I agree with everything you're saying..though my first thought is to take a step or two back and ask about the total-design question. If one were to design a bike without any knowledge of materials, and knowing that frames will fail for various reasons, I'd think some indication of on-coming material failure would be a key design criteria that would fall into the "need to have" column, while "sudden failure without warning" would fall into the column of design attributes to be avoided at all costs.

It's certain the engineers in the various CF frame design groups have discussed this ad nauseum, though have decided** that sudden severe failure is acceptable. Whether the failure is due to a owners normal (careful) use (for traditional-metal bikes) isn't relevant as good design includes robustness toward normal, expected use. Of course that's the ideal world..the real world boils down to money to be made vs manageable claims due to failures. Lower weight, riskier designs will continue until some (newly quadriplegic) user, somewhere, is awarded a sizable damage claim in court. At that point the risk of potential claims will tilt the "managable claims" into the "unmanagable claims" column and the designs will lean toward more robust frames, or some technology to indicate over-stressing and potential failure.

**slight correction:..It wouldn't be the engineers that make the decision on "acceptable risk"..the risk would be presented by the engineers, heavily evaluated by attorneys, and signed off in some way by someone at or approaching C-level management.

Well, it was his comment about Chain-L in some thread that got me to buy it.
I'm appreciating all the good sharing of experience and advice as a member here. Some members advice is better than others... :roflmao2:

This is a bit deeper as to my liability statement in an earlier post. For sure, lawyers and liability have to be considered and there is some proof of that in the cost of a new bike.

Also, it is generally accepted that triangular designs are stronger than let's say square, rectangular, etc. The flaw may be that all the force in a triangulated design (think truss here) is focused to points designed to counter each other but allow some of the force to be tolerated. I think with such a rigid design, CF would need a modified connection design over what is being produced today, but oddly enough, not all failures are at the joints.

I agree with a previous statement, there is more to be learned about using CF in bike frames.

Drilling down to first principles, carbon fiber composite will, theoretically, eventually fail given enough stress cycles even with small amounts of stress. I understand that it's due to the breaking of covalent bonds between monomer units of the polymer chains (a fancy way of saying that atoms of two molecules both hold onto one electron, holding the molecules together in a long chain). Once wrested away from a molecule, most polymers don't "self-heal" at normal temperatures by grabbing it back somewhere. So the breaks pile up until the material fails.

Just visualizing this, with polymer chains in all directions and random connections breaking, it's easy to see how the material might not give any reliable indication in its reaction to stress - until it breaks. But it's also reasonable that it all depends on how many of these bonds there are, how dense it is, how much mass and how strong those polymer bonds are, so that "enough stress cycles" is more than you'll ever see. Which is why I'm personally not worried about my CF fork, except where bonded to the aluminum. I think it's over-built, considerably.

What I don't understand is why frame manufacturers don't build a "canary" into the frames at critical stress points, perhaps another polymer which is known to fail with fewer stress cycles than that part of the frame.

So are you saying that carbon bikes aren't suitable for 6'3" 240 lb guys? I thought carbon was stronger than steel? Then why are steel bikes always suggested for clydes?

:innocent::innocent::p

Again -- it's not the material per se. It's the application, meaning the overall design, construction, and intended purpose.

It's perfectly possible to build a CF frame for a 300# rider or even heavier. But that's not what the available frames/bikes are built for. To set the record straight, I wouldn't recommend a superlight steel frame for a heavy rider either.

High end bikes built for sport, whether metal or CF aren't for heavy riders the same way that sports cars aren't for hauling bricks.

And to further that insight, it's relatively easy for a framebuilder to spec heavier tubes for the large rider. It's possible, just not likely, that someone could come up with new molds, fabric layups, etc. to build a slightly heavier CF frame. Those things are so automated and specifically tooled that it's not financially viable to build a custom CF frame for a heavy rider.

The point is general is very valid..... Carbon fiber composite strength depends on the unity of the matrix of carbon fibers and resin. If this integrity is compromizsed, say by a rock hiting a stay, something falling in a top tube, or significant cut, a failure point is introduced and strength when stressed is reduced with the potential for the catastrophic failure that carbon is knon for.

as noted in other threads, this is especially true if the carbon build is super light. A heavier build would be much less susceptable.

I also think that design with longer seatposts (levers) and fewer sizes with sloped top tubes results in more bikes (carbon and aluminum) haveing more stress when a rider is at the high end of the size the frame is intended for.

