Rotor 3D+ broken crank

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maquisard
Posts: 3767
Joined: Thu May 01, 2008 8:51 pm
Location: France

by maquisard

Not happy, today while out riding my 2013 Rotor 3D+ crankset failed at the point where the drive side crank attaches to the spider. I literally had no warning, one section I was riding out of the saddle. The next I found myself on the ground with my Cervelo R5 within which the crankset was installed. Pics below

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I slammed my chest into the handlebars, cracking ribs and then fell to the left badly injuring my left shoulder and index finger on my left hand. I'm going to have to replace my left Dura Ace shifter and most likely my Ergonova carbon bars which took a lot of impact.

What makes me most angry about this though is that these 3D+ cranks were bought by myself around the same time in 2013 when my Rotor 3DF cranks brok at the pedal spindle. See here :- http://weightweenies.starbike.com/forum ... 3&t=119922 Rotor replaced my 3DF cranks under warranty and I upgraded to the 3D+ with my own money in the hope the 3D+ would be stronger. Now this happens.

In 15+ years of road cycling I have never had a crank arm break apart from the failures in the past two years from Rotor.

Rotor you are a joke and risking the lives of cyclists with your products! :x
Last edited by maquisard on Sat Apr 29, 2023 7:34 am, edited 1 time in total.

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Mackers
Posts: 482
Joined: Wed Sep 05, 2007 2:02 pm

by Mackers

Wow!

Glad you didn't take more of a beating than you already have.

rma
Posts: 169
Joined: Mon Apr 21, 2014 9:17 pm
Location: Belo Horizonte, Brazil

by rma

Was it properly installed? I can't see the internal lockring on the first picture. The next question should be about the torque used on the bolts.

Hope you are recovering. Really odd to see this kind of failure. You must be putting out serious numbers out there. Get well soon!

Marin
Posts: 4035
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

Wow, not good. What do you weigh and how many kms on the cranks?

highdraw

by highdraw

Sorry to hear.
May I ask how much you weigh and how strong a rider you are? Can you get to high 30's mph in a sprint?

I hope you mend quickly. I wonder what Rotor would have to say about that failure?
Not sure what legal recourse you have. If they do replace that crank, you may consider ebaying it and going with a DA crank. Don't think I would tempt fate again by riding a Rotor crank with your power.

KH
Posts: 196
Joined: Fri Feb 27, 2004 3:56 pm

by KH

Nasty...hope you heal fast and glad it wasnt worse.

I live in fear of crank failure.

Have had two Dura Ace 7800s snap on me, plus a Truavativ crank and an FSA one. Only hit the ground on one of the four occasions but it was quite unpleasant. Have posted details on here previously.

I weigh 66kg and am a tall skinny climber.

It does play on my mind to a certain extent as it could so easily result in a fatal accident.

I had those Rotor 3D cranks on my team bike for a season without problems by the way.

For what it's worth (probably not much!) I have put the most kms on Cannondale Hollowgram Si and Si SLs over the years, also without any problems.

maquisard
Posts: 3767
Joined: Thu May 01, 2008 8:51 pm
Location: France

by maquisard

I'm 79Kg and about 185cm so relatively big for a cyclist. The crank has done about 16km since new and is two years old, it is on my summer bike, a Cervelo R5 and replaced a 3DF which broke at the threads of the pedal spindle.

The crank was installed by a Cervelo dealer so I assume they know what they are doing.

I wasn't sprinting when this occurred either, simply cresting a short steep hill out of the saddle. My Powertap reported power of 593W and 34.3 Nm of torque just before failure. That is not a lot...

highdraw

by highdraw

As it turns out we are the same size and weight.
You say almost 600W's isn't a lot.
What kind of watts can you lay down in a sprint? Maybe a fatigue failure.
Will say that some strong guys break stuff and you maybe such a guy.
Very sorry to learn of your injury. I wouldn't ride another Rotor crank if I were you.
Good luck.

Omiar
Posts: 385
Joined: Wed Dec 14, 2011 8:20 pm

by Omiar

I little googling reveals that these occasional failures do happen with Rotor cranks. Probably with other manufacturers too.
Guess I will have to check my crank now :)
Cannondale SystemSix R8170
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Raineman
Posts: 185
Joined: Mon Oct 06, 2014 2:03 pm
Location: Kent, UK

by Raineman

Looking at how the crank broke, I would say it broke due to fatigue. This would tally with the power and how long the crank had installed and where it broke (as close to the fixed point as possible). I also wouldn't be surprised if you also have a relatively low cadence (higher force = faster fatigue).

None of this is your fault as this is how you ride but I would say rotor cranks may not be as suitable for you in terms of fatigue resistance. Carbon tends to do much better against fatigue so carbon cranks could be a smart move in your case, assuming you don't put so much power to snap the crank on your first sprint. :lol:

Hope you can get back on the bike soon

maquisard
Posts: 3767
Joined: Thu May 01, 2008 8:51 pm
Location: France

by maquisard

So modern alloy cranks cannot cope with 600W for a second or two... really?!

