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

19 comments on “Carbon fibre fork failure”

  1. Stephen Almond wrote:

    And there's never been a sudden failure of a steel fork?

  2. Alan wrote:

    Thanks for this, Patrick. Best wishes to the casualty.

    A recent discussion about carbon forks on the CTC forum: http://forum.ctc.org.uk/viewtopic.php?f=5&t=55259

    It seems to me that carbon components are fine until they unexpectedly and rapidly fail. Failure is difficult (impossible?) to predict, especially for the hidden steerer tube. A sudden failure of steerer or forks is certain to have bad consequences.

    I've never been tempted by carbon. Yes, it looks good, and it weighs less than steel. But the potential cost is too serious for me to consider it.

  3. Patrick wrote:

    Thanks for the link Alan. It seems in this case it was the blade(s) that snapped.

    Stephen Almond wrote: And there's never been a sudden failure of a steel fork?

    There has, to be sure. Poor manufacture, neglect (rust), excessive abuse. And millions of cyclists use carbon forks without incident. This not a denunciation of carbon fibre for bicycles. The cyclist in question had banged his carbon fork before – a 6/7 year old fork from a reputable manufacturer – and presumably weakened it without knowing, nothing visible. That's the point, I think. You can keep tabs on a steel fork and be reasonably sure it's sound if properly manufactured.

  4. Hilary wrote:

    Heartfelt sympathy to the casualty, his friends and family.

  5. Keith Edwards wrote:

    Bets wishes to the gentleman for the future.

    My wife and I have a Trek bikes with Carbon forks that we have owned from new. When we bought the bikes Trek give a lifetime guarantee on the forks and frame to the original owner.
    I would never dream of selling the bikes with those forks or even just the forks. I feel that you have to know the history of such things from the start then cut them up if there is any doubt about any damage you may have caused cut them up.
    I have heard about failure of steel forks in the distant past but these were old and uncared for bikes.
    The moral for me is take care of the bike and know of any crashes or bashes it has had. I hope more people can do as the cyclist has said and learn from this.

  6. Kern wrote:

    My road bike has a mixed steel-carbon fibre frame. I wanted an all-steel frame but Gilles had this one on the floor and made me an offer I couldn't refuse. I wondered about pulling our BoB trailer with it; having read this article I will never do so. Best wishes indeed.

  7. Jim wrote:

    The stories about fork failure on the CTC website are quite alarming. I was off to France for a weeks loaded touring and was now concerned about the carbon fork on my light touring bike. Stripping the fork down to check condition I found some alarming marks and headed off to the LBS for advice. He said "it's just a bit of surface rust" "er no. It's an ali steerer" "no it's all steel. look" Out comes the magnet. Talk about feeling like a dope. I've been riding a bike around that I thought had a carbon fork for years. Still saves me buying a steel fork that I was thinking of doing for peace of mind. I do wonder what the weight difference is between the two though.

  8. Kevin Kennnedy wrote:

    I emailed Trek re the above 11 Jan 2012. I have a Trek 2.1 from new, which is a really nice bike for the price-just wanted some reassurance. As yet have received no reply, which is disappointing.

  9. Patrick wrote:

    Kevin, I wouldn't worry about it unless the bike has been crashed, especially with Trek. There are millions of perfect bikes with carbon forks – enjoy yours.

  10. Campbell wrote:

    Interesting comments. I am a keen cyclist but also have 15 yrs service in the aerospace industry where i daily inspect impacted carbon fibre components in an research and development field using ultrasonincs. I was considering starting an inspection service from home. Have inspected a few stems , bars, seat posts and frames in the past and yes damage was evident. Perhaps due to impact or fatigue as a result of forces exerted by rider over time on the road. Problem highlighted above is yes you may find damge but will the supplier replace expensive components free of charge. I currently inspect my and friends bike for piece of mind / reassurance of saftey. (UK – N.Ireland based) Interested in your views on my potential venture?? Worth while? Not based on profit but firstly for saftey in mind and potentially to improve the use of carbon fibre within cycling world.

  11. D Guise wrote:

    I had the down tube on a steel frame snap without warning and recently ran across a young disabled friend whose steel trike had snapped in the middle and dumped him on the road, luckily with only minor injuries. Seems to be less cases of breakages with alloy!

  12. S Lemanski wrote:

    As someone who has around 10 years of research experience with CFRP and other composites, I can categorically state that carbon fibre DOES suffer from fatigue (although the behaviour is more complex than metals). However, just like with metals, fatigue failures can be eliminated in practice by ensuring that the structure is correctly designed to keep the stresses low enough to ensure a fatigue life of millions or billions of loading cycles.

  13. barny wrote:

    I find it fascinating that with all this knowledge of the sudden failure ability of carbon, people still go out and buy the stuff. The only explanation is that they want to have a nasty accident. Nutters. I've had four aluminium frames fail in various places due to fatigue NOT due to sudden impact, all after about 15000 miles from new. For that reason alone, i would never chose a material for a fork that can suddenly fail.

  14. Patrick wrote:

    To be fair, carbon fibre doesn't suddenly fail without a reason. I've not heard of that anyway. It appears it can break without warning once it has been damaged, even when the damage is not visible.

  15. Ian Johnson wrote:

    Hi all, Heart felt sympathy to the rider above.

    I was racing my 2010 Boardman limited edition yesterday- a bike I had owned from new and cossetted. Accelerating out of a turn the steerer snapped inside the head tube- no warning and as a result I went down the road- very minor injuries luckily as I was only doing about 25kms but pretty sore today. Since then I have done some digging and it seems this kind of thing is far from unusual. I have been riding for 40 odd years on all sorts of bikes and never experienced anything like this 'catastrophic' failure and more to the point none of my mates have either. I am awaiting a response from Boardman currently and counting my lucky stars. We know there is inherent danger when riding a bike- but to have a key element give up this regularly you have to ask why is this material still used? I think the business checking the frames mentioned above is a great idea. I must say though why would you check something like your forks if you know the history of the bike.

  16. Matt Forrester wrote:

    Hey guys...

    I know that – apart from Ian's post from only a couple of weeks ago – my post is a rather belated one but for anyone who is interested, I found the article (that I've pasted a link to below) in question-and-answer format & then with information from some of the biggest names in frame production to be very interesting, & extremely surprising in many respects...

    And if you ever still "drop in" upon this article from time to time Patrick, I sincerely hope that your friend has adjusted as well as possible to his tragic crash & resulting injuries...

    And a Merry Xmas to all from "Down Under", where we endured 37 degree (Celsius) heat today...was bloody awful!!

    Cheers & best wishes, & STAY UPRIGHT!!

    Matt

    http://velonews.competitor.com/2002/12/bikes-and-tech/technical-faq/technical-qa-with-lennard-zinn-carbon-forks-2_3270

  17. JEFF WRIGHT wrote:

    Just so you know , the carbon steerer tube on my fork just failed catastrophically , it broke just below the stem which resulted in the bars becoming detached from my road bike . Go in for surgery next week for a separation of the AC joint .. Yeah carbon !!

  18. Jim wrote:

    Jeff.
    Sorry to hear that. What bike was it? An old or new one? Did you hit a pothole etc?
    Good luck. Jim.

  19. rum buba wrote:

    in my opinion nobody should use carbon on account that its structure is very similar to asbestos and some experiments with carbon fibre and rats show that it causes asbestos like diseases in them. i asked the british lung foundation if there was proof that carbon fibre does not cause asbestos like diseases in humans and they said there was none. the the health of workers that work with carbon fibre, we should stop buying it.

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