Tech Mailbag #3: Carbon fiber can be almost indestructible, so why isn’t it?

Carbon fiber bicycle products could be far more durable than they are currently, but only if we're all willing to accept some compromises.

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Welcome to the CyclingTips Mailbag column, where you send us your tech questions, and our team of nerds gives you answers. Got a question about wheel and tire standards? Want to know how to diagnose that weird shifting issue? Wondering where that darn ticking sound is coming from?! Send your questions our way at to be featured in an upcoming CT Mailbag column.

In this week’s edition, James Huang discusses quick-disconnect hose couplings for hydraulic disc brakes, the pros and cons of various frame finishes and surface treatments, and whether carbon fiber can ever be considered a “forever” frame material. 

Hi CT,

I’d love to hear from an expert on different finish options. Cerakote, powdercoating, PVD, different paint options. It’s something I think about a lot and would love to know more about.

 — James Wynn

Hi James,

I’m far from any sort of expert on this subject (nor is anyone else on staff), so I reached out to someone who knows a lot more about it: Drew Guldalian of Engin Cycles. Drew has firsthand experience with just about every type of surface finish under the sun, so I asked him to provide some insight. Here’s what he had to say:

“Cerakote is an interesting hybrid of a powder coat and a paint job. It is a single coating much like a powder coating. It also has a mechanical bond much like a primer used in a wet paint job. Powder coating does not have a mechanical attachment. It is essentially a membrane that is shrink wrapped onto the frame. The lack of mechanical bond is what everyone says is the issue with being an outdoor product liability. It can still rust underneath. PVD [plasma vapor deposition] is an interesting coating, much like gun blue and other chemical coatings. They seem to have a place, but again, on an outdoor item that gets a good amount of wear and use, it is just not viable. Cerakote to me has a place because it is cheaper than wet paint and stronger than powder coating. Detail and art style finishes still work best with wet paint. The weak links with Cerakote are bright colors, anything with white and glossy finish. They exist but are not as good as a flat finish in a more earth tone color, or even better, black. Red is another color that it seems to not do well: [it’s] more of an orange than a proper fire engine red.

“Anodizing aluminum and titanium has a unique look when used as a single-color complete covering. The biggest challenge is the welds and how they have a different composition compared to the tube it is attaching. Also, the solid parts like dropouts and cable stops often are different. This difference in material often causes the color to have variation. Using anodizing for titanium finishes is essentially an accent. It has absolutely zero effect on longevity of the product.  

“Aluminum, unlike what people think, does corrode. 7XXX aluminum definitely needs a finish. It can be clear anodizing, paint, or powder, but it needs to be sealed from oxygen or it will oxidize and corrode. 6XXX aluminum is much more forgiving to corrosion, but still will dull over time and is better with a finish that is sealing it from the elements. Since 6XXX-series frames need to be heat treated, that often leaves a gold-like coloring on the frame that is protecting it from the elements. It is not very strong and will scratch right off.”

 — James

Hi everyone,

Why aren’t hydraulic quick disconnects more common on bikes with hydraulic brakes?  Seems like they would be helpful in making those sweet looking integrated cockpits more manageable or traveling with a tri bike easier.

 — Andrew McCormick

Hi Andrew,

Great question! Formula’s SpeedLock has been around for several years now, and offers exactly the functionality you’re asking about. It’s a quick-release inline hydraulic coupling that lets you easily split and reconnect disc-brake hoses, supposedly without the need to rebleed the system. They can be found at various online retailers, and while I’ve never used one myself, plenty of others have, seemingly without any major issues aside from the overall bulkiness of the coupling, which will likely prevent their use in integrated cockpits where there’s very limited room.

SRAM has a similar technology that it calls Connectamajig. Their design is a thread-together system instead of a true quick-release, though, and the company is more conservative when it comes to how many times the hose can be split without doing a re-bleed. It’s also unfortunately only available pre-built into various OEM hydraulic brake systems and isn’t offered aftermarket.

