Are All Carbon Cycling Shoes Made equally? What to Look Out For

Carbon soled cycling shoes have become quite a benchmark for performance in the cycling world, but just because it has carbon written on the materials list, does not mean it performs any better than one without. In fact, some shoes just have a single layer of carbon on the outside to appear solid when they're not. So what are you paying for? And even if they are solid, are all carbon soles made equally? With such a strong stance on carbon soles, we ask Bont Cycling what they think.

What is Carbon?

Carbon fiber is a revolutionary material that is as strong as steel with a fraction of the weight. The material is mainly comprised of carbon atoms that are bonded together and aligned to form the long axis of fiber. Several thousand of these fibers are twisted together to form a yarn which is then woven into a sheet of fabric. Being able to control the weave allows manufacturers to control if and where the material flexes. Bont have been producing carbon footwear since 1989, and this is what they've learned.

It's all in the Weave

There are three main carbon weaves that you will see used in the manufacture of cycling shoes. There is the '3k Plain', 'Unidirectional', and the '12k plain'. The 3k plain is a tightly woven carbon that is used in the aircraft industry for its minimal resin (the glue to hold the fibres together) and low weight. The resin to carbon ratio in the weave of the 12k Plain is a lot higher than the 3k Plain, which makes it around 20% cheaper, but more resin means less carbon, and therefore a much weaker fabric. Unidirectional carbon is the stiffest of the lot. As carbon is stronger in certain directions, but flexible in others, unidirectional carbon weaves involve laying down layers of carbon in different directions to overcome this inconsistency. More carbon does mean more expensive materials though, which is why this  method tends to be saved for the best of the best products, like the Vaypor+.

What To Look Out For:

If you buy a plastic or nylon based shoe, you know what you are getting, but it's tougher to identify with carbon. Not all shoes are what they appear to be. Here's what Bont say you should look out for:

• One layer of carbon: When you buy a shoe and you see that it has a carbon base, chances are that only the outer single layer is carbon. Under that carbon layer can be an injection molded plastic or nylon base or a fiberglass base. If the price tag seems too good to be true, it probably is.
• Unidirectional carbon: You see unidirectional carbon printed on a variety of shoes, however, many of them use injection molded carbon in the plastic and call this unidirectional carbon. This is a misuse of the terminology, so do some research.
• Silver fiberglass: A number of shoes use a plastic injection molded base, with some carbon particles in it and a single layer of silver fiberglass for the outer layer. They are allowed to print ‘carbon’ on the base because there is carbon dust in the plastic mold under the fiberglass, but the fiberglass woven material on the outside is certainly not carbon. Check the materials listed, but note that carbon fiber is always black.
• 100% composite: This term is often used, but the question you need to ask is; a composite of what? Usually it is a nylon fiberglass composite that you will find in shoes, so be wary of this label.
• Monocoque: A monocoque shoe is one where the carbon has been directly laminated onto the liner. Some companies are jumping on the monocoque band wagon and calling a carbon shell with integrated heel cup a monocoque shoe. It isn’t.

More About Resin

The carbon fibres themselves are the strongest part of a carbon weave. The resin, or the glue that holds the fibres together, are not as light or as stiff, hence, you want a high carbon-to-resin ratio if you want stiff and light shoes. Epoxy or polyepoxide is a thermosetting epoxide polymer that hardens when mixed with an agent. The process of polymerization is called "curing" and can be controlled through the temperature and choice of resin or hardener compounds used. What's interesting is that these choices can make a process take minutes or hours, which obviously affects production costs through time and man-power. Resin development is something that Bont have been doing for over 36 years. They have formulated a resin that is super stiff, yet becomes moldable at low temperatures and has a fast cure time. This is critical for Bont's unique requirements in their post-purchase custom fitting shoes. In fact, they are possibly the only cycling shoe manufacturer who develops their our own resins in-house. The temperature of the air and the amount of humidity are critical in determining the amount of hardener that needs to be added to the resin, so Bont have a computer that mixes the resin and hardener together and dispenses the resin after measuring the air temperature and humidity every time a shoe is made.

Why is Bont So Different?

Most manufacturers use a process known in the industry as "pre-preg". This is where the resin is "pre-impregnated" into the carbon fiber. In virtually all applications, the resin is chosen by the carbon fiber manufacturer in a 'one shoe fits all' kind of deal (excuse the pun!). The shoe manufacturer has no way of altering the resin to meet the heat moldablilty requirements of modern shoes and that is why most companies require very high temperatures to make the shoes slightly heat moldable. Pre-preg manufacturing is fine for most cycling products, but Bont's recipe of resin becomes soft at just 60^oC / 140^oF (the lowest in the industry) so that the end user, namely you the cyclist, can heat their shoes up and mold them to your feet.  Once it cools, it is permanently set without the need to remold. You can also reheat the resin as many times as you like. Although Bont are well-known for heat-moldable shoes, they don't have to be set in the over to fit your feet. Infact, a recent chat with Bont at Eurobike 2016 revealed that they don't actively encourage it unless you have particularly unusual feet, or certain sizing differences between the left and the right. After all, they've spent a lot of time designing the out-of-the-box version for comfort, so why tamper?

For more information, head over to Bont Cycling and keep an eye out for their new 2017 range coming this Spring.