andjones

I'm in the market for a new bike, but I keep getting mixed information each time I go to a different lbs. What is the expected lifespan for a carbon fiber frame vs aluminum vs aluminum + cf (eg. the Six13 frame). Is there any significant differences between companies? I'm looking at either a Trek Madonne SL 5.2, Scott CR1 Pro, or a Cannondale Six13 Pro2.

I've heard that companies like Trek put a "life time" warranty on their cf frames, but any manufacturer defect should show within 3 years, and after that you are in a 'grey' area as to whether they will do anything for you.

Realistically, I don't plan on doing any significant racing, but want a good bike that will be reliable over the next 5-7 years. Any thoughts?

edzo

if not crashed, 1 million cycles

daytonian

Ah oh, here we go.

johnny99

Superlight aluminum racing frames are made from such thin tubing that they may be less strong/durable than carbon, especially in a crash.

Eatadonut

5-7 years, it doesn't matter. Any of those frames will hold up that long barring a defect from the factory, a crash, or assembly error (clamping a front derailleur too tightly, etc)

khuon

Theoretically, most CF materials have a near-infinite fatigue life. From a materials standpoint, CF can be cycled far longer than steels and titaniums at higher stresses. And they definately surpass aluminum in terms of fatigue life because aluminum has no fatigue limit. In the real world, it all has to do with the design. If the design promotes conservative stress application on the material such that applied loads do not exceed the fatigue curve then materials such as carbon fibre, steels and titanium will last forever. Aluminum because it has no fatigue limit will continue to lose strength as it's cycled so eventually it will fail. However, most designers build in an adequate lifetime for aluminum bike frames regardless of material such that it is almost impossible for one to accumulate that many cycles as to cause fatigue failure.

The other thing that effects a bike frames useful life is overstress which can cause instant material failure. Generally speaking, CF has a very small plastic region in that the yield and UTS are spaced pretty close to one another. In other words, instead of bending, most CF will catostrophically fail. Steel on the other hand tends to have a pretty large plastic region in that once yield strength is hit, they will permanently deform before breaking. However, there are two things to keep in mind here. One is that CF is typically stronger in all aspects than most metals. And secondly, it can be engineered with a tensile modulus that will allow it to bend before reaching yield. As long as stresses are kept between the tensile modulus and yield, CF will simply bend and rebound back to shape. This can be done with metals too but they generally have a smaller region at a lower strength. The beauty in CF is that the tensile modulus of the material and by combining different types of CF layed in different directions, the structure can be micro-engineered and tuned to a much greater extent than metals.

blandin

khuon, I've rarely seen so much information so clearly articulated in the space of two paragraphs. Thank you!

cydewaze

Grey area shmay area. If you have a Trek carbon and it breaks, you get a new one. I bought one in 93, and after 12 years and 30,000+ hard miles, the bb shell came unbonded. I got a brand new one, no questions asked. The bike shop that sent my frame in said that they've never been denied a carbon replacement from Trek, even for crashed bikes, and even in the case that it was not the original owner.

I can't see why this would differ by location, but who knows. I just know that everyone I know who's had something go wrong with a Trek CF bike has gotten a new one. Trek has a lot of $$$ and for them I think they'd rather just send a new frame out than have bad PR by knit picking.

DannoXYZ 

This is very similar to the debate we have in the auto-racing world between chromoly vs. DOM rollcages. One fails suddenly while the other bends first. And you have to do testing and get some numbers to see the actual failure scenarios. Basically chromoly is superior due to its much higher strength and when it finally takes a slight bend, the DOM cage will have been crushed 50% down to the doorsills. When chromoly finally snaps after 25% bending, the DOM cage will be crushed all the way to the floor, yet without snapping. In a wreck, I'd much rather have a cage snap with some minor helmet damage rather than have that helmet pushed down to my ankles....

Yeah, I'll backup basically everything that khuon said. The identical forces that will dent and permanently bend a steel frame will just bounce off most CF frames with no damage. By the time you start unbonding/unravelling/fraying the CF frame, the steel frames will have been twisted into a pretzel. Aluminium frames fall somewhere in between.

