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Shimano denies design problem with Hollowtech cranks despite reports of cracked arms

Component giant says its engineers are trying to find out if there is a specific cause of crank failures

Shimano says that there isn't a design problem with its Hollowtech cranks despite reports of a pattern of failures – although its engineers are continuing to investigate other factors or causes.

The hollow design of Shimano’s Hollowtech crank arms makes them light; decreasing the rotating mass helps with acceleration. A lot is to be gained and Shimano says on its website, “The challenge is to reduce the weight of the crank without reducing its strength and rigidity.”

So, is the balance right?

Image from Shimano's website Tech_Image_HollowtechCrankArm_01

road.cc reader hawkinspeter shared with us all in a forum post last month the result of an uninvestigated creaking noise. The photo shows the Hollowtech crank arm cracked completely and split in two. This failure resulted in the rider hitting the deck.

hawinspeter crank arm failure

He explained that the noise repeatedly occurred when accelerating from a standstill, but that he was unable to get to the bottom of the issue until the crash when it became clear Shimano’s Hollowtech crank arms had been the source.

This is one reader’s incident, but there are more. When we shared the photo on our Instagram page we got countless replies detailing similar incidents, so much that it spawned a whole road.cc Podcast episode on scary cycling incidents. An Instagram account with 11.1k followers, @thanksshimano, shares photos documenting similar issues, with new posts every day or so.

@thanksshimano reckons the issue is that “none have properly treated internal surfaces and all rely on 'perfect' bonding which we know to be sometimes imperfect”.

It’s clear hawkinspeter’s failure isn’t a one-off, but we have no way of putting a definitive figure on it.

Shimano sells a vast number of these cranks – there are far more out there than cranks of a similar level from SRAM or Campagnolo, for example – so it’s almost inevitable that there will be more reported failures. It would be interesting to see the number of incidents versus the number sold, but we have no way of getting these figures. Nor can we tell you about the history of any particular product that has failed. 

What we do have, though, is a response from Shimano on the issue.

We brought the reported failures of cranks to the company’s attention and in a nutshell, Shimano says there is no design problem, but that it is still looking to find out if there is a specific cause. 

Here’s the full response we received:

“Thank you for bringing the reported failures of cranks to our attention. We take customer complaints seriously and, as a result, we initiated an investigation.

“Crank failures do occur, even though our cranks do not have any design problems or if there are no other easily identifiable issues.

“During our examination of usage cases, and through our own internal testing, we have not identified a design problem with the cranks, and we are continuing our investigation to discover other factors or causes.

 “We would like to be able to give further details, but we cannot at this point because our investigation has not resulted in the identification of a cause of the crank failures your readers reported.

“We would like you to know that your readers' complaints are not being ignored, and Shimano's engineers are trying to find out if there is a specific cause.”

Have you had a Shimano crank fail? Please get in touch and tell us what happened.

Anna has been hooked on bikes ever since her youthful beginnings at Hillingdon Cycle Circuit. As an avid road and track racer, she reached the heady heights of a ProCyclingStats profile before leaving for university. Having now completed an MA in Multimedia Journalism, she’s hoping to add some (more successful) results. Although her greatest wish is for the broader acceptance of wearing funky cycling socks over the top of leg warmers.

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124 comments

Avatar
Prosper0 | 3 years ago
3 likes

I know 2 people in my club where their top end Shimano cranks have failed alone. It's clearly a very serious global problem. Do more digging, get them to do something about it!

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topsound54 | 3 years ago
4 likes

My 6800 Ultegra suffered this cracking in April 2020. Unexplained creaking for a while before I spotted the fracture as per photo. Luckily replaced before it failed totally. 4.5 years old at that point. So out of warranty. Found a few references to the problem on the web and that Shimano's response was "that there are very many cranks of this type out there and failure numbers are minimal". Problem is a failure can be catastrophic!

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Sriracha replied to topsound54 | 3 years ago
2 likes

So let me get this straight; Shimano are saying that just because yours failed, there is actually nothing wrong with it because others didn't. Genius!

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sparrowlegs | 3 years ago
4 likes

This has happened to Hambini's crank as well. He's taken it up with Shimano and had the door slammed in his face.

I await his video of this and the ensuing lawsuit from the big S suing him 😂

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Griff500 replied to Lance ꜱtrongarm | 3 years ago
1 like

70kg here! Must be a low weight limit!

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Awavey replied to Lance ꜱtrongarm | 3 years ago
1 like

it wouldnt be the riders weight per se,  it would be the torque forces or the twisting force being applied by the rider on the pedal to get the bike moving,and the metal is just suffering from fatigue cracks which grow over time till the component fails completely.

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simon davies me | 3 years ago
4 likes

I was 2mile from home on a slight incline, stepped out of the saddle and ended up on the floor in front of a bus. Had no idea what went wrong until I saw the crank arm still fastened to my shoe.

