The freehub on my new Hunt 40 carbon wheels, see spec below, is much louder than the wheels that came with my bike. I thought I would do some digging around and find out why. The freehub is a HUNT H_Ratchet 36T SGL hubset, which Hunt says:
The HUNT H_Ratchet 36T SGL hubset provides a 10-degree engagement angle with improved durability. It offers increased engagement surface area while using less shell materials relative to our race-proven pawl-based systems.
Ratchet freehubs tend to be noticeably louder than pawl freehubs. And on carbon rims, that sound can be amplified even more. But why is this the case?
The Mechanics Behind Freehub Noise
Ratchet Freehubs
Ratchet systems are designed for efficiency and durability and are often found in high-end hubs like those from DT Swiss. Here’s why they are louder:
- Mechanism: Ratchet systems employ a pair of toothed rings that engage with each other. As you coast, these rings disengage and create a clicking sound as they slip past one another.
- Surface Contact: Ratchet systems’ engagement surfaces are larger and more direct than those in pawl systems. This extensive contact area results in a louder and more pronounced clicking sound.
- Spring Tension: The springs used in ratchet systems are typically stronger to ensure a solid and reliable engagement. This strength also contributes to the louder noise when coasting.
Pawl Freehubs
Pawl systems, common in many standard hubs, operate differently:
- Mechanism: Pawl systems utilize small metal pieces called pawls that engage with notches inside the hub shell. The pawls click over the notches when coasting, producing the characteristic freehub sound.
- Number of Engagement Points: Pawl systems generally have fewer engagement points than ratchet systems. This means that the pawls engage and disengage less frequently and with less force, resulting in a quieter operation.
- Surface Area and Contact: The pawls have a smaller contact area and engage with less force, contributing to a quieter sound than ratchet systems’ more robust engagement.
The Impact of Carbon Rims
- Resonance: Carbon fibre is a stiff and resonant material. It can amplify vibrations and sounds more effectively than aluminium. When the freehub engages, sound waves travel through the spokes and resonate within the carbon rim, making the noise louder.
- Damping: Aluminium rims offer better-damping properties, which means they can absorb some of the sound and vibrations. In contrast, carbon rims reflect and resonate the sound, leading to a more pronounced noise.
In summary, ratchet freehubs are louder than pawl freehubs due to their design, which includes larger engagement surfaces and stronger spring tensions. When combined with carbon rims, which amplify sound due to their resonant properties, the overall noise level can become even more noticeable.
HUNT 40 Carbon Disc Wheelset
Rims
Hooked tubeless-ready tim profile. Full carbon fiber construction with re-enforced spoke holes. 30mm external and 22mm internal width 40mm depth UD finish with matte white contrasting graphics.
Spokes
24 front and 24 rear with a 2-cross lacing pattern. J-bend cold drawn. Made from high grade T302 (18/10) stainless steel wire by Sandvik Sweden Front Triple butted 2.0-1.5-2.0 (then 2.2 at the head for the patented Pillar Spoke Re-enforcement). Rear Triple butted 2.0-1.6-2.0 (then 2.2 at the head for the patented Pillar Spoke Re-enforcement). Patented Pillar Spoke Re-enforcement, butted again just before the spoke head providing more durability in high stress area. Black stainless treatment.
Nipples
Alloy square body for external adjustment and square head for easy internal adjustment/tensioning. 16mm length with washer for a strong connection to the spoke added durability. 14 gauge. Black anodized finish.
Front Hub
Forged and CNC’d 6061-T6 heat treated aluminum alloy body. 7075-T6 aluminium alloy axles. Polished anodized black finish with laser graphics. Center-lock disc mount. If you require a 6 bolt adaptor you can purchase separately here
Rear Hub
HUNT H_Ratchet 36T SGL H_CERAMIK freehub body reinforcement coating provides excellent durability and protects against cassette sprocket damage to the freehub often seen on standard alloy freehub bodies. Ships with Dumonde Tech Pro X freehub grease applied for long service life and contamination resistance. Single 36T Ratchet Ring equals 10° engagement. Hunt Race Season Disc straight-pull super-light alloy. Forged and CNC’d 6061-T6 heat treated aluminium alloy body. 7075-T6 aluminium alloy axles. Center-lock disc mount. If you require a 6 bolt adaptor you can purchase separately here Polished anodized black finish with laser graphics.
Bearings
Super smooth precision bearings with waterproof grease specially selected for even the worst weather. Sealed cartridge replaceable units. Dual full-contact seals.
Tyres Info
HUNT recommends a 25-35mm tyre for best performance, tyre widths between 25mm and 50mm are also safe to use. Note: best performance is usually gained by using tyre pressures lower than the maximum, you can see our blog post about this, read here. Tubeless-ready for lower weight and rolling resistance. You must not exceed the maximum tyre pressure limits set out in the table below or the maximum limit set by your tyre manufacturer if this is lower.
Axle Sizes
Front: 12x100mm Thru-Axle, 15x100mm Thru-Axle, 9x100mm Thru-Axle, Quick Release 9x100mm Rear: 12x142mm Thru-Axle, 12x135mm Thru-Axle, 10x135mm Thru-Axle, Quick Release 9x135mm