I have Shimano alloy 105 and Dura ace cranks that are five+ years old without any damage. They probably have 40k+ km on them.

Rotor just have a poor and dangerous product.

highdraw

by highdraw

maquisard wrote:So modern alloy cranks cannot cope with 600W for a second or two... really?!

I have Shimano alloy 105 and Dura ace cranks that are five+ years old without any damage. They probably have 40k+ km on them.

Rotor just have a poor and dangerous product.

Don't think you understood what Rainman stated. Fatigue isn't about just a single application of 600 watts but rather repeated cyclic loading. You really never did address my questions about your maximum wattage. You said that you thought 600 watts wasn't that much but you never said what your maximum wattage was. So bending the aluminum beer can coupon until it fatigue fractures isn't about a single bend...but repeated loading.

As to Aluminum being the sole culprit, you are right. There are many factors...not only the material properties of the Aluminum including heat treat chosen...but also the mechanical properties known as section modulus of the crank arms where they meet the spider of the crank. Its this combination relative to repeated loading that determines fatigue life. Aluminum can do fine and does everyday in the context of fatigue life provided the strength is there based upon material selection and part section modulus.

So quite possible Rotor cranks are weaker than say the average Shimano cranks. This is only revealed through outlier loading and perhaps you are a candidate OP. As stated, I would switch to a Shimano crank as there are very few reported failures.

But to say Rotor has a dangerous crank...for you perhaps because of your power. But they do fine for average riders and of course even pros have raced them in the peloton. Fatigue is cumulative loading FWIW and of course pros ride fresh gear...many times no more than a couple of races...because they can.

In summary, if the failure is fatigue and it likely was, and say you have power underneath that a pro rider can put out and sustain...say a beefy sprinter...it is the period of time of riding a given crankset that exposes weakness even though your power is less than a pro sprinter. Pros replace their gear constantly and fatigue is less of a concern...they ride new gear in an effort to reduce the element of fatigue failures because of the consequences you experienced.

maquisard
Posts: 3767
Joined: Thu May 01, 2008 8:51 pm
Location: France

by maquisard

highdraw wrote:Don't think you understood what Rainman stated. Fatigue isn't about just a single application of 600 watts but rather repeated cyclic loading. You really never did address my questions about your maximum wattage. You said that you thought 600 watts wasn't that much but you never said what your maximum wattage was. So bending the aluminum beer can coupon until it fatigue fractures isn't about a single bend...but repeated loading.


I'm an engineer, admittedly I work in semiconductor design but I have studied materials science and am familiar with Young's modulus, stress/strain curves etc. Whilst I agree this was fatigue, designing a load bearing part that cannot withstand a reasonable number of cycles of normal load is simply poor design. It is also dangerous.

My max sprint wattage is 1200W but I do not sprint that much, little to none in fact this year. Reviewing my power data for the year to date I have not sprinted beyond 1000W this year.

My average cadence per ride is typically 80-85rpm.

I don't buy the argument I am an outlier, so as an amateur rider with an FTP of 330W and a max sprint of 1200W I am at the extreme end of a gaussian distribution?! Sorry, but that is utter nonsense, if this is true then Rotor have no place making equipment for pros. This was a crank that was two years old and mounted on my summer bike, it was mostly only ridden in good weather and had seen 16k km of use over two years.

cobrakai
Posts: 76
Joined: Wed Jun 24, 2015 11:19 pm

by cobrakai

To be fair googling rotor crank failure brings up this thread, your previous thread and dcrainmaker's post, and that's pretty much it. I would think if there was a design flaw there would be a lot more reports of failures out there. Your power is probably towards the upper end of amateur riders but nothing outlandish. So it seems to me that it is more likely that you are either very unlucky, or there is something unusual about your pedaling style that is causing a failure.

by Weenie


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highdraw

by highdraw

You have quite strong views on the subject maquisard. I am a mechanical engineer btw and provided by view point.
You are at least 3 standard deviations to the right of mean in power output. We can dispute the definition of outlier. I know you believe the design should be robust to encompass your strength. Point is, it is power over time that affects fatigue and I believe you may even concede this looks like a fatigue failure. There is no disputing it broke and discussion revealed your power output and time duration aka how long you have owned the crank and your mileage. Yes...the design is likely marginal relative to your power. Suffice to say a 150 lb rider that never exceeds 400 watts would never have a problem.

Generally, I believe you know this....designs are vetted during design and production validation phases during product development. But what typically isn't tested are the margins of material specification. Materials like the Al alloy in your Rotor crank have a specification tolerance. A guess is your failure can be explained by a confluence aka stack up...your power....time...and likely a low side of tolerance material spec that created greater weakness in the part.

Or...there is simply insufficient section modulus at the vertex where your crank broke. And...of course greater web thickness increasing moment of inertia and stress tolerance will desensitize the design to variation in material properties as you likely know. No refuting physics. Sorry about your crash. A strong rider like you shouldn't have to endure such a fate and you are completely correct to be critical of Rotor's crank. I would be too. Hard to accept.

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