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  1. #1
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    Steerer tube snapped on Trek 7.6FX - serious accident

    The aluminium steerer tube on my 2009 model Trek 7.6FX suddenly snapped with no forewarning, leading me to have a nasty accident. I'm curious if anyone has had a similar experience, or can help me understand how this could happen?

    I used the bike for commuting short distances to/from work and for part of that journey I would have my three year old son on the back. I also commute with a backpack on and so all up am probably slightly heavier than the average cyclist, though still well within the design specs for the bike. The bike was always well maintained and only ever used for normal on road use. Strangely (fortunately!) the final breakage happened on a perfectly smooth concrete surface as I rode through the basement of my work building. I just mention this because it's odd that the fatigued steerer made it over all the bumpy London roads to work and then finally failed on a really smooth surface. That was very lucky for me, as had it happened on London city streets I'd likely have ended up under a bus, or with more serious injuries.

    Trek took the bike back for inspection, but eventually denied responsibility, concluding I likely either had an earlier crash on the bike, or else was subjecting it to abuse - riding it down stairs was given as an example of abuse. None of that happened - the bike was only ever used for normal on road cycling. In contrast to Trek's findings the bike shop that did the initial inspection concluded that there were no signs of an earlier crash, abuse or anything of that sort. If Trek's claim that the bike had suffered an earlier incident involving the front wheel hitting an immovable object at speed, wouldn't the carbon forks have snapped or been damaged?

    Trek did give me a new bike, but it's another FX model with the same carbon forks and alloy steerer. Since I know product abuse / an earlier crash were not features of the last one breaking I'm not sure how much confidence I can place in this new bike and whether I can safely put my son on the back. Basically I'm disappointed that a three year old safety critical component could fail like this. This bike has the exact same fork as fitted to many Trek road models and if there is a problem with it the recall would be significant. I also notice that when I bought my bike originally Trek used to advertise the FX models as being hybrids capable of some light offroad/trail use. They are now advertised as a cross between a road bike and a city bike, with no claims of any light offroad capability. I am cautious that Trek might have more awareness of a potential issue here than they've acknowledged to me. I expect the fork is fine for most light cyclists, but potentially a concern for heavier fast riders.

    I'll post photos of the snapped steerer if there is interest.

  2. #2
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    Where did it snap, at the fork crown or at some point above the headtube?

    Edit: It's not particularly implausible for it to have failed on a smooth surface. All you need for a fatigue crack to extend is a cyclic stress on the material (i.e. one that changes in magnitude), and most of the stresses on a bike are at least partly cyclic, regardless of the surface.
    Last edited by Airburst; 01-11-13 at 02:15 AM.

  3. #3
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    Quote Originally Posted by Airburst View Post
    Where did it snap, at the fork crown or at some point above the headtube?

    Edit: It's not particularly implausible for it to have failed on a smooth surface. All you need for a fatigue crack to extend is a cyclic stress on the material (i.e. one that changes in magnitude), and most of the stresses on a bike are at least partly cyclic, regardless of the surface.
    It snapped at the fork crown. It's basically just sheered off right through the steerer tube at that point.

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    Maybe it was damaged during assembly? I wouldn't worry about riding the replacement too much, a heavy rider on light terrain is no worse than an average rider on rougher terrain, and surely people are hopping up and down kerbs with these bikes all over the world. If it were a systematic issue, you would find evidence of that on the internet I think.

    I haven't actually searched for similar evidence, but I assume you have.

  5. #5
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    Curious about one thing. You mentioned that TREK denied responsibility for the failure, yet they provided you a replacement bike? Interesting.

    If you have a great deal of uncertainty about the fork on your new bicycle, replace it with either a aftermarket aluminum or even a cro-mo model with the same geometry.

    While I am pretty confident that modern assembly practices and engineering will yield a fork you could ride with out any hesitation, there is always the " the juncture of two dissimilar materials is a question" philosophy.

  6. #6
    The Recumbent Quant cplager's Avatar
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    Quote Originally Posted by 100bikes View Post
    Curious about one thing. You mentioned that TREK denied responsibility for the failure, yet they provided you a replacement bike? Interesting.
    I found that very intersting as well. Kiwi, I'm hope you weren't injured too badly and I'm glad to see you back up on the horse, err... bike.
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  7. #7
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    Quote Originally Posted by 100bikes View Post
    Curious about one thing. You mentioned that TREK denied responsibility for the failure, yet they provided you a replacement bike? Interesting.

    If you have a great deal of uncertainty about the fork on your new bicycle, replace it with either a aftermarket aluminum or even a cro-mo model with the same geometry.

    While I am pretty confident that modern assembly practices and engineering will yield a fork you could ride with out any hesitation, there is always the " the juncture of two dissimilar materials is a question" philosophy.
    A lot of companies will do this where there might be a liability issue, they know there is some sort of issue, but they dont want to admit to it for fear of lawsuits, cheaper to replace the frame and keep it quiet then argue with the customer

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    Quote Originally Posted by lauradogin View Post
    yeah,thinks. replace it with either a aftermarket aluminum or even a cro-mo model with the same geometry.thanks
    All-aluminum forks, both aftermarket and OEM, are pretty much gone now and even aluminum steerers are rare. Cr-Mo steel, all-carbon or carbon with Cr-Mo steerers are the norm. I agree that your steerer failure was a rarity or Trek would certainly have been forced into a recall by now but George Hincapie lost a possible win at Paris-Roubaix when his Trek's aluminum steerer failed so it's not unheard of.

