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Ponder this scenario: crank arm/pedal snaps off

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Ponder this scenario: crank arm/pedal snaps off

Old 02-06-16, 11:04 PM
  #1  
Abu Mahendra
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Ponder this scenario: crank arm/pedal snaps off

Ponder the following scenario:

You are standing on the pedals on a climb. All of a sudden the crank arm or pedal snap off, separating completely from the bike.

Is there any recovery, or are you simply going down?
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Old 02-06-16, 11:47 PM
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Prepare for your heels to smash into a million pieces. I rode on metal platform pedals in the rain once and slipped, hitting the ground really hard. Your body should tense up and reduce injury by bracing against the handlebars. I don't run those pedals anymore, now I have those grippy mtb style ones.
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Old 02-07-16, 01:16 AM
  #3  
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I snapped a steel crank arm right in the middle on my Robin Hood climbing a 15% grade, and surprisingly it was a total non event. Just mashing on the pedals, and suddenly no resistance on the left, like WTF? Really?

I wasn't sanding so I don't know if it would have made a difference.

FWIW, I welded it back together, and it snapped again with the same non event result, except it wasn't a surprise.

Last edited by kickstart; 02-07-16 at 01:19 AM.
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Old 02-07-16, 02:50 AM
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I haven't broken a crank, but I've yanked cleats loose, had a chain skip, and spun the tires without traction. They don't have to be catastrophic failures.

Also missed a clip-in, and had the feet slip off of the pedal (standing). It gives a bit of a jolt, but one doesn't go down.
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Old 02-07-16, 05:36 AM
  #5  
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Originally Posted by kickstart
and surprisingly it was a total non event. Just mashing on the pedals, and suddenly no resistance on the left, like WTF? Really?
This was my experience too. A certain local shop neglected to torque down the pinch-bolts on my 7800 left, non-drive crank. The thing popped off, and I was immediately standing on the side of a narrow, busy uphill with the crank and pedal still clipped to my foot. First instinct was to take the shoe off, but I had to put it back on my foot and sit down to unclip it from my shoe, then screw it back onto the bike, clip back in, and continue.
Not all bike shops bother using torque wrenches, nor follow the specific directions to stagger the bolt-tightening sequence, but I do now. It might have been a fluke that nothing happened, that the crank popped off at just the right moment, but I can imagine 359 worse alternate outcomes.

Last edited by calamarichris; 02-07-16 at 05:39 AM.
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Old 02-07-16, 06:29 AM
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There is a famous picture of Laurent Fignon who crashed when the bottom bracket axle on his bike broke; you can see the crank arm and pedal next to him after the crash:

inrng : fignon remembered
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Old 02-07-16, 06:35 AM
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Originally Posted by bikemig
There is a famous picture of Laurent Fignon who crashed when the bottom bracket axle on his bike broke; you can see the crank arm and pedal next to him after the crash:

inrng : fignon remembered
I broke one of those BB axles too.
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Old 02-07-16, 06:39 AM
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Originally Posted by Homebrew01
I broke one of those BB axles too.
apparently it's not just carbon that assplodes,
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Old 02-07-16, 06:41 AM
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During a full sprint, in traffic to get through a Red Light.

My Left Crank arm came OFF.

I was able to put it back on and slowly pedal home.



Attached Images
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Old 02-07-16, 06:43 AM
  #10  
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I've worried about this when climbing and out of the saddle. I know that I would go down hard and probably do some major damage to myself.
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Old 02-07-16, 08:14 AM
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Something that makes this scenario even more daunting, is that if you snap a crank arm while climbing, the chain is likely on the small ring. This means that the big ring has exposed teeth (ie. not covered by the chain) and is posed to do more damage to your unsuspecting flesh.

Having said that, I did have a crank arm come off (on level terrain) and to coin the phrase, "it was a non event".
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Old 02-07-16, 08:42 AM
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I had a pedal fall off while accelerating through an intersection. No injury, just very surprised. I'm still not sure how it happened: the threads were perfectly fine, and I just re-installed it a rode home. And it's been fine ever since.
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Old 02-07-16, 08:50 AM
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A possible outcome.
https://vimeo.com/122073389
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Old 02-07-16, 09:06 AM
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I dont want to think about this. OTOH, breaking a crankarm on a sprint puts you in the beast category.
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Old 02-07-16, 09:28 AM
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I don't think you can prepare for it, and it's going to hurt if you are not incredibly lucky.
A friend had that happen and had 17 staples in the back of his head.

Originally Posted by Abu Mahendra
Ponder the following scenario:

You are standing on the pedals on a climb. All of a sudden the crank arm or pedal snap off, separating completely from the bike.

Is there any recovery, or are you simply going down?
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Old 02-07-16, 09:29 AM
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Originally Posted by JohnDThompson
I had a pedal fall off while accelerating through an intersection. No injury, just very surprised. I'm still not sure how it happened: the threads were perfectly fine, and I just re-installed it a rode home. And it's been fine ever since.
Wow. You were lucky, John; I've seen that happen with ambulance results.
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Old 02-07-16, 09:31 AM
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This is making me think I may just get a new crank for a bike I'm building on rather than relying on some old ones in my parts bin; geez thanks.
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Old 02-07-16, 10:02 AM
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Originally Posted by rex615
Something that makes this scenario even more daunting, is that if you snap a crank arm while climbing, the chain is likely on the small ring. This means that the big ring has exposed teeth (ie. not covered by the chain) and is posed to do more damage to your unsuspecting flesh.
That's why I always climb in the big ring
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Old 02-07-16, 03:23 PM
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Originally Posted by bikemig
There is a famous picture of Laurent Fignon who crashed when the bottom bracket axle on his bike broke; you can see the crank arm and pedal next to him after the crash:

inrng : fignon remembered
Just sits there and mocks him.

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Old 02-07-16, 03:43 PM
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I had this happen one time in recent years. The right crank arm broke on a road bike I had and I went down but not hurt minus a few scrapes. All my bikes but one have a one piece (Ashtabula Crank) on them and I don't think I will ever have to worry about breaking one of them. However, when I was a kid I remember jumping my Huffy BMX and I did bend the one piece crank on that bike.
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Old 02-07-16, 04:19 PM
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Over my 50+ year cycling career I've snapped a decent number of cranks and/or pedal spindles. Of course they always snap under peak load, but only once in the well over 10 incidents has it led to a crash or injury. The one exception was a cut over my ankle bone caused by the stub of a pedal spindle.

Broken cranks and pedals happen, but aren't a worry except for the inconvenience factor.
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Old 02-07-16, 05:01 PM
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Originally Posted by slimyfrog
A possible outcome.
https://vimeo.com/122073389
I think this video shows it pretty well. And, as my story below underscores, note how the helmet probably saved his life.

As for the famous photo of Fignon, that was the first generation Titanium Campy spindle that was hollow and they all broke. It was quickly replaced by a solid Ti version.

My own experience was quite recent. I was out for a nice ride on a lovely afternoon just pre-Xmas, and into a standing mash up a residential hill as I headed home when . . “BAM” My left leg suddenly cut loose from the bike and I went tumbling.

At first I thought I’d broken the crank arm, but discovered it was the left steel spindle of my pedal. I have never, ever, snapped a steel pedal spindle before. Call me shocked.

And I was lucky, as I did my inelegant cartwheeled in the middle of an otherwise empty residential street. Sadly, no video of the acrobatics. Bummer. But that video above feels very, very familiar. Surprisingly, there was almost zero bike damage, although I was a tad stiff and sore. The bike rotated right-round with me and stayed hoisted in the air due to my right foot remaining connected.

The most important lesson came as I rolled onto my back at a speed just a bit too fast to keep my neck muscles tight. As I heard/felt my helmet crunch as it performed the bounce off the pavement, “Thank you, dear helmet,” I whispered. Hence: Always wear your helmet!


For the record, going up hill when this happens is much better than flat out racing or mashing down a hill. Gravity kicks in and your forward motion is slowed. So it is mainly how your leg/foot comes down and how nicely you do that 1/2 cartwheel. At speed? Major road rash, just to begin. I shudder to think.
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Old 02-07-16, 05:07 PM
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Head knocker..
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Old 02-07-16, 05:13 PM
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The closest I've come was cracking a plastic pedal in half while climbing a hill. No drama, but I was much slower back then... Plus it gave me good reason to try clipless...
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Old 02-07-16, 05:13 PM
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Originally Posted by Homebrew01
That's why I always climb in the big ring
I've been having troubles with cross-chaining under full power off of the big ring causing my chain to drop

But, fortunately I don't go down. I suppose one difference is one still has the feet in the pedals even with a dropped chain, whereas a broken crank, and one side is just hanging.
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