Walked back. Bike shop never seen it, Shimano Europe not interested as I was out of warranty but if I send the parts in at my expense they would have a look. So I bought a new crank and went on. It's a shame I didn't know others experienced the same

Avatar
kezzers | 3 years ago
3 likes

This isn't exclusive to Shimano cranks, I had some Cannondale Hollowgram ones fail in exactly the same way.  Bond went and then sheered off the crank arm.   I think @thanksshimano nail the problem when they said the bond needs to be perfect.  In this type of design the error rate for an imperfect bond seems too high.  It's a shame really as it's a nice idea, but I now avoid cranks based on this type of technology.

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chuckd replied to kezzers | 3 years ago
0 likes

This, and I'd add is this really where you want to be testing the design limits? I have older Dura-Ace 7600's, 177.5 which I think are solid. But they're on a 2015 Trek Domane that originally came with 6800's (I needed the length, not available in 6800s). They're going into the box with the custom steel fork rusting out around the crown.

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KnightBiker | 3 years ago
4 likes

For all interested: @peake torque (on YouTube) made a brilliant in depth analysis of the problem.

I had my crank broken like this two years ago, and it was just inside 2 years warranty and op of more then 30.000 km's in. It's not a new issue by any means and Only introduced when they converted to the four arm spindle design.

the things is, Shimano not addressing it is plainly stupid: it's by no means clear the new cranks of the new group sets use a new methodology for construction. This will make me think twice or 3 times about buying a new groupset, although I overall like Shimano and especially it's shoes and wheels.

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Pilot Pete replied to KnightBiker | 3 years ago
1 like

I like Shimano too, but not their cranks. That's why my builds all have Rotor cranks. Think their old 5 arm design with NoQ rings look classy too.

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nopants | 3 years ago
1 like

My Ultegra 6800 cranks failed recently as well. The 2 halves of the arm came unstuck at the axle end. It had been creaking for a while, and luckily I was able to get home before it failed completely.
It did have a lot of miles on the clock. Worth checking if you have an old ultegra/dura ace crankset. In my case I could see (and feel) the outer shell flexing away from the chainrings when I weighted the pedal. The inner shell of the arm is cracked down by the pedal.
Almost impossible to find spares at the moment too...

Avatar
Daveyraveygravey replied to nopants | 3 years ago
1 like
nopants wrote:

My Ultegra 6800 cranks failed recently as well. The 2 halves of the arm came unstuck at the axle end. It had been creaking for a while, and luckily I was able to get home before it failed completely.
It did have a lot of miles on the clock. Worth checking if you have an old ultegra/dura ace crankset. In my case I could see (and feel) the outer shell flexing away from the chainrings when I weighted the pedal. The inner shell of the arm is cracked down by the pedal.
Almost impossible to find spares at the moment too...

I had the same problem, it looked exactly like yours. I was about 6 months outside the warranty but persued it with the UK distributor rather than Shimano, and got a replacement. Ultegra 6800. I also knew there was something wrong but couldn't find it, until it got to the stage where it was flexing as I pedalled. I was on my way to Rosedale Chimney, luckily I spotted it before the climb 🙄😉 I still had about 25 miles to roll home gently though, expecting it to let go any minute.

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TheBillder replied to nopants | 3 years ago
3 likes

Probikekit have 105 chainsets at £116. Different construction and should work nicely.

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capedcrusader replied to TheBillder | 3 years ago
0 likes

Thanks for that. I have 6800 groupset and had experienced squeaking, have oiled and changed everything except the flipping cranks - though i did check the bolts. Will have ot check it's integrity. Still have old 105 crankset kicking around so will swap out check to see if the creak/squeak has gone.

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anke | 3 years ago
1 like

This problem has been known and discussed for a long time. It seems to affect mainly the pen-ultimate generation of 11x DuraAce and Ultegra (6800).

By comparision to Ultegra 6800, the successor Ultegra 8000 (and respective 105 and Dura-Ace) crank arm have already been "beefed" up very visibly - probably to address this mode of failure -- and I'd assume that the latest (12x) generation has been improved even further.

Nevertheless: Cudos to Shimano for their elegant and cost-effective designs! Having the same strength and weight as (non-recyclable) carbon-fibre cranks arms from other brands is an impressive achievement - and the number of failures (even in the old 6800 generation) is very small. Let's hope they'll handle them more gracefully in the near future...

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KnightBiker replied to anke | 3 years ago
1 like

Also a lot of Ultegra r8000. Actually didn't see it with models before r8000 yet, but it might be from the moment the hollow tech technique was introduced.

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Griff500 replied to anke | 3 years ago
4 likes

Dura Ace R9150 crank weight 614g, SRAM Red AXS crank weight 561g, so bang goes that argument.  

As for recycling? Bearing in mind the heavy steel axle through the middle plus steel inserts for pedal attachment, how much of that 561g of the SRAM crank do you suppose is carbon fibre, compared to the weight of Lycra (non recyclable) the average cyclist goes through during the life of a carbon crank? Back to merino wool it is then! 

