rear wheel failure

[scottmastrocinque]

Not out of line at all! I apologize that I even caused you to think that. Pardon me please.

We are all just speculating at this point.

I would just love to have 10 of these bikes side by side, where I could tap the spokes with a drift, and listen to the resulting tones.

I’m betting that instead of them sounding almost identical, they are all literally over the place.

What would be even more telling, is to do that to a brand new one still on the showroom floor.

 

[JasonC]

So the heads on the spoke nipples failed rather than the nipples pulling through the mounting holes in the hub?

If this is the case, this type of failure is really unusual.

I have experienced multiple spoke failures on an assortment of vehicles from Jaguar to bicycles. In these failures the spoke, not the adjustment nipple failed. The two failure areas are at the thread root on the spoke or at the bend on the opposite end of the spoke. The thread root is often the thinnest cross-section on the spoke, hence it will experience higher stress than the spoke body. And the bend in the spoke may have residual stress from being formed and additional load may over stress this area, causing failure.

But never have I seen the head of the nipple fail as it typically has considerable shear area compared to the spoke.

Are any pictures available of the failed spoke nipple, assuming it is the nipple that failed?

Jason

 

[scottmastrocinque]

The photos on page 1 are consistent with the damage I would expect from loose spokes causing the wheel to flex out of round, and then the associated slackening and then immediate violent tugging as the wheel experienced centripetal vs. centrifugal forces during the rotation.

This push-pull would break the spokes at the threaded end and also at the peened head end. Once two spokes died in this fashion, the wheel would have immediately become out of round and unstable. After this, the point to complete failure would have been no more than a couple seconds later and very sudden which is how the OP described it.

 

[GerryAZ]

I noticed that several spokes visible in the photos have the threaded portion of the adjustment nipple still on the spoke with the large head missing. I also looked at the holes in the hub in the photos and did not see any indication of failure of the hub itself. I had to look at my rear wheel to see what they look like without damage. Since the heads broke off of the adjustment nipples, I speculated they were overstressed.

Scott’s explanation of how the failure could progress is very helpful. I have a little less than 4,000 miles on my bike and will tap all of my spokes this weekend to see if I can learn anything. Unfortunately, my hearing is not as good as it once was and tires on the rims may dampen the sounds.

 

[scottmastrocinque]

In a properly assembled spoke wheel, you should expect the pitch of each spoke to be very close to each other. If you hear, "ting", "ting", "ting" "bonk"...then something is amiss..

 

[GerryAZ]

Do you think I should carefully tighten the ones that go “bonk” if there are a few? I did check the wheels when the bike was new to confirm they were true (no run out). I don’t know of any shops near me that specialize in wheel truing. I am familiar with tuning by sound, but have not done it for a long time.

 

[JasonC]

Since the heads broke off of the adjustment nipples, I speculated they were overstressed.

There is no doubt the nipples were over-stressed. Again this is an extremely odd failure mechanism because the nipple is typically not the weak link.

The question in my mind remains: what was the failure mode?

I squeeze my spokes as a quick check for loose spokes. Keep in mind that the rear wheel rim is typically offset and the spoke tension will be different from side-to-side. So keep this in mind if you opt for the spoke pinking method, as one side will produce a different tone than the other side.

Jason

 

[scottmastrocinque]

Do you think I should carefully tighten the ones that go “bonk” if there are a few? I did check the wheels when the bike was new to confirm they were true (no run out). I don’t know of any shops near me that specialize in wheel truing. I am familiar with tuning by sound, but have not done it for a long time.

I don't give advice on spoke wheel maintenance because it's a loose cannon topic, like oil threads. Everybody has an opinion yet precious few actually know and understand.

You have to use your best judgement.

This is a good video to give you an idea of how to evaluate and GENTLY tighten loose spokes. LESS IS MORE! SMALL INCREMENTAL TURNS. NOTHING BIG!

Please click WATCH ON YOU TUBE to avoid burning bandwidth on GuzziTech. Thanks!

 

[JasonC]

I wonder if hydrogen embrittlement could have been the failure mode?

I've seen evidence of hydrogen embrittlement on several occasions, which caused catastrophic failure of bolted connections.

High-strength fasteners that are plated with zinc or cadmium or other protective coatings that are "plated" can trap elemental hydrogen in the grainular boundaries of the steel. The trapped hydrogen then begins to expand and sets up a stress in the steel. The result is failure of the component at stress levels less than the material's yield strength.

You may have noticed that socket head cap screws that you purchase at the hardware store are are coated with phosphate rather than zinc or cadmium. The reason is that the material that the cap screws are made from is susceptible to hydrogen embrittlement if plated with a protective coating. Notably hydrogen can be baked out of the material by heating it to an elevated temperature and allowing time for the hydrogen to diffuse out of the steel. It can then be plated without trapping any hydrogen in the steel. However, to keep costs down, your hardware store socket head cap screws a merely phosphate coated, which does not trap the hydrogen.

So, if the spoke nipples are made from carbon steel with a yield strength of about 135kpsi or greater and then plated, hydrogen embrittlement could be the failure mode.

