Friday, October 11, 2013

Carbon Forks - No Way

In No Carbon for Me, Thanks, I laid out my problems with carbon fiber in general, as used for frames, forks, and components. In this post, I want to focus just on the forks. The fork of a bicycle is a particularly vulnerable part of the frame system, absorbing a lot of the force of many kinds of impacts -- often like the "front line" of an assault. In addition, the fork is like a large lever, which can magnify the forces put upon it. Many bikes today come with carbon forks -- including many bikes that have frames made of steel, aluminum, or titanium. To me, the notion of making the most vulnerable part of the frame, and a part that is particularly important for controlling the bike, out of a material as sensitive to damage as carbon fiber (especially when that damage can be so difficult to assess), is ludicrous.

In researching for this post, I happened upon this article in VeloNews. In it, Lennard Zinn answers readers' questions about carbon forks. In response to a question on the life span of carbon forks, Zinn got answers from several manufacturers. Here's one from True Temper:

True Temper’s . . . test is a ramped load, meaning the load is increased periodically until failure occurs. Starting at 180 lbs, the load is increased 45 lbs. every 5000 cycles. Every fork will eventually break. Strong forks will last more than 10,000 cycles with a load of 270 lb. But our minimum standard begins at over 15,000 at 315 lbs. for road forks and 18,000 for cross forks and tandem. But our production forks are stronger than that, often going into the 20-25K range and beyond at loads of 360-405 lbs.

Even I have to admit, that sounds pretty impressive. In lab tests, carbon beats everything -- even steel. Then again, there's more to the story. The rep from True Temper continues:

Obviously, crashes are uncontrolled events and it is not easy to guess what loading was applied to a component by the speed or violence of the crash. After any crash it is important to thoroughly inspect the frame and components for visible cracks, dents, and bends. An Alpha Q fork that has been damaged (usually evident as a crack) should be replaced.

The question anyone should be asking is what about the damage one can't see? Short of getting the fork X-ray'd (and even that might not reveal anything) how is one to know that a carbon fork that appears to have completely "shrugged off" an accident is actually sound? A steel fork will bend, or it may show a crack that will spread slowly. The carbon fork may show that crack as evidence of structural damage -- but it may not. Then days, maybe weeks, maybe months later, it can break suddenly.

Here's the response from Deda:

Carbon lasts longer than metal. Only love is stronger than carbon. Bonding is a different story. I believe that a good glue (epoxy) can last for 2000 hours of work, or about 800 days, not in continuous daylight, and below 35 Celsius. Whenever a carbon “part” has crashed, even if you cannot see a failure, if there is any reasonable doubt about having surpassed the elongation limit, the part must be replaced.

This isn't making me any more confident. Keep in mind, when they talk about "bonding" it goes beyond joining the fork blades to the crown, or joining the crown to the steerer (not that that isn't totally critical -- it is). The carbon fibers themselves are bonded with some form of epoxy just to hold them all together and give the tubing its shape. What does that mean, "a good glue (epoxy) can last for 2000 hours of work, or about 800 days, not in continuous daylight, and below 35 celsius"? I mean, now we're not even talking about crash damage -- we're just talking about too much sunlight, or temperatures being too hot or cold, breaking down the integrity of this very critical frame component. And 800 days? That's barely over two years! I can only hope that this is just some language barrier, or maybe I'm misinterpreting the answer -- because this doesn't sound so impressive.

I liked this answer from Look:

There is no limitation because carbon has a natural flexibility. It can be used a hundred years while maintaining the same stiffness.

That kind of ignores the whole "composite" nature of carbon fiber as it is actually used in the manufacturing of a fork, frame, or other component. It also sidesteps the real concern -- carbon itself may not lose stiffness, but what keeps it all from de-laminating, which is where the plastic/epoxy/resin or whatever it is "lets go," leaving the carbon fibers free to come apart? Remember, without that plastic "matrix" holding the carbon fibers together and giving the tubing its shape, it would be like trying to ride a bicycle made of string.

In further reading, I found this blog post by Isolatecyclist. In his argument for carbon forks, he cites the above-mentioned Zinn article from VeloNews pretty extensively. He then goes on to say:

If carbon forks are so prone to catastrophic failure, why are there no high profile carbon bike or fork class action lawsuits circulating on the internet? In a litigious society like the U.S. at least one carbon fork manufacturer would have been sued out of existence by now. Instead, many carbon fork manufacturers offer a lifetime warranty on their forks. Just from a business standpoint, if the failure rate was high, they would go out of business.

