You guys are killing me. Pound for pound, carbon is stronger than aluminum.
If you build up a two identical frames of the same weight, one from carbon and one from aluminum, the carbon frame will be stronger.
The reason why carbon gets a bad wrap in the bike industry is because lots of frame manufacturers try to build two identical frames of the same strength, but use less material in the carbon frame to make it lighter. I think GT these days has a all carbon DH bike that weighs in the same as an aluminum DH bike and is very durable. Carbon doesn't have to be just for XC frames or short travel forks.
As far as scratching a carbon frame on rocks, you guys do know the top layer with that cool carbon fiber looking weave is mostly cosmetic right? You actually need to gouge a carbon frame or bars or helmet or whatever pretty deep to make it unsafe.
All that said, I have no idea if trek, spesh, ibis, SC or any of those other dudes are skimping too much on material just to make the frame lighter and justify the blingin price tag or not.
I'm not a materials engineer, but I know Carbon is stiffer but I'm not convinced it's stronger.
yeah okay, maybe the surface layer is only cosmetic, but once you hit that hard on a rock, what reassures you it's still structuraly sane? That's the problem with carbon, once it's compromised (in any way) it's pretty much useless.
A crack or even seemingly benign surface penetration renders it untrustworthy. A simple ding on aluminum does far less to the integrity of the frame. Don't get me wrong, it's strong, however, it has it's drawbacks.
carbon fiber is just that: FIBER. It has high tensile strength, but like mentioned in the Mountain Bike article, the fibers will break when stretched which constitutes a weakness.
anyway - this is just my $0.02. Like I said, nothing wrong with Carbon bikes - just be aware of what you ride and keep a close eye on the frame. Especially the head tube and areas exposed to rocks.
Last edited by ThePunisher; 03-02-2010 at 05:43 PM.
A crack or even seemingly benign surface penetration renders it untrustworthy. A simple ding on aluminum does far less to the integrity of the frame. Don't get me wrong, it's strong, however, it has it's drawbacks.
carbon fiber is just that: FIBER. It has high tensile strength, but like mentioned in the Mountain Bike article, the fibers will break when stretched which constitutes a weakness.
A crack in an aluminum frame is also bad and renders a frame untrustworthy.
Fiber having a high tensile strength just means that it won't stretch until it has reached its breaking point. Aluminum will deform slightly at less pressure before ultimately breaking. The breaking point of carbon fiber is much higher than aluminum.
You guys are killing me. Pound for pound, carbon is stronger than aluminum.
If you build up a two identical frames of the same weight, one from carbon and one from aluminum, the carbon frame will be stronger.
I am not sure "stronger" is a proper term here. If by stronger you mean resistant to stress - yield, tensile and fatigue stress, then sure, proper made carbon is by far stronger. Impact strength - I am not sure. But that is only a part of frame durability. Plasticity for example (ability to make a dent without breaking apart) is another factor. Deflection - how far will it bend without breaking - is another.
I have little doubt that most everything that is on sale is strong enough for its purpose.
My personal semi-educated concern about the modern state of this technology is mostly about inspection for damage. When picking up a hardtail for adventure racing I chose titanium as I think that after tossing my bike down a rocky slope at night I will be able to tell the damage on a titanium frame and keep riding it, and I would not be so sure about a carbon one. Even if the carbon one is twice "stronger" - it still breaks.
I am not sure "stronger" is a proper term here. If by stronger you mean resistant to stress - yield, tensile and fatigue stress, then sure, proper made carbon is by far stronger. Impact strength - I am not sure. But that is only a part of frame durability. Plasticity for example (ability to make a dent without breaking apart) is another factor. Deflection - how far will it bend without breaking - is another.
From what I remember, or think I remember about carbon fiber is that in the realm of plasticity- carbon is brittle and has none it just goes straight to a breaking point, but aluminum's breaking point even after denting, is still lower than properly constructed carbon fiber. So sure aluminum would dent before breaking, and carbon would just break, but the aluminum would dent and break long before carbon.
