Is this safe ??

[bad boy]

I was just about to mention that. So that was definitely the steerer that sheared? At the time no one seemed to know whether it was that or stem/bar failure. Do you have a link? I think George got a broken collar bone out of that.

All the top manufacturers seem to cover themselves when reading their service guides.

Trek said that FSA stems should not be used with their steerers, I mean what a ridiculous blanket statement to make and commit to. Saying that Astana had a steerer break at the 2009 TDF using a Bontranger stem which makes a mockery of all this denied responsibility talk.

Carbon steerers need checking until they get there act together its a free for all.

saying that here is a Hincapie link:
http://www.cyclingne...-brush-up/10012

 

[gbb]

There's another side to the breaking steerer issue, ive never heard of a 'normal' cyclist having a problem. Dont forget that pro riders probably stress their equipment way way beyond what we ever will. I'm just imagining the stresses that go through the bars and steerers on a pro bike as they're climbing mountains.

I'd hope that very average riders like me will never stress components enough to get anywhere near having a problem.

 

[Wobblers]

I'm with Snail Racer on this.


I've no idea how safe carbon steerers are and what their failure rate is, but any component that needs removing regularly for inspection (if that is the case) is crap. How often are you supposed to inspect it anyway, every year / six months / weekly?

If you have to go through that pulaver to save a few grams you wouldn't even notice well feck that.

Umm, and you think that metal steerers are safe?

Aluminium has a finite fatigue life. A steerer tube is subjected to large bending forces, particularly if you like to get out of the saddle. An aluminium steerer will fail, it's just a matter of when. So will steel.

Ironically, carbon fibre may be the material which is best at resisting fatigue failure.

It's a good idea to periodically check your steerer tube, whatever it's made of, for damage or cracks - every few months seems sensible.

 

[RecordAceFromNew]

Umm, and you think that metal steerers are safe?

Aluminium has a finite fatigue life. A steerer tube is subjected to large bending forces, particularly if you like to get out of the saddle. An aluminium steerer will fail, it's just a matter of when. So will steel.

Ironically, carbon fibre may be the material which is best at resisting fatigue failure.

It's a good idea to periodically check your steerer tube, whatever it's made of, for damage or cracks - every few months seems sensible.

It seems to me you are saying a steel steerer will fail somehow eventually, which is hard to argue against over a loooooong enough time horizon, e.g. due to rust.

The issue though is that while carbon and aluminium are liable to fail suddenly and catastrophically, that is not the case for steel due to its very different ductility/plastic range. Furthermore steel is far more resistant to abrasion than either of the other materials, which is a rather significant issue for things like bicycles, given a nick can fundamentally weaken a carbon tube, and can increase the stress concentration factor thereby lowering the fatigue life of an aluminium one.

I don't believe one needs to check a steel steerer tube every few months. Fatigue life is generally accepted not to be an issue for steel.

 

[raindog]

saying that here is a Hincapie link:
http://www.cyclingne...-brush-up/10012

Cheers - that photo's enough to give you sleepless nights.

 

[rusky]

I had a steel steerer snap but it was at the fork crown, above the weld.

The result was a faceplant at speed

My Allez has a cracking sound coming from the headset, I'm sure it's the bearings & will check in the next couple of days.

 

[snailracer]

Umm, and you think that metal steerers are safe?

Aluminium has a finite fatigue life. A steerer tube is subjected to large bending forces, particularly if you like to get out of the saddle. An aluminium steerer will fail, it's just a matter of when. So will steel.

Ironically, carbon fibre may be the material which is best at resisting fatigue failure.

It's a good idea to periodically check your steerer tube, whatever it's made of, for damage or cracks - every few months seems sensible.

Extrapolating the laboratory properties of materials to the real-world behaviour of complex fabricated assemblies is too simplistic. Fatigue life is a mechanical design decision: a B52 airframe made of aluminium has a fatigue life of 90 years, which is long enough to make it a non-issue. Fatigue failure of bicycle wheels made of aluminium rims and steel spokes is also a non-issue.