Now, I don't want to sound like some kind of conspiracy theorist whack job, but the lack of news about lawsuits in relation to broken carbon forks isn't that hard to explain. All one has to do is look at the examples from other, much larger and very successful industries, such as the auto industry. Somebody gets hurt because of a defect in your product, pay them whatever it takes to settle any possible lawsuit, then have them sign a non-disclosure agreement as part of the settlement. In terms of the bike industry, obviously I have no proof whatsoever that they take this route (and I'd like to think they don't), but it's what a lot of other industries do, so why wouldn't they? And if they did, the whole point of non-disclosure agreements is that people don't talk about them, so there is no proof.

And the thing is, there ARE lawsuits against the manufacturers. But since bicycling is still, in the big scheme of things, considered by many to be something of a "fringe" activity, the lawsuits aren't going to make big headlines. Nevertheless, here's an article about one such lawsuit: Carbon Fiber Forks on Bicycle Can Hold an Insidious Danger. In it, one can read the actual settlement (spoiler alert: the plaintiff won).

Regarding those lifetime warranties, considering all the disclaimers about crash damage and abuse, they don't have to honor the lifetime warranty if they can show that the fork was either in an accident, or the owner didn't follow specified guidelines for use. What kind of guidelines? How about these, from Trek, released after a string of fork failures?

1) Always use a torque wrench, and never over-tighten stem clamp bolts.
2) Always use spacers above and below the stem. Although less obvious than correct torque, a minimum of 5mm and a maximum of 40mm spacers under the steerer, plus a 5mm spacer above the stem are required. Riders should factor in these spacers when sizing their bike.
3) Use only the stem brand and model that came with the bike, because not all stems will work with carbon steerers. Often the lighter the stem, the less chance it will be compatible with a carbon steerer. Weight-relieving cutouts on the stem clamp and steerer interface can create stress risers.
So now a rider can't even change stems unless he uses the exact same make and model of stem that the bike came with from the factory. Otherwise the warranty is voided. Great. It's nice to know that carbon forks are so much better than steel. Such an improvement. And only love lasts longer.

Isolatecyclist (please don't think I'm attacking him -- he's not an expert -- just a blogger like me) also pointed out this interesting note about the reports of broken carbon forks:

Most of the "unexplained catastrophic fork failure" reports are located on personal websites or in bike forums. There aren't well-known consumer or professional cycling websites warning consumers about the "dangers" of carbon forks.

Of course, the "well-known consumer or professional cycling websites" aren't going to take a shrill "sky is falling" tone about carbon fork dangers (remember who actually pays them and keeps them in business) -- but the stories are there. The reports are more than just anecdotes from faceless, nameless nobodies on forums. How about this story from VeloNews: "Steered Wrong? Racers Concerned About Broken Carbon Steerer Tubes. In it we get to see Trek blame the owners for their broken forks because they were using the "wrong" stems (i.e., not the Trek-owned Bontrager ones) with their carbon forks. Then there's this one, also from VeloNews: Cervelo Founder Calls for Industry-Wide Fork Steerer Test. Here's a quote:

The cycling industry isn't doing enough to prevent fork steerer failures.
That’s the opinion of a man who would know: Cervélo co-founder Phil White, whose company suffered a large fork recall in 2008 following fork failures that resulted in multiple crashes and injuries.
Cervélo is not alone in that sorry episode.
The cycling industry has seen a rash of fork steerer-related problems in the last few years, from nearly every major brand sold in North America. Big brands with big test labs have experienced consumer injuries and expensive recalls that the manufacturers say resulted from a mix of engineering and manufacturing flaws. 
Clearly, the industry is aware of the problem. But they keep chasing the chimera of lighter weight, knowing full well that weight-obsessed roadies will pay a premium to be used as crash test dummies. Many of these riders will try to dismiss the reports as unimportant, unconvincing "anecdotes" from faceless nobodies who didn't take care of their bikes, or who crashed and ignored the obvious signs of damage. They'll remain certain that their own forks are sound. They'll hope or expect that engineering or manufacturing flaws, such as voids buried deep in between the layers in the carbon layup, only happen to "other" brands, but not the one they've chosen. But the problems seem to be happening with every brand.

