Holy crap..

Hope you are ok...

From the fracture surface shown in the second picture, it looks like a fatigue failure. It also looks like the crack has been growing for a long time.

Thanks for the input. I have a couple of manufacturing engineering friends that came to the same conclusion. Now I have to figure out how it got cracked / fatigued in the first place.

Is that a 3D30 (3D+) crankset?
It looks like the lock ring bolt is on the outside in the 2nd photo. The 8mm bolt should be on the outside when the crank is installed. You would flip it to the way picture only for crank removal.

I could be wrong, but double check that.

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Alex Arman

Strava

I'll have to have my bike shop check that, I am clueless regarding your question.

Holy toledo.

You're lucky that you still have your teeth. If you don't mind saying, what happened to you in the resultant accident that required a hospital visit?

Any estimate of the miles on the crankset before break no. 1 ?

Any estimate of the miles on the new crankset before break no. 2 ?

Where do you live, near any oceans? Do you ride on salted roads in the winter?

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First time the crank had about 14,000 miles on it, and I ended up in the hospital for a CAT scan as the ER doc was concerned about internal bleeding, luckily it was just some hemorrhaging in the hip area.
The new crank also has about 14,000 miles on it. Winter riding does have some salt, but with Zwift, my winter riding is 80% indoors these days. Luckily, I still have my teeth, just some road rash and bruises from the latest fall. Thanks for the input.

Looks exactly like that to me, i.e. in the remove crank position. Here are some shots of my 3d+ with the ring in both positions:

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Do you live pretty far from the nearest ocean?

It is further surprising that both cranks failed at very very similar mileages.

Did rotor insist on getting both broken cranksets for forensic analysis? I would sure hope they did.

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He has the newer one piece extractor bolt not the two piece

Type of crank it is will tell the story here. Based off the bolt style, I am thinking that is not a traditional 3d+ and is instead an inPower unit? Not thinking it is a 3D as those guys attach from the other side. Anyhow, disregard my previous post if this is not a 3D+, which I am leaning to it not being.

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Ah, gotcha. I thought that might be inPower specific, but I guess it's a smart move to switch them all over. Like that style much better.

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WOW!!! That is something crazy to see in those pictures of the broken crank. I hope you are okay and road rash is healing.

I have 3 Rotor 3D cranks with 24mm axles. I haven't had any problems at all with them. But, in looking at your broken crank arm, I wanted to just add in my .02 cents worth of thoughts.....

To me (and no, I am not an ME), it looks like a stress fracture based on an inward lateral force. By this I mean (let me see if I can explain this in words well enough...), that the break looks like if the crank arm was in the 6 o'clock position, and you applied force laterally inwardly to the arm towards the BB bearing, that it then cracked off. Essentially, say when you're standing and rocking the bike left-right-left-right (as in climbing), that when on a down stroke at the 6 o'clock position as the bike is leaning over and your leg is pushing straight down, that's when the crack happened???

Maybe someone with an ME degree can properly explain what I'm thinking may have caused the break?? But, it still does not explain or excuse the break itself. Maybe just a bad batch of trinity drilling that got too close to tolerances???

Again, I am not throwing blame anywhere, rather just thinking about what forces may have caused such a break.

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Team Zoot-Texas, and Pickle Juice

Ahhh. I haven’t seen the new design before.

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Alex Arman

Strava

Glad you weren't hurt too badly. Sucky situation. Goes without saying that maybe you should try a different brand of cranks. If you're invested in the Rotor ecosystem (i.e non-round chainrings), maybe you just have to suck up the expense and proactively replace them every 10-12k miles. That hurts, but probably less than hitting the pavement every ~14k miles.

In the meantime, I'd put a ribbon through the pedal hole, wear it to the next tri-club or bike-club meeting like a medal, and brag about how I was so strong I've broken two of these SOB's.

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"They're made of latex, not nitroglycerin"

Thanks for the input. Rotor tells me that they don't see this often and will examine the parts and try to determine why I am so unlucky.
They also offered to provide replacements and pay labor to have them installed. Maybe the third time is the charm.

Thanks again.

Wow. I cracked two mountain bike frames in quick succession a few years back, when the company sent me a third replacement I immediately sold it.

Is that at 3DF or 3D+ crank? or inpower?

I would be buying some Shimano cranks.

That is a little concerning as I have the exact same setup 3D+ crank, rotor rings and aero spider on my road bike. I have had it on there for several years now with no issues however. I have the 3D+ with Power2max meter the same as posted pics on your thread on my tri bike and no issues either. Both have the older style removal bolt. What were you doing when the crank went? Sprints, hills?

+1

You guys should do a google search for Shimano 6800 cranks failure. You'd be surprised at the amount of pictures out there and posts of those cranks breaking. IMO that is what you skirt with threading on the line of trying to make as lightweight as possible crank using aluminum and thin walls. But then again I do have a set of Rotor cranks and am a bit alarmed by that failure though.

So sorry to hear about this. I have broken several sets of cranks - in the old days when I was younger and stronger. I have had Rotor cranks on 3 bikes now and never a problem (knock on wood). I have way, way more miles than you on my 2012 P5 and no problems at all. It sort of appears like possibly a lateral force at least created a weak spot . . . is that possible? From traveling, a crash, falling over in the garage, laid on its side and bouncing in the car, or anything like that? There is a lot of leverage applied if they get hit with a lateral force at the pedal end. Let us know what you figure out.

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David
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Thank you so much for posting this. Because of your post I went and checked my own P2M ng rotor 3d24 crankset and I found pretty bad corrosion not too far from where yours snapped off. You can see it just inside the spindle. 2 year old crankset with maybe 4000 miles on it. The thing is I don’t live near the ocean and I take immaculate care of my bikes with regular cleaning and lubrication so I do a good job removing salts etc. In fact I doubt this crank has ever been used in the rain. see pic

Indeed… you only need to look at an S-N chart to realize that every aluminum part will fail sooner or later. In the case of a bonded structure there is the additional challange of the adhesive.


Source http://www.spaceflight.esa.int/...perties/Fatigue.html