Jason

 

[tobinh]

looks like some of the spokes detensioned to me, leading to the scenario scott describes above. you see it in bicycles sometimes, far more rarely in motorcycles because everything is just larger, heavier and stiffer.

spokes must be checked for tension at regular intervals.

 

[JasonC]

looks like some of the spokes detensioned to me, leading to the scenario scott describes above. you see it in bicycles sometimes, far more rarely in motorcycles because everything is just larger, heavier and stiffer.

spokes must be checked for tension at regular intervals.

So how did you determine that some of the spokes de-tensioned?

Jason

 

[davethewelder]

Scott, good video. Even a welder can do it!

 

[tobinh]

So how did you determine that some of the spokes de-tensioned?

Jason

I didn't. there's just a pretty short list of things that go wrong with spokes wheels. as I said, you see this in bicycles all the time. well, not *this* exactly, but this is one of the scenarios that can result from spokes detensioning.

 

[JasonC]

I didn't. there's just a pretty short list of things that go wrong with spokes wheels. as I said, you see this in bicycles all the time. well, not *this* exactly, but this is one of the scenarios that can result from spokes detensioning.

Hmm, I'm an avid bicycle rider and have built dozens of bicycle wheels and have ridden many many bicycles with wheels in various states of tension have never experienced a total "zipper" effect that we have seen here.

Perhaps you're a more experienced wheel builder and bicycle rider than I am.

Jason

P.S. Nor have I ever seen the head of a spoke adjuster separate from the shank on ANY spoke -- car, bicycle, motorcycle, etc.

 

[tobinh]

Hmm, I'm an avid bicycle rider and have built dozens of bicycle wheels and have ridden many many bicycles with wheels in various states of tension have never experienced a total "zipper" effect that we have seen here.

Perhaps you're a more experienced wheel builder and bicycle rider than I am.

Jason

:|

of course a bicycle is not going to pull out this many, because people do not make as much horsepower as motorcycles.

 

[Davy]

I have never owned a V7 so this may not have any merit; -
A number of years ago, on my Cali, I was slowing gently for the traffic in front, down to about 15mph. Then on accelerating as the traffic cleared the bike wobbled at just over 20mph. Thinking I had a puncture, I stopped to check, and couldn't see anything. It got worse, so I checked more thoroughly, there were a number of loose spokes. When I got home I took the wheel and the tyre off and discovered 13 broken spokes (heads off at the hub end).
My guess is that the drive plate in the hub had stuck as it took a puller to remove it and spokes broke because of shock loading. So every time I replace a tyre the drive plate gets cleaned and lightly greased, it has never happened again.
I have asked around and nobody had heard of spokes being broken in such a manner.
Hope this helps and doesn't confuse things even more.

 

[GerryAZ]

I finally took time to check the "tune" of my rear wheel. The bike is 15 months old and had 3511 miles when I checked the rear wheel this afternoon. Don't criticize me too much for the low mileage--I have too many toys and not enough time to play. Almost all of the spokes sounded the same when struck with a metal tool. The ones on the left side have a slightly different pitch than the ones on the right side because of the offset. There were a couple of spokes that had slightly lower pitch than the rest so I would have tightened them if it were possible without removing the wheel. Therefore, I will be carefully inspecting and adjusting the spokes whenever I have the wheels off.

Each spoke has a flat spot to accommodate a spoke wrench which should be used to hold the spoke while turning the adjustment head (Moto Guzzi parts catalog calls them nipples). There are 36 spokes and nipples in the rear wheel. The nipples have hex wrench openings for turning them, but they are not accessible with the wheel installed. The ABS tone ring needs to be removed to access the nipples on the left side of the hub.

 

[JasonC]

When I got home I took the wheel and the tyre off and discovered 13 broken spokes (heads off at the hub end).

I assume the spoke adjuster/nipple reacts against the hub on your Cali, rather than the rim?

And if so, when you say "heads off at the hub" you mean that there was a failure at the thread root on the spoke, causing the complete nipple to separate from the spoke?

Jason

 

[Dinsdale Piranha]

II saw a lot of rust on the wheel and the spokes.

I'm pretty sure that aluminium and ss don't rust. There's clearly some dirt there from the gravel road he was on though. 9,xxxKm is not much. Surely it's a manufacturing or material fault?

 

[Dinsdale Piranha]

The ones on the left side have a slightly different pitch than the ones on the right side because of the offset. There were a couple of spokes that had slightly lower pitch than the rest so I would have tightened them if it were possible without removing the wheel. Therefore, I will be carefully inspecting and adjusting the spokes whenever I have the wheels off.

I've NEVER seen spoke nipples on the hub of a wheel. Doesn't mean it hasn't been done, but it must be rare as rocking horse shite. You can get purpose made spoke wrenches, which definitly make it easier, but are, by no means, essential. I've not seen what obstacles you have on the rear of your bike, but I've also never seen a spoke which can't be adjusted (on a bike).

I've no idea what manner of obstructions are on the rear of your bike, but if you can attach a tyre pump connector to your valve stem then you can tweak your spoke tensions.