Here’s what SRAM road PR communications specialist Brook Fowler had to say:

“Most of those sweet looking integrated cockpits don’t leave enough space for enough hose connector, or are not able to fit a connection fitting through their confined spaces. For a quick connect/disconnect on a hydraulic line, we have offered the Inline Connectamajig for some time, which is a quick connector for things like brake lines on road bikes, and Reverbs with hoses through a frame to the remote actuator. The Inline Connectamajig is only available as a limited OEM option for hydraulic lines. The goal was to be able to build a bike with fluid systems pre-bled, ready to connect and go. There is a limited amount of re-connects (about 5) with this system [before having to bleed the system].

“The Stealthamajig system is a similar concept (essentially a fitting so that you can connect or disconnect the hose and not lose fluid from the reservoir in a dump) BUT not the same system. The Stealthamajig is a hose barb and olive system and connects at the lever. It is not an inline connector, which is what your reader is looking for. We do not currently offer an inline connector/coupler for hydraulic lines that would allow you to disconnect and reconnect down system (after passing hoses though the bar and stem) repeatedly. The Formula Speedlock would be the way to go here.”

 — James

Hi CT,

I know people usually think of steel or titanium being forever bikes. Do you think advances in quality and manufacturing processes have made carbon fiber a viable forever bike material?

 — Brennan Chopin

Hi Brennan,

I strongly believe the idea that carbon fiber is fragile is partially a matter of perception, but also a consequence of how composite products have been positioned by the bike industry.

As a material, carbon fiber is far stronger and stiffer than any of the metals commonly used in cycling (steel, titanium, aluminum, and magnesium). And because it’s an anisotropic composite, its mechanical properties can be tuned to be direction-specific, which provides all sorts of design flexibility to engineers. 

In short, it’s truly amazing stuff.

Those incredible stiffness-to-weight and strength-to-weight properties make it a prime candidate for high-performance structures, which is why it’s the number one material for so many high-end bicycle products these days. And yes, continual advancements in how companies process the material during the manufacturing process, along with steady gains in knowledge about how to design carbon fiber products, have dramatically lessened the common modes of failure that plagued older composite products.

However, those properties also tempt engineers into pushing the material as far as possible. More often than not, the goal is to make carbon fiber items perpetually lighter and stiffer while maintaining acceptable levels of durability. But if the goal was instead to provide weights and stiffnesses in carbon fiber products that were similar to what you can get from metals, the strength and durability would be off the charts. 

The bike industry could absolutely produce carbon fiber frames and components that would essentially last forever. However, human beings are notoriously poor at looking at things from a very long-term perspective; even when something is purposely billed as being exceptionally durable, it will usually lose out to something with more immediate appeal. 

That said, there are some companies making carbon fiber frames that are specifically billed as being more durable, especially ones that are made using thermoplastic resin matrix materials instead of the more common thermoset stuff. Most of these are in the mountain bike space (such as frames from Guerilla Gravity, and wheels from Revel, Chris King, Evil, and a few others) where durability and impact toughness are more at the forefront of buyer’s minds. But my guess is we’ll start seeing that technology trickle into the drop-bar space soon, too.

For further insight, I also contacted Australian composites expert Raoul Luescher of Luescher Teknik, and here’s what he had to say:

“I wouldn’t say that steel or titanium are forever bikes: steel rusts and titanium fatigues, particularly at the welds. Besides, the industry standards change so often you can’t get parts for a forever bike, but that is a whole other topic in itself. From a materials perspective, there is no reason that a carbon/epoxy part should not last a very long time if done right. This is one of the reasons that commercial aircraft use it as there is a reduction in maintenance costs due to low corrosion and fatigue risk. The aircraft parts I used to work on were guaranteed for 25 years and many of those parts built in the early 90s are still flying.

“However, the parts need to be made well and the epoxy used needs to be appropriate for the use and also cured correctly. Often we see failures where flaws were present and occasionally where there has been degradation of the epoxy. The majority of carbon frames in the market are produced with lower cost as the driver, not longevity, as many are a fashion item so they are expected to be replaced frequently, which comes back to the forever bike question. I myself have carbon frames that I built in the 90s, which I still use and are structurally good, though tire clearance is tight and 1″ headset bearings are scarce.”

 — James

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