Back at the Berlin Bike Show we got a glimpse of the unique two-speed Doppio planetary gear bottom bracket/crank combo setup from Kappstein. Now with their collaboration with the Barcelona titanium builders at Nua, we get to see it built into a new high-end urban commuter with a clean and simple drivetrain. Kappstein approached Nua to craft a bike to showcase the new system, and what resulted was this quick flat bar Nua Doppio with a wide gearing range able to get up hills or jump from a start, while delivering speed for cruising city streets…
At the heart of the Nua Doppio, is the Spanish company’s $1500 Ti-Core frame. Built with sliding Paragon drop-outs, disc brakes, and a host of braze-ons for racks and fenders and even a belt-drive split seatstay, the bike is the epitome of flexibility. With 700c wheels and pretty conventional relaxed ~72°/73° geometry with 70mm of BB drop, the Ti-Core is most often built up as a multi-purpose, mixed-surface road and trail riding bike.
The Nua Doppio sticks with those standards and didn’t even stray from the standard internal routing with the idea to maintain future flexibility. That said, if you are set on a particular drivetrain, features, or geometry, Nua also offers the bike in full custom.
Nua calls the Ti-Core their “Swiss Army Knife” bike. It includes a new full carbon, tapered steerer fork, and can clear up to 44mm tires front and rear with QR dropouts. Like all of their frames, it is welded from 3/2.5 titanium.
Starting from the Ti-Core, Nua built the bike up with a red Gates CenterTrack belt-drive system to bring the focus to the unique drivetrain solution, that from first glance looks like a single speed. The entire drivetrain gets highlighted in red, even down to the minimalist shifter’s gear cable so it stands out even more.
Kappstein’s Doppio bottom bracket drive system is a fairly unique gear box alternative. It uses 6 outer rotating planet gears, all contained in what amounts to a relatively normal looking oversized bottom bracket, just adding 10mm to the overall width. Even though everything is quite compact, by using 6 planets vs. the 3 or 4 in most planetary gear boxes, the Doppio claims extended durability. It also threads in to either a standard 68 or 73mm shell, so can be retrofitted to a huge number of frames already out on the road. The Doppio has a wide 1:1.57 gear ratio, for good versatility, and a claimed weight of 735g for BB and a 4x104mm spider or 695g for a 5x65mm spider.
Since the gearing step is inside the bottom bracket, the chainring and spider are attached to the BB and not the crank arms. So in the 1:1 ratio, crank arms and spider spin at the same speed, but at 1:1.57 they spin independently. That means that both right and left crank arms attach to the bottom bracket spindle directly (and unaffected by the spider.) This current urban-use version uses a square taper JIS interface, while Kappstein is working on an ISIS axle version for off-road and cyclocross application. Kappstein does supply their own crank arms, but presumably you could use other square taper arms, assuming you get a right/driveside arm without a spider or designed for tandem use. Pricing isn’t yet set for the Doppio, but we’ll keep you updated when we know more.
Hidden behind the spider and chainring on the bottom bracket shell is the shifting mechanism on this Doppio CX version (as seen here on a different aluminum frame, or the ti Nua elsewhere.) It is controlled either by Kappstein’s 2-position flat bar shifter, or apparently any current Shimano double front shifter. Kappstein also offers a Doppio BX version, with a second gear changing method. On the BX there are no shifters, just back pedal to change to the other gear, and start again pedaling forward.
This complete Nua Doppio weighs in at approximately 9.5kg/21lb. Built up with Crank Brothers Cobalt 29er wheels and wide 35mm Schwalbe Kojak tires, the ti frame lends a smooth and sure-footed ