A patent filed by Lauf outlines a freehub system that combines pawls with flexible leaf springs, potentially offering increased reliability, reduced weight, smoother pedalling performance and other benefits.
A conventional ratchet freehub generally sees two to six (or more) pawls attached to the freehub body.
Separate springs, which sit beneath the pawls, push them outward to engage with a ratchet ring in the hub shell.
The patent from the Icelandic brand – which made its name (fittingly) with its leaf-sprung gravel and mountain bike forks – proposes manufacturing flexible one-piece “pawl members”, which combine the pawl at the head of flexible leaf springs that engage with a typical ratchet ring.
Speaking to BikeRadar, Lauf’s CEO and founder Benedikt Skúlason explains the system’s advantages: “Rather than engaging with a ‘clunk’, the system ‘tightens up’ (or ramps up).
“As engaged pawls [flex]... more pawl members then engage. That, in turn, can provide robust/reliable load sharing between multiple pawl members.
"This results in a more pleasant and energy-efficient engagement and reduces the risk of damaging drivetrain components.”
Skúlason adds that Lauf’s system could provide more robust and secure engagement: “The flexible nature of [the pawls] can eliminate engagement mishaps. If one pawl member misses out on its engagement… another can pick up the slack.”
Skúlason claims the flexible nature of the pawls mean hubs do not need to adhere to such exacting – and often unrealistic – manufacturing tolerances.
“A standard ratchet/pawl hub relies on very high accuracy for simultaneous engagement of opposing pawls.
“When tolerances are slightly off in a standard hub – as they inevitably always are to a degree in real life – there are cases when, for example, only one pawl member engages.
“This causes extreme loads on the pawl member and the hub axle, which can eventually damage the freehub mechanism.”
One proposed implementation (shown in figures 21 and 22) shows versions where the spring element of the pawl members is split into multiple springs. Skúlason says this design would "enable an order-of-magnitude higher flexibility towards bending moments, for a given tension strength, lowering drag friction and enabling more tension."
He explains this increased flexibility would increase load-sharing between pawl members.
Depending on the implementation, combining the spring and pawl into one unit would reduce complexity, potentially offering lower weights and costs.
Skúlason suggests the pawls would likely be manufactured by 3D printing with a suitably strong, flexible and fatigue-resistant material, highlighting titanium as the most likely candidate.
The proposed system differs from chain dampers from OChain and Rimpact or decouplers from Race Face. Although these can improve pedalling smoothness, they are designed primarily to enable the chain to move back and forth, improving suspension performance on mountain bikes.
Lauf’s system is closer to a conventional freehub, with the added benefit of “springiness of the pawl members… which can provide a suspension element in the engagement [of the drivetrain].”
The system could be applied to any bike, with the implementation "tweaked to amplify desirable properties for a given segment", explains Skúlason.
Skúlason says Lauf can’t disclose “exactly where we are in the prototype process”, but the brand “are excited”. Illustrations are only available now with a full patent due to be published soon.
