pigmode

How do those applications relate to carbon bicycle frames where a 2.5 lb frame is asked to support a 180 lb rider season after season after season? Are there any similarly engineered components in aircraft or yachts that relate to the stress and longevity requirements of bicycles?

derath

Maybe due to the fact that CF has a better strength to weight ratio? So if you expect a 2.5lb steel frame to support a 180lb rider, shouldn't a CF as well? Or does Cf have a lower strength to weight ratio when it applies to bicycle frames?

-D

stonecrd

Whether you are discussing an airframe, yacht or bike it is a matter of physics and engineering. I am saying that CF is stronger measured by tensile strength than steel and its density is about 4.5x less than steel so thus has better strength to weight. I must assume that the bike designer understands the intended use and forces involved and designs appropriately. So if the Bike will not support a rider greater than 180lb then that is by design and has nothing to do with CF. You can easily make a bike to support a 200lb rider and have it still weigh less than steel or AL. I don't own a CF bike but would like to, just can’t afford it right now. For those of you who ride CF, is there a warning sticker on the bike or in the manual that says explicitly you must weigh under such and such to ride? If not then I don’t think it is an issue because I can guarantee that the lawyers would require that if it was true.

Disclaimer: I am not an engineer nor do I claim to be, but I have stayed at many Holiday Inns

pigmode

Thanks, but that doesn't quite relate to what I am asking, and will probably lead to more questions and answers that will be over my head. Its a simple question that I should probably clarify. Looking at the practical requirements of a bicycle frame in addition to the relatively small scale of the materials involved (tubes, lugs, joints etc), where on a boat or yacht will you find a similarly engineered structure? The closest I can think of would be a carbon fiber spar, especially on a small boat such as a Melges 24. But even that tube is much bigger than anything seen on a bicycle. Bigger, BTW, means easier to build properly.

There's no questioning the strength to weight ratio of carbon, but you can't just look at it in isolation. If one is to compare an aircraft or a boat to a bicycle, then the comparison should include structures of similar scale and with similar stress requirements. Looking at strength to weight ratio and engineering alone is an abstract exercise that does not take into account any manufacturing difficulties that might come into play in *attaining* maximum strength of the material in the real world. I'm questioning the comparison and the application, not the material.

P.S. I used 180 lb just as an example of the stresses involved, not as a hard and fast case. feel free to substitute any rider weight.

derath

Fair enough. But you also have to look at comparable loads. Yes a CF mast is physically larger. But I guarantee the forces put on that mast by the wind in the sails is far greater than the comparable loads we put on a bike.


How do you figure? I don't see how size has any direct correlation on the process. A CF seat tube is far smaller than a bike frame. Which is easier to do properly? A small straight tube or a full frame?

There may not be any way to answer your question.

-D

P.S. I used 180 lb just as an example of the stresses involved, not as a hard and fast case. feel free to substitute any rider weight.[/QUOTE]

wagathon

I know what you mean.

There was a link to an interesting video a few months back: it was a segment from a television news show reporting what it said was a big upsurge in bicycling.

Part of the video showed a tour of the Serrotta factory (probably the part about how much dough some people were spending), as a backdrop to the news piece. They had an assembled frame/fork in a jig with the CF fork repeatedly being pulled from the frame by pulling at the axle. It looked like the CF fork was being pulled away by about 4 or 5 inches at least--maybe more.

It was an incredibly simple and persuasive proof of performance. It's always fun to see engineers just doing it instead of blabbing on and on about something that others don't know squat about.

It also is fun to see real examples of the laws of physics at work in the real world and see actual results instead of listening to someone promoting irrational fears based on abstract notions and ignorant superstition.

pigmode

Its easier to manipulate fibers, resin, and plastic bladders without error on a larger structure--that stands to reason. I'm a long time fan of carbon fiber, and years ago was lucky enough to go down to Cookson Boats in New Zealand to see my friends racing boat being laid with pre-preg before being bagged and stuffed into the oven. Its careful work but I'd imagine its not nearly as fiddley as with bicycle frames.

Obviously the bicycle industry has their carbon construction technique down. My main point was that its not very accurate to make across the board comparisons of boats and planes to bicycle frames.


P.S. FarHorizon,
Your use of hard numbers followed subsequently with caveats and conditions basically renders your exercise mostly acedemic and of little use in terms of practical application.

cheers

FarHorizon

You are correct, derath - NOT all carbon parts are made for 150# racers. In fact, I've a carbon Winwood cyclocross fork on my bike that I think would survive WW-III.

The numbers used in my risk matrix were specific to "light-weight, built for road racers" carbon-fiber parts.

For a true clydesdale such as myself to go riding on an all-carbon-fiber Pinarello racing bike, I'd have to be suicidal.

FarHorizon

And here is the crux of the matter, stonecrd. Nobody argues that carbon fiber has superb strength-to-weight ratio, nor that a properly designed carbon fiber part can do what it is intended to do. The issue at hand is - bike designers design racing bikes for bicycle racers. Bicycle racers typically weigh 150# or less. Such a racing bike (steel, aluminum, or carbon fiber) has little safety margin because light weight was a high design priority. When heavier riders use that bike (or racing parts thereof), the failure rate will rise exponentially with increasing rider weight.

