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Carbon Fibre Fatigue Life(9 posts)

Carbon Fibre Fatigue LifeMart
Sep 27, 2001 3:16 AM
Anyone out there any idea on the fatigue life of carbon fibre as compared to for instance aluminium. Also anyone know anything about the Look KG241 frame. I have found the KG281 on the web but can't find anything about the 241 in particular weight or a review.
A few months back someone posted a site ....Live Steam
Sep 27, 2001 6:14 AM
with the fatigue life test results reported by some consumer testing lab for different frames. I did a search but can't seem to locate it. Maybe the person that originally posted it can re-post.
A few months back someone posted a site ....BritRacer
Sep 27, 2001 7:10 AM
Carbon doesn't fatigue - only metals have a fatigue life.

Having said that, I'm assuming that you're asking what the life of a carbon frame is and unfortunately the answer is the same as 'how long's a piece of string'.

While carbon frames don't fatigue, they can become more flexible and weaker with time if the layers of carbon fibre separate (called delaminating). In a carbon frame that's well designed, this shouldn't really happen to any noticable extent, even over several years (I've ridden a well used 6 year old carbon frame that felt pretty much the same as the current ones) but unfortunately, it does require a high level of expetise to do this and that's why many carbon frames (especially the early ones) got a reputation for breaking.

Regarding the Look frames, I personally would steer clear, mainly due to anecdotal evidence that they become quite flexy after a year or two but also because I think that for the price, a good quality alumninium frame or others such as the OCLV are better.
Lugged carbon fatigueMick
Sep 28, 2001 6:08 AM
The comment on failure of aluminum-lugged carbon frames is interesting.

I've read where Look has had fatigue problems but that it applied to the frames of the early-to-mid 90s and that they'd solved those problems. True or not??

I have a Giant CFR Team - which is a carbon bike. Giant makes aluminum exclusively so when I bought the frame I wondered what brand it really was.

After some investigation, I've concluded they sourced from either from Look or Look's own source. The CFR I have very much resembles a Look frame, down to the butting methods on the tubes. The only difference is the B-Stay type yoke the CFR has on the seat stays.

I've ridden it one season and am very pleased. I'll know in another year if the fatigue problem shows up. Does anyone know if my assumption is correct, that my Giant CFR is really a Look?
Lugged carbon fatigueDave Hickey
Sep 28, 2001 11:13 AM
Your Giant is not a LOOK. LOOK frames for the most part are made in France. Some of their lower end frames are rumored to be made in Asia. Giant frames are all made in Asia. Your Giant frame might have been made in the same Taiwanese plant as some of the lower end LOOK's, but it's not made by LOOK in France. You are correct in saying LOOK frames in the early 90's had problems with the joints coming unglued. They have solved the problem by not having an actual carbon/aluminum bond. There is a barrier between the two to prevent the joints from coming apart. Most of the problems you here about with carbon/aluminum frames are frames made by LOOK,TVT,Vitus, and Specialized in the late 80's and early 90's. LOOK's and all the other new aluminum/carbon rear triangle frames use a different manufacturing method
re: Carbon Fibre Fatigue Lifepmf1
Sep 27, 2001 7:21 AM
There is a website out there somewhere showing data of tests of how much force a frame can take before breaking. As I recall, carbon was at the top.

I've got a well used Kestrel I ridden for over 7 years and its still as stiff as when I bought it. All these folks who tell you that carbon bikes don't last are wrong. They don't crack or break everytime a pebble hits them. The stuff is used on jet fighter and race car bodies.

I'd avoid frames that are put together with aluminium lugs. I know the Look is one such frame. Supposedly, many early frames of this design had problems with a reaction between al and the carbon. Also, Trek OCLV bikes have a lot of complaints associated with them, but that could just be the law of large numbers (i.e., there are so many out there)

Never heard of the Look 241 frame.
re: Carbon Fiber Fatigue LifeTig
Sep 27, 2001 9:57 AM
Here's something from Calfee's white paper about carbon fiber in general. Also, frame material is secondary to the importance of good design and quality building. Not all CF bikes are created equal!

Pros: lightest, strongest, best shock absorption, unlimited design applications, non-corrosive, material has high fatigue resistance, some designs are easily repaired.
Cons: expensive, technology still evolving, strength and stiffness are design dependent, bonded, lugged designs can fail at joints, fully molded styles have very limited sizes.

Here's the CF site that was posted last month:
LOOK KG241Dave Hickey
Sep 28, 2001 3:04 AM
I have a 241 frame. It's the third frame in LOOK's 2001 lineup. The top end is the 281, the next is the 261, and then the 241. The frame and fork is 200 grams heavier than the 281. The 281 has variable shaped tubes while the 261 and the 241 have round tubes. The main difference between the 241 and the 261 is the 241 has a carbon fork with a cro-mo steerer, while the 261 has an all carbon fork. I only paid $520.00 for my frame/fork at Look is not making this frame for 2002. I have about 1000 miles on the frame so far and I'm very pleased.
Sep 28, 2001 5:45 AM
You got a sweet ride and an even better deal.

BTW: the KG281 has also been discontinued for 02. The replacement is the 381.

Ride on