Anecdotal only. A friend at work is long term bike racer (cat 1) whippet thin. He started riding in the days of steel and campy parts as the only way to go.

he rides carbon now as he is performance oriented. he went through 3 carbon frames (trek or specialized forgot which) that cracked, broke, or had other issues before he switched to a different brand (Leopard if makes diference) he noted this never happened when is was steel frames.

Overall just talking to people i know it seem like there are more frame issues (carbon and aluminum) and it seem design and build weight are alwasy key issues in root cause

Certainly a deep gouge or something similar MIGHT eventually compromise strength, but we have people on this thread saying that you can induce a failure-inducing crack by leaning the bike up against a brick wall. This is patently ridiculous. Normal road debris hitting a stay? The same.

Carbon fiber is, in general, not a "fragile" material where small surface imperfections, scratches, etc. eventually propagate and cause failure. One just needs to exercise reasonable care.

- Mark

I think this is it. The real allure of CF is that you can lay it up in ways that make it lighter than other materials. Then you start telling the market that they want light bikes. And the lighter the bike, the better it is and the more money you should pay for it. This ultimately leads to CF frames that are too light and subsequent catastrophic failures.

I think its just a numbers game. Lots of folks know stories of broken CF frames. Very few know of any broken CF fork stories. I don't know anyone that has had a CF fork fail. Maybe the industry overbuilds them to be safe?

Agreed. I don't think there is a CF road bike out there that was built with a 250+ lb rider in mind. Many companies have weight limits on their CF bikes in the range of 200-240 lbs max. Ride one at over 250 lbs and it will probably work, but it was never intended to do that and will one day fail if continued to be used in that fashion. We just don't know which day.

I hear this said, but wonder what the reality is. What is a specific example of this?

Talking to friends about CF is what started the ball rolling to steel frames for me. Talking to seasoned riders and they all brag about breaking CF frames. Cracked this one, snapped that one, etc. Pointing out cracks on current frames that they keeping an eye on. They have the mindset that these frames have short life spans and replace them more frequently. Get new CF every 2-3 years or so.

When I think about CF road bikes, I think about this release from Specialized that applies to their most popular CF road bikes:

HIGH-PERFORMANCE ROAD
• CONDITION 1: Bikes designed for riding on a paved surface where the tires do not lose ground contact.
• INTENDED: To be ridden on paved roads only.
• NOT INTENDED: For off-road, cyclocross, or touring with racks or panniers.
• TRADE OFF: Material use is optimized to deliver both light weight and specific performance.

You must understand that:
(1) these types of bikes are intended to give an aggressive racer or competitive cyclist a performance advantage over a relatively short product life,
(2) a less aggressive rider will enjoy longer frame life,
(3) you are choosing light weight (shorter frame life) over more frame weight and a longer frame life,
(4) you are choosing light weight over more dent resistant or rugged frames that weigh more.
All frames that are very light need frequent inspection. These frames are likely to be damaged or broken in a crash.
They are not designed to take abuse or be a rugged workhorse

you used to (3 - 5 years ago) see a fair number of reports of carbon forks failing, often with not good results. Overbuilding would seem to be a logical reaction to that.

While my initial "jab" was a joke at the argument going on over in general, your response brings up another question. If you frequent the clyde's forum, you'll find that people often recommend older steel mountain bikes for them.

So were bikes built stronger back then?

My guess is its just a safe recommendation for most. MTB bikes are typically built stronger than road bikes. Steel is considered the most durable material. Hence, steel MTB's for really big first time riders.

My personal recommendation for anyone over 250 lbs that wants a road bike is to go steel, unless they plan on racing.

YES, and NO.

There are inherent differences in various metals and CF, that designers need to factor.

Bicycles are designed around 3 criteria, weight, strength, and ride (flex/rigidity). Leaving weight aside, it's a question of how strength and ride play out with various materials. In most cases, the frame is spec'd around strength, then ride is adjusted by playing with tube diameters and wall thickness, to bring a final result which meets both needs.

But steel is different, high strength steel is too strong, and from a purely strength standpoint it would be possible to use less. But there are limits to wall thickness, so they can't go thinner, nor can they use thinner larger diameter tubing. So in order to dial in ride, they end up using more steel than necessary for strength, ending up with an overbuilt frame.

So, there is some truth to the notion that steel frames are stronger. Combine that with steels ductility, which causes bending before breaking, and you have a higher safety margin.

---------------

There's also another reason CF frames tend to be (or seem) less reliable, and that's in designer to product process controls. In a frame built from metal tubing, the tubing company can exercise very precise control over the product working to close tolerances. Plus the very process of drawing tubing tends to show up any flaws in the material, which will break while processing. So, the only control needed is in the assembly (glue, braze, or weld), and this is pretty easily managed and/or inspected.