The fault lies not with the designer - the racing bike had adequate safety factor for the forces it was designed for. The fault lies with a) the bike company who sells the bike to riders manifestly not suited for it and b) the rider who buys the bike despite the fact that it is a bad match.

I would contend that most riders who buy racing bikes (AND who are bad matches for those bikes) do so out of ignorance. The manufacturers are complicit in this because the racing bikes (or parts) are NOT labeled with maximum recommended rider weights.

Kudos to those racing bike and racing part manufacturers who DO label their products properly! I believe that the majority of manufacturers just take the money and run, though.

FarHorizon

Hi pigmode!

Let me state the conditions clearly - all severity and likelihood data refers to carbon-fiber frames and parts designed specifically for bicycle road racing. No other caveats - no other conditions.

Cheers!

p2000

Gentlemen I certainly had no idea this thread would drift into this realm. I really was looking for more of an 'experience related' opinion thread. While CF is great in certain applications that I am familiar with (arrows for example) I do know it's built specifically for that exact function. Therefore aircraft CF is, likewise, built to specific standards for aeronautics and so on & so on.

Perhaps my question should be more directly stated: In average road riding conditions do CF frames tend to fail more than none CF? Do frames with some CF fail more than frames without? Is it a non-issue?

Or, probably more likely, is it just too broad of a question to lay out any definitive answer?

wagathon

I heard a report on the way to work today that the San Andreas fault was overdue for a huge earthquake. The reason reported was that a big quake along that fault had not occured for more than 300 years so a lot of tension must have built up over that time. That was the entire factual background upon which the earthquake warning was founded upon. That's "academic," e.g., like you say: theoretical and speculative with no practical purpose.

Academic speculations about the survivability of CF bike frames and forks is crazy because the truth of the matter can easily be arrived at through scientific testing. To think that manufacturers have not done such testing, or that such testing has not long since progressed from bench testing to real life experiences on the road is crazy too.

FarHorizon

Hi p2000!

I apologize for hijacking your thread. To answer your question directly (and keep in mind that this answer is just my opinion):

For "average road riding conditions" a properly designed carbon-fiber frame that is used by a rider appropriate for the design is just as durable as any other frame. Whether the frame is full-carbon, or just partial carbon should not be an issue.

If you buy an ultra-light carbon-fiber road racing frame and expect it to hold up for a decade or more in "average road riding conditions," then you'd be asking for trouble, IMHO.

p2000

Hey FH no problem on the hijack. The info (and ensuing discussion) was, most definately, interesting for sure! I just hope no feathers were ruffled.

Thanks for the opine also.

FarHorizon

Nothing bothers me. I'm afraid I've upset some others, but that's just life.

derath

I don't know about that. It's all good here. Actually it was kind of fun. I got to watch you go from "all carbon fiber is potentially dangerous for heavier riders" to "any racing bike regardless of the material is potentially dangerous for heavier riders"

the only thing I will add, is that one major difference in CF is that it can hide damage. So while I feel perfectly safe on my CF bike, I know it is very important to have it inspected after a crash. That is not to say CF is more fragile in a crash. Plenty of CF bikes have successfully survived a crash. It is just that while metal will general deform or otherwise show damage, while CF generally will not.

-D

FarHorizon

An accurate summation - that is what I actually meant in the beginning...

I completely agree.

stonecrd

Well it seems that everyone agrees that CF bikes can be as strong as any other material. We have now moved to whether Bike mfgs are building CF bikes for heavier riders. My contention is that the mfg knows the stresses and weight their product can handle. With the current product liability situation if they know the bike can only support a rider of a certain weight they would be forced to label the product so that this could not be missed. So I guess I would expect a big red sticker saying this bike may fail if ridden by a rider over xlbs just to CYA the company. Without such warning I believe you should be comfortable riding a new Orca or Madone and not feel you are taking a risk.

wagathon

There is such a sticker: it's a big red tag saying that the bike is sale-priced this weekend only for just 7,500.00

FarHorizon

Wanna bet your life on it?

stonecrd

I will, when I save enough money I plan to get a full CF bike and I weigh 192lbs. I am much more concerned about the cars than I am the bike failing.

derath

Oh ****. Here we go again. And we were finally getting along.

-D

pigmode

I like both the Giant OCR Composite and the Trek Pilot OCLV, although both are a little beyond your price range. I'd expect that both frames are built a little heavier than racing frames. Both come equiped with long reach brakes that will accomodate bigger tires than your average racing frames--a big plus.

stonecrd

I have the Trek Pilot 2.1 (AL) right now and am considering the 5.2. However, I am also looking at the Orbea Orca, Scott CR1 or Kestrel Talon. There is no info on the mfg websites about rider size limit, I guess if I weigh too much I will have to loose some more weight. I will never be <180lbs though

Bob Ross

And who would those manufacturers be?

I must admit the only time I have *ever* seen a maximum weight limit specified for a bicycle part was on some Look Keo carbon pedals with titanium spindles. But if I'd never seen that one example I'd say this entire premise is a crock; clearly no one with major market visibility is labelling their products conspicuously. Or am I just blind?