Deflection also sort of falls into the same realm. Carbon Fiber won't deflect much, but it will take a lot more force to break it. It will remain stiff the entire time up until failure. That failure point should be much higher than a comparable aluminum frame if I remember right.
Good point on inspection though. I think I'd avoid a carbon frame for adventure racing just on that and carbon's susceptibility to moisture if not properly laminated. For big hits on something like a 6" AM ride or even an 8" DH bike, I'd probably feel pretty confident on carbon.
I bet this same discussion happened years ago when aluminum was the next bike material.
Some folks probably said it will never work and they will only ride steel until they die, while others decided to give it a try.
I bet in another 10 years, we'll be having the same discussion, but stating "I won't ride anything but carbon. That new [insert technology] is [insert fault]."
I think all the materials have their place, and carbon is trying to prove it's useful in a 6" AM bike now.
Those who know, ride a Mojo AND a Mojo HD. Quadzilla
Originally Posted by benja55
Ok, whatever, cold water on my bike boner right there.
Factoring in the weight savings, the increased stiffness, and the better dampening of carbon, it seems to be the clear winner in every category save one: impact resistance. I'm actually pretty concerned about this since I seem to crash more frequently than most of the people I ride with.
Should I stay with aluminum?
You're never going to get an answer for which is better. However, I really don't think you need to stress about a carbon frame as much these days. Quality carbon frames have come a long way. Plus, you say your'e mostly XC, so I really doubt you'll be putting yourself in situations very often where you'll have a hard enough impact to really destroy the frame. The rear triangle on the Enduro is aluminum, so what impacts are you really worried about for the front triangle? If you're worried about cosmetic damage to the down tube, just put some 3M tape on it. Carbon can take blunt impacts extremely well. A sharp edged rock, however, can possibly score a carbon frame beyond the cosmetic layer. Note, this type of impact will also damage aluminum. BUT, these types of damage can be repaired by carbon frame builders. I know Calfee offers a repair service.
Everyone can come up with tons of "what if" scenarios. What are you realistically going to be putting your bike through?
Just curious, did you get to ride both bikes to compare the vibration dampening? I know you mentioned that's a huge plus for you.
I own aluminum bikes, and I've ridden carbon bikes. I wouldn't hesitate to buy a carbon frame. But I'm also a lightweight and ride mostly XC. I do crash, but most of my crashes result in scrapes rather than breaks.
I bet this same discussion happened years ago when aluminum was the next bike material.
Some folks probably said it will never work and they will only ride steel until they die, while others decided to give it a try.
"Yeah, you stick with your fancy Coke can frame. 4130 all the way, baby!"
I bet this same discussion happened years ago when aluminum was the next bike material.
Computers and internet forums weren't around back then, but it was definatley a topic that was discussed. Remember the PK Ripper? Everyone always knocked it because "aluminum is weak and it will break." However, that had more to do with the welding technology than anything else and they've improved on that problem since then.
Composite materials don't yield like homogeneous metals. That means, at a certain point in the stress strain plot, the composite material will break and not take any more strain. Homogeneous metals will keep straining after the yield point, but will not take any more stress.
If you guys really want to learn something and not just listen to people blabbing on the internet, study up on young's modulus and how they differ between composite materials and metals. You'll understand where all these theories about composites come from.
The main thing with composite materials is that the material does not have equal material properties in all directions (non-homogeneous). With homogeneous materials (almost all metals) you only have to worry about the thickness. With composite materials, you have to worry about the thickness and which direction the load bearing fibers are positioned within that thickness.
