one word for me... Six13 by Cannondale..... what a blessing. Great bike!!!

any experienced mechanics out there? there seems to be differences in opinions here... the newer carbons.... the stuff you buy in lbs today.... will they not last as long as aluminum?

This guy majored in material science. He's got his Bachelors and a PhD in Material science. It is a well known FACT that aluminum doesn't hold up as long as carbon. Oh and by the way. I bet you Lance rides a much more wrapped bottom bracket than a regular 8. I bet you he rides 10 wich is about the same as aluminum. I have seen charts on Carbon, Titanium, Steel and Aluminum at the University of Miami's Science Department where my LBS guy got his bachelors and PhD. I was just putting in my 2 cents. If they don't make sense to you fine then just don't say anything. If it doesn't make sense then close your mouth. I don't need a lecture or to be badgered about my OPINION.

Seriously curious: why does a guy with a PhD in material science work at a bike shop?

It's all about how the materials are used (in regards to stiffness and probably comfort as well).
Just as some examples...

Who can say? They've only been out a few years. I will say, that basically 9.9/10 frames we get in the shop that are cracked are aluminum, but you also have to realize we probably sell 8 or 9 aluminum bikes for every steel or carbon bike we sell. And the steel bikes we sell are overwhelmingly low end hybrids that either get ridden 5-10 miles a week or hang in someones garage 364 days a year. So really, who's to say at this point? Old lugged carbon bikes come apart, thats seen on all the old Giants, Univegas, and Specializeds, but they fixed that with the new lugless monocoque designs supposedly.

I got a mechanical engineering degree and specialized in materials science. I also worked with both heavy iron/steel at an oil/gas company, as well as with composite materials (carbon, aramid (Kevlar [R]), and glass). Not taking sides here, as there is a bit of truth to both. My opinion is that a statement like "It is a well known FACT that aluminum doesn't hold up as long as carbon" is akin to a statement like "gold is heavier than feathers." It all depends.

Carbon fiber in the practical sense as applied to bicycles is a composite material comprising carbon fibers in an essentially plastic (resin) matrix. The carbon has high strength/weight and strength/stifness ratios, but you wouldn't want a solid beam or tube made of it (which would be nearly impossible to construct). The matrix itself has poor mechanical properties, with very low compression and tensile strength as compared with Ti, Steel, and Al. However, the plastic matrix is just strong enough to orient the fibers in such a way that when the frame tubes are placed in bending, half the carbon fibers are placed in tension, which is where carbon fibers excel. So long as that plastic matrix is intact, the carbon can do its job. However, if you impact the matrix (such as in a crash), or you fatigue the matrix, you weaken the plastic matrix, and no longer can the matrix do its job to position the fibers, and no longer can the fibers then do their job.

Aluminum alloys, on the other hand, don't have nearly the tensile strength and stifness of carbon (on a gram to gram comparison). But aluminum is an essentially isotropic material (same properties in all directions), and is ductile enough to withstand a pretty serious impact without failing. Pure aluminum fatigues to almost zero strength over time, but the way in which it is engineered, the useful life of the frame will generally far exceed how long you want to own it. Also, the various Al alloys can minimize fatigue. Steel, by comparison, will fatigue to about 50% of its properties, and it reaches a limit, so its a bit safer. Carbon fiber composites have the trade off that they are more prone to impacts and other unexpected stresses.

If you look at the charts of material properties, you will indeed see a variety of strength/weight ratios, stiffness, density, fatigue life, etc., but there is enough technology to engineer each of these materials to perform in a desirable manner. CF is the newest technology, but its commercial appeal has generated enough $$$ in relatively recent years that bike mfrs can now construct reliable and generally affordable equipment from it.

One type of test your friend might perform is an impact test, where you subject specimens to a weight dropped from a known height. You might use a sandwich beam - having Al, Steel, Ti, or carbon skins, and a 1" thick core. You might also subject such a specimen to slow (non-impact) bending. If you use the same thickness for each material, you will get drastically different results. However, in practice, engineers account for the difference in material properties to engineer parts with different cross-sectional areas, facing thickness, etc. That is why so many frame materials are successfully used in bicycles today, and none have yet to become obsolete. Thanks to engineering, the differences in the end products are more subtle, and people can choose the ride characteristics they prefer. All of these involve trade offs.

Ill shut up before I ramble too much.

Well, I just thought your opinion was BS.That's my opinion.. A 'much more wrapped BB than a regular 8'.??? Why don't you tell us what that means. FWIW, I know lots of so called educated people with advanced degrese that couldn't pour whizz out of a boot. HE must be one if he works in a bike shop.I'm also impressed that you have seen some charts.Do you really know what they mean?

