Lightweight Material
for Speed

However, the bike-sharing system has revived bikes by relieving people from the burden of bicycle ownership. In large cities, bikes seemed to be a more effective means for the Last Mile Mobility that connects public transportation and destination. Also, bikes were a beneficial transportation tool in satellite cities where public transport is not as dense as in large cities.

The growth of the bike-sharing system began in Europe, which has a small and medium-sized city-based living environment, and public transportation is less developed than in Korea. This is true in Southeast Asia, too, where the car infrastructure and penetration rate are low. In Korea, Sangju City was famous for being the city of bikes (an average of two cycles per household). Even there, the introduction of the sharing system proliferated the use of bikes. In addition, as Kakao T, which aims at a mobility-integrated platform, also adds electric bikes to their service line, the bike-sharing system is expanding and accelerating.

The last reason concerns Last Mile Mobility, which is also related to the sharing system mentioned before. However, the point here is not a service platform but a new device, the electric bike. For example, I have experience commuting to and from 50 km. Although it felt great being away from the busy roads and enjoying the peaceful Han River, there was one big problem: I always got sweaty and needed a shower after every ride. However, as the electric bicycle came out, it served the purposes of both exercise and mobility when I needed them. As I will discuss later, the electric bikes' potential goes beyond even this.

To sum up, bikes have made a comeback in the public eye. This was made possible because bikes as tools for exercise have evolved through technology.

The first material that should be mentioned is aluminum alloy, which is commonly and widely used for bike frames today. Unless it's a very cheap bicycle, most casual bicycles are produced with aluminum alloy material. Aluminum has a lot of advantages. The biggest benefit is that it does not rust, i.e., it still has excellent durability and is lightweight. Also, it is easy to process, so it's suitable for fits mass production and recycling. However, as aluminum alloy lacks strength compared to steel or carbon fiber, the frames need to be made thicker. Still, since the aluminum alloy is lighter than steel, it is a perfect fit for being an upper mid-level bicycle's frame material.

Carbon fiber can exert an impact on parts other than the frame. The bike's wheels are probably the most important of these. The wheel-set is lightweight and stiff when made with carbon fiber, so it has excellent acceleration, cruising performance, and shock absorption. With this in mind, carbon fiber is widely used for MTB, which requires incredible stiffness and shock absorption, and road bikes for races that do not have independent suspension. Since it's a complex material, a combination of the carbon fiber's type and weaving direction, resin's thickness, and physical properties can change the carbon fiber's physical properties. In other words, a wide variety of changes can be made in the production of carbon fiber so that it can suit different needs.

However, there are some weaknesses to carbon fiber as well. These originate from the internal structure, where the adhesion between carbon fiber and synthetic resin weakens. The bonding can get impaired when the air or distant subjects enter the complex form of the carbon fiber and resin, caused by surface damage from a thrown stone, etc. Such cases might lead to a sharp decrease in stiffness. This can lead to situations where the bike frame, which looks fine from the outside, can suddenly break.

For the most up-to-date frames for road bikes, in particular, one needs to be careful to find any damage on the surface. In road bike frames, for extreme light weight, the thinnest layer of paint is applied to the point where one can see the internal carbon fiber. Products from carbon fiber need extra care compared to those with other materials. Time permitting, it is advised that one conduct regular, non-destructive testing. This is why more and more quality management services have recently become available.

The next material we'll talk about is steel, which first led bicycles in its heyday. Just as human civilization evolved in the order of the Stone Age, Bronze Age, and Iron Age, steel, which is now ever present in everyday life, is an excellent material in various ways. Steel is inexpensive and has excellent workability and rigidity. So, steel has become widespread as a versatile material for structure as bicycle frames. Its disadvantage, however, is that it rusts easily.

Steel for bicycles mainly consists of high tensile strength steel and chrome molybdenum steel. As its name suggests, high tensile strength is used in inexpensive, daily-use bikes. Alloy chrome molybdenum steel, made by adding chromium and molybdenum to iron, has almost twice the strength of high tensile steel, so it can be made thin and light. It has been recently increasing again in popularity as a high-end bicycle material.

Chrome molybdenum steel has high tensile strength and fatigue limit, so the shock does not accumulate and does not deform the frame. Even if there is a deformation, it is comparatively easy to repair, so it has excellent durability and processability. Of course, this material still isn't perfect. It is heavy and easy to rust compared to aluminum. Despite those drawbacks, it is a suitable material for producing high-end bicycles with excellent riding comfort.

Most of today's Ferrari models also use aluminum space frames. For reference, some experts say it is surprising that Ferrari has achieved weight reduction and steering performance that were only possible when competitors extensively applied carbon fiber with aluminum alone.

As with high-end bicycles, high-end auto markets prefer carbon fiber materials. Automakers use a generous amount of carbon fiber for racing cars for motorsports (similar to professional athletes' bikes participating in the Tour de France) and for the highest models of supercar brands to construct the body parts. The approach of using carbon fiber to realize extreme weight reduction and high rigidity suitable for performance is in line with the carbon-fiber road bikes.

However, it is not worth it in terms of cost, mass production, and material recycling to construct the body of a large car (except for race cars) with only carbon fiber. The caveat here is “only” with carbon fiber. In other words, it does not mean that carbon fiber is the problem, but rather, it is too disadvantageous to limit construction to just a single material. The latest Audi A8, for example, uses an intelligent mix of steel, magnesium, carbon fiber, and an aluminum space frame.