All these extra variables make composite material that much harder to analyze for various load cases, so the engineers heavily rely on testing. If you wanted to know how much the tip of a metal beam would deflect if you pushed down on it with a given force, you could calculate that by hand without a calculator. If you wanted to do the same thing for a composite beam, you'd have to know the exact lay up (not just material average density, remember it's non-homogeneous) and be pretty good with a computer and super up to par on your linear algebra. You guys should all call these big bike companies and ask them how many hours they spend per bike breaking them on the test machines and using that data to better the design instead of just going with the original prototype tooling and saving money.
On that note, I run a composite skid plate on my dirt bike and trust that thing to keep my engine from getting blown up when I'm 50 miles from camp and doing 40mph through the worlds gnarliest rocks.
I bet in another 10 years, we'll be having the same discussion, but stating "I won't ride anything but carbon. That new [insert technology] is [insert fault]."
Quite possible.
Look at Boeing 787. It has been delayed since somebody was not doing layup of the wing to fuselage assembly quite right - if I remember correctly. They had to fix it with some extra layers.
Now - do you trust some underpaid underage employee in a Chinese village to layup your headtube just right?
I would rather trust some underpaid underage welder - that is a more developed production technique as of right now.
Cheaper and works just fine - what's not to like? In any case - for things like handlebars carbon is certainly already well proven, we probably would be able to say the same about frames in a few years - they are just showing up..
My only experience with composites was watching my collegues design and test a support structure for a sattelite experiment. About as cutting edge as it was a few years ago. We gave up and went with a metal construction - could not make it reproducible enough. Of course that bit was designed for operation in vaccum and withstanding launch, but then it was not made in a Chinese village either..
In any case - for things like handlebars carbon is certainly already well proven, we probably would be able to say the same about frames in a few years - they are justs showing up..
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I might be wrong about my facts -- the I think the point is will be clear.. In 1975 your statement would have been perfectly placed as the first carbon tubes and lug frames were showing up -- the bond wasn't all that good until TREK got involved, About a decade later, luggless construction we use today was introduced. That was about 25 years ago or about the same time of the first suspension MTBs! Trek has been making carbon MTBs for over 15 years! One of my riding buddies still rides a old, old OCLV HT rim brakes and all - it is a rocket (however he is slow ;-) )
I think it was about 20 years after CF, that hydro discs were available.. Should we wait until the brakes prove themselves ;-)
since i got a C in all my material science engineering classes, i'll ask you a few questions, mainly for my own eddification:
to what extent can FEA be used w/ a material like carbon fiber (if at all) given how complex and non-homogeneous it is? seems like applying FEA to any sort of alloy would be a relative no brainer. is carbon fiber primarly tensile strength (like steel) or compressive (like concrete), or is it both (i.e. the fiber strands provide tensile resistance, and the epoxy/resin provides compression resistance)?
Originally Posted by beaverbiker
Composite materials don't yield like homogeneous metals. That means, at a certain point in the stress strain plot, the composite material will break and not take any more strain. Homogeneous metals will keep straining after the yield point, but will not take any more stress.
If you guys really want to learn something and not just listen to people blabbing on the internet, study up on young's modulus and how they differ between composite materials and metals. You'll understand where all these theories about composites come from.
The main thing with composite materials is that the material does not have equal material properties in all directions (non-homogeneous). With homogeneous materials (almost all metals) you only have to worry about the thickness. With composite materials, you have to worry about the thickness and which direction the load bearing fibers are positioned within that thickness.
All these extra variables make composite material that much harder to analyze for various load cases, so the engineers heavily rely on testing. If you wanted to know how much the tip of a metal beam would deflect if you pushed down on it with a given force, you could calculate that by hand without a calculator. If you wanted to do the same thing for a composite beam, you'd have to know the exact lay up (not just material average density, remember it's non-homogeneous) and be pretty good with a computer and super up to par on your linear algebra. You guys should all call these big bike companies and ask them how many hours they spend per bike breaking them on the test machines and using that data to better the design instead of just going with the original prototype tooling and saving money.
On that note, I run a composite skid plate on my dirt bike and trust that thing to keep my engine from getting blown up when I'm 50 miles from camp and doing 40mph through the worlds gnarliest rocks.
