Bicycle frames - materials, functional features, advice

From the very beginning , we at Antymateria have focused on steel bicycle frames . This was partly a deliberate strategy, partly a coincidence. Nevertheless, we still believe that this material, although far less popular than aluminum, has its advantages. Steel was also the first material historically widely used in bicycle production.

In this article, we aim to provide a detailed discussion of the properties of various bicycle frame materials. As well as, of course, the benefits and limitations associated with their use.

A bit of history

As early as the 1920s, steel frames were being mass-produced in many parts of the world. The first bicycle boom occurred immediately after the Industrial Revolution. Among the most renowned producers of steel tubes were, and still are, Columbus (Italy) and Reynolds (Great Britain).

Aluminum was well-known, but the limited development of processing technology and its high price hindered its popularity. The situation changed in the 1980s, when aluminum frames began to be mass-produced. This is when the global expansion of companies like Trek and Cannondale began. First in Taiwan, and soon after, China became the leading supplier of aluminum bicycle frames and finished bicycles.

The 1980s also saw the emergence of the first composite frames: resin and carbon fiber—carbon. Their pioneer was the Italian Ernesto Colnago . Interestingly, this was in collaboration with Enzo Ferrari , whose history is associated with a different form of transportation. However, due to its price, carbon fiber has only become popular on a mass scale in recent years.

Steel, aluminum or carbon?

Currently, we have the three materials mentioned above to choose from on the market. Plus, there's a special type of steel alloy that deserves a special mention. Titanium, in our opinion, is an excellent material. However, it's a rarity, found almost exclusively in custom-made bicycles. Magnesium alloy frames are also common. These are completely unusual designs, made on a small scale or even made to order.

Steel bicycle frames, or strange abbreviations: hi-ten and cro-mo

First, let's focus on steel, which has by far the longest history as a bicycle frame material. Steel used in bicycle production comes in two most popular alloy types. The first is so-called hi-ten, or high-tensile steel. This is a low-carbon steel with low stiffness. However, it is easy to machine, weld, and is resistant to overload. It can be found in inexpensive bikes, most often the so-called "supermarket" type. It is a relatively unstiff material, so to compensate for this, frames made from this alloy have thicker walls. This, in turn, results in a significant increase in weight. Furthermore, a frame with thick-walled tubes and a large cross-section very effectively transfers vibrations from the bicycle to the rider, resulting in poor riding comfort.

Another problem with cheap steel frames is their susceptibility to rust. Given the thick cross-section of the pipes, this is more of an aesthetic concern than a practical one. The only advantage of such a frame is its repairability – if it cracks, it can be easily welded, and if it bends, it can be straightened.

Cro-Mo steel bicycle frames

The second type of steel used in the bicycle industry is chromoly steel (also called chromoly chrome-moly, Cro-Mo, CrMo, CRMO, CR-MOLY). Currently used in more expensive frames (all our bikes are built on these frames). The addition of chromium is intended to make the frame less susceptible to corrosion. Although it's not stainless steel, stainless steel bikes are also available on the market. Above all, Cro-Mo steel, a member of the 41xx alloy family, has a special property. Through carburization, it can be significantly hardened externally, while its core remains more flexible and durable. This provides an excellent compromise between resistance to overload and hardness that protects against external micro-damage.

Thanks to its high stiffness and durability, Cro-Mo frames can be constructed using very thin-walled, small-diameter tubes. This allows for flexibility (of course, to a very small extent). It also allows for damping of small vibrations caused by uneven terrain. This is a characteristic feature of good steel frames. Achieving this is only possible with high-quality steel; using aluminum requires tubes with a larger cross-section.

Another advantage of steel is its durability during long-term use. While aluminum experiences constant fatigue, regardless of the force applied, steel only experiences fatigue when significant force is applied.

