Why carbon fiber bike rims are so durable

 

Serious cyclists who ride hundreds of miles a week can expect the life of alloy bicycle rims to be 3-5 years. If you use the alloy for more than 5 years, you are doing very well. But what about carbon fiber? This is a completely different material. The aging of carbon fiber bicycle rims is so good that they may never need to be replaced.

Although this may seem far-fetched, it is theoretically possible to use a set of carbon fiber rims for a lifetime. This is all about the fatigue limit. The fatigue limit of carbon fiber is almost non-existent, and for alloys, it is one of the main factors that determine the speed of rim wear.

How do materials handle energy

Alloys are made by combining two or more metal elements, and sometimes one or more non-metal elements. 6061 aluminum is a good example. It is an alloy formed by combining metal elements such as aluminum, copper, chromium, iron, and magnesium with non-metallic elements such as manganese and silicon. This combination creates an alloy with good toughness and excellent corrosion resistance. The combination of elements in 7075 aluminum gives it high strength and average corrosion resistance.

Bicycle manufacturers have long appreciated aluminum alloys because they absorb energy well. Bicycles with aluminum frames and rims are actually very comfortable to ride. However, the energy absorption properties of aluminum are also its disadvantages. Aluminum alloy absorbs energy mainly through compression. This is where the fatigue limit comes into play.

Even if the alloy does not exceed its bending limit, fatigue settings and repeated cycles will shorten the life of the product. The bending limit of all aluminum alloys is much smaller than that of carbon fiber composites. In fact, some aluminum alloys are considered brittle and are prone to fatigue fracture. For example, 7075 aluminum is easy to machine, but also very brittle, while 5052 is easier to weld and shape.

The bending limit of carbon fiber composites is much higher than that of aluminum alloys. The design of carbon fiber products takes into account specific restrictions. Fiber orientation allows the designer to optimize the design for strength, stiffness, damping, weight, or any combination of these properties.

Parts made of carbon fiber composite materials excel at damping vibrations, reducing energy loss by allowing the material to return to its natural state faster than aluminum alloy. However, it is not through compression. It suppresses vibration through deflection. Therefore, no fatigue limit is involved. In theory, this means that carbon fiber bicycle rims can be used permanently-as long as they do not delamination or break internally due to events that exceed the design limits of the part.

Riding on the rims is difficult

Needless to say, it is difficult to ride a bicycle rim frequently. The front fork and frame are equally difficult, but let's stick to the rims for the time being. Every bump, every pothole, every sharp turn at the corner will put pressure on the rim. The reaction of these rims to pressure affects their overall wear.

The main advantage of alloys is that when they fail, the failure will not be catastrophic. In other words, your aluminum rim will bend before it breaks in half. It will be distorted rather than broken. Chances are, long before the alloy rim becomes a problem, you will be able to discover its severe fatigue.

Carbon fiber is just the opposite. It is superior to aluminum alloy in damping vibration. Carbon fiber can also withstand huge penalties. But when it fails, the failure is catastrophic.

So why risk using carbon fiber? Because normal riding and maintenance are unlikely to cause catastrophic failures. Any event that will cause the carbon fiber rim to fail will also cause the aluminum alloy rim to fail. As with aluminum alloy rims, you should check your rims regularly, and ask professionals to check if there are any abnormalities. As long as there is no internal damage, your carbon fiber rims will be used forever. Their age is very good because they are not restricted by fatigue.

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