Gearbox bikes remain one of the last unresolved desires of many mountain bikers.
The benefit of a gearbox, as opposed to an exposed rear-derailleur drivetrain, is obvious. Without a derailleur cage hanging off the rear axle, there is no potential rock strike damage, rendering you immobile and with a substantial repair bill.
Mountain bikes with gearboxes also theoretically require much less servicing and consume fewer parts, due to the purity of their encased oil lubrication, as opposed to a chain and rear-wheel cassette, which is more exposed to abrasive mud and dust.
A new patent discovered by BikeRadar suggests that Shimano is in an advanced development trajectory towards a gearbox mountain bike drivetrain system. The Japanese component supplier is a huge influence in the mountain bike industry, which means that its recently discovered patent drawings for a gearbox system is very big news.
With the engineering, design and production resources to finally deliver a gearbox solution that many mountain bike brands could adopt, Shimano’s #0011037 patent application could be the start of a true drivetrain revolution for mountain bikers.
In terms of configuration, the Shimano gearbox patent appears to leverage the brand’s recent experience in developing e-bike motors. The global surge in e-bike popularity has created an incentive for drivetrain manufacturers to think way beyond the traditional drivetrain.
The Shimano patent design sees an encased dual-cassette set-up, driven by the crankset, via a smaller internal contact gear and chain. Each cassette has seven cogs and the drivetrain yields a total gear spread of 13 ratios.
One of the cassettes can slide horizontally, to ensure a perfectly straight chain line, no matter which ratio is engaged. Reducing drag is an enormous issue in gearbox design and to this end, Shimano’s sliding cassette, which will mitigate the drag of an angle tensioned chain line, is a crucial innovation.
Beyond the mechanical properties of this new gearbox design, there is an interesting lubrication solution, too. Shimano makes mention of a special chemical coating applied to the metal contact points in this new drivetrain design, which promises a breakthrough in friction reduction.