The main riding sensations directly depend on the quality and geometry of a frame. A low-quality carbon frame will tend to flex much more than a high-quality carbon frame; and I assure you that when you're descending at maximum speed around a bend, you can definitely notice the difference between the two.Below we will look at what characterizes the frame more than anything else: the material it is built from. Carbon fiber, aluminum, steel, and titanium (or a combination of them) are the most common. The material used offers a range of different characteristics that can alter the cost, comfort, weight, stiffness, strength, and durability of each frame. Often, however, it is not just the chosen material but also how it is used.Before getting into the details of each material, it is good to identify the main factors to consider when choosing.
Weight
Your bike must be strong enough to carry you and any additional weight you plan to carry (side bag, various equipment, etc.). Each material has different characteristics, but there is always a trade-off between weight and strength. In fact, the strongest materials are also the heaviest. A bit like the saying about having your cake and eating it too, you have to accept a compromise. Another aspect to consider is how important it is to have a lightweight bike. If you are looking for maximum performance, you will have to take this into account.
Purpose
If you are considering racing, a light but stiff bike is ideal. Conversely, if you plan long tours or off-road adventures that require the ability to carry equipment, then robustness is one of your priorities. Bikes are designed with different features related to the type of use they are intended for; and to achieve certain characteristics, a specific material must be used.
Strength
All materials wear out over time, but some faster than others. Steel, for example, if not cared for, rusts faster than aluminum. Carbon fiber and titanium frames, on the other hand, have optimal durability over time. However, materials like carbon are less resistant to impacts than steel and aluminum.
Budget
Certainly the most influential factor in choosing a bicycle, and consequently its materials. Generally speaking, from the most expensive to the least expensive we find titanium, carbon, aluminum, and steel. As always, however, one must consider the trade-off between cost and use.
Carbon
Carbon fiber is undoubtedly an exceptional material for building bike frames. Stiffness, lightness, malleability, high stress resistance make us currently live in the so-called carbon era. While some materials are difficult to work with, carbon is easily moldable and adapts best to the designer's needs. The ability to customize shapes and the way the material is used make frames aerodynamic, light, stiff but also comfortable.Carbon was introduced by manufacturers in the early '90s after being tested on professional cyclists' bikes in the late '80s. The material was chosen for its lightness compared to steel frames and thus became the first choice. Initially, its high cost, the fair quality of the carbon used, and the manufacturing methods prevented its rapid mass distribution. Today, carbon fiber can be incorporated into almost all components of a bicycle.When talking about carbon bikes, it is important to understand that the final product is made up of two elements: the carbon fibers and the resin that acts like glue and holds the fibers together. The thickness of a single fiber can vary widely but is always much thinner than a strand of hair. These individual carbon filaments are bundled into a "spool," which is woven into sheets resembling a fabric. The resin is often the weaker and more rigid part, so the goal is to make sure the filaments are as close to each other as possible. The carbon used in bicycles is often unidirectional, and therefore the angle at which it is laid is extremely important. Laying at a specific angle, in fact, creates resistance and stiffness in the necessary direction. For example, if the force applied on the frame is opposite to the direction of the fibers' layup, they are strong and resistant; whereas if the fibers are arranged at an angle for which they cannot oppose the applied force, the frame will flex. Other parts of the frame or simply cheaper carbon frames may use woven carbon fibers that have more or less the same characteristics in all directions they are laid.Beyond all these technicalities, it is important to know that the type of fiber changes the final product. The fibers can be strong or stiff or both. So when engineers have to design a frame, they must use stronger fibers in areas where the bike requires more strength, such as in the head tube. In that position, the fibers need to absorb forces to prevent fracture. Other areas of the frame need to be stiffer, like the bottom bracket shell. In that point, high-end frames will surely use stiffer fibers compared to lower-level frames.Manufacturers claim that their high-end frames have approximately even 400 sheets of carbon. Modifying the bike's performance will involve the complex processes of choosing the right carbon fiber, reinforced with the best resin, arranged with the best technique, and directed in the best way. However, it is never just one of these factors that determine the quality of a frame, but they must be analyzed together.If you intend to cover several kilometers in the saddle of your bike and you are competitive people who want to approach competitions, then you cannot give up a carbon bike. As already mentioned, the frames are lighter and more aerodynamic than frames in other materials. This will allow you to tackle even long climbs without carrying unnecessary excessive weight. Only the essentials!Carbon frames, despite their lightness, are also very strong and stiff. Stiffness will therefore allow you to best transform the power expressed on the pedals. Finally, carbon also ensures a good riding comfort because it manages to absorb vibrations well.Clearly the quality of the frame varies depending on the quality of the carbon and the type of processing. A high-quality carbon frame will guarantee all the benefits we just talked about, while a low-quality frame may not be as performant in every aspect.The downside of carbon is that some areas, if subjected to strong stress, caused for example by a fall, may break. Once the integrity of the carbon is compromised, the frame can become extremely fragile and dangerous to use. At that point, it needs to be replaced or repaired.To briefly summarize:Pros: high stiffness-to-weight ratio, excellent resistance to temperatures and corrosion, durability.Cons: price, once damaged (cracked) most of the time it is irreparable, more elaborate and complex production.
