Confirmed details of new Dura-Ace: Discs, power meter
The best is getting better. The next generation of Shimano’s top-tier Dura-Ace group, already our favorite on the electronic and mechanical fronts, will include a power meter, road-specific disc brakes and rotors, improved Di2 integration, drag-free hubs, and the same clever shifting firmware debuted on the XTR Di2 mountain bike group.
We reached out to a Shimano representative, who refused to comment. But weeks of research, including conversations with industry insiders briefed on the group (who all requested anonymity), and analysis of published and unpublished spy photos, indicate that the group is an ambitious update that closes a few important holes in the current group. The most obvious of those is a Dura-Ace level disc system, which is both lighter and better tuned to the specific demands of road discs than the current technology, much of which is borrowed from Shimano’s mountain bike division.
New Dura-Ace will still be an 11-speed system and will retain the shiny aesthetics of the current generation (somewhat similar to the old XTR 960 finish). But most of the fine details, from hub internals to front derailleur cable routing, have been changed or updated. The Di2 version has been slimmed down, with smaller motors and batteries, and features firmware borrowed from XTR Di2.
Road-specific disc brakes
The addition of a Dura-Ace level hydraulic disc system is the single greatest change. This is the first hydro group from Shimano that appears to be designed from the ground up for road use. (R785, available now, was launched with a rebranded XT mountain bike caliper.) The rotors are road specific, with a new aluminum carrier that presumably cuts down on weight. The steel braking surface of the rotor has fewer holes, which has been shown to reduce brake pad wear.
Internally, the flat-mount caliper has some sort of internal brace for (we assume) improved stiffness and has more clearance for frame manufacturers. Other internal changes offer slightly more pad clearance, which should reduce rotor rub.
The new crankset, which retains the current four-arm design, includes a power meter with strain gauges on the crank arms and a “brain” mounted on the inside of the crank spider. It is Shimano’s first power meter.
Integrated junction box
Perhaps taking a cue from the Trek Madone’s control center — a port in the down tube that hides the Di2 junction box — Shimano has developed a sleek, integrated junction box that secures into the bike’s frame. That means no more hanging the junction box off the stem, and more options for internal routing. It also means frame builders will have to build frames that can accept this new feature.
But don’t worry if your favorite manufacturer doesn’t offer this nifty new pocket, because it also appears the junction box will fit in a bar end, as well. The box seems to press into the handlebars much like a bar end plug.
Updates to the Dura-Ace Di2 firmware also look imminent. It appears that Shimano will bring the Synchro system debuted on XTR Di2 to the road. Synchro is essentially automatic front shifting, requiring the use of only two shift buttons to shift the entire drivetrain. When the derailleur reaches a certain point (which is customizable) on the rear cassette, the front derailleur shifts, while the rear derailleur shifts in the opposite direction. The idea is a rider gets similar gear jumps with each button push. It’s a system that is made possible by Di2’s incredible front shifting. It’s similar but not identical to Campagnolo’s new auto-shifting options made possible through the My Campy app.
Front derailleur cable routing has been changed for the cable-actuated group, further reducing shift force. The system is apparently much easier to set up now, too.
Radical new hubs
Some of the most exciting advancements are hidden in places you’ll never see. Patent applications for Shimano’s Scylence hub leaked months ago, and now it seems like we’ll see it in action soon. Unlike a typical freehub body that relies on pawls that engage with grooves when the rider pedals, or a star ratchet system that features notched teeth on two rings mounted against each other, Scylence works more like the clutch on your car, but somewhat in reverse, if patent applications are telling the whole tale. An engagement ring is mounted around the axle inboard toward the hub shell, and it’s spring-loaded in such a way that the spring pulls the ring toward the hub shell. A specially designed freehub body with splines essentially pulls that ring toward it, against spring tension, to engage the hub when the rider pedals. When the rider coasts, the engagement ring disengages, creating nearly drag-free coasting.
It wouldn’t be the first pawl-free design to hit the market — Onyx showed off a sprag clutch hub at Sea Otter 2015 — but if history is any indicator, Shimano has taken the drag-free idea and perfected it.