Carbon Fiber Tubing with Wheels Isn't Necessarily a Good Bike

Carbon Fiber Tubing with Wheels Isn't Necessarily a Good Bike
There have been quite a few news articles in recent years detailing catastrophic failures of carbon fiber bikes. Such
stories seem contrary to what most people know about carbon fiber as a replacement material for aluminum and steel.
What some do not realize, and this even includes bike manufacturers, is that a couple of pieces of carbon fiber tubing
with wheels does not necessarily make for a good bike. There is a lot more to it than that.
One of the main challenges of carbon fiber as a manufacturing material is the fact that its strength is anisotropic. In
other words, the characteristics of carbon fiber tubing that give it such strength are not uniform. Rather, they are
directional. In short, the strength of a carbon fiber product is subject to its fiber orientation.
The anisotropic nature of carbon fiber is such that bike makers have to be very careful with their designs and
construction methods. They have to be choosy about the carbon fiber tubing they purchase. Get it wrong and a
company could be building bikes incapable of standing up to years of punishment. A worst-case scenario would be a bike
that shatters underneath its rider.
Designing for Purpose
In addition to carbon fiber tubing, sheets, plates, materials etc., Rock West Composites also offers composite
prototyping services. One of the first things we discuss with prototype clients is the purpose behind the piece they want
to create. This is important because purpose is that which determines the various loads and stresses the finished part
will encounter.
Bike makers should be doing the same thing. The truth is that different bikes have different purposes. There are racing
bikes, mountain bikes, specific bikes for triathletes, and on and on. The truth about carbon fiber tubing as material for
bike frames is that there is no one-size-fits-all product. Designing for purpose requires choosing the right kind of tubing
and using it the right way.
According to a great article recently published by Composites World, bike designers have to think about four things in
the preliminary stages of designing a new model:

Weight – One of the main purposes for using carbon fiber instead of aluminum is to reduce the weight of the
bike. Designers have to consider how light they want a new bike to be.
Stiffness – The stiffness of a bike will determine how much energy its frame will be able to handle during a
typical ride. Stiffness affects everything from the overall strength of the bike to the amount of work the rider has
to put into peddling it.
Safety – It should be the goal of every bike maker to ensure that every bike that rolls out of its factory is safe. The
purpose of a given model is critical here. Bikes have to be designed to withstand purpose-determined loads and
stresses with very little risk of catastrophic failure.
Cost – Designers have to think of the full range of costs associated with building and selling a new model. Those
costs cover everything from prototyping to large-scale manufacturing.
Anybody can purchase carbon fiber tubing from Rock West Composites, cut it into sections, and create a bike frame out
of it. They can attach it to wheels, a handlebar, and a seat before riding off into the sunset. But there are no guarantees
that the bike will make it to the end of the street.
Bike makers owe it to their customers to create safe and sturdy bikes. Doing so starts with an understanding of
composite materials and their individual strengths and weaknesses.