Aluminum
Aluminum frames are perhaps the most common in the modern bicycle industry, also because it is a material widely used for components. It is not a very “dense” material, so it can be used for light structures, making it perfect for bicycles. These frames are relatively cheap to produce, especially when compared to carbon frames, for which it takes approximately 14 times longer to produce.As we have already said for carbon fiber, aluminum is available in many forms and is always bound with a small amount of other metals and minerals added. Regardless of the choice of materials, some recent discoveries in the sector have allowed for greater customization of the frame design, with an actual improvement in ride quality. Not only can the shapes of the tubes be modified, but also the thickness can be balanced to obtain structures in some areas more resistant and in others lighter, according to the needs. Essentially, the center of the tube is thinned to reduce weight, while more resistance is maintained near the welds.“Straight gauge” tubes do not vary, indeed, in thickness ensuring uniform resistance throughout the tube (at the expense of weight). The “single,” “double,” and “triple butted” have different thicknesses that allow the frame to withstand, in the points where the tube is thicker, greater resistance; without having, thus, too much weight in the center. The “single butted” will have one end thicker than the rest of the tube, while the “double,” intuitively, will have both ends thicker than the center. The “triple butted,” instead, will have two thickness levels at both ends. The “single” is used for example for the seatpost collar, the “double” for the bottom bracket area and for the head tube. Since thickness modulation requires more time in processing, cheaper frames will not use this technology and will, therefore, be “straight gauge.”Aluminum tubes can also be shaped in a process called “hydroforming”; a way of shaping metals using a mold and fluid. The aluminum tube is placed in a precise-shaped mold, and a high-pressure jet makes the aluminum tube assume the desired shape. This technique is commonly used to optimize the shape of the tubes so that they gain more stiffness, without requiring additional material for reinforcement.Modifying the design of a frame can help achieve a light bike that is strong and comfortable. Aluminum allows for low density and, for the same thickness, is not as strong as steel but is lighter and much more resistant to corrosion.On the downside, aluminum has a lesser resistance over time compared to carbon. If structured and maintained properly, aluminum can also last a lifetime.If you are looking for a bike that lasts forever, then aluminum is definitely for you. As said, it is light but very strong as a material. Children's bikes are mainly built in aluminum, for cost reasons, but also for reasons of resistance. If you are a beginner and want to delve into the world of cycling, aluminum is definitely the best material to start with. The right balance between low price and good performance.To briefly summarize:Pros: cost, easier to produce, high strength-to-weight ratio, corrosion resistance.Cons: difficult to repair, lesser resistance over time.
Steel
Until about 1980, steel was the universal choice for bicycle frames. Subsequently, first aluminum, and then carbon, took over. Today, steel is used only for the production of a few niche “custom classic” bicycles.There are two different types of steel used in the bicycle industry: the first is called “hi-ten,” being much more elastic (“high tensile” = highly elastic) it is often used for cheaper bicycles. It has a very low strength-to-weight ratio, and for this reason, manufacturing companies choose this material when they want to produce extremely economical pieces. High-end steel bicycles, on the other hand, are built with so-called “chromoly” (also known as “CroMo” from chromium and molybdenum), a steel alloy that offers greater resistance compared to “hi-ten” and that can be shaped to have tubes that thin or thicken, just like with aluminum. Steel is economical, durable and resistant, easily repairable and moldable. Unlike carbon and aluminum, damages on a steel frame are easily repairable and rarely jeopardize the frame's safety. Contrary to what one might expect, given its resistance, steel also allows to absorb shocks thanks to its elastic properties. The downside is that it is prone to oxidation (rust), and compared to other materials it is definitely heavier. “Touring” and mountain bikes are often made of steel thanks to its renowned durability over time. This material is also ideal for carrying, in addition to the weight of the cyclist, also the weight of side bags and accessories used by hikers, without compromising the bike's performance. Steel is found in most cases in entry-level bikes, children's bikes, or leisure bikes, where weight, in short, is not such an important factor.To briefly summarize:Pros: cost and ease of maintenance, durability, resistanceCons: weight, prone to oxidation.
Titanium
Titanium shares many of the properties of steel but is lighter, more resistant to oxidation, and is undoubtedly more durable over time. The downside is that it is much more expensive to produce and requires many more hours of work. Producing a titanium bicycle frame requires specific skills. As also happens for steel and aluminum, the titanium used in frames is in the form of an “alloy,” often composed of a percentage of aluminum and vanadium.Titanium has never become as famous as the competing materials, even though it landed on the scene at the same time as aluminum and carbon fiber, both cheaper and easier to work with. Nevertheless, titanium has a better ratio in terms of stiffness and weight, which leads it to have a shock resistance similar to carbon and is virtually indestructible. Almost all manufacturers of titanium frames offer a lifetime warranty on manufacturing defects.To briefly summarize:Pros: resistance, durability, oxidation resistance, ride quality, weight.Cons: high costs, difficulty in production.
