flaw in steerer tube kills cyclist

[jags]

this is bad.

http://cycling.today/hidden-flaw-in-4000-bike-causes-death-of-cyclist/

 

[mjr]

I'm confused about what happened. Did the aluminum steerer snap inside the head tube or did it come unbonded from the carbon forks as in previous examples?

Anyway: steel seems the obvious material for forks because it doesn't fail as messily.

 

[r04DiE]

How tragic.

 

[Tin Pot]

Heard about it last year when it happened, seems to have taken two years to get a coroners report?

Maybe search for the previous thread for more details.

 

[jefmcg]

Heard about it last year when it happened, seems to have taken two years to get a coroners report?

That's how long it takes. A friend spent two years trying to forget as much as she could about witnessing the aftermath a friend's suicide, then was called to be a witness at the inquest.

 

[Blue Hills]

I'm confused about what happened. Did the aluminum steerer snap inside the head tube or did it come unbonded from the carbon forks as in previous examples?

Anyway: steel seems the obvious material for forks because it doesn't fail as messily.

Question. No agenda. You mean it would fail more gradually and hence you would notice a problem?

 

[mjr]

Question. No agenda. You mean it would fail more gradually and hence you would notice a problem?

Mostly, plus the different properties mean it shouldn't fail at all if stresses remain below the fatigue limit. I may be wrong and Mr Saddle will be along in a minute to correct me

 

[Ticktockmy]

Any component failure on a bike in my mind is unpredictable, so many factors can cause a component to fail, how we use the cycle, do we service it regularly, etc, but then there is manufacturing faults. No doubt the manufacturers could apply aircraft industry checks as proposed in the news item, but that would impose a considerable increase to the price of the cycle. I think we have to trust in the component manufactures, and those who assemble and service the cycle prior to purchase.

 

[andrew_s]

I know of 5 failed steel steerers amongst local riders, over the last 30 years or so.

2 were detected because the headset bearings didn't remain adjusted for very long, prompting investigations which found a crack at the steerer/fork crown joint.
1 was noted and ignored for as long as possible whilst riding home from Bristol to Cheltenham. The front wheel was gradually getting further away from the bottom bracket, and the rider eventually had to walk the last 3 miles or so when the BB height got low enough that the pedal wouldn't go round the bottom without grounding. This could have been a failing fork crown rather than steerer.
1 failed at the top with no warning, low speed, the stem & steerer top coming away from the lower part of the steerer. This was due to a quill stem expanding into a threaded section of the steerer.
1 failed at the steerer/fork crown joint with no warning at fairly high speed. This seemed to be due to an under-specified tube having been used on a tandem (solo/unbutted).

 

[mjr]

That gets a like for the description of the one ignored as long as possible

 

[Ajax Bay]

From the coroner's report (with my editing and selective emboldening):

· The failure of the fork was caused by a fatigue fracture occurring in the aluminium alloy steering tube inside the bonded fork assembly;
· The fatigue crack occurred in a location where it was not visible to persons following the manufacturer-prescribed owner pre-ride inspection and technician service inspection methods; and
· The fork has a finite structural life and, upon reaching that finite structural life, can fail catastrophically without warning.

• Expert opinion: the fracture appearance at the fatigue origin was typical for a fatigue crack caused by a cyclic stress of sufficient magnitude and number of cycles.
• Coroner: any recommendation I make should be appropriate and capable of implementation.
• Trek: there is no cost effective or practical method to identify internal fatigue cracks of this type in routine maintenance checks in the consumer setting, as specialist expensive equipment is required.

Recommendations

a. Noting Trek’s owner manuals already warn owners that bicycles are not indestructible and every part of a bicycle has a limited useful life, I recommend that Trek update its owner’s manuals and consumer information to expand upon this warning and to note the risk of catastrophic failure without warning in some circumstances.

b. That Standards Australia and other relevant international standards bodies investigate fixing an upper “safe life” limit (safe life) for the bicycle front steering fork, depending on the manufacturing process and material construction of the part, after which the owner is encouraged to replace the part irrespective of whether damage is visible.
HTH

 

[Ajax Bay]

Did the aluminum steerer snap inside the head tube or did it come unbonded from the carbon forks

From the above, this was an aluminium fatique failure rather than failure of the carbon/metal bonding. Bike was 9 years old and (quote) "bicycle had previously been involved in one or more accidents". Careful when you use the word 'snap' .

 

[Chris S]

If a bit of a steel bike fails, the final bit where you notice it usually occurs sufficiently slowly that it feels odd for a bit before it breaks. Aluminium, on the other hand, usually fails rapidly, with little to no warning.

When my steel seat-post failed I thought the saddle clamp bolt had come loose and the seat was rotating upwards!

 

[Deleted member 1258]

When I had a seat post fail it just started to creak a lot, then one morning I was lifting the bike into the bike rack at work by the saddle and handlebars and the saddle came off in my hand.

 

[steveindenmark]

When my steel seat-post failed I thought the saddle clamp bolt had come loose and the seat was rotating upwards!

There seems to be a lot of seat post there and makes me wonder how much is left in the tube. I am guilty of doing the same thing and it must make it easier for te seat post to give way.