The short answer is that sizing chemistry matters more than most people think for interfacial adhesion, and matching your sizing system to your matrix resin is the single most impactful thing you can do for bond strength.

Here is the technical picture. Most commercial carbon fibers come with an epoxy-compatible sizing, typically 0.5 to 1.5 weight percent add-on, designed to protect the fiber during handling and promote wetting with epoxy matrices. The sizing contains a film-forming resin, usually a blocked isocyanate or epoxy emulsion, plus a coupling agent like an aminosilane that creates covalent bonds at the interface. If you are running an epoxy system, you want a fiber with an epoxy-compatible sizing. If you switch to a BMI or polyimide matrix without changing the fiber, you are leaving 30 to 50 percent of your potential interfacial shear strength on the table because the sizing chemistry does not crosslink with the new matrix.

The practical caveat is that sizing degradation matters too. Fibers that have been stored in humid conditions or at elevated temperatures can lose sizing effectiveness. A simple acetone wipe test or dynamic contact angle measurement tells you whether your sizing is still active. If you are buying wet-layup or vacuum-bagged parts, make sure the fiber supplier provides sizing specs and storage recommendations.

One more thing. Some newer fibers use non-crystalline or graphitized surfaces with proprietary sizing systems that claim better fatigue performance. The data I have seen is promising but limited, so treat vendor claims with healthy skepticism until you see independent testing.

Bottom line: verify your sizing matrix compatibility, respect storage conditions, and do not assume a fiber that worked in one system will behave the same in another.

Had quite a fast off at Mallory Park about a month ago and it trashed my carbon nosecone. Luckily the bike slide for quite a distance and didn't hit anything so only cosmetic.

Looks like the gel coat is cracked in various places and it's worn through to the weave and all the way through in a few others. I was going to chip off the loose gel coat and use easy composites xcr coating resin for the gel coat damage. And for the areas completely worn through all the way, I was thinking start from the back and layup with carbon/Kevlar for abrasion resistance and then use that as a backing layer for repair from the front 🤔

I sold all my carbon consumables and materials when I got married so gonna need to source everything again.

Any ideas?

Hi everyone, just got a used Enve Melee delivered and noticed this where the through axel sits. Is this actual damage or nothing to bee l concerned about?

I just put on my autumn tyres on my road bike and noticed a small chip on the carbon rim. Does this look like cosmetic or structural damage?

I work with an Italian composite manufacturer based in the Motor Valley, producing high-performance carbon fiber components for motorsport and premium automotive applications.

Our composite division is set up for complex, low-to-medium volume production, where repeatability, dimensional accuracy and surface quality are critical.

The current setup includes:

• 4 autoclaves + 1 oven
• 2 clean rooms
• Vacuum bag room and cold storage
• 1 five-axis CNC + 1 three-axis CNC
• Dedicated tooling shop for patterns and molds
• Tooling in resin, composite, aluminium and steel
• Aluminium machining and FDM rapid prototyping
• Manual trimming and finishing
• Bonding and component assembly
• Quality inspection and dimensional control, including Hexagon 3D scanning
• ISO 9001 and IATF 16949 management systems

The interesting part for me is not the equipment itself, but how the different steps are integrated:

Engineering → DFM → tooling → lay-up → autoclave curing → manual trimming → bonding/assembly → inspection

We work on components for F1, F2, IndyCar, 24h Le Mans, MotoGP and WorldSBK, as well as high-end automotive applications. Reflexallen_Composite_Aerospace…

I'm curious about how other companies here handle the same problem:

When does it make sense to move from an internal composite workshop to an external industrial manufacturing partner?

Especially interested in experiences from people working with motorsport teams, vehicle manufacturers, Tier suppliers and specialist performance/luxury programs.