The Insider’s Guide to Carbon Fiber Bicycle Frames

Carbon fiber, or “Magic Plastic” as I like to call it. I don’t really call it that, and in reality, carbon fiber is much more than your run of the mill plastic. The fact that they build F1 car parts and airplanes out of the stuff makes it quite the versatile material. When carbon fiber was introduced as a bicycle material, it had several things going for it: it was lighter, stiffer, and soaked up road vibration/shock unlike the metal frames. On the downside, it was expensive to manufacture, and had a nasty reputation for catastrophic failure. It still has that reputation.

English: Velokraft No-com. Rigid carbon fiber ...

English: Velokraft No-com. Rigid carbon fiber monocoque frame, wheelsizes: 700C/406. (Photo credit: Wikipedia)

Another advantage of carbon fiber was the myriad of tube and frame shapes it could be made into. Carbon fiber sheets are laid in a mold similar to the fiberglass is made. Resin is then used to coat the layers, after which an internal bladder is inflated to compress the layers in the mold as the resin cures. Frames are typically made in sections then joined with more carbon fiber and resin. Hydroforming has led to more complex metal tube shapes, but the flexibility of carbon takes it further. Check out the image of the carbon fiber recumbent there. Also, carbon fiber sheets flex one way, so depending on how the sheets are laid, a tube can flex in one direction, while being rigid in the other. For example, the seat stays are vertically compliant, but are rigid sideways to offset the flex induced by hard pedaling.

After the break, I’ll go over what you need to know about carbon fiber.

First, let’s dispel some myths about carbon fiber:

  • They don’t “just break” because they’re more fragile than a metal frame. Sure, there are frames that do break, but there is a teeny weeny percentage that break under normal use. Nearly all breakage occurs from hard impacts in a direction the frame wasn’t built for. Usually hitting a tree, or a pothole at speed.
  • They don’t melt in a hot car. Seriously. Urban legend. It may smell hot, but it doesn’t get hot enough to melt the resin. Besides, leaving you carbon bike in a hot car is deplorable.
  • You can’t repair them. Ask Calfee about that

Here’s an article that in rebuttal to a New York Times article that purported the fragility of carbon fiber frames due to the rash of breakages at this year’s Tour de France: That’s Not How Carbon Fiber Works. It does a great job explaining that the “fragile” carbon fiber bicycle is a myth.

Let’s sum this all up in a pros and cons list.

  • Lightweight. This goes without saying. The lightest bicycles are made out of carbon fiber and its variations. If weight is important, this material is for you.

  • Smooth Ride Quality. It has the wonderful ability to soak up road vibrations. Some riders may feel like this is a “numb” feeling, and it depends on what ride quality the manufacturer is going for.

  • Stiff and Compliant. At the same time. Though metal framed bicycles have come close, when comparing top of the line bicycles in any material, carbon fiber tends to win this round.

  • Corrosion-free. It’s plastic.

  • Expensive. Relatively. There are less expensive carbon fiber bicycles to be had, but the entry level carbon bikes are low-spec’d.

  • Catastrophic Failure. Even though this is a rarity, when carbon fiber fails, it is usually a complete, ride-ending failure. You dent a tube on a metal frame and as long as the wheels spin, you could conceivably still ride the mangled thing.

  • Impact Resistance. Carbon hates those impacts, especially sharp, sudden impacts. Manufacturers have tried to lessen the impact (see what I did there?) by introducing Kevlar panels and such into the molding process. Carbon still hates those impacts though.

That’s it. You should have enough information on the common frame materials to at least be dangerous in a bicycle shop. Remember, there is more to frame materials than I can possibly write. The main take away from all this is to ride as many bicycles, in the budget you’re looking for, to get a feel for how each rides. You want one that is comfortable to YOU and only you.

Next post on frame materials will touch on the niche materials.



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