While the original continues to impress, rumors have leaked of an 11-speed, disc-equipped Shimano Di2 group (Matt Pacocha/BikeRadar)

Rumors began to circulate after this autumn's Eurobike and Interbike trade shows that Shimano's next generation Dura-Ace Di2 group – set for release in the 2013 model year – will feature not only a jump to 11 sprockets out back but also hydraulic master cylinders integrated into the STI lever bodies.

As it turns out, that's only partially true, at least according to BikeRadar's exclusive industry sources. We've been told that the next-generation Dura-Ace group will indeed make a jump to 11-speed cassettes – first on the mechanical version, followed by the electronic Di2 flagship. And Shimano are apparently readying a lightweight disc brake caliper for road and cyclo-cross use.

However, our sources tell us the initial brakes will be mechanical, not hydraulic, and the MY2013 levers won't be hydraulic-ready. Buyers looking to be on the cutting edge may be a bit disappointed with that news but a lightweight cable-operated caliper would allow riders to use their current STI Dual Control levers while offering more power than a standard side-pull or cantilever brake. Mechanical discs are also easily user serviceable.

Naturally, all of this information can be considered conjecture as Shimano provide us with their standard response to these sorts of inquiries. "We always have products in development," US road media relations representative Eric Doyne told BikeRadar, "but we don't have anything to say at this time." That being said, we consider our sources to be highly reliable.

Regardless, next summer's product launches, from both Shimano and affected bicycle companies, should be very interesting. Buyers shouldn't go rushing to place orders any time soon, though – according to our sources, projected delivery is slated for very late in 2012.

Devil is in the detail

Dura-Ace 2013's 11 sprockets will apparently be packed onto a new freehub body that's wider than current 10-speed bodies; it's unclear at this point if the proprietary body width and spline pattern will at least share cog spacing with Campagnolo. It's also unclear whether that extra gear will require wider rear hub spacing though that seems unlikely given that frame manufacturers won't have had enough time to update tooling.  We can only hope that Shimano will stick to 130mm and also emulate Campagnolo spacing, though, as that would have huge implications for wheel choice.

Indexing control will supposedly be moved to a front-derailleur-mounted microprocessor, turning the levers into 'dumb' switches that merely send binary signals – just like on the recently introduced Ultegra Di2. The new Dura-Ace Di2's updated wiring harnesses will be fully compatible, too, meaning that users will be able to mix and match as desired. 

Since the indexing is housed outside the levers, that opens up the possibility of an 11-speed setup matching Ultegra levers to Dura-Ace derailleurs, though the new harness means old Di2 bits won't connect to new ones. In addition, our sources tell us that the long-awaited race day battery is coming, with half the capacity of the current unit but at a quarter of the weight.

Shimano may also be finally moving on from their long-running 24mm-diameter Hollowtech II bottom bracket spindle design. In fact, we've been told that they may actually be adopting FSA's new BB386Evo standard, which would certainly help lop off some weight as Shimano would then be able to move to a larger-diameter, relatively thin-walled aluminum spindle.

That move would make sense from a developer's standpoint, too. Shimano's own PF86 bottom bracket standard uses widely set press-fit cups and industry supporters would essentially only have to switch to a larger-diameter shell to keep things compatible (and backwards-compatible) rather than have to design an entirely new frame.

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