Broken steerer tube - result of a crash or not?

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mrlobber
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Joined: Sat Oct 23, 2010 9:36 am
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by mrlobber

So a race today and a huge pileup with me also falling prey to it, and a couple of riders later over me...

Got up, examined my wounds (luckily, nothing too serious) and rode 20km back to the start zone where (at a small speed - essentially pedestrian) this happened suddenly...

https://goo.gl/photos/Kf2bBvfGzzzcLzu37

Anyone experienced this as a result of a crash? The steerer tube essentially has failed exactly at the point where the upper headset bearing ends.

Just interesting whether the crash caused it or a catastrophic failure was inbound anyway and so I was lucky it happened at an "appropriate" moment.

Bike is Cannondale Supersix Evo 2013
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LionelB
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by LionelB

Ouch, glad you are OK and it happened shorty after the crash at low speed.... Much better than on a fast downhill. It seems to be due to the crash as it happened right after it.

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sungod
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by sungod

scary, good that you are ok

does seem likely to be the crash, though if there were any scoring from the bearing it might have weakened it earlier

i'd have a long hard look at stem and bars as the force that finished the steerer probably went through them

mrlobber
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by mrlobber

Stem is ok, haven't unwrapped the bars yet.
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F45
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by F45

Wow, unlucky in the crash but oh so lucky you found the problem at a low speed. This could have been you!

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Valbrona
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by Valbrona

What was the arrangement of spcaers under the stem? Some say that stem directly on top of a shallow headset top cap can encourage steerer breakage at this point.

clm2206
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by clm2206

Where is your fork steerer tube expander? That's the piece that should have gave integrity to the whole system. For racers, a solid expander must go way down from the upper headset bearing and way up to the upper stem steerer bolt. Without the adequate height, the stem is always giving shear forces to your fork steerer tube. You should always avoid those half inch height expanders, only suitable for weight weenies bikes. In my humble opinion.

em3
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by em3

An expander wedge/bung, whether the screw-in type or the glued-in type is not going to give a steer tube "extra" integrity. Forks are not designed to yield their maximum strength with bung installed. It appears that the failure on this fork was about 1cm below the edge of stem so excessive torque on stem bolts was not the cause of failure, unless the stem had been previously over-torqued in lower position and scored the steertube. Otherwise the failure was due to force of crash.
Last edited by em3 on Mon Sep 07, 2015 6:21 am, edited 1 time in total.
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F45
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by F45

clm2206, just to be clear, you're just stating your opinion, true? If a short expander was not structurally sound then every bike with a couple of spacers, which includes about every oem bike manufactured, would be unsafe.

mrlobber
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by mrlobber

There was a 1cm spacer under the stem. The expander plug was not extending below the stem, and was original from Cannondale, with their "System Integrated" top cap. Stem was torqued to 5nm, standard stuff :) After the crash, the bars were not aligned with the steering axis, I loosened the stem bolts slightly and straigthened the bars, before riding back.
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mrgray
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by mrgray

how extremely fortunate this didn't end terribly. from what you say about having to realign the bars post crash, doesn't that add weight to the idea the crash caused the subsequent total failure? of course perhaps other actions weakened it prior, but surely the crash is enough plausible cause.
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