No, I'm not being flippant. In the UK, household waste amounts to 400kg per person per year, of which only 44% gets recycled. If you really want to reduce landfill, say 100g of carbon crank per cyclist every 10 years (10g per cyclist per year) is hardly the place to start.

 

 

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rct replied to Griff500 | 3 years ago
1 like

Reduce, Reuse, Recycle in that order.   Needing to buy replacement cranks is hardly reducing comsumption.

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Griff500 replied to rct | 3 years ago
0 likes
rct wrote:

Reduce, Reuse, Recycle in that order.   Needing to buy replacement cranks is hardly reducing comsumption.

Absolutely, and I would expect cranks to last pretty much the life of a bike. My Ultegra crank failed after 5 years.

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marmotte27 replied to Griff500 | 3 years ago
1 like

"Dura Ace R9150 crank weight 614g, SRAM Red AXS crank weight 561g"

Theres still lighter and better : https://www.renehersecycles.com/shop/components/cranks/rh-11-speed-doubl...

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anke replied to marmotte27 | 3 years ago
0 likes

Reneherse is only lighter without the shaft (in the bottom bracket), no?

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HiFi replied to anke | 3 years ago
4 likes

Is kudos really an appropriate response to a product that endangers users like this?? You should perhaps ask instead why such fragile thin-walled aluminium is still being used in a premium groupset (9100 and 9200).

Flagship bike products (framesets, groupsets, wheelsets) are carbon for good reason. Carbon is stiffer, lighter, and stronger than alloy. Your frame and wheels are probably carbon.

The failure modes on the insta page are all the same, not random, showing a common design fault in a thin-walled aluminium design pushed just too far in its struggle to match the low weight of carbon.

With the new 9200 DA shimano have finally given-up pretending aluminium painted black is even comparable with carbon, making the c/set heavier (690g vs 624g before) due to 9100 breakages. Zero surprise, the campag SR carbon c/set is 11% lighter and 6% stiffer.

Using relatively low-cost aluminium and some black paint for manufacture may generate great DA profits for shimano, but it’s hardly the pursuit of marginal gains (and safety) expected in a flagship groupset.

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open_roads replied to HiFi | 3 years ago
1 like
HiFi wrote:

.

Flagship bike products (framesets, groupsets, wheelsets) are carbon for good reason. Carbon is stiffer, lighter, and stronger than alloy. Your frame and wheels are probably carbon.

I snapped a pair of Specialized s-works carbon cranks so I'm not sure it's all down to material choice.

Avatar
Prosper0 replied to anke | 3 years ago
3 likes
anke wrote:

Nevertheless: Cudos to Shimano for their elegant and cost-effective designs!

Is this a joke, I can't tell if you're trying to be funny or not. I hope you are. 

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anke replied to Prosper0 | 3 years ago
0 likes

Look, the design for manufacture, mass-production, weight, and affordability, based on cheap materials, as mastered by Shimano, is most impressive. -- Just producing an expensive clunk from the most expensive material available is child's play compared to this (but can be done by smaller companies without the production and engineering resources, if these companies can demand high prices).

But as I wrote before, I totally agree that Shimano did not seem to handle this problem (cracked crank arms) in a graceful way. 

Avatar
Griff500 replied to anke | 3 years ago
3 likes
anke wrote:

Look, the design for manufacture, mass-production, weight, and affordability, based on cheap materials, as mastered by Shimano, is most impressive. -- Just producing an expensive clunk from the most expensive material available is child's play compared to this (but can be done by smaller companies without the production and engineering resources, if these companies can demand high prices).

This post has no more fact than your previous post. Shimano have "mastered" nothing here, the cranks break, people get hurt, have you not been listening? As for the nonsense about affordability and cheap materials versus "the most expensive material available" if you had actually checked you would find that  SRAM Red 22 (carbon) are cheaper (by msrp) than Dura Ace R9100. The company "demanding high prices" as you put it, is the one using cheap pieces of cast aluminium badly glued together.

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anke replied to Griff500 | 3 years ago
0 likes

I think you're exagerating a little, my dear Griff500. It also seems you didn't read my post properly, did you?

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Griff500 replied to anke | 3 years ago
2 likes
anke wrote:

I think you're exagerating a little, my dear Griff500. It also seems you didn't read my post properly, did you?

In defence of Shimano you have so far said they are light as the opposition, (they aren't in all cases eg DA versus Red), lauded them for use of cheap material, despite the end product in some cases being more expensive (eg Dura Ace versus Red), and described them as masters of DfM, despite a clear pattern defect in use. Now which bit do you think I got wrong?

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anke replied to Griff500 | 3 years ago
0 likes

Right. So Mr ex black belt would design bike-parts to a six sigma level of reliability, so there might be just shy of 4 failures in one million parts, over many, many years, in possible highly corrosive environments? What's the weight penaltiy? Pro-level bicycle parts (or at least very high-level ones) - not the stuff for the daily commute?!

 

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