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Carbon fibre fork failure

A couple of weeks ago an acquaintance’s cycling companion snapped the carbon fibre fork on his Trek bike. He crashed badly and:

Quote: is paralysed from the neck down with little prospect of recovery. This is of course a total horror for a cyclist. He’s 61 years of age.

This acquaintance wants the exact circumstances to remain anonymous but the bike was apparently 6 or 7 years old and his cyclist friend had previously had a few bangs on it and is on the heavy side. My acquaintance again:

I’m going to sell my own carbon fibre bike which is I know a psychological reaction as I’ve not crashed it and it’s only done 3000 miles or less, or maybe I’ll just change the fork … My immediate thought was that’s the end of cycling for me, but I’ve had that thought more than once in the past … I’ve intermittently thought down the years that carbon fibre was potentially very dangerous … this brings it to our notice that this is a potentially catastrophic material and it is just not a good idea to use it in forks, especially.

Trek is a pioneer in carbon fibre development apparently. My cousin rides a Trek Madone and it looks superb (it is superb). I don’t know much about the material except it’s a lightweight composite used for components on performance bicycles: frames, forks, seat posts, handlebars etc, and in the rare instances where it fails, it can do so without much warning.

The CTC’s Chris Juden, quoting (on the CTC website) a Chartered Mechanical Engineer with experience of carbon fibre in aerospace applications, wrote:

If well made and cared for, any amount of hard usage is unlikely to lead to failure of the carbon-fibre reinforced polymer (commonly abbreviated to ‘carbon’). It does not suffer fatigue like metals. Fractures are more likely where this is bonded onto metal inserts due to different stiffness and thermal expansion of the two materials … There is also the problem that a severe blow may leave no external sign … Mistreatment that bends a metal fork can leave a carbon fork apparently unscathed but fatally flawed inside … The safest thing is to regard carbon forks as a consumable … this is a safety-critical component and the last place we want unexpected failures.

So it appears that most failures start inside the material that you cannot see or inspect. No matter how meticulously you check it visually, you might not know if your carbon fibre fork is failing because the material won’t always show damage on the outside. Frames and forks made in China or Taiwan may also be subject to lower manufacturing standards than those in Europe or the USA. That’s just my guess. Either way, construction and material quality are paramount for safety.

What does seem clear is that when a carbon fibre bicycle component has been badly bumped or if its surface shows any sign of damage – even a tiny crack – it should be considered potentially unsafe, especially the frame, fork or bars where breakage can lead to a serious accident. While steel and aluminium (and titanium) can also fail after prolonged use – or misuse, the warning signs are easier to spot.

Special care should obviously be taken when buying a second-hand (used) carbon fibre bike.

Photos of broken carbon fibre on www.bustedcarbon.com

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