It really does look like Shimano – the biggest drivetrain manufacturer on the planet – is going produce a gearbox system for mountain bikes.

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Kudos to the BikeRadar patent spies for spotting this one.

For those of you who haven’t the time or inclination to wade through the info or the patent itself, we’ve tried to boil it down to the essential need-to-know info. Here goes…

• It’s similar to the old Honda DH bike; cassettes, chain loops and a chain tensioner inside a box in the bike frame. There are intriguing rumours that Shimano acquired gearbox patents from Honda back in the noughties.
• It uses two cassettes inside a sealed box with chain loop running between them. One cassette is fixed in position laterally, the other moves laterally (side-to-side) along an axle. This means the larger loop of chain that runs to the rear wheel has consistent, perfect chainline for minimal drag and wear.
• It needs frames designed specifically for it. It is not retro-fittable.

• It looks like it uses the same fitments as Shimano STEPS e-bike motor. Why? We don’t yet know. Suffice to say, how this gearbox fits in the bigger e-bike picture is one of the more intriguing aspects here.
• It can be removed from the bike for repair and/or replacement.
• It will weigh more than a trad derailleur system but it will be significantly lighter than rival gearboxes (Pinion, Effigear, Rohloff etc).
• It has a 470% gear range, which is actually not as broad as most modern 1x systems that offer 500% or so.
• It offers 13 speeds.
• It appears as though an electronic servo motor will do the actual shifting inside the gearbox, with commands coming from a handlebar mounted ‘shifter’ (which probably won’t be a Gripshift style for this gearbox – hurray!)
• The lubricants and coatings of the cassettes and chain appears to be A Big Thing and almost worthy of a patent itself. Again, reducing drag is the name of the game here.
• The sealed part of the system will also contain some lubricant ‘storage’. The internal looped chain loop will also have some sort of way of storing (or at least better retaining) lubricant inside its rollers.

• The geabox’s size and location on the bike will significantly limit what bike designers can do with suspension layouts; this gearbox signifies back-to-the-drawing-board for most bike designs.
• Shimano are going to produce this gearbox. This patent is so in-depth and so specific (relative to typical patentspeak!) that it’s unlikely to be ‘vapourware’. This gearbox will see the light of day.

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What are the advantages of a gearbox?

More bullet points? Yep, more bullet points.

• Less susceptible to damage from rocks, roots, crashes etc compared to dangling derailleurs.
• Ability to change gear whilst freewheeling.
• Much less weight on the rear wheel; rear suspension performs massively better.
• Lack of varying forces coming from the drivetrain affecting how the suspension behaves; suspension can be designed to behave consistently no matter what gear is selected.

What are the disadvantages of a gearbox?

• Heavier than a derailleur system (but the weight is in a much better place than a trad derailleur and 50T cassette layout).
• Expensive.
• Requires a bike frame being designed specifically, and solely, for that gearbox.
• Can’t easily change gear whilst pedaling. This Shimano gearbox very probably won’t suffer from this.
• Gripshift-style twist-shifters are required for push/pull cable actuation of gear changing. This Shimano design will probably use a regular Rapidfire-style trigger shifter.
• Significantly increased system drag compared to a trad derailleur drivetrain.

After falling behind SRAM in recent times (and their Eagle 1x pioneering) it seems Shimano may have had their eye on the bigger picture after all.

Or, possibly more likely, having seen that they’ve arguably already lost the battle on modern mountain bike derailleur drivetrains (especially with OEM bikes), Shimano have decided to move the goalposts completely.

All in all, really exciting stuff. Watch this space!