Contrast that with CF structures. The makers of the sheets can control what they provide. However, there's much more involved as those sheets are laid up to make a frame, and the potential for error, shortcuts, or poor design choices is greater. It's also more difficult to inspect final product to be sure it meets spec. So the band of variation frame to frame is greater than with joined tubing, and the likelihood of a poor mix like a heavy rider getting a frame at the low end of the range is greater.

IMO - a quality CF frame from a builder with good engineering and controls will be an excellent, safe, long lived product. But other than reliance on the builder's reputation, there's no way a consumer can make a judgement call about what he's buying.

An example of my fears would be that while my road bike is CF, my Mtb is not.... it is alum.

I love the discussion and now realize points of view that I have not considered but that doesn't mean I agree with them yet.

When you drill down to the bare facts, a so call CF frame is a plastic frame reinforced with CF. Plastic ages rather fast, and is probably the reason for the failures. Add to that all the marketing hype and huge profits, mfg of course are promoting CF frames on a high level.

As some mentioned, the problem probably also lies in the fact that mfg are now making frames that are too light for their own good. Weight weenies are driving this fact.

I recall using paper thin MTB and road bars in the early 90s. One crash (hardly more than the bike falling over) and they cracked in two like eggshells. There was much marketing hype and gram counting, and similar talk about safety, and if legal standards were not required to fix the situation. I don't believe you can buy such bars any more.

my take on all this:

buy a c/f bike with a good groupset such as Ultegra or better.... and which has good wheels

ride the crap out of it .... when the frame starts giving problems, buy a new frame and transfer the groupset etc over

a brand new good c/f frame with forks can be bought here in the UK for as little as £350:

Planet X Pro Carbon Road Frameset | Planet X

if you need to change the frame every 3 years, it's not a major issue especially if the price of good c/f frames with forks are becoming cheaper

I just can't believe how long the CF scam has been going on in the bicycling industry.

It's almost as if bicyclists want to spend as much money as they possibly can for a product which is as dangerous and as unreliable as a manufacturer could make them. Oh wait, no that's exactly what cyclists are doing.

C'mon guys, there must be a few of us who aren't gullible enough to believe that saving 80 grams compared to an aluminum frame is enough of a difference for anyone to notice. Most of us would save more weight just picking the lint out of our navel or shaving our nose hairs.

The only aluminum frame bike I have is a fatbike. I like it fine, as four inches of low psi tires soaks everything up. My other bikes are steel and CF. I've had two aluminum frame road bikes. After every ride I felt like I'd been beaten with a stick. CF is plenty durable for its application (I would not get one for mountain biking) and if you're willing to shop around you won't pay more than a good (if there is such a thing) aluminum frame.

I know lots of folks will take issue with this. Don't care. Never do. Here goes. Way too many (and I mean WAY TOO MANY) cyclists and triathletes are overly concerned, some to the point of what I would call paranoia, over weight of frames and components. Sure, you don't want something really heavy when you could go lighter and still maintain safety and durability. But there comes a point when spending big bucks to save a few more grams and sacrifice durability and some measure of safety makes no sense. Manufacturers know there a lot of people out there looking for "the lightest", so they're going to give it to them. It makes them money. Perhaps if more people were a little less concerned with getting a frame that weighs less than their morning bowl of oatmeal the manufacturers wouldn't have to come so close to that bad place of frame failure and/or short life. Let the pros worry about getting the lightest things out there. Most of us should worry more about tuning the engine, because that will always be the most important aspect.

I can only wish that one day I will be athletically good enough that a few grams of bike weight will affect my performance, lol..... in the mean time, I will continue to work on my abilities rather than seek expensive short cuts.

Besides, there is a thing called "enjoying the ride" and while that is a vague term covering a whole lot of area, for me, it means I should not forget why I ride in the first place, to get out and enjoy an honest workout and even better if a few friends join in. When I feel like turning up the heat, I will and when I don't, there are lot's of things to witness and take in when riding a bike.

About a year ago, I started cycling on my $400 Mercier Galaxy, a alum framed carbon fork, Claris drive train cheap bike from BD. My Strava times are no slower on that bike than my CF Cannondale, so the rider is more the variable than the bike in my opinion.

...hey now. Hurtful. :(

^^^^True. Fly rods and bike frames are not a very good comparison. Because their function is so totally different, they are two very different types of structures. A bike frame is by nature much more impact resistant.

At least nobody has suggested that exposure to water is going to cause a carbon bike frame to fail like what would happen just a few years ago in one of these discussions. The fishing rod comparison does at least put that one to rest.