If you’re going to believe what the professional cycling peloton broadcasts as gospel truth, you will at some point develop a snobby prejudice against anything that isn’t made out of carbon fiber.
Why wouldn’t you? The wonder material is lightweight, yet very strong.
The longer I immerse myself in the world of bicycles, however, the more I realize that, outside of a few applications, carbon fiber isn’t necessarily a must-have for me.
Carbon fiber fans say the material has a fatigue life that outlives any metal. It can theoretically live forever when taken care of.
That final phrase “when taken care of” is what gives me pause. In an ideal world, we wouldn’t get involved in crashes, accidents, or simple mishandling incidents. Any fatigue life advantage carbon fiber has over all other metals used in bicycle manufacture frequently goes out the window when a crash is involved.
It doesn’t stop there. Notice how torque wrenches have become ubiquitous in bike shops and with bike mechanics? One thing carbon fiber definitely doesn’t like is crushing forces, which come into play any time you are installing a carbon fiber seat post, or clamping a stem onto a carbon fork steerer tube. In that latter case, a compression expander plug is required to give the inside of the steerer tube some reinforcement against the clamping loads of a stem tightened against it from the outside. Many a carbon fiber component has been ruined by fasteners with too much torque. Even then, in some cases, correct bolt torque isn’t enough to stop, say, a carbon seat post from slipping.
COST OF PRODUCTION
The main appeal of carbon fiber to engineers is that unlike metals, it is an anisotropic material – its load strength isn’t the same in all directions. In other words, a carbon fiber structure can be made stronger in certain directions, where loads are anticipated, then made weaker in all other directions where loading isn’t as significant. This is done by modifying the layup of the multiple layers of carbon fiber sheets according to the design of the component and its predicted loading vectors. This selective “tuning” of strength goes some way into the lightness of carbon fiber as well.
That versatility doesn’t come without a cost. These top-secret layup schedules have to be implemented in some way, and as of this writing, there are few ways to implement a carbon fiber layup schedule other than to do it by hand. Simply put, almost all carbon fiber part production is hand-made. Have you ever bellyached about the price of carbon fiber parts? This is why.
I’ve since heard of technologies such as “forged composite,” a collaboration between Callaway Golf and Automobili Lamborghini, where chopped-up carbon fibers are mixed with resin and essentially forged into their finished shapes with reduced dependency on manual labor, and therefore reduced cost. Apart from the 2011 Sesto Elemento concept supercar that used this technology though, news on forged composite has been thin on the ground, and forged composite parts aren’t quite as strong as their traditional woven/laid-up counterparts.
The final nail in the coffin for me is how bad for the environment carbon fiber actually is. You can recycle steel, aluminum, and titanium at the end of their useful lives, but in terms of sustainability, carbon fiber composite is nothing more than a type of plastic. Breaking it down into its component epoxy resin and carbon fiber filaments is a challenge I haven’t really heard progress on…at least, not at the scale where it can be done en masse yet.
A NECESSARY EVIL?
With the incremental improvements we’ve seen in the bicycle industry, there are a few areas where I consider carbon fiber use optimal.
The main one is forks. Despite aluminum’s resurgence and abandonment of its reputation as a harsh-riding frame material, the same isn’t necessarily true of forks. Very few bicycle manufacturers use aluminum on their fork legs; frame makers who have to use metal on fork legs would normally go steel or titanium instead. Carbon fiber to me is a great fit for fork legs, as it delivers stiffness and tuned compliance at the same time, but I can’t quite shake off my apprehensiveness towards fork steerer tubes made of the same material.
Seatposts for road bikes are the second area. Bike manufacturers are still at it, trying to dial in compliance via deflection of frame tubes, even though various styles of suspension now exist. A carbon seat post is an easy way of introducing ride comfort to an otherwise rigid bike, as it can act as a leaf spring if designed and made properly. The leaf spring effect is more pronounced when more of the seatpost sticks out of the frame.
On the flip side, there are five good reasons why carbon isn’t necessarily the best – and I’ll let BikeRadar do the talking with a pretty good video of theirs.