Shimano cranks failing. Time to do something about it?

You should probably worry about your ability to reason, but don’t worry too much. Life goes on.

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Might want to check the quotes you’re defending there champ…

If a crank failure could produce a movement anything like chains skipping over worn chainrings, then the abrupt weight transfer has a very high probability of causing a rider to lose control. This exact thing happened to me and I broke my hand.

Might want to brush up on your reading comprehension there lil guy… I know it’s your MO to avoid making sensible points and jump right to trying to attack people with ad homs when your silliness gets exposed but I very clearly said a sprint situation is the one scenario in which you might reasonably have an accident caused by a broken crank.

You know, if you spent as much time working on your bike skills as you do running your mouth online, you probably wouldn’t be afraid of such silly shit as a broken crankarm. :man_shrugging:

Fairly clear.

Well, I expect Shimano have fixed it on the new generation of Ultegra and DA cranks, rendering the issue with now old generation cranks pretty much immaterial. If not, their reputation for quality will suffer for it.

Bro! You are nothing but a fact monger. You and all your facts, just so “facty”.


It is not immaterial at all…if there is a design defect, there will thousands of cranks out there for years to come.

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is there anything wrong with previously made Shimano cranks which were also hollow and not glued or bonded together? Is there a functional purpose or true measurable advantage to the clamshell design, the hollow spider designs?

That’s a fair point. I assume they’d argue they were making the design lighter and maybe stiffer. If the redesign is inherently more likely to have manufacturing defects and they didn’t mitigate that risk, then that’s a problem. The point I was trying to make was that focusing on glue per se may not be the true issue. I mean, say what you like about capitalism, but it has at least given us glues in various strengths, ranging from hold a kid’s art project together to hold two halves of a CF frame together, and probably stronger even than that.

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Not that I think Hollowtech is a great design, but with formally reported injuries being so low (are there any that have been written-up in a police accident report, or reported to insurance?) and Shimano replacing failed cranksets, the likelihood of any regulatory/oversight body recommending a recall is virtually zero as there’s no documented safety issue and the manufacturer has undertaken remediation for affected consumers.

In the U.S., for example, how much did it take before Ford agreed to recall PIntos, and before Chrysler agreed to recall Grand Cherokees? A lot of people DIED. And Goodyear has never done anything about the G159 tire in RV applications - and no government body pushed a recall on them.


Make that more than a hundred thousand, and you’re inching closer to reality.
I agree it’s a huge problem which would make me nervous if I was the resposible engineer @ Shimano.
The failure mechanism seems to be faulty bonding seam lets get water in which leads to corrosion which weakens the material and deteriorates the surface the glue adhered to.
I wouldn’t say it’s impossible that those failures in the bonding seam also develop only over time.
Which probably wouldn’t be an issue if the inner surface of those cranks was properly protected against corrosion.

We don’t know but I would not bet that they have take care of that issue.
The new cranks are still of the same design: hollow and bonded together. They were probably trying to get those bonding seams as perfect as possible right from the beginning. As otherwise not protecting the inner surface against corrosion was not an oversight but almost intentionally causing trouble.
I’m not sure that they found a way to make that bonding process any more reliable.
So they must have accepted that the bonding seams on some of those cranks will have voids. Which means water will eventually get in there. Accepting that means you’ve got to protect the inner surfaces of those cranks against corrosion. This can be done, no problem. But it adds cost and it might reduce the strength of the bond.
So, I guess we’ll only know a few years from now whether Shimano has learned the lesson or not. Because they’ll never admit that there was a problem. That’s the sole certainty in this case.

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Except the evidence indicates that it is not a huge problem….if it was, I firmly believe Shimano would have issued a recall.

And yes, I agree that the number is likely hundreds of thousands of cranks, but I was being conservative in my estimate.

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Please define “huge problem”.

It takes one rider in the US whose crank fails while riding out of the saddle causing him to fall and then getting hit by a car and serverely (maybe even permanently) but not fatally injured. If he’s bright enough to seek for legal advice and sue Shimano for damage compensation he will certainly win the case. Because the evidence has been out there for quite a while that those failures happen.

In this day and age this will cause big headlines in the cycling world.

I’d call this a huge problem.

On the other hand a safety recall of all those 6800, R8000, 9000 and R9100 cranks would cost them a high double figure million USD number. At least.

So they wait. And probably pray.


??? Why am I supposed to define the term you used?

As you note, this issue has been known for years. It is well documented across social media. Given that awareness, and the fact that there are so many cranks out there, this indicates that Shimano does not feel that it is a “huge problem”.

Do you have evidence for that? That mechanism doesn’t sound particularly likely to me so I’d be interested to see any evidence you have.

Initially that was exactly what I was also thinking. And no, I don’t have any evidence like a new or not yet broken crank carefully, precisely cut open along the bonding seam showing voids in the bonding seam. I have asked some friends who have FC-6800 cranks on their bikes if they’re ready to give them to me and get a new one because I want to have a look into cranks that have been in use for years and are still intact.

So I applied logic - at least that’s what I think, please correct me where I might be wrong:

Those cranks don’t feature any protective measures against corrosion on their inner surfaces. That’s what all the photos of broken cranks show. The alloy(s) used for those cranks seems to be (highly?) susceptible to corrosion as many aluminum alloys with high tensile strength are.
If a rather small percentage of those cranks fail, sometimes even during their first year of usage, while the majority does not even after years of extensive and intensive usage I conclude that those which have not failed have not corroded internally. For if they did they would have broken.

So why did those which broke corrode? I’d argue because water got in there. And the only way how water can get in there is through imperfections of the bonding seam, right?

Having inspected bonded interfaces in other designs I know that it’s quite hard to reach a 100% perfect coverage of the glue even if you try. Often that doesn’t matter as long as the glue covers enough of the interface to create a strong enough bond. With this design though we’re talking about a very thin interface which has to be 100% sealed. As otherwise atmospheric differences between the air trapped inside the crank and the air in the environment will cause gas exchange and thus bring humidity into the crank arm.


I don’t agree but since I don’t have any evidence either we’ll just have to leave it at that.

You grossly overestimate how much the court system values the lives of cyclists.

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I will not speak out about the severeness (in number of incidents) of the issue.

Please note, however, that Shimano says that there is no design issue. Where the design itself may or may not take things like environmental conditions during production and usage into account.

What Shimano does NOT say in their statement is that there are no or have not been quality issues with the used materials during production. Nor do they state that the manufacturing process isn’t/wasn’t to blame.

So while perhaps technically and legally correct, Shimano did not say that there is/was no issue during usage. And while incidence of the issue may be low or even very low, the examples of failure are quite similar.

(Sidenote: as far as I’ve seen there are no mentions of pro cyclists that experienced the issue. Is/was the issue that minor? Are failures with pro cyclists kept silent? Does/did the issue only occur after time, and are/were pro cyclists switching gear long before it happens/happened? We simply don’t know.)

Very relevant to today’s pseudo-scientists
“The plural of anecdote is not data”