FarHorizon

You're right again, wag, but here, instead of talking carbon fiber specifically, we're talking about risk. In fact, risk has two parts - likelihood and severity. We'll call them "L" and "S." For general purposes L * S = Risk.

Let's look at severities first. Assuming your carbon fiber frame, fork, or handlebars fail while riding, I'd estimate that you have a 10% chance of no injury, a 40% chance of minor injury, a 40% chance of major injury, and a 10% chance of death. We could argue the percentages a bit, but they're probably ball park right.

Looking at likelihoods:

if you weigh A, your likelihood (over the service life of the carbon-fiber part) of a failure is B for the chart below:

A - B
150# or less - 0%
150-180# - 1%
180-220# - 2%
220-250# - 4%
250-300# - 25%
300-350# - 50%
350-up - 100%

Given these estimates, let's assume I weigh 275. The likelihood of failure (0.25) times the probability of a given severity (let's say death at 0.10) provide a risk (over the service life of the part) of 0.025 that I'll be killed if my carbon part fails.

I don't like those odds.

All of this fails to account for design of the part. If a part is designed with a large safety margin, then the likelihoods of failure change significantly (the severities, however, stay the same). The estimates provided above assume carbon fiber "racing" parts designed for light-weight racing riders. These wouldn't be accurate at all if we were looking at a heavy-duty, carbon-fiber cyclocross fork.

The bottom line is, provided you've selected the right part for your riding style and body weight, the risk declines significantly. If you're a serious Clydesdale and try to run high-buck carbon-fiber racing parts, you're playing roulette.

p2000

Thanks for the sage advice. Trek and Specialized both have what the salesmen called full carbon frames for $1500. Specialized has 105/Ultegra and I'm not sure on Trek.

That said, I am not hell bent on a carbon frame either. To be quite honest I really just want to know what others with more experience think. What I might look out for, avoid, etc. because I get leery when I see a $1500 'all carbon fiber really great bike' sitting next to an all carbon $3000 bike. I figure there has to be a reason it's 1/2 price considering the components are pretty decent. And perhaps the Bianchi Eros is the next one regardless!

sfend002

Wow, the difference between 250 and 251 is ALOT! 19% more

nebby

I have a full carbon mountain bike. It's been throught eh ringer many times, and is still sound. Carbon can be engineered to take a severe beating and hold up as well as any metal.

Bob Ross

BZZZT! I'm sorry, thank you for playing, next contestant please.


The PURPOSE of carbon fiber, insofar as it applies to bicycles, is to provide a material with a higher strength-to-weight ratio than traditional bicycle materials...so that 1) for an equivalent weight, the carbon part would be stronger, or so that 2) for an equivalent strength, the carbon part would be lighter. We probably both agree that the majority of bike manufacturers are opting for #2, the lighter weight. Note that there is NOT a fragility penalty associated with this weight reduction.

wagathon

I think you accidently left out the fact that the "estimates," that you say are "[g]iven," are actually hypothetical, right?

FarHorizon

Absolutely - This isn't quantitative, except for the S*L=Risk part. All likelihoods & severities on these are "seat of the pants" estimates. The staff at my LBS, using their experience, doesn't disagree significantly, though. Do you?

FarHorizon

Yes, we agree. Where we disagree is whether the manufacturers are stopping at option #2 or going for the option you didn't mention: Continue to reduce weight beyond the "same strength" level in order to gain market share. Sound like a likely scenario?

pigmode

So where does the Giant OCR Composite fit into your scheme of things?

wagathon

You are so full of crap . . . do you have some reputation here that I'm the only one that doesn't know about . . . . like a real kidder or some kind of idiot?

FarHorizon

None of the above. I call'em as I see'em. The severities and likelihoods I listed are credible and logical.

There is an exponential increase in carbon part failures as rider weight increases. I believe that this statement is factual and accurate. My chart of likelihoods reflects this. Do you disagree?

There is also a bell curve of distribution on the severities of injury that occur when a part fails while under stress. I believe that this statement is also factual and accurate. My list of severities reflects this. Do you disagree?

