Words: Seb Stott & Matt Beer
We always keep an eye out for patents
that might reveal what the bike industry has in store for the years ahead, but in this case, Jessie-May Morgan over at Bikerumor
got the scoop on a very juicy patent from Fox.The patent itself
describes two separate inventions both aimed at improving suspension sensitivity. One is a freehub where the pawls can automatically and electronically disengage, effectively giving a neutral or "coasting" gear for the benefit of suspension sensitivity, before automatically reengaging when it's time to pedal. The second is a derailleur where the clutch can automatically switch off during especially rapid suspension compression events (such as hitting a large bump), thereby allowing the suspension to compress more freely without the clutch engaged. The clutch would automatically switch back on the rest of the time to prevent chain derailment.
The specifics of how they would achieve this are quite open-ended as patents usually are. The Theory
As shown in the diagram below, as the suspension compresses, the rear axle gets further from the bottom bracket and the upper span of chain between the cassette and the chainring gets longer. This is known as chain growth. To allow this chain growth, the derailleur cage has to extend to provide chain slack and the cassette has to rotate clockwise in order to allow some of that slack to move to the upper chain span.
Occasionally, if the rear wheel is locked up or spinning very
slowly (picture hucking off a railway platform at a walking pace) then the cassette/freehub catches up with the wheel rotation speed and so cannot rotate fast enough to allow the chain enough slack for the suspension to compress freely. When this happens, the cranks may rotate backward as the taught chain pulls on the top of the chainring. That rotation of the cranks is called pedal kickback.
Matt Beer's take:
Canyon's freehub disengagement mechanism was controlled by a bar-mounted remote and was soon abandoned.
While the incorporation of sensors to detect forces through the suspension makes Fox’s patent highly elaborate, the idea remains the same as the mechanical systems we've seen; isolate the suspension action from the chain forces.
The electronically controlled derailleur clutch and hub pawls work in unison with sensors on the wheel axles and crank spindle to calculate when to engage and disengage. Opposite to most freehub designs, the Race Face Vault hub, and the one in the drawing, features pawls that are installed on the hub shell, as opposed to most designs that place them on the freehub body. That leaves plenty of room inside the two-piece shell to house servo motors with the ability to retract the pawls away from the teeth on the freehub body, thereby creating a neutral transmission. Similarly, a servo would simultaneously release the tension on the derailleur clutch.
How long has Fox been working on this? That’s hard to say, but the large volume, two-piece Race Face Vault hub shell that debuted in 2016 could offer a hint. Last season, we saw Fox use similar sensors on Jesse Melamed's Rocky Mountain Altitude
during testing of the Float RAD shock that measured the force acting on the suspension and calculated the pitch of the bike. This patent could be Fox and Race Face’s maneuver to battle SRAM’s electronic component front.
We've reach out to Fox for comment and will update this article as any further information comes in.