This question was recently asked to us by a cyclist who was interested in buying a carbon bicycle, whether it be a road, mountain, or gravel bike. He had read in a forum that frames made from this material have a maximum lifespan of 10 years, but was surprised that some brands offer a lifetime warranty on certain carbon bike models. The truth is, this isn't the first time someone has asked us about this topic. So, we are going to try to answer one of the most frequently asked questions among cyclists: How long does a carbon frame really last?
Before going into detail, it is important to know that carbon frames are no longer reserved exclusively for top-of-the-line models. The manufacture of bicycles with this material has become popular, and there are mid-range and even entry-level ranges in certain brands and models whose frames are made from carbon fiber. Carbon fiber is an artificial material. Unlike aluminum, which is extracted by mining for its transformation, carbon is made from very fine and strong threads that are interwoven to form a rigid and lightweight structure. These fibers are derived from petroleum, and their manufacturing process is more expensive and requires more energy than what is needed to make aluminum frames.
On the other hand, carbon is very versatile and can be molded into complex shapes and adapted to different geometries and frame designs. Aluminum bicycles are built with solid tubes that are welded at the joints between them. Carbon frames, on the other hand, are made from molds whose pieces are then assembled with resin. If you want to know more about the properties, differences, and qualities of the different materials used to make bicycle frames, we recommend reading our definitive guide to bicycle frames: which material is best?
Factors that affect the lifespan of a carbon frame
Do carbon frames have an expiration date? The answer is not as simple as saying "they last X years" or "their lifespan is so many kilometers." The longevity of a carbon frame can vary depending on several factors. We mainly highlight three:
The quality of the materials
As with any other product, the quality of the raw material used fundamentally determines its strength and durability. The better the quality of the carbon fibers and resin used in the frame's manufacture, the longer its lifespan will be. And no, not all carbon frames are the same. There are different types of carbon used in bicycle frames:
- High modulus carbon
- Intermediate modulus carbon
- Low modulus carbon
- Unidirectional carbon
- Multidirectional carbon
- Braided carbon
High-modulus carbon bikes are lighter and stiffer and therefore more resistant and durable than intermediate and low-modulus bikes, which are used in lower-end ranges. Hence the phrase you’ve probably heard more than once: “A good aluminum frame is better than a bad carbon one.” Unidirectional carbon fiber, on the other hand, is used in the manufacture of high-end frames. This type of carbon is made up of carbon fibers oriented in one direction, which provides great resistance to tension and flexion in that direction. Unidirectional carbon frames are extremely stiff and efficient in transmitting pedaling energy. Multidirectional carbon is a type of carbon used in the manufacture of bicycle frames that need to be flexible and absorb terrain vibrations, so it is common in mountain bikes. As for braided carbon, it is highly resistant to torsion due to the way its fibers are intertwined, and it is usually used in time trial and long-distance triathlon bikes.
The maintenance performed
Carrying out proper maintenance is essential to prolong the useful life of a bicycle. What usually happens is that we generally focus on maintaining the components, drivetrains, and mechanical parts and forget about the frame. Carbon frames require a series of basic care. It’s also important to learn how to wash and clean them properly. You can learn how in our article on how to properly clean your bike’s carbon frame.
The intensity and frequency of use
Intense and frequent use of a bicycle can wear out the carbon of the frame more quickly than occasional use. This is because carbon is a material that degrades over time and with exposure to high temperatures and radiation. Other factors also influence this, such as the type of cycling practiced or the weight and strength of the cyclist. Some disciplines, such as enduro, put more stress and torsion on bikes than other, more relaxed activities like simply riding on flat routes or on relatively smooth terrain.
Main problems of carbon fiber
Carbon is a material with excellent properties for cycling. But it still carries the stigma of being more fragile than aluminum and degrading more over time. What are the main problems we can encounter regarding the expiration of a carbon frame? We highlight three:
Aging of the fibers
Carbon fiber is a composite material that has a chain molecular structure. When this molecular chain is modified by internal causes (due to variations in the polymeric structure), aging of the material occurs, making it less resistant and more brittle, meaning it tends to break suddenly without warning or deformation. Aging is therefore reflected in a deterioration of the fiber's performance, which is no longer original at the molecular level and, essentially, can no longer withstand the loads of cycling use. There are three types of factors that cause the aging of carbon fibers:
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Molecular scission: this occurs in situations where the frame receives a very high energy input, for example in a fall or a strong impact. The rings of the chain are split and thus weak points are created in the carbon structure.
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Free radicals: within the molecular structure of the fiber there are external elements that are not bonded to any other molecule, as they are residues from manufacturing processes or heat treatments. These elements, called free radicals, can bond with the fiber's molecules, creating a new structure that no longer has the characteristics of the previous one.
- Cross-links: this is the most feared circumstance. It happens when two fragments that were combined join together.
Carbon degradation
Unlike aging, which is essentially due to internal variations in the compound's molecular structure, degradation is caused by external agents that, when combined or exposed for a prolonged period, reduce its resistance. The main causes of degradation are three: temperature, radiation, and humidity. Exposing carbon fiber to excessively high temperatures leads to thermal expansion that over time weakens the carbon. The sun, in addition to heat, also does not do any good to carbon: ultraviolet rays can penetrate inside and be absorbed, creating molecular-level changes that reduce the strength of the compound. But don't worry, your carbon bike won't get ruined just by going out for rides in the sun. Manufacturers usually use special paints that protect the frame from solar radiation. That's why the painting process of a frame is a fundamental part that goes beyond the chosen color or design. And that's why when repainting a frame, it's essential to go to a professional and use the right products. Good paint also protects against humidity, which is another element that carbon frames don't get along with.
The breakage
Carbon is a material that has a very low elastic limit, much lower than steel or aluminum. And what is the elastic limit? The elastic limit is the maximum point to which a material can deform and return to its initial state without deforming or breaking. In other words: carbon frames do not dent, they simply splinter. Sometimes it's a small crack that over time weakens the material and ends up resulting in a fissure. And sometimes it is directly a fracture as a result of an impact or excessive tension. That is why it is crucial to be alert to signs of a possible crack or break growing, such as a change in color, a strange sound, or a loss of stiffness. If any problem is detected, it is essential to take it to a professional who can assess the situation and repair the carbon fiber safely and effectively.
So, how long does a carbon frame last?
The lifespan of a carbon frame can vary depending on several factors, such as the quality of the materials, proper maintenance, and the type of use. It is an extraordinary material, but its complexity and the need for attention and care may intimidate some. If you have the patience and knowledge necessary to take proper care of it, this material can offer an incredibly satisfying and long-lasting cycling experience. A well-maintained and properly used carbon frame can last between 10 and 15 years. However, it is most likely that it will start to lose its properties and show some signs of wear between 7 and 10 years.