The L*S=Risk is a commonly used definition in industry. Refer to any system safety text if you doubt it. This is not an opinion - it is a fact.

late

Hi,
there are a bunch of GREAT frames around $1K. There is my Gunnar Sport,
Habanero Road, and a zillion others. You could get the frame, and swap parts over.
With the $500 left over you could either get a nice set of wheels or start upgrading to 105. If you can, test ride a Jamis Quest.

wagathon

Ok fine but at least we know this is not statistics. You can "call'm as I see'em" as some kind of stochastic projection based on preconceptions, prejudices, fear of organic compounds or whatever but most of us call that unfounded opinion, not liklihood based on credible logic.

derath

Actually I usually call that reasoning bulls**T.

Sure L*S=Risk is a real definition. But when you make up numbers for L and S your Risk can be whatever you want it to be.

You have shown NOTHING quantitative that supports even your guesstimation of risks is even close to accurate. You do make them sound good though. Do you work in a government statistics office per chance? If not you should.

-D

soze

Does carbon fiber, as constructed for bicycles, tolerate high lateral stress loads well? I'm kind of curious if it's more of a race-only kind of material instead of an every day thing. I don't have much experience with the stuff.

FarHorizon

Both you guys want to attack my numbers but you ignore the two (logical and credible) statements that the numbers are based on:

There is an exponential increase in carbon part failures as rider weight increases. and:
There is a bell curve of distribution on the severities of injury that occur when a part fails while under stress.

If you want to dismiss my numbers as "unfounded opinion" or "guesstimation," then disprove those two statements. Both statements are logical and credible. I don't think that any carbon-fiber parts designer would disagree with the first statement. I don't think that any EMT who had extensive experience with bicyclists would disagree with the second.

Ball's in your court...

nemonis

A couple of thoughts on the carbon debate. A Carbon frame can be made STRONGER than a steel frame for the same or less weight. A carbon frame will handle the stress of riding quite well.

Part of the reason a carbon frame can be made lighter than a steel frame is that the fibers can be oriented to be strong in the directions it needs to be, without adding weight strengthening something that doesn't matter in riding. The problem with this is a crash can stress things in directions they are not designed to deal with. With steel you could end up with a bent, cracked, or dented frame. All of these can be spotted by inspecting the bike carefully after a crash. With carbon the inner layers of carbon could fail, but the outer layer stay intact. This would leave you a frame (or fork) that looks just fine, but is much weaker than it used to be. It could fail catastrophically while you are riding later on.

Again, carbon is fine for riding, but I wouldn't trust it too much after a crash. Your opinion may be different.

God bless!
Wayne J.

derath

You have a great way of clouding the issue, but I will bite. Let's see if I can explain


Ok, let's assume those 2 statements are correct. I am not positive, but they sound feasible.

So step1: Draw a pretty exponentially increasing graph Something like this:


Step2: Draw a pretty bell curve. Something like this:


Pretty aren't they? Unfortunately they mean NOTHING without numbers. Right?

You see the problem with your argument is NOT the graphs. It is the numbers. Your "unfounded opinion" or "guesstimation" is that carbon parts are designed to be safe only for riders 150# or less. I don't need to DISPROVE your graphs. YOU need to PROVE that carbon parts are only designed for light people. I would submit this is a false assumption.

I will agree that some race worthy parts are designed for a certain weight. I know this because those items have a CLEAR warning about their maximum weight capabilities. And I would almost guarantee that any bike manufacturer that made a bike that was only deemed safe for a certain weight would plaster that all over the place. Why? Because we are the land of litigation and disclaimers. The manufacturers' attorneys would make sure they have those bases covered.

I would also submit that the OP is looking for a bike in the $1500 range. I don't think he would be getting a superlight, weighweenie bike at that price.

Back at ya.

-D

Bob Ross

I dunno. Last time I picked one up it struck me as being conspicuously heavier than other >$2000 full carbon bikes, so maybe it's splitting the difference?

Or maybe it's a really stupid design? There's always that option...

Bob Ross

It does, albeit not as one of the initial reasons that carbon was introduced to cycle building. Foolhardy design as a method of jumping on other's coattails for market share is an epidemic in any industry. In fact, I don't think you even need to qualify the statement by including the part about >>Continue to reduce weight beyond the "same strength" level<< in order to make a valid observation; some unscrupulous companies will do just about anything in order to gain market share.