Steel once reigned supreme among the materials used in bicycle production. The production of steel frames is still, to a greater or lesser extent, manual. Furthermore, the highly precise machining of a steel frame, required to produce a top-quality frame, is expensive and difficult. Today, the production of aluminum frames is much more automated (including the use of welding robots).

The search for cost efficiency led to the replacement of steel in mass bicycle production with aluminum.

For the performance of a frame, the size of the tubes themselves is more important than the material. Steel is heavier by weight, but it is also the strongest of the bicycle construction materials. Therefore, steel frames can use smaller tube sizes.

Aluminum bicycle frames

Aluminum is the softest and weakest material, but we use it in tubes with a very large cross-section, which provides high frame stiffness. This, of course, translates into a heavier frame, and also to the overall bike's weight, which is most noticeable on less expensive bikes. Aluminum also "performs" differently in sporty applications – when accelerating on an aluminum frame, it feels stiff and fast. Aluminum can be made from very inexpensive to more expensive (and lighter), though not extremely expensive, yet very light and stiff. Aluminum frames offer an excellent price-to-quality ratio, especially given the expansion of carbon frames.

An aluminum frame is practical – it doesn't rust and is quite impact-resistant. Unfortunately, serious damage results in a visible dent. This type of damage isn't repairable, but it's clearly visible (unlike carbon fiber). More serious damage will render an aluminum frame unusable. In a bicycle repair shop, repairing such frames (besides possibly replacing the dropouts) is asking for trouble in the future.

ADVANTAGES	DEFECTS
good price-quality ratio	often low driving comfort
strength and stiffness	more serious damage is generally not repaired
corrodes, but without any practical effect on use	weight, especially in cheaper bike models

Carbon bicycle frames

The most expensive material used for mass-produced frames is carbon fiber, a composite of epoxy resin and carbon fiber. This material is very light and stiff. Rigid frames weighing 700-900 g and forks weighing less than 300 g can be mass-produced from it. Aluminum lags far behind in this regard.

Carbon has two drawbacks: one is its price, the other its susceptibility to damage. When properly manufactured and not subjected to impact or excessive compression, carbon is a completely reliable and safe material. The problem arises after an impact, such as a fall, or excessive compression, such as when mounting a stem on a carbon steerer tube. This can lead to delamination and subsequent breakage without warning. While impacts and compression are visible and allow for a quick assessment of delamination, manufacturing errors can lead to catastrophic failure without warning. This is also possible with aluminum and steel, for example, on welds. Furthermore, epoxy resin is not salt-resistant. Using it in winter or at the seaside can result in unexpected delamination after several years.

Carbon fiber is generally a bit riskier than other materials. You have to be more careful with it, and a serious injury could result in the loss of an expensive carbon frame. Carbon fiber seems to be an ideal material for sporting applications, as well as for those with a larger budget who can accept the potential need to replace an expensive component. Unfortunately, accidents are an inevitable part of racing.

When writing about carbon, it's important to note that carbon composite technology in the bicycle industry is constantly evolving. All the reservations about carbon and its durability are becoming less and less relevant.

Carbon frames - comfort and safety

Carbon fiber is considered a comfortable material with vibration-damping properties. However, it's important to note that much depends on the fiber arrangement in the frame. Carbon bikes can vary greatly in terms of riding experience. Generally, this material uses thick tubes, often with aerodynamic or other unusual cross-sections, which doesn't necessarily promote comfort.

When discussing the comfort offered by individual materials, it's important to note that the material from which the frames are made, and even the tube cross-section, is of marginal importance. Compared to elements such as wheels and tires (especially!), saddle, and tape.

ADVANTAGES	DEFECTS
low weight	In many cases, repairing damage is impossible
stiffness	high price
no risk of corrosion	serious damage may not be visible until an unpleasant surprise on the road

To summarize, considering the materials from which frames are made, we can say that the ubiquitous aluminum meets the requirements of most cyclists very well. Steel is the domain of connoisseurs on the one hand, and market bikes on the other. Carbon, on the other hand, is intended for racers or those with a larger budget.