I might be wrong about my facts -- the I think the point is will be clear.. In 1975 your statement would have been perfectly placed as the first carbon tubes and lug frames were showing up -- the bond wasn't all that good until TREK got involved, About a decade later, luggless construction we use today was introduced. That was about 25 years ago or about the same time of the first suspension MTBs! Trek has been making carbon MTBs for over 15 years! One of my riding buddies still rides a old, old OCLV HT rim brakes and all - it is a rocket (however he is slow ;-) )
I think it was about 20 years after CF, that hydro discs were available.. Should we wait until the brakes prove themselves ;-)
Oh
Yes, thank you. Finally someone who knows bike history.
As a side note, if people saw how much load it takes to break a specialized carbon enduro, they'd be spending more time researching doctors and physical therapists than e-debates about strengths of materials.
Now - do you trust some underpaid underage employee in a Chinese village to layup your headtube just right?
no, but I would trust some underpaid Taiwanese employee in a Taiwanese village to layup my head tube just right. Those guys know what's up.... as long as they have an american QC engineer riding their butt for anything that goes wrong.
since i got a C in all my material science engineering classes, i'll ask you a few questions, mainly for my own eddification:
to what extent can FEA be used w/ a material like carbon fiber (if at all) given how complex and non-homogeneous it is? seems like applying FEA to any sort of alloy would be a relative no brainer. is carbon fiber primarly tensile strength (like steel) or compressive (like concrete), or is it both (i.e. the fiber strands provide tensile resistance, and the epoxy/resin provides compression resistance)?
Great questions and I'll do my best to address them for you. You can use FEA programs (like NASTRAN) for composite materials just like any other material, but behind the scenes, there are a lot more assumptions being made than with homogeneous materials. The more assumptions that go into a computer model, the higher the risk factor. In addition, any engineer who solely relies on a computer to tell him if his product will break or not should be fired immediately.If you listen to the beginning of that BOEING 787 wing testing video, you'll hear the engineer say that the testing is just to verify their computer models. The computer models have so many assumptions in there that they want to make sure what they're designing and building matches the computer model, and that the computer model matches real life load cases.
Composite materials do very well in compression and tension, and torsion, and bending, and shear TOO. This is all due to the fact that you can put the highest load bearing pieces (the fibers) in any direction you want. If you have a tube like a drive shaft on a car that see's primarily torsion loads, you would put most of your fibers wrapped around the tube at a 45 degree angle (where the cosine and sine are equal) and the fibers will see equal load. If you ran all of the fibers at that 45 degree angle and a big rock slammed into the middle of the drive shaft (putting the fixed-fixed shaft into bending) it might not be able to take the bending load, even though it can take the extreme torsion loads. So...you put some fibers at 0 degrees and 90 degrees to take load in the transverse directions. Ultimately, and especially if you see a lot of thermal loads, is to make sure your layups are isotropic or quasi-isotropic.
Trek has been making carbon MTBs for over 15 years! One of my riding buddies still rides a old, old OCLV HT rim brakes and all - it is a rocket (however he is slow ;-) )
I would not have bought a CF hardtail for adventure racing 15 years ago, and I would not do it now. Not much that have changed.
Originally Posted by diver160651
I think it was about 20 years after CF, that hydro discs were available.. Should we wait until the brakes prove themselves ;-)
Hydraulic brakes are around for ninety years - Lockheed used them for cars in 1918. Took twenty years before it was used more widely. They are still only found on expensive bikes.
As a side note, if people saw how much load it takes to break a specialized carbon enduro, they'd be spending more time researching doctors and physical therapists than e-debates about strengths of materials.
Aren't you sponsored by the big "S"? If you crack or damage your bike, you'll probably have a new one the next day. unfortunately it doesn't work like that for everyone.
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Originally Posted by benja55
.........get Ti
