An angry swarm of bees vs. the sound of Scylence

Here in the Philippines, many cyclists will put a bike on a stand, shift to a hard gear, and hand-pedal the cranks to a high cadence, then suddenly let go…all to listen to, and savor, the sound of a freewheeling freehub. The louder the freehub, the better.

They even have a name for it: “tunog-mayaman,” roughly translating to “it sounds [like a] rich [person].”

The first time I heard this expression, I let out a mild chuckle. Because I’m a curious son of a gun, though, I did a bit of research as to why people say so, and why they prize the sound of a loud freehub.

For the uninitiated, a freehub is two things. Its exterior allows the mounting of cassette sprockets (usually via splines and a lock ring), while its interior is essentially a one-way ratchet mechanism.

A freehub body (left) removed from its hub shell, which contains the ratchet gear teeth (right). Note the pawls on the freehub body. Photo credit: MBR.co.uk.

While there are other variants, the most common freehub internal design sits on the rear axle on bearings, and has a number of spring-loaded fingers, called “pawls,” that will catch on ratchet gear teeth on the inside of the hub shell. When they catch and engage, your pedaling motion at the cranks gets transferred from the chain and sprockets into the hub and rear wheel. When you stop pedaling, however, the pawls will slide and skip over the ratchet gear teeth, allowing you to coast.

This high-frequency skipping of the pawls over the ratchet gear teeth is what we hear as the sound of the freehub. Conventional wisdom states that more expensive freehubs use a number of tricks — either using stronger strings on the pawls, installing more pawls in the freehub, or something else entirely — all in order to improve engagement and drive of the mechanism. The sound is really just a byproduct.

Indeed, many premium hubs do have a noise to them, and this noise is a quality in and of itself. Chris King’s R45 rear hubs, for example, are prized for the “angry swarm of bees” sound they make, but as the video above suggests, they are handily beaten by other competitors.

That hasn’t deterred many locals from asking bike groups or forums about how to make their freehubs sound louder, i.e. how to make them tunog-mayaman. Most of these modifications involve replacing the pawl springs for something with higher spring rate, although this is a questionable practice at best.

Leave it to Shimano to throw a wrench in the works, though…

Photo credit: BikeRumor.

At the end of May 2018, Shimano announced the M9100 generation of XTR, its top-tier mountain bike groupset. While I didn’t really care about the divisive new Micro Spline freehub body superseding the tried-and-true Hyperglide design that has served riders for 30 years, I was very curious about what lay inside the polarizing freehub. Instead of the classic pawl and ratchet system, Shimano used a new drive mechanism they call “Scylence.”

Exploded view of the Scylence hub drive mechanism. Photo credit: Shimano/BikeRumor.

Ridiculous spelling aside, it’s obvious what they were going for with these hubs: silent running. Instead of pawls catching on a ratchet, Scylence transfers drive via angled slots on two sides of the hub that mesh, which pull a pair of ratchet rings (yellow and green above) together. This is somewhat similar to the helical-cut gears meshing in a car’s gearbox, plus a clutch disc mating with an engine flywheel, but implemented in another way. When coasting, springs pull back on the ratchet rings and disengage the angled slots, resulting in zero friction and noise.

As XTR is Shimano’s flagship MTB groupset, the notion that these very expensive hubs are designed to be silent is hilarious in its irony. It flies in the face of the whole “tunog-mayaman” philosophy – and the one major thing that I wish ended up included into future versions of Shimano’s road bike groupsets.

LitePro’s hubs make a moderately noisy freewheeling sound.

Needless to say, I don’t really buy into the whole tunog-mayaman phenomenon. For me, it doesn’t really promise or mean anything other than the fact that your freehubs are loud. Proof? My folding bike Bino, which has gearing that tops out at a 37 km/h cruise in top gear, has a louder freehub than my fast bike Hyro…