But it's a bit of a strawman arguement until someone starts naming names & pointing fingers. Who do you think is making carbon bike frames whose strength is compromised by their desire for ultralight weight?

derath

I dunno, my OCR C3 is sub 20#. Light enough for me. And cost me under $1000 (clearance).

-D

FarHorizon

Numbers are most frequently NOT quantifiable in risk assessment other than by using a team's opinions. In fact, even "quantitative" risk analysis methods, such as event-tree and fault-tree, most-often rely on estimates.

You want iron-clad numbers? It isn't going to happen. Why? Because they don't exist. NOBODY (not even the insurance industry, much less a bike manufacturer) has comprehensive data on what failed, why, and what injury was sustained.

The most common method of industrial risk assessment is for estimates ("guesstimates") to be made of BOTH likelihoods AND severities. Management accepts these assessments as a basis for decision making not because they are fully-quantitative, but because they are the best available. In general, these estimates are relatively accurate (this statement isn't an opinion - it is a fact).

I've provided what I believe are relatively accurate assessments. If you disagree with my numbers, I'm open to argument. You say that carbon-fiber racing parts are NOT typically designed for 150 pound racers. Your reasoning is that liability law would insist on posted weight-limit labels for such parts and that some manufacturers do so label. If that is the case, what weight are non-labeled parts designed for? Why aren't they labeled?

In fact, the majority of carbon frame, fork, seatpost, stem, and bar manufacturers do NOT label their parts with a maximum safe weight (or any weight limit at all). The fact that very few manufacturers label would argue against your idea that liability law drives labeling.

Given two carbon-fiber parts that have the same weight, one labeled with a "safe-weight-limit" and one not, is it reasonable to assume that the non-labeled part is just as subject to fail if abused as the labeled part? If so, then my contention that the carbon-fiber parts industry is focused on 150-pound racers seems justified.

pigmode

Your LBS has experience with 350+ lb riders on carbon frames? 250 to 350 lb?

stonecrd

Let's look at specifics:

Tensile Strength
CF = 3.5 GPa
Steel = 1.3 GPa

Tensile Modulus
CF = 230 GPa
Steel = 210 GPa

Specific Strength
CF=2.00 GPa
Steel=0.17 GPa

There is a reason why CF is used in aeronautics and sailing and that is that its strength to weight ratio is so good. Do you think you put more stress on your bike than a America's Cup Yacht or Airbus 350 gets during use? I think not. Now can CF be used in a way by a mfg that makes it fail, sure, but are you more confident in the welds used for steel and Al? My 2c

derath

Agreed

Agreed. Never asked for Iron-clad numbers.

Agreed

I disagree with your assessments. And I never said Carbon-fiber parts are NOT typically designed for 150 pound racers. Some parts are, some are not. You are the one that have made the blanket statements. Reply #13 [QUOTE=FarHorizon]This is the question that you should ask when looking at carbon anything. If you're 150# or less, carbon is probably safe.[/QUOUTE]

I will get to the rest of my argument on that point below.

But if liability law doesn't play, why would a company such as Speedplay put a recommended maximum rider weight of 175# on their titanium pedals as an example? They don't put a weight restriction on their heavier chromoly pedals, but I guess with your logic my 200lb girth would still be unsafe on them?

What am I getting at? If carbon parts were as dangerous as you would lead us to believe for anyone over 150# i guarantee manufacturers would be all over weight restrictions. They would have to as the risk of litigation would be too high.


Or maybe they have tested their equipment to handle higher weights? Many components have weight limits when they are known to be designed for light riders. Wheels etc. The lack of limits on other components is not proof of conspiracy however.

But they don't. This is the crux of the matter. Every manufacturer has different levels of carbon construction for their lines. A Trek Pilot 5.0 frame is NOT made with the same carbon as a much more expensive Madone frame. And they DON'T weight the same. I would contend that the heavier Pilot, which is designed for comfort and durability over weight would be perfectly save for a heavier rider.

The bottom line is this. You seem intent on proving that ALL Carbon components are made for racers, and thus should fit your 150# weight assertions. I disagree.

-D