The new Foss Zero Drag Silent Hub debuted at Taipei Cycle Show by displaying a bike that could spin the rear wheel freely in both directions with no noise…and without the crankset moving at all. Even when rotating the wheel in reverse, the cranks stayed still, which indicated something was different about these hubs. The trick was making the ratcheting mechanism inside disengage during coasting. Here’s how they did it…
When coasting (or any time there’s no pressure being applied to the drivetrain), the freehub body’s ratchet ring (silver) retracts away from the ratchet ring inside the hub shell. When retracted, it’s resting on a toothed ring (bronze).
Once you start pedaling, the angle of the teeth on the bronze ring use the forward rotation of the freehub body to push the ratchet ring away, putting it into contact with the hub shell’s ratchet ring. Their teeth then hold together under the pressure from the driving force, thereby spinning the hub and wheel to make you go forward. Here’s the closeup:
It’s a clever system that’s very simple, and it works slightly differently than Shimano’s silent hub design but with a similar end result. At 237g for the rear hub, it’s lighter than similarly-quiet Sprag clutch design, but doesn’t have the instant engagement. In fact, it’s close to 10° because it takes some rotation to bring the ratchet rings into contact.
Wanna see it in action? Check the video on the Bikerumor Instagram page!
Currently, it’s not listed on their website (but there is an interesting explosion-proof inner tube on there). They say they are mainly going after OEM sales, and that a disc brake version will follow early next year.