When I started riding again last year I bought a used 1990 Specialized Allez Epic carbon frame. The ride was very smooth but I quickly discovered how flexy the bottom bracket area was when going uphill. The first time I actually thought we had an earthquake. I got used to it but when a 2000 Bianchi XL EV2 aluminum frame came on ebay I went for it.
To my surprise the ride was not uncomfortable but the feel of the bike was so much better. No flex in the bottom bracket, superb response on acceleration, and vastly superior climbing efficiency. Keep in mind this was a top of the line frame in 2000 with injected foam to reduce vibrations, so probably a vast difference with cheaper alu frames. The main drawback of aluminum is the rattle. Big bumps on the road result in cables hitting the frame and noisy feedbacks.
Last week I got myself a used 2003 Time VX Special Pro, a carbon frame with alu lugs. After my first week of riding it I have a good sense of the difference between a good alu frame and a good carbon frame. The ride is almost silent except for the humming of the tires and my rear end and neck feel a lot better at the end of the rides. So comfort is definitly better. The frame is very responsible as well but because of the silent ride I don't get the same feeling of speed, so much so I first thought the new bike was slower as I didn't have my computer installed on my first ride.
Since, all is installed and I learned there's a difference between perception and reality. I am going faster with the carbon frame and I pull larger bracket/cog combos.
So after a week I am very happy and can confirm that a carbon frame can be as stiff as an alu frame but add comfort to the ride. I have also no doubt that the frame will last longer. Have you heard of an alu frame with a life time warranty?

I think CF in bike frames has been around about 15 years. Trek OCLVs use lugs and don't come apart,and so do Looks among others. Technology marches on and that doesn't mean monocoque.

A standard OCLV Trek had 8 wraps. That's 8 wraps of carbon. You still with me? Good. I would like to see one of Lances bikes up close. He might have a 10 wrapped bottom bracket. As a matter of fact syd, can I call you syd? Well i'm going to anyway. I have a Bachelors in Science and I will be going for a Phd at Brown University.

Watch out! He's whipping out credentials!

hahahha floppy. Oh well i don't care. I VOTE ALUMINUM *CRICKETS*---- Awww dang it.

Yeah, yeah. When you get a job at a bike shop, come back and see us.

Just kidding. Your post was very interesting, thanks for taking the time to bring some rational thought to this thread.

As to the durability of aluminum, I have some anectodal evidence that the 5 year life span stated earlier is bunk: All three of my aluminum bikes are still fine, and they're 5 and 6 years old. (I guess I should expect a failure any day now.) But I feel rather confident they will hold up for quite awhile longer because of my riding partner's old bike. He is, how shall we say - extremely frugal. He kept riding and riding this bike that I just knew was going to fall apart any minute. That went on for about three years, until the bottom bracket joints started looking really iffy. It was a 1982 Klein, that he raced and rode recreationally for 18 years before he finally replaced it.

...which really proves that it is not necessarily the material, but the design. If Aluminum was so bad, then why do they make airplanes out of it?

I believe the first carbon fiber production frame was a Graftek, made by Exxon. I think it came out in 1983 or so. Greg LeMond rode a carbon fiber Look frame (rebadged from time to time) in most of his tours.

It's funny how all the new high-end alu frames now have...carbon stays????

OK...it Graftek came out in the 70s'...here is a link...

https://www.classicrendezvous.com/USA/Graftek.htm

Flex is a must. Skyscrapers flex. No flex, cracks.

You are just slinging BS with that wrap business. Any given OCLV model is the same. Differences in the OCLV makeup aka, 110,120,150 refer to the weight of a square yard of the CF material used. And then you throw guessing into it. Before, it was a statement of fact. You plan on working at LBS when you get that 'Phd' ?

Yeah, it's bunk and BS,just like the 3 year life of aluminum often touted by many 'expert amature metalurgical regurgitators.'. Haven't you figured it out? The durability aluminum is totally a function of whatever idiot happens to expousing about it. Said with all due respect to any real metalurgists, especially ones in the business of fabricating aluminum,but not 'science' majors working on 'Phds'.

I'm way not as smart as some of you but doesnt CD and Felt to name a few almost say in the warr the bikes wont last long?

I know the carbon stays are purportedly for damping vibrations.

I mentioned Al and most metals/alloys are isotropic, meaning same properties in every direction. CF composite is "anisotropic", meaning different properties in different planes. Largely due to the fact that the fibers are oriented in a selected, deliberate arrangement. Then stresses to the frame in a direction that place the fibers in pure tension will yield the stiffest behavior, whereas stresses in transverse directions may allow more flex. I haven't studied the vibration damping properties of CF, but my guess is the anisotropic nature of the composite is largely responsible for their ability to absorb vibration. Another possibility is that the relatively soft and flexible plastic resin matrix dampens those vibrations, because the vibrations have low enough amplitude that they are not significantly stressing the carbon fibers, and the vibration damping properties of the matrix itself may dominate in that realm.

carbon for me.

I second that....

So it seems that the durability of a CF frame would be dictated by the longevity of the resin and its ability to retain its structural integrity whereas the feel of a CF frame is dictated by the fibers. Am I right?

Well, I don't have th specific experience that people like Trek engineers and aerospace engineers have, but my guess is you are correct that the resin matrix is the "weak link" in the frame's durability, simply because it is the softer/weaker of the two materials and is externally exposed to the elements. However, the matrices they use in CF bikes may be exceedingly durable.

As for the feel, as I explained a few posts above, I'd guess the matrix has alot to do with the "feel" inasfar as I imagine the plastic matrix helps absorb (dampen) vibration.

But a composite material is best viewed not only as to its individual components (CF and matrix, which may individually fail), but also as the synergistic (i.e. greater than the sum) properties of the materials in combination. That's what a composite material is -- two different materials in combination to produce a net result better than or unobtainable by its components individually.