The Fat Cyclist Explains: Carbon Fiber

A Note from Fatty: I’m pleased to announce a new series, wherein I explain difficult cycling techniques and technologies in clear, simple English. Except for when it makes better sense for me to explain in French, in which case I will of course explain in English anyways, because I don’t know French.

If you have a cycling-related question you would like explained, simply email me. Due to the volume of email I receive, however, I cannot respond to all questions individually. In fact, I to hardly any of it.

OK, the truth is I haven’t checked that email address in months. But I will soon. I promise.

And now, on with the explainification!

What is Carbon Fiber and How Does It Work?

I recently received an email which I had slightly less-recently sent to myself. This email went as follows:

Hi Fatty,

First, let me begin by saying that I’m a big fan of your blog. I don’t know how you come up with your insightful, witty, and down-to-earth cycling commentary on a near-daily basis. The only person I’m aware of who writes more about cycling than you is Lennard Zinn. Oh, and Bike Snob NYC writes more than you, too. So that’s two people who write more cycling-related stuff than you. And they’re both better than you, too. No offense.

Anyway, the reason I thought I’d email you is to ask a question that’s been bugging me lately. It seems that more and more biking stuff is made from carbon fiber. Frames, cranks, handlebars, seat posts, brake levers, stems, bottle cages. Practically everything.

I understand why they’re doing this: carbon fiber is light, it’s strong, and it can be made into practically any shape. Fine, I get that.

But what the heck is carbon fiber? I mean, I know what the two words are, kind of. “Carbon” is what pretty much everything in the universe is made of, and “fiber” is a thread of some sort or another, and if you eat enough of it, you poop on a regular basis. Excellent.

But when you put those two words together — “carbon fiber” — somehow you’ve suddenly got this outrageously strong stuff that’s really light that you can make into any shape?

It sounds like dark magick to me, Fatty.

Please help me understand what this stuff is and how it works, so I can explain it to other people without giving you credit.

Best Regards,


PS: Please also explain how CDs work.

Duane, you’ve asked an interesting question, and a timely one at that, since I am currently in the process of revising the Wikipedia entry on carbon fiber for accuracy and completeness. And also, quite frankly, for interestingness, because the current entry is so dull that I simply have not been able to bring myself to read it.

Here, in plain and understandable English, is my explanation of what carbon fiber is, how it can be shaped into practically anything, and why it is is so light and strong.

What is Carbon Fiber?

Carbon is the most plentiful element on Earth. Except hydrogen, I think. And oxygen too, maybe. And probably nitrogen, or was it helium? But after that, carbon for sure.

My point is that there’s a lot of carbon.

But what does carbon look like? Well, coal is pretty much pure carbon. So there you go. Carbon is black and flaky, and it’s pretty heavy. And if you drop it it shatters into a bunch of pieces.

“But Fatty,” I hear you say, “Heavy and rock-shaped and flaky and brittle aren’t the kind of properties I generally associate with carbon fiber bikes at all! Or at least not for the past couple years!”

And that’s because carbon is only like that (heavy, brittle, and coal-colored) before you turn it into fibers. Now a “fiber,” as you know, is really nothing more than a thread. And threads are flexible (not brittle) and light (not heavy) and don’t shatter when you drop them on the sidewalk.

So you definitely want to make your carbon fiber-y if you’re going to make a bike out of it.

To do this, you extrude coal through something that’s kind of like a pasta maker, except the pasta is really, really thin. And it’s not extruding a semolina-based dough, it’s using carbon.

And then, once you’ve put the coal through the pasta machine, you boil it for eight minutes. Any longer than that and you’ve got soggy, limp carbon fiber and no amount of pasta sauce and cheese will ever fix it. Believe me, I’ve tried.

[NOTE: Since coal is 99% pure carbon, and coal burns, and most threads burn, be aware that your carbon fiber bike is very, very flammable! And it will give off a thick black smoke when it burns, and the EPA will come and have a very stern conversation with you. Still, the knowledge that your bike burns can be useful in survival situations. But if someone dares you to jump your carbon fiber bike over a bonfire, do NOT take the dare.]

Why Is Carbon Fiber Light?

Now that you understand what carbon fiber is, your next question is, undoubtedly, “Why is it (i.e., carbon fiber, not your question) light?” The answer to this (i.e., carbon fiber, not your question) is really quite simple. Carbon fiber is light because a fiber is nothing more than a thread, and threads are light.

Here’s a way to prove this to yourself and friends.

First, pick up a thread, maybe a foot or so long. See how light it is? Put the thread on your bathroom scale. On most scales, it doesn’t even register. Pretty amazing, if you ask me.

Now, just for fun, put another thread of about the same length on the scale. See? Still doesn’t register, does it? You know why? Because fibers have no weight. Mysterious, I know, but demonstrably true.

The real question is: since fibers are weightless, how come carbon fiber bikes weigh anything at all? My personal theory is that bike manufacturing companies put ball bearings in the downtubes to add weight, putting in slightly fewer ball bearings each model year. This allows them to claim less and less weight (and hence a reason to upgrade) every year.

It’s a lousy trick.

Bicycle manufacturers of the world, I’m putting you on notice. Stop putting ball bearings in the down tubes and give us our weightless bikes now!

Why is Carbon Fiber Strong?

As you know, carbon is the primary element in diamonds, and diamonds are unbelievably strong. Here, try this. Look around you and pick up a handy diamond — the biggest one you can see. Now, try to bend it.

You can’t, can you?

Now, place it between your palms and try to crush it, like you would an orange.

Not easy, is it?

See how strong diamonds are? That’s why carbon fiber bikes are strong.

But there’s even more to why carbon fiber bikes are strong. In fact, the strength of your carbon fiber comes from a number of different factors:

  1. The weave of the carbon fibers. Three-strand braids are extremely strong, but are rarely used. The reason why is quite interesting. Long ago braids were almost exclusively used in factories, but since most guys cannot braid to save their lives, most of the carbon fiber braids were executed by women. A discrimination lawsuit was brought to bear by a man that felt put upon, and that was that. Now the basket pattern is used most often, although some people are working on a new “interlocking pretzel” pattern, which sounds both promising and delicious.
  2. The thickness of the carbon fibers. Thicker is of course stronger, and the best carbon fiber bike would be where each tube is one really thick fiber. But science doesn’t know how to do that yet, and I haven’t told them because they haven’t offered me enough money.
  3. The kind of glue they use to hold the fibers in place. Most manufacturers go with a kind of epoxy, which is fine. Be aware, however, that some of the cheaper manufacturers use straight-up Elmer’s school glue. The best way to tell if your carbon fiber bike is mixed with Elmer’s is to smell it. If it smells like Elmer’s, it probably is. The BEST kind of glue to use, of course, is Super Glue, because that stuff is strong. But hardly anyone ever uses this anymore — even though it’s incredibly strong — due to the fact that factory workers kept gluing their fingers together.

How Is Carbon Fiber Shaped?

The final aspect I’ll cover is how carbon fiber can be formed into practically any shape. Well, first the manufacturing plant mixes some glue up and then they slather it over a layer of the carbon fiber weave, and then they do that same thing again and again — sort of a glue-and-carbon-fiber lasagna — and somehow make it into the shape they want it to be.

Or something like that.

Honestly, I have no idea how. Maybe they pinch it into the shape they want just before the glue hardens. Or maybe it’s magic. It’s a total mystery to me.

Anyway, that’s how carbon fiber works. I’m glad I could explain it to you.

PS: CDs work by using lasers!

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