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    A few things about this are unusual. It sounds like you were dealing with Trek yourself rather than a dealer doing it for you. And it sounds like you may still have the fork? Or did you take pictures before returning it.

    Nice to hear you did end up with a new bike - pictures would be interesting, but only if good quality. Normally a progressive shear is pretty clear because the final area to let go is the brightest and easy to pick out.

  10. #10
    coprolite fietsbob's Avatar
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    As you describe what you use the bike for, now , you may have fancier parts than you really need ..

    see if the shop that sold the bike to you and got the replacement, can find an adequate steel steerer fork..
    Last edited by fietsbob; 01-11-13 at 01:28 PM.

  11. #11
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    One of the problems with aluminun is a finite fatigue life. With steel as long as it is not pushed past it's yield point and there are no stress risers it will not break because of fatigue.

  12. #12
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    IMO, (just my opinion for what it's worth, Qualified as knowledgeable about bikes but not a qualified metalurgical opinion) aluminum is unsuitable for steerer tubes because it's prone to notch failure at stress risers and/or metal fatigue. I'm not saying it's poor material, and cannot be used safely for steerers, but with all the variables in the form of abuse, and no protocol for periodic inspection, there's no reliable way to predict the useful life of an aluminum steerer.

    Since crown failure of a fork is the one structural failure most likely to lead to an injury, I prefer the prooven reliability of steel steerers, and as an alternative carbon steerers designed to prevent steerer/crown failure.

    That's not to say that Trek isn't right that the bike had suffered a prior collision. However a ductile steerer would have bent slightly before failing, while an aluminum one might not.

    I don't know the extent of your injuries, but wouldn't use the fork sent, especially given the prior experience. I'd try to negotiate with Trek or the dealer for a different, more proven fork.

    BTW- don't assume that a carbon blade fork would fail at the blades rather than the steerer. It's a question of relative strength and ductility (carbon has none) between the blades, steerer and frame which determines which suffers the most damage in a collision.

    Unfortunately, it's impossible to determine whether and to what extent prior abuse contributed to the failure, but if it's a significant issue related to possible damages for your injury, a metalurgist, or engineer expert in structural failure could render a proper qualified pinion if he inspects the fork and frame.
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  13. #13
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    Go with steel. Works for me. YRMV. I don't trust carbon.

  14. #14
    Retro Grouch onespeedbiker's Avatar
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    The Trek response is, "Give him a new bike and he hopefully will not pursue a law suit". It's pretty much your choice, but a personal injury attorney would pick this up in a minute. This is not the way I would handle it, I'm just saying..
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  15. #15
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    Quote Originally Posted by onespeedbiker View Post
    The Trek response is, "Give him a new bike and he hopefully will not pursue a law suit". It's pretty much your choice, but a personal injury attorney would pick this up in a minute. This is not the way I would handle it, I'm just saying..
    Since the OP commutes on London roads, I assume he's in the UK, where civil tort law is quite different from here in the USA. Even in the USA, whether a lawyer would "pick it up in a minute" depends on the extent of his injuries and an examination of the fork.
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    I'm not a huge fan of aluminum either. Nor carbon fiber for that matter. But that's just me.

    I too tend to believe that steel often gives you a bit of a warning before it "lets go" on you.

    Funny thing is that my wife and I own an aluminum framed urbanized mtb. It's full suspension though.

    Go figure.

    Meanwhile, it seems likely that it was a manufacturing process failure; i.e. a slightly over-sized dia. steerer tube being pressed into the fork crown S. tube bore, improperly (factory) installed lower headset race, or even an improper radius on the fork crown S. tube bore (all of which could create a stress riser on the S. tube).

  17. #17
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    Are you sure the steer tube broke or did it lose its bond with the crown lug?
    Is the break ragged or straight?
    If the break was caused by a frontal collision then the front of the tube should show tension stretch marks.
    There is nothing wrong with using aluminum alloy for a steer tube. There must be at least a jillion bikes out there with Al steer tubes. And it's still used in airplane construction. And the strength properties vary with every alloy. Trek bikes have a good reliability reputation. But I have heard of some bonding problems at the tube joints, but those were on old bikes. if you care to look it up at wikipedia.

    I see you Brits still call it aluminium. There's a story behind that if you care to google it.
    Last edited by Al1943; 01-11-13 at 04:29 PM.

  18. #18
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    Quote Originally Posted by davidad View Post
    With steel as long as it is not pushed past it's yield point and there are no stress risers it will not break because of fatigue.
    That's not quite accurate. The "fatigue threshold stress" below which steel (or titanium) will tolerate infinite stress cycles is well below the yield point.

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