Here's another sign that carbon forks are known to be problematic, and have been from the beginning. Look at the way the dimensions of forks have changed so much in the last few years. Note that steerers for steel forks were 1-in. diameter for generations. Then 1 1/8-in. after the advent of mountain bikes. It wasn't necessary for steel forks on road bikes to go larger, but when steerers started showing up made of aluminum, the additional diameter was needed for strength. But the junction between aluminum steerers and carbon fork crowns was problematic. Different materials with different properties. Add salty sweat into the bonded joint between those different elements and it becomes battery acid -- galvanic corrosion could eat at the joint. Then the manufacturers started making the whole fork out of carbon fiber, but the strength was still at issue. The "step" or transition between the crown and the steerer was thought to be a weak point -- so we now are seeing tapered steerers with 1 1/4-in. at the fork crown, and 1 1/8-in. at the top. They're still more prone to failures. It makes me wonder what we'll see next.

Of course, the ads will never say "We had too many of 'em breaking before, so now we're making the steerers bigger." But the strength issue and failure rate is why carbon forks are evolving in the way we're seeing. There isn't really a better explanation for it.

Can steel forks fail? Yes. There have been recalls on defective steel forks due to manufacturing errors. But it's a much rarer thing. Accident damage with a steel fork can be seen and diagnosed much more readily. Damage that goes unseen tends to develop more slowly, giving more time and more clues before failure. I'm not trying to be some kind of Cassandra, stirring up irrational fears of carbon -- but for me, the safety and reliability of a good steel frame and fork are worth a lot more than a couple pounds.


19 comments:

  1. Thank you for a thoughtful and well argued post. Carbon has remarkable properties and some equally remarkable disadvantages. For myself, steel is the preferred material because that's what they built vintage bikes out of as well as for its own remarkable properties!

    It is ironic that IsolateCyclist used the failure of a steel fork to support his argument in favour of carbon. The comparatively long period leading to failure filled with warnings in the form of anomalous noises and handling are perfect arguments for the fail safe mode of steel compared to catastrophic, unannounced and sudden failure mode of high performance carbon. Steel would have to be invented as a frame material if it did not already exist!

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    1. I did find the steel fork failure to be an interesting example -- obviously, nobody wants their fork to fail (regardless of what it's made from), but the fact that it happened slowly and gave some warning means that it failed exactly as one would want it to under the circumstances.

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  2. Chicken Little stirred up irrational fears. Cassandra was spot-on, though unbelieved.

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    1. Oh man -- you're right. Good point.

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  3. I've recently purchased a new aluminum bike with a carbon fork. Sometimes I think that I need to experience some things to believe, bought it even knowing I'll have trouble in less than two years...

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  4. A quality steel fork will only weigh about 400grams more than a carbon one. Worth that bit of extra weight for the piece of mind.

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  5. You neglect the common carbon forks that have alloy steerer tubes. That does remove some of the issues with stem selection, spacers and stress.

    I'm sure carbon will be with us a long time. I understand they make airplanes from it, and those airplanes do not all fall from the skies (although the tails have been known to come off http://www.washingtonpost.com/wp-srv/nation/Composite18.html)

    A prediction - future "cheap" bicycles will be carbon fibre and steel bicycles will become ultra-expensive luxury goods. (I also predict that in ten years we will see someone walking with a newspaper and say "Wow! He must be rich! He has a *printed* copy of the New York Times!")

    The difference is in material usage (and tolerance for abuse). Jet airplanes are operated under rigorous controls and with excellent maintenance. Bicycles are crashed, left in the rain - often never maintained. It's amazing there are not more bicycle accidents. Even people with fancy bikes often have no idea how to maintain them or what situations to avoid.

    A steel bicycle usually gives up the ghost in a predictable, gradual fashion. You feel something's not right, hear a noise that wasn't there and discover that crack that also wasn't there before. Carbon tends to explode (or appear to).

    I have a carbon fork I pulled out of the trash at a(n) LBS. The alloy steerer tube has started to separate from the carbon fork blades, so it was replaced (warranty). I'm going to do some destructive testing of my own on it, just to get a feel for how tough it is. My guess is that it's plenty tough but that when it goes, it goes quickly.

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    1. What you mention about carbon forks with alloy steerers is true -- at least as far as the stem and spacer issues. However, the problem with those (which is a large part of the reason many are going to all-carbon construction) is the galvanic corrosion between the aluminum and carbon, which leads to separation -- probably like the one you pulled out of the trash.

      That is the beauty of a good steel fork. Sure -- they can fail. But it's usually much more predictable and gradually, as you say.

