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Why do I see what looks like wrinkles on my new P5X?

By Richard Matthews, Senior Composites Engineer, Cervélo

Question: Why do I see what looks like wrinkles on my new P5X? Are they a problem?

That’s a very good question. If you’ve read our article on the Myth of Modulus, you’ll know that our bikes use unidirectional carbon fibre composite for the best performance. On the P5X frame, which is handmade at HED Cycling in Minnesota, USA, these unidirectional layers, called plies, are put into the frame tool by hand, one at a time, by skilled craftspeople. Once all the plies are put into the tool and it is closed up, a special latex balloon called a bladder is inflated inside the tool. This bladder compresses all the plies together and onto the tool surface, while applied heat softens the material. This lets the resin flow to fill any space between the carbon fibres, and then hardens into a solid part. The pressure provided by the bladder is key. It compacts the different layers of the carbon fibre together for the highest level of performance while squeezing out excess resin. As a result we use very high pressures to get the best parts possible.

However, when the bladder inflates to high pressure, small areas of the carbon fibres can move a little when the resin is liquid. Once the resin hardens and the part is removed from the tool, these small movements of some of the fibres are fixed in place. These slight variations in carbon fibre orientation are small and have a negligible effect on the structural performance (strength and stiffness) of the frame. Our frame design and testing process takes these normal, small variations in fibre orientation into account.

If you were to look at the raw surface of most our competitors’ unidirectional carbon frames you would see these variations. On the P5X, our U.S. manufacturing facility and the specific process we developed with HED, provides us with a finished article with significantly less variation. We at Cervélo are very proud of this and wanted to showcase this by not hiding it away under a thick layer of solid paint.

Alternatively, you will see that many other bike manufacturers, and most automotive companies, use woven carbon fibre on the outer layer of their parts. In this material, the weaving of the fibres helps to join them together and makes them less likely to move under the bladder pressure. This gives a more uniform surface appearance, yet, this same weaving also reduces the performance of the material. A frame with woven carbon fibre will be heavier, for a given stiffness, than a frame with unidirectional carbon fibre.

At Cervélo, we choose to have the highest technical performance by using unidirectional carbon fibre. This leads to the variations you see in the surface of your P5X. Don't think of them as flaws but rather as unique fingerprints of the high performance, handcrafted bicycle you have purchased. Every frame is different and you can take pride in the handmade artistry that produced it.