Metal forks are reliable because they are designed correctly - the material properties and conditions of use have been taken into account in the design, which has been refined over decades with feedback obtained from failures in the real world. Full-carbon forks haven't had that "benefit", yet. Even Trek, who have every engineering resource available in the development of their forks, designed their full-carbon fork wrong. Think about it, if they had actually known the limitations of their product, they would have issued their service bulletin before selling the forks, not months after they had started failing in the field.

Checking your forks is good advice, however your ability to check it is very limited, unless you have an endoscope and an ultrasonic scanner handy and know how to use them.

 

[Wobblers]

Extrapolating the laboratory properties of materials to the real-world behaviour of complex fabricated assemblies is too simplistic. Fatigue life is a mechanical design decision: a B52 airframe made of aluminium has a fatigue life of 90 years, which is long enough to make it a non-issue. Fatigue failure of bicycle wheels made of aluminium rims and steel spokes is also a non-issue.

Metal forks are reliable because they are designed correctly - the material properties and conditions of use have been taken into account in the design, which has been refined over decades with feedback obtained from failures in the real world. Full-carbon forks haven't had that "benefit", yet. Even Trek, who have every engineering resource available in the development of their forks, designed their full-carbon fork wrong. Think about it, if they had actually known the limitations of their product, they would have issued their service bulletin before selling the forks, not months after they had started failing in the field.

Checking your forks is good advice, however your ability to check it is very limited, unless you have an endoscope and an ultrasonic scanner handy and know how to use them.

Fatigue failure of steel spokes is quite common, as is the rim cracking at spoke nipples. There's people over at yacf who'll bore you to tears on the subject...

An aluminium fork will eventually fail through fatigue (corrosion is more likely to do for steel). This isn't a laboratory property - it's a fundamental property of the material. There are no shortage of real world catastrophic failures through fatigue - that's why engineers spend so much time worrying about it. How long depends on the design and quality of manufacture. I would expect most forks to last for many decades - unless someone got something wrong, of course. But new designs come out in metal as well as carbon - how can you be sure the design is right there?

Fatigue is progressive. It takes months or years. With luck, you ought to be able spot a crack before brittle fracture.

 

[snailracer]

Fatigue failure of steel spokes is quite common, as is the rim cracking at spoke nipples. There's people over at yacf who'll bore you to tears on the subject...

I would argue that most broken spokes and cracked rim eyelets are not true fatigue failures. And it's also a non-issue in the sense that it doesn't put a rider in hospital, or even stop them from riding home on the other 30-odd intact sets of spokes/nipples, unlike a fork failure which you'll be lucky to walk away from.

...An aluminium fork will eventually fail through fatigue (corrosion is more likely to do for steel). This isn't a laboratory property - it's a fundamental property of the material...I would expect most forks to last for many decades - unless someone got something wrong, of course...

I do not hear much about fatigue failures in metal forks, aluminium or steel, which is to say I think it is very rare. People who buy up old frames for "conversion" don't worry about how much life is left in the forks. I can only surmise that the designed fatigue life (i.e. thickness of metal and stiffness of the structure) of metal forks is sufficiently long for it to be a non-issue. As you say, the fatigue life of metal forks is probably in the decades, and I am not confident CF components will last decades - they haven't been around that long on bikes, and there are long-term effects (e.g. UV exposure) that are slow but, like metal fatigue, cumulative.

...There are no shortage of real world catastrophic failures through fatigue - that's why engineers spend so much time worrying about it. How long depends on the design and quality of manufacture...But new designs come out in metal as well as carbon - how can you be sure the design is right there?
...

Engineers have "worrying" about metal fatigue for a very long time and it's now very well understood and thus easily avoided. Of course a new metal fork design can be dodgy, but that is rather unlikely, IMO, because there are very few metal fork manufacturers around (rather like the situation with groupset manufacturers) and they are rightfully very conservative in their design because they're big enough to be worth suing. CF, at the other extreme, positively encourages small-scale, piecework manufacture and the result is widely varying standards of design and fabrication. The shocker here is that a big company, Trek, screwed up (and their abysmal response to it) - what of the numerous smaller concerns?

...Fatigue is progressive. It takes months or years. With luck, you ought to be able spot a crack before brittle fracture.

That's another thing that makes CF problematic - delamination is often buried, where you can't spot it with a visual check, and the failure is sudden and catastrophic. With metal fatigue, you have a sporting chance of seeing it, and, especially with steel, bends before it breaks.

At some point in the future when all the quirks are known and ironed out, I think CF will be the material of choice, but I personally don't fancy being a guinea pig for CF "prototyping" failures.

 

[Wobblers]

I would argue that most broken spokes and cracked rim eyelets are not true fatigue failures. And it's also a non-issue in the sense that it doesn't put a rider in hospital, or even stop them from riding home on the other 30-odd intact sets of spokes/nipples, unlike a fork failure which you'll be lucky to walk away from.

What evidence do you base this on? Overtightening a spoke is most likely to break the spoke or rip the nipple out of the rim.

I do not hear much about fatigue failures in metal forks, aluminium or steel, which is to say I think it is very rare. People who buy up old frames for "conversion" don't worry about how much life is left in the forks. I can only surmise that the designed fatigue life (i.e. thickness of metal and stiffness of the structure) of metal forks is sufficiently long for it to be a non-issue. As you say, the fatigue life of metal forks is probably in the decades, and I am not confident CF components will last decades - they haven't been around that long on bikes, and there are long-term effects (e.g. UV exposure) that are slow but, like metal fatigue, cumulative.

Carbon fibre composites have been routinely used in the aerospace industry for over twenty years now. UV degradation hasn't been an issue in such an extreme environment (high UV flux at 30,000 feet!), I rather doubt it's anything to worry about on a bike.

Engineers have "worrying" about metal fatigue for a very long time and it's now very well understood and thus easily avoided. Of course a new metal fork design can be dodgy, but that is rather unlikely, IMO, because there are very few metal fork manufacturers around (rather like the situation with groupset manufacturers) and they are rightfully very conservative in their design because they're big enough to be worth suing. CF, at the other extreme, positively encourages small-scale, piecework manufacture and the result is widely varying standards of design and fabrication. The shocker here is that a big company, Trek, screwed up (and their abysmal response to it) - what of the numerous smaller concerns?

Don't you think that liability issues won't prompt conservative designs in carbon? Not to mention that if a small company gets a reputation for producing even one batch of duff forks, it'll soon have no customers! And there certainly are small metal fork designers: they've got to get their design and manufacture right too.

That's another thing that makes CF problematic - delamination is often buried, where you can't spot it with a visual check, and the failure is sudden and catastrophic. With metal fatigue, you have a sporting chance of seeing it, and, especially with steel, bends before it breaks.

At some point in the future when all the quirks are known and ironed out, I think CF will be the material of choice, but I personally don't fancy being a guinea pig for CF "prototyping" failures.

Delamination is a result of impact damage. How much would you trust an alloy fork after a heavy collision - it can also harbour serious but undetectable damage. There are no shortage of cyclists on carbon bikes. Many, indeed, who've crashed them with no ill effects (on the bikes, at least!)

I really don't get this attitude of "it's carbon, you're going to die!!!!". It's a material. It has strengths and weaknesses, just like any other material. You need to understand its limitations, just like alloy, or steel. But once you do, there's no reason why you can't design safe, reliable structures with it that will last. The aerospace industry have been doing exactly that for the last two decades. Simply put, I don't worry about catastrophic failure on my carbon bike any more than I do on my steel one. Or titanium one. Or aluminium one.

 

[dellzeqq]

I'm old enough to remember steel handlebars going, and I've got through a couple of aluminium bars. I bent a pair of aluminum bars going in to the back of a bus, but the carbon fork/steerer was unharmed.

Si, chief mod on the CTC forum has had six aluminium frames fail - and he's not a heavy item

You pays your money and you takes your chances.

 

[snailracer]

What evidence do you base this on? Overtightening a spoke is most likely to break the spoke or rip the nipple out of the rim...

Let me clarify...the failure is due to fatigue, but that's the symptom and not the cause - which is spoke mistensioning, either due to poor manufacture or inept user repair.

...Carbon fibre composites have been routinely used in the aerospace industry for over twenty years now. UV degradation hasn't been an issue in such an extreme environment (high UV flux at 30,000 feet!), I rather doubt it's anything to worry about on a bike...

Not routine, not proven. Following the composite tailfin failure of American Airlines flight 587 in 2001, James H. Williams, Jr., Professor of Applied Mechanics in the Mechanical Engineering Department at the Massachusetts Institute of Technology, wrote:
"There are several unvoiced issues that remain; two of which are the aging and the repair of nonmetallic fiber reinforced composites. By aging, I mean the deterioration that occurs during long-term in-service mechanical and environmental loading, in the absence of an overloading or catastrophic event. When subjected to the loading histories of some aircraft, composites will lose both strength and stiffness. Furthermore, studies of the long-term effects of exposure to aircraft environments of moisture, pressure and temperature, as well as fuels, hydraulic fluids, lubricants and deicers remain to be conducted for many composite materials."

 

[snailracer]

...Don't you think that liability issues won't prompt conservative designs in carbon?

IMO Trek are pretty conservative, how many of their bikes and components have a reputation for ugly failure? But they still managed to design their full CF fork wrong.

...Not to mention that if a small company gets a reputation for producing even one batch of duff forks, it'll soon have no customers! And there certainly are small metal fork designers: they've got to get their design and manufacture right too...

In general, small companies are more innovative, i.e. they take more risks than big ones. If they survive long enough and are successful, they then get bought up by bigger companies. Of course there are small metal fork designers, but every mainstream bike brand's metal fork will have been made by a large forkmaker with the very expensive tooling required to economically make the compound curving and tapering tubing profiles you see in metal forks. Similarly, a small, custom framemaker can make a perfectly good metal frame, but it won't have the swooping curves of BigBikeCo's frame because he can't afford the hydroforming tooling and dies.

...Delamination is a result of impact damage. How much would you trust an alloy fork after a heavy collision - it can also harbour serious but undetectable damage. There are no shortage of cyclists on carbon bikes. Many, indeed, who've crashed them with no ill effects (on the bikes, at least!)...

There are lots of CF forks that come factory-fitted on new bikes. But they are pretty chunky items, not the lightweight full-carbon units that kicked off this thread. I agree that they have proven reliable - so far. While we're arguing about why metal will fail because of fatigue, why don't we start another thread of why CF snaps because it isn't ductile?

...It's a material. It has strengths and weaknesses, just like any other material. You need to understand its limitations, just like alloy, or steel. But once you do, there's no reason why you can't design safe, reliable structures with it that will last...

OK, Trek sold about $800M of bikes last year, and their engineering department hasn't figured it out yet.

I really don't get this attitude of "it's carbon, you're going to die!!!!"... Simply put, I don't worry about catastrophic failure on my carbon bike any more than I do on my steel one. Or titanium one. Or aluminium one.

If it doesn't worry you, that's fine. But others, such as myself, have concerns.

 

[fossyant]

Don't ride your bikes folks, they might break , then again, they might not.

 

[Chris James]

Fatigue is progressive. It takes months or years. With luck, you ought to be able spot a crack before brittle fracture.

Yes, fatigue is progressive, unfortunately once the crack reaches a critical length it will fail immediately and catastophically. It is many years ago but I did my B Eng dissertation on the subject.

If you are interested then google 'fracture mechanics'.

Steel is pretty ductile, even the high strength ones so will tend to bend prior to snapping, which is a useful property in a safety critical component. As far as I can see the only real drawback to steel is the weight...