General Cycling Discussion - ::Carbon Fibre Strength::

In the near future I hope to be getting a Trek 5200 (my dream bike:D )I know carbon fibre is a very strong and light material, but it seems fairly fragile. What types of stresses are these frames able to withstand and which will cause the frame to fail catosrophically? I feel much more comfortable having a minor reck on a "metal" frame than on a composite. What if the bike falls over when its against the wall, will it crack or anything like that? I just want to be 100% sure of the integrity of the frame before I blow, I mean "invest" a few grand on a bike. Thanks :)!

Trek offers a lifteime warranty on new Cf frames(material and workmanship defects).If you worry about that kind of stuff tho maybe you shouldn't.Any maaterial can suffer ina crash or fallover.

For an interesting discussion of bike frame materials, read: http://www.sjsu.edu/orgs/asmtms/artcle/articl.htm
All bicycle frame materials may fail when placed under sufficient stress. The particular problem with carbon is sudden failure without warning, once its particular limit is passed. This was a problem in certain seatposts. However, I ride a Trek carbon frame and have heard of no unusual problems. This is getting to be a fairly mature technology, and Trek has sufficint expereience.

I ride a Look carbon frameset.

In answer to your question, will the frame brake if it falls standing leaning against wall etc. Three times I crashed over when unused to the clipless pedals without any harm to the frame.
A scuff or two to the brake/shifters and a few scuffs and bruises to me :o but the the frame was un-affected

It is true, any material can suffer during the crash. Most materials, under stress suffer by bending and twisting. Carbon fiber will bend or twist - it will snap like a twig.

Pound for pound, CF is stronger than steel. It has, hovever, much less ductility and very little resistance to abrasion. Also, UV light can cause it to decay, as will moisture. Most CF frames have metal in the joints, and the adhesive used to bond the metal to the CF can sometimes be a problem. Buy a CF frame only if you can justify the possibility of it only lasting 5 or 6 years.

D*Alex raises an interesting point. Are there any statistics on the longevity of CF frames? They've been around for a while, although the big popularity explosion has been in the past 5 years or so. We should have some empirical evidence by now.

Trek had some problems with CF failure on its framesets. I believe that the rear triangle became 'unglued' ---the problem became so bad that they HAD to then offer a lifetime guarantee due to the fall off in sales...

most CF is durable enough for super light riders.
it's hard to measure its usefulness in everyday riding when one sees the pro's ride it then discard it when a wreck happens or the season ends.

i'd love to get an in depth report about how the bike did after a collision during a tour....the support cars scoop it up before the sponsors can see their beautiful creations destroyed....

The original Graftek frames (produced by Exxon?)
were made in the 70's. they are still around and
still ridable despite all the concern about failures
of CF Galvanic Corrosion etc.
I'd feel safer on old CF than on a Viscount aluminium
death fork :lol:

Marty

Originally posted by D*Alex
[BMost CF frames have metal in the joints, and the adhesive used to bond the metal to the CF can sometimes be a problem. [/B]The Trek OCLV CF frames,which the question was about,have no metal. The lugs are CF.

what about those old-school trek 2100s and 2300s, with the carbon fiber main tubes? Is there a warrenty on them? It would be cool to pick one of them up ofr 200 dollars, have it "fail" on you (funny how a crowbar can do that) and have a new 2300 afer that.

Originally posted by Phatman
what about those old-school trek 2100s and 2300s, with the carbon fiber main tubes? Is there a warrenty on them? It would be cool to pick one of them up ofr 200 dollars, have it "fail" on you (funny how a crowbar can do that) and have a new 2300 afer that. Nice try,but warrranty is to original owner.

Educate yourself in bicycle frame materials:

Bicycle metallurgy
http://www.sjsu.edu/orgs/asmtms/artcle/articl.htm

Exploratorium
http://www.exploratorium.edu/cycling/frames1.html

Bicycle paper
http://www.bicyclepaper.com/bp/issues/summer02/bp2.htm

Frame delection test
http://www.sheldonbrown.com/rinard/rinard_frametest.html

I have a Trek 2120 about 5 yrs old with no troubles. However, I work as a TV news Photographer and we have several tripods with carbon fiber legs. They look practically identical to the tubes on the Trek frame. One night I was shooting a AA minor league baseball game from the press box. The night was chilly so I had the window slid shut except for a 7 or 8 inch opening in which the lens protruded and allowed me to cover the whole field with a pan. A sharply hit foul ball astonishingly came back, passed though the slit and squarely impacted a tripod leg. The leg smashed and separated into fibers. The lesson? CF has a lot of strength in the directions for which it was designed to be strong. However forces from other directions can damage it fairly easily.

The original question was about the Trek 5200. It is a strong, long lasting frame and you don't need to worry about wasting your money. It is a good bike.
As for impact strength, obviously a tripod leg and bicycle frame are completely different. CF is not good for impacts but look at any high end aluminum frame and you will find equally fragile tubes. They draw the tubes so thin that any minor impact will put a huge dent in it. I think the CF tubes on the Trek are a safe bet.

The USPS and many other teams use the Trek carbon frames. This means shipping, millions of miles on them, more tear downs than any consumer will ever do and more stress than anyone will put their Trek through. The USPS bikes probably put more miles on airplanes bumping around in shipping containers or transport trucks than a consumer would ride. Not to mention the thousands of miles put on by each team member.
Besides that, there are many amateur and regional pros that successfully campaign Trek carbons for years without incident.

All the info on materials is interesting but doesn't mean anything to a cyclist. You get the fit, the ride and enjoyment out of a frame. This you can do on a Trek carbon for many years.

I could care less about material properties because I look at individual frames and how they ride. I don't care about molecules or stress graphs,etc. Book knowledge on a material means nothing. There are too many variables. I only care about quality of workmanship, style, handling and fit & feel. Only riding tells you that. These are things only personal experience will tell you. It is interesting to know "why" it is the way it is but you shouldn't care about "why" --you should care about "is it right for me?"

Thanks guys! I just needed a little reassurance. Deep down I knew that Trek frames are of high quality and were rigid but just needed another opinion. :D

I don't use CF.

Since some have suggested that a "lifetime warranty" somehow speaks to the quality of the product, I recommend checking out the recent Trek thread in the racing section at http://www.bikeforums.net/showthread.php?s=&threadid=16696

As the experience of several posters suggested, a "lifetime" for quite a few manufacturers means perhaps 3 years.

All I know is that my next bike will be steel--for reasons of ride comfort and durability.

Cheers,
Jamie