Is Carbon Fibre Viable for Disc Brake Rotors? Samuel Tests.
Carbon fibre disc rotors raise eyebrows. The material's reputation for poor heat dissipation is well-earned in the rim-brake world, so it's a fair question to ask whether it belongs near a braking surface. Samuel put the TC-160 through third-party certification testing to answer that with data.
The Carbon Rim Brake Argument, and Why It Doesn't Apply with Disc Rotors
Image 1: Source: dandyhorse.cc, image of a failed carbon rim brake track.
The criticism goes like this: carbon fibre is a poor thermal conductor, and thus, under sustained braking, the carbon rims fail to dissipate heat, increasing rim temperature and potentially leading to rim failure or even tyre blowouts.
Carbon fibre composites consist of 2 materials: Carbon fibre filament and the epoxy resin to hold it all together.
The heat resistance of the carbon fibre filaments themselves is usually not the issue, but rather, the epoxy resin, specifically its glass transition temperature (Tg).
When resin reaches Tg, it softens, and the structure loses integrity.
Many rim manufacturers use high-Tg resins rated to 200-230°C on paper, but skip the critical post-cure stage during production. Without proper post-curing (typically 90-120 minutes at elevated temperature), the resin never achieves its rated Tg, and failures can occur at temperatures as low as 100°C.
Post-curing conflicts with production throughput. It is time-consuming, limits daily output, and adds cost.
Many mainland Chinese rim brands advertise high output and low prices. In many cases, the reason is simply that the post-curing stage is skipped entirely. Without it, you cannot produce a rim with high-temperature resistance. This is another reason the industry shifted from rim brakes to disc brakes, as the quest for aerodynamically optimised wheelsets means compromising on braking safety.
Image 2: Aero Samuel Rotor with carbon fins.
However, with disc brakes, the heat load on a carbon structure changes entirely. The braking surface is a separate material, typically stainless steel or steel+aluminium+steel, such as done by Shimano. The carbon in the wheels is no longer in the thermal loop.
So now, the question is: how do carbon fibre finned rotors perform under thermal load?
But first, let's explore how the TC-160 carbon fibre finned rotor differs.
How is the TC-160 Different?
The TC-160 uses aerospace-grade resin, complete with post-curing, allowing the carbon fins to maintain structural integrity for up to 350°C.
In comparison, aluminium alloys only have a safe operating range of around 110-120°C.
Combined with mid-to-high modulus carbon fibre layups, the rotor is structurally stiffer than an aluminium equivalent, reducing the risk of rotor warp under heat, causing brake rub.
The post-cure process runs for 8-9 hours per batch. Parts cool naturally inside the oven to avoid internal stresses from rapid temperature change, which limits output to one oven cycle per day and only two to three cycles per week.
You can see why many companies are tempted to skip the post-curing process to keep up with demand. Samuel, however, does not take shortcuts and chooses to do things the proper way, at the expense of their production capacity.
Another point which many people are unfamiliar with is that carbon fibre has a higher natural vibration frequency compared to metal. This means the TC-160 is inherently less prone to brake squeal caused by friction during braking, than regular rotors with aluminium fins.
How Does The TC-160 Compare With Shimano?
Samuel did tests with thermal imaging cameras. The colours displayed are relative temperatures, not absolute temperatures.
For absolute temperatures, the parameters must be adjusted to correspond to the emissivity of each material in order to obtain the true temperature at each location. Hence, the current colour blocks are only for visual identification purposes.
Two-piece rotors with aluminium fin designs (Shimano Dura-Ace as reference) conduct heat well, drawing it away from the stainless steel braking track efficiently.
Image 3: Thermal imaging of the Dura-Ace rotors
Image 3 indeed shows strong thermal conductivity. Heat is drawn from the brake track to the aluminium fins, as shown by the red highlights.
Image 4: Thermal imaging of TC-160 rotors.
The TC-160's carbon fins indeed have less thermal conductivity compared to the Dura-Ace rotor, however:
- Stainless steel rivets at the junction between the carbon fins and the braking track act as a thermal barrier, limiting heat transfer into the carbon structure.
- The carbon composite itself has low thermal conductivity and high heat resistance.
In short, aluminium fins have good thermal conductivity but are less stiff compared to carbon fibre.
The TC-160 does not dissipate heat as efficiently, but the structural design is built around high heat resistance rather than heat conduction, reducing the risk of rotor warping by maintaining excellent stiffness through the fins.
How Does the Carbon Fins Perform Under Thermal Load?
Image 5: Temperature data collected after a 15% steep slope and heavy braking.
Image 6: Temperature data collected 10 seconds after 15% slope.
Image 5 indicates high temperatures at the stainless steel brake track, while the surrounding areas still remain cool, as shown in the cool blue/light green zone after heavy braking down a 15% incline.
Image 6 shows that the temperature of the stainless steel brake track gradually decreases. Meanwhile, the heat at the stainless steel ribs slowly transfers to the rivet points and diffuses to the top of the carbon fibre fins.
This indicates that the high heat of the stainless steel friction plate gradually spreads through the ribs to the rivet point. Therefore, a greenish warm patch can be seen around the rivet point.
Although the resin is a heat storage medium, the axial thermal conductivity (k)-value of the carbon fibre is still surprisingly high, so colour patches are still observed where heat is pulled away by the carbon fibre.
Third-Party Validation: CHC Testing Report
Samuel submitted the TC-160 for independent testing through CHC (Cycling and Health Tech Industry R&D Center), a Taiwanese testing body with TAF (Taiwan Accreditation Foundation) accreditation. TAF accreditation means results carry international recognition.
The CHC report confirmed the TC-160 meets thermal performance benchmarks for disc brake rotors.
In real-world testing on the test machine, the stainless steel braking surface exceeded 600°C, while the carbon fin section measured just over 100°C under the same conditions, well below its 350°C limit.
In reality, road bikes cannot generate disc brake friction temperatures exceeding 600°C, validating the robustness of these rotors.
The Aero Variant
The TC-160/140 Aero version uses a modified fin profile to minimise axial tangential airflow disturbance. The trade-off is slightly increased crosswind sensitivity versus the standard TC-160. It suits dedicated aero road bikes and triathlon setups where that trade-off makes sense.
Summary
Carbon disc rotors are not carbon rim brakes. Carbon disc rotors are not susceptible to the failures of carbon rim brakes due to the difference in engineering.
Proper post-curing of carbon fibre composites is essential and adds to the robustness of these rotors, such that under real-world conditions, failure of the TC-160 rotor due to softened epoxy is just not possible, allowing it to pass CHC certification, accredited with the Taiwan Accreditation Foundation.