you look at the hub flanges you'll note the close to the flange's edge that the spoke holes are located at. Check out other, more current, hubs and you see more flange edge to spoke hole material being the usual. The late 1990s to just a few years ago of radial spoke pattern trends have made the current hub companies a bit more aware of what's good weight savings and what's not so.


Additionally if your drive side has about a 150% difference of spoke tension ON THE SAME SIDE it speaks to the rim being in bent enough condition to look straight at the expense of massive spoke tension unevenness. 185KGF is really high spoke tension, I wonder if Ringle ever had a suggested max tension.


Last is the 14g straight spokes being used on light weight hubs. One reason why butted spokes are often a better choice is that they tend to have more elasticity, allowing lower static tensions yet still keeping the least tension moments high enough to not suffer nipple unwinding.


Just some thoughts. Andy

...just thinking about it, I'm not certain it's possible for some of the spokes to increase in tension in this way.
Certainly, some of them lost a lot of tension as the ones that broke that were balancing them broke loose.

And when I see some sort of damage like that, where a few spots on the flange have broken at the same time, my mind always goes to some sort of incident, like a crash or a very hard landing off a curb.

Is the rider a really big guy who likes jumps to get air time?

Bike was donated but I wasn't in the shop and didn't get to meet the owner.

There was no sign of any damage to spokes or rim.
I'm not an engineer. IF a wheel had a total KGF of "X" and several spokes were cut, do the remaining spokes pick up the slack, leaving the force at the same level or does the "total KGF" drop?

If one has a wheel like this (excuse my crude drawing).

Attachment 594124

Deletes the dashed spokes.

Then the two red spokes at the bottom will increase in tension due to being the only spokes that compensate for the black spokes on top.

The tension of the black spokes will likely decrease slightly (fewer spokes pulling on them).

One might expect the wheel to naturally taco somewhat, which I presume would also decrease tension. However, if one deletes the spokes symmetrically, then in theory, one could have a moderately true wheel that would remain.

Oh, I could also imagine field-truing a wheel that just lost half the spokes in a crash :eek:

I vote for a poor quality hub flange.

Wouldn't call it poor quality, as these were high end boutique hubs BITD, and that's the problem, this hub is from the early 90's, and time has caught up with it, add to that, and from the comments on the facebook post about this specific hub, there was a design issue with the flanges.

Those flanges in the photo appear to have mighty little depth.

For Shimano, by the 90's and fat center spindle, most of their flanges were also made much thicker.

hub design & execution left insufficient metal outside of the spoke holes..

one more cross, where the spoke passes over the head of it's neighbor and It May have survived longer..

But as a MTB wheel on fast single track? maybe not.





;)

It also helps if the hubs are forged and not simply machined from stock.

You can also get forged billet as well. Most likely not used in this case though.

"Spoke tension for the remaining spokes on the DS measured from an average of 117 KGF to (185KGF?) two blank boxes above the numbers on the Park Tensionometer conversion chart. NDS averaged 117KGF as well w/a couple hitting 131KGF." Rubato


Does anyone else see the tension issue that I mentioned? For a wheel to have a 50% difference of spoke tension on the same side and not be out of true means that it took this inbalance of tension to get the rim to look straight.


As a data point with another but current high end hub maker- I sent back to the hub company a 36* wheel with a Mavic Open Sport rim which was loose in the bearing adjustment. This brand of hub uses angular contact bearings with a threaded pinch collar to hold said adjustment. This adjustment range was "used up" yet the bearing was still loose. Turns out that the 115-120 kgf with 36 spokes (14/15 butted) was too much outward force for the hub to resist and the bearing seat in the hub shell had opened up so the bearing was loose in the seat. The hub company installed an oversized bearing and all is good for the few years that have gone by. Who would have thought a high end hub would have an unwritten max spoke force (and one well within some rim limits) amount after which the shell would expand enough to render the brand's design unable to tolerate it. Andy

This can happen if you have the "off by one hole" error when lacing up rim. Or yes, rim was taco'd and they tried to straighten using spoke-tension only fix.