05-19-2019, 05:30 PM
(05-17-2019, 10:47 AM)The ferret_imp Wrote: That's a shame that happened.
Spoke breakage is not common but not rare either. The early Bonnevilles 2000-2003 had the issue so often the forums were asking for a recall. It happened to my 2003 Centenial Edition Bonnie as well. I went around a left hander and felt a pop, then more pops and the back end got all wobbly. Had probably a dozen or so broken spokes all together. Triumph thankfully paid for a new wheel.
Right now there is a internet blog of a guy on a BMW GS who's front wheel spokes all disintegrated on him. More reports of similar problems followed. They are wanting a recall on BMW spoked wheels.
Spokes are like the span of a bridge. EAch spoke shares and spreads the pressure between them. If one spoke goes, that puts extra pressure on the remaining spokes, which end up flexing more than they are designed and then another breaks, putting even more pressure on the remaining spokes. pretty soon it's a lost cause and most break.
Spokes look good, they flex making the ride softer, but they also sometimes break.
Well... spokes are like "stay-cables" on a bridge. The work in tension only, so they don't flex: they just stretch.
Preload on them has to be high enough so load cycles are small and fatigue is minimized (load will be small compared to tension, so cycle amplitude is small). If load is to high, you could have metal yield (so tension becomes VERY low), ir it can just snap (this depends on the alloy). In any case: spoke preload is VERY important.
Without knowing this case, I'd point the probable causes to be:
-wrong servicing (i.e. bad preload on spokes) -> most probable
-bad batch of spokes -> unlikely: we would have heard of more.
-corrosion failure -> unlikely: we would have heard of more.
-bad design -> VERY unlikely: spoke rim design is not exactly a new unknown technology
This is just my opinion, but if I had to bet... this failure can be from something very simple like a unit conversion problem from [Nm] to [lb·ft].
I'm glad nothing irreversible happened!
Some interesting info I've just found regarding spoked wheels:
http://poehali.net/attach/Bicycle_Wheel_...Brandt.pdf