      Carbon fiber used in commercial jetliners scares the hell out of me. I try to take comfort from the fact that the aerospace companies have HUGE budgets (many times greater than the bicycle industry) for R&D,and testing, etc. to hopefully eliminate the dangers.

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    2. Steel rusts, even after a paint chip. It also rusts from the inside out so that you can't see. In humid coastal environments I've lived in this can happen quicker than you'd believe. Even in Cornwall UK, let alone Queensland. I love a classic steel bike for nostalgia but times have changed.

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    3. Yes, steel rusts. But it's totally manageable, even on the inside. I've seen lots of frames that were truly neglected and badly rusted -- but it takes a lot to destroy it to the point of failure. It's not just nostalgia.

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  6. Airplanes are scrapped after they crash - unlike carbon forks - so any load they're subjected to is entirely within the design limits. They're also regularly checked using highly sophisticated equipment - again, not something that can be said about forks.

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  7. Thanks for taking the time actually ask - Deda provided good insights because most manufacturer avoid acknowledging the UV factor - what happens to carbon fiber in light. Lets ask this from a different angle, have you ever seen a discoloured carbon fiber bike. Generally not new ones, but if you have been around bike for a while, older ones can show signs of fading.

    When engineers calculate how carbon on a bicycle moves which subsequently influences layout - what are they missing - for example, riding a carbon fiber bike on an indoor trainer introduces different stresses for which the bike has less resistance.

    Carbon fiber is great - and for bikes it has become cheaper and cheaper, but it would be worth knowing more about it, more about the reasons it fails, failure rates and longevity. I get it when parts have a lifespan, I expect to replace tyres - of not worn they will break down over time. Carbon Fiber in consumerable products is very very young and I expect that in 10 and 20 years we will know a lot more about the lifespan of the carbon fiber bikes which we are riding today.

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  8. I crashed a bike with a carbon fork and alloy steerer and managed to delaminate a fork leg. I however rode the bike for another 4 miles after crashing it without issue. I had to ride the bike 4 miles to the nearest parking lot so I could find someone with a car that could drive me the 20 miles to the hospital.

    As a matter of fact I didn't even know the fork had been damaged until I returned from the hospital and inspected the bike.

    So no, my carbon fork/alloy steerer combo didn't fail on me even though it had been damaged in the heat of battle. I had crashed hard enough to knock the stem and shifters out of alignment, but even then, the carbon legs/alloy steerer interface didn't fail me, and neither did the fork leg that was cracked.

    I promptly replaced the cracked fork with another carbon/alloy fork.

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    1. That's great that it got you to the parking lot. You were lucky -- at least in that regard.

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  9. maybe not pertinent here??? but I have bent 2 Ti seatposts and shattered (scrunched?) 2 carbon posts and 1 carbon handlebar. Went back to my old alloy serfas seatpost and raceface h-bar...seen the light after too much $$ spent. hype don't make right. FWIW...195 lbs on a kona explosif 853 steel for 16 years...and yes, i do ride a Ti hardtail mtb as well. I sold the carbon bike with the press-in BB after 3 rides full of creaks...hype don't make right.

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  10. I had a Reynolds Cross steel fork fail on me years ago. I could not figure out why my bike was suddenly out of line while riding no-handed. Then I saw that one fork blade was cracked at the crown, held only by 1/4" of material. I rode that fork for four more days before I could replace it...essentially on one dropout and one blade. Sure I was taking a risk but I was a poor student with places to go! I marveled at the forces at play the whole time. I have always loved steel. Built 35 frames, countless forks and many many steel repairs. I am well aware of this carbon problem and I have been working on the solution. Steel will always be around as long as at least one of the big four still makes the tubes but carbon is here to stay. It is simply an inflation/economic issue.

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  11. I've sheared a butted chromoly steel frame at the top tube + head tube, folded steel forks, cracked a steel bike at the seat tube, bent steel chain stays in a crash, cracked aluminum dropouts from fatigue, and had aluminum handle bars snap in-two during a sprint. I'm giving carbon fiber a chance.

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  12. >> If carbon forks are so prone to catastrophic failure,
    >> why are there no high profile carbon bike or fork
    >> class action lawsuits circulating on the internet?
    dead men dont litigate.

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  13. What is sometimes overlooked is how the scrap is handled. Steel is infinitely recyclable. There are no practical carbon fiber recycling methods.

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