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The longevity of a carbon fiber frame(11 posts)

The longevity of a carbon fiber frameGino
Aug 1, 2001 2:58 PM
Any thoughts on the useful life of a carbon frame? I've been riding a Kestrel 200sci for the past 6 years, and every now and again the thought of a frame or fork cracking pops into my head. The roads in northern Illinois can be quite bumpy. Can I expect about the same useful lifea as an a steel or aluminum frame. Am I just being a worry -wart or do they ever crack under hard riding conditions? Gino
re: The longevity of a carbon fiber frameseamus
Aug 1, 2001 3:23 PM
First, everything can break, regardless of what it is, especially if it's abused. But that doesn't mean that it definitely WILL break, no matter what material its made of.

Carbon fiber, at least in theory, is stronger and more durable than everything else out there because it has an infinite fatigue life. That's why they build F1 cars and other light, high-stress items ouf of CF. But who builds a bike or component is more important than what they build it out of---a well designed,engineered and constructed bike will hold up, regardless of the material. A well-made carbon fiber frame (kestrel, Calfee, C40, Look, Trek's more recent stuff)should last a long, long time, even compared to other materials, barring really big riders crashing and doing dumb things.

As for those noises, are you sure they're coming from the frame and fork? Carbon tends to transfer creaks and noises elsewhere, making a creaking crank, bb or headset sound like something else. I doubt they're coming from the tubing itself, and even if it isnt I doubt its actually structural.
re: The longevity of a carbon fiber frameGino
Aug 1, 2001 3:59 PM
Thanks for your insights. Lance rules. Gino
re: The longevity of a carbon fiber frameLone Gunman
Aug 1, 2001 4:56 PM
Possible a fissure crack forming. Probably won't cause a frame to break/fail but it won't go away either.
Composite failuresKerry Irons
Aug 1, 2001 5:11 PM
There are three mechanisms for failure of fiber reinforced plastics: 1) fiber breakage, 2) fiber pullout, and 3) matrix breakage. The actual failure of the part (frame in this case) is tied to these mechanisms, but it is not clear when it fails how it got there. At any rate, there were constant failures in early CF frames, but the issue seems to have abated quite a bit. My own take (from 30 years of skiing on composite downhill and XC skis) is that even if composites don't fail, they do "break down" and lose some of their original properties. A question of when, not if. However, proper design can push both catastrophic failure and performance degradation way out into the future, so there is no way to specifically state how long a part will last. Also, the reason to build anything out of CF is strength/weight, not fatigue life. The theory of infinite fatigue life is not borne out in practical applications. Talk to any plastics engineer.
Composite failures ???JohnG
Aug 1, 2001 5:48 PM
Let me start by saying I'm not a composites engineer..... however, I suspect that the stresses and on a composite ski is quite a bit higher than a bicycle frame. Just look at how much a ski bends.... yikess, sometimes it's rather scary. So, comparing skis to bike frames might not be such a good thing to do.

Anyway, is there any REAL evidence of CF bike frames "changing" over time? I'm not talking about joint failures or the other failures you mentioned.

Thanks JohnG
Composite failures ???seamus
Aug 1, 2001 6:57 PM
Yes and no. I've heard of some older carbon frames (made ten years ago, and still on the road) which are now, in the owner's words, softer than they were originally.

But then again, carbon fiber tech used in bikes has come a long way in 10 years, so who can say what the current crop of improved CF will do in another 10 or 20?
Composite failuresseamus
Aug 1, 2001 8:22 PM
A lot of good info here from a qualified source, no doubt, but IMHO it's a little too generalized, like the old "aluminum is too stiff, CF rides dead, Ti is springy" cliches of the '90s. It's like saying ALL aluminum frames will wear out, or ALL titanium frames will last forever. It ain't necessarilly so. As for CF going soft, much of the real world result will come down to how well the frame/fork is engineered (or overengineered) and what stresses are placed on it; i.e. big track sprinter rider, smaller rider at high cadence, whatever, and these broad-sweeping statements about a given material doing X or Y in every application is an antequated theory.

Most bike industry fatigue test machines are turned off after 100,000 cycles, ususally the CF frames and parts still intact. If built properly, CF is beyond reliable. Just ask any Formula 1 composites engineer.
Calfee CF Frameset = 25 year warranty...MrCelloBoy
Aug 1, 2001 8:56 PM
I think that says something as to the expected longevity of their product. This warranty is on a tandem frame that will probably endure more stress than any "single" bike.
Calfee CF Frameset = 25 year warranty...seamus
Aug 1, 2001 10:17 PM
And if you ask him, Calfee believes his frames (if not abused) will last way longer than that in real-world riding conditions. The 25-year warrantee is a business decision.
Durability testsStampertje
Aug 2, 2001 6:01 AM
www.efbe.de
has tested a number of lightweight frames. They just pound them with increasing force for a number of times and see when they break. They never broke a Trek OCLV. Cannondale, Klein and Principia also score very well in their "durability" vs. weight ratings.