As an avid cyclist willing to spend whatever it takes to get the bike you want, you might be convinced to invest in carbon fibre wheels with the hope that they will last for as long as you own your bike. Find the right set and you might take them with you when you sell that bike and move on to something new. However, a word of caution before you dive in: carbon fibre bike wheels will not last forever.
In fairness, wheel manufacturers are not making any such promises. But assumptions are made by consumers, nonetheless. Carbon fibre wheels are passed off as being so tough and rugged that they can withstand anything for any amount of time. Consumers misconstrue that as a lifetime guarantee.
There is no such thing as a bike wheel that will last forever. There is no material that could offer that promise. Carbon fibre wheels are likely to last longer than aluminium under normal circumstances. Yet they can fail. The key for cyclists is to understand how and why they fail, and when it is time to consider purchasing a new set.
Failing from the Inside Out
Aluminium and carbon fibre deal with energy in different ways. An aluminium bike wheel absorbs energy at the point of impact. Once absorbed, the energy is not dispersed very well. That is why you can dent an aluminum wheel by hitting a pothole or curb at speed. This also explains why damage to an aluminium wheel is clearly visible.
According to Rock West Composites out of Salt Lake City, Utah, carbon fibre deflects energy. Hit a pothole or curb with a carbon fibre wheel and the energy the wheel takes at the point of impact is deflected and dispersed across a larger surface of the wheel. This property, combined with the rigidity of carbon fibre, explains why wheels made with the material do not bend or dent.
This is not to say that carbon fibre wheels don’t fail. They do. What makes them different is that they tend to fail from the inside out. Where you can see a dent in an aluminium wheel, you cannot see the damage to a carbon fibre wheel because it is internal. It’s all due to delamination.
How Carbon Fiber Wheels Are Created
Carbon fibre bike wheels are created through a process that layers multiple sheets of carbon fibre fabric onto a mould that is impregnated with epoxy resin and cured to create what the industry calls a carbon fibre reinforced plastic (CFRP). You essentially have a laminate product consisting of multiple layers of carbon fibre fabric encased in plastic.
The problem with such an arrangement is that the various layers of carbon fibre can begin to separate over time. This causes tiny cracks to form. Moreover, these cracks tend to be internal in their earliest stages. Thus, you cannot see them with the naked eye.
A crack that goes unnoticed is only going to grow over time. And once it grows big enough, failure is imminent. This is the one downside to carbon fibre wheels. When they fail, they fail completely. They do not simply dent or bend. They completely disintegrate as each of the layers separate.
Carbon fibre wheels are definitely better than aluminium in some respects. But they are not impervious to damage. They will also not last forever. If you are planning to purchase carbon fibre wheels, also plan to have them inspected from time to time at a cycle shop with the necessary equipment. Regular inspections will tell you when it’s time to replace them.