I've had a Trek '92 5500 replaced under warrantee after 5-years (the 1st generation was a little too thin where the chainstays join the BB). I'm still riding on my '91 Specialized Allez Epic to this day. Went through two crashes severe enough to total the forks and wheels. Just replaced those parts and we're back in business. I do have a 3mm deep groove on the left chainstay where too-large a 28mm tyre with a bent wheel rubbed, keeping my eye on it, so far everything's held up. I've bent two rear axles this past year bunny-hopping kerbs and speed-bumps due to my hefty 245-lb weight. The carbon frames will probably outlast most owners, with failures only due to overstressing the part beyond it's ultimate yield point, which would destroy any other frame as well.

onkey

I have a Scott Cr1 team issue and a Trek 5200. Both are obviously carbon bikes and have been very reliable and show absolutely no signs of wear. The cr1 has about 6,000 miles on it, and the trek about 3,000. im positive that they will both exeed 20,000 miles. the cr1 in particular is stiffer than almost any bike out there. research has shown this. i would go for the scott.

bjkeen

How do carbon fiber and aluminum and steel and titanium stack up next to abrasion damage? Meaning, how likely are they to take a deep nasty scratch from something, and how serious is that scratch, and how repairable is it?

Reason for asking this question is that it's conceivable to me that you might one day wake up and see a nasty scratch on a seatpost/fork/frame, and the likely implications of such a thing have got to be pretty different depending on the material. Once a stress riser or crack has started to develop, how fast does it typically progress?

khuon

It really depends on the material and the exact structure. A scratch on many modern tubes used in cycling today regardless of material is something to be concerned with simply because even with metals which generally have a high abrasion tolerance, the materials are bing made thinner and thinner. In general however, steel is more abrasion resistant than titanium and titanium is more abrasion resistant than aluminum.

However, CF is very notch sensitive. Once the weave in the layer has been compromised, it loses almost 90% of its strength. A single surface/superficial abrasion is usually nothing to be concerned with as long as it's only a clearcoat scratch. A deeper scratch however can be a problem and if the weave has been cut then that layer is done for. The good news is that most CF structures are layed up in several layers. This is done for several reasons. One is to increase not only the amount of material through cross-section padding and thus increase strength in that respect but also to add some redundancy into the material such that a failure of one layer does not compormise the entire layup. Another reason is that CF is anisotropic in nature and oftentimes the prepregs used in the layup are unidirectional as opposed to multidirectional thus it will be stiff in one direction but compliant in another. Rather than using a multidirectional weave which in actuality would limit or make it more difficult to tune the structure, the designer will specify different weave biases for different layers thus creating a more isotropic layup in the end so that it will be stiff in multiple directions.

I run a CF seatpost on my MTB. My frame has an interrupted seat-tube and even a short-length road post is too long because it comes very close to the top of my rear shock when at extension. If I compress the shock, there is a good chance it would impact the bottom of my post. Thus I decided to trim it. The post is an Easton CT-2 which is now called the EC-70. You can see from this cross-section of the trimmed portion that there are five distinct layers.




Most of today's bike frames and I believe all road bikes use a themoset bonding method for their CF construction. Technically this type of construction does not yield itself to being repaired. There may be some tricks you can do to some frames with debonding the epoxy at the lugs (assuming the frame uses lugged construction). In which case, the damaged section could be replaced and a replacement could be rebonded into place. But other than that once damaged, it's a goner. One-piece molded thermoset frames cannot be repaired. My CF MTB frame and a scant few others were produced using thermoplastic methods. In theory, this type of CF material can be repaired. However the technique is complicated, prone to errors and not easily accomplished by someone who doesn't have a lot of experience working with composites and CF.


This is a very difficult question to answer. The reason a stress riser is a problem is because the loads at that portion exceed the tensile strength of the material thus the material fails in that region. Thus to answer your question, one would have to know what the loads are imposed around and in that area of the stress riser. A stress riser without enough load to exceed the material's tensile strength won't grow the fracture.

DocRay

facts:
the only frames to survive >150,000 EFBe cycles are CF
the R3 has done >200,000 EFBe cycles and has the highest BB stiffness, by far.
this year, a stock R3 won the Paris-Roubaix, the toughest frame-breaking race.

here's the data:

https://www.efbe.de/testergebnisse/rennwiege/enindex.php

Most good CF frames have lifetime replacement warranties. Even my ally soloist has a lifetime replacement warranty.

wagathon

And then . . . there's Scandium to consider.

Bob S.

Khuon; Well stated. Thank you very much. Bob

jet sanchEz

I am upgrading my old 1986 steel Ciocc with Columbus SL tubing to have a carbon fibre fork and seat-tube....is there anything I need to consider before just jammin' them in the frame and riding?

Iffacus

we had a recent discussion on this topic on the MTB forum, and I am currently using a 15 year old carbon framed MTB (Giant Cadex), whilst the application is probably more ardueous than road riding I still think ta that a carbon frame should easier last 7-10 years as long as its not crashed to often