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Why did this crash happen?

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John Allen photo
by John "Forensic" Allen
video footage by Greg Seyranian, Big Orange Cycling
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You figure it out

A friend recently sent me the video embedded below in which a cyclist suddenly loses control and takes a hard fall. My friend had told me that he had figured out the reason for the loss of control, but it was not obvious. My friend asked me whether I could figure it out. Can you?

OK, now you have seen it. What caused the crash? There is a short strip of black tar on the road, but the cyclist is entirely past it before he loses control. He doesn't collide with any of his companions...

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Let's look at it in slow motion

If you look carefully at the slow-motion segment of the video below, you will very likely see what caused the crash. Hint: no film was used at any step from the original shoot to the display on your screen. Every step was digital.

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The answer

Did you see that jagged black line flailing around in the image? As I said, it is not dirt: no film was used in the making of this video.

It's the bicycle's chain, which broke, leaving the pedals free to spin. The cyclist was standing out of the saddle, and suddenly lost support from the pedal he was pushing down.

A chain's breaking is only one of several kinds of drivetrain failure which can lead to a crash. Lets look into them now.

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Lessons

How can drivetrain-failure crashes be avoided, or made less bad? Here are things you can do:

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Equipment choices:

And here are some considerations about equipment .

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Links:

Our main article about chains

Our article about re-engaging a chain which has come off a sprocket

Our article about chain wear

If you have a single-speed or internal-gear system, we have an article about a special technique for extending chain life.

Bike Friday offers a good selection of cyclocross rings and its special chain retainer

Pardo.net on chain operation and chain wear

Friction Facts Chain Lube Test

Friction Facts test reports (they charge money for some of these reports! The complete report package is $14.95.

Velo News article with comments about chain waxing

Another Velo News article with comments about chain waxing

See also Damon Rinard on chain stiffness, and Jobst Brandt on Chain Maintenance
and if you are a real fanatic about chain cleaning...try this.

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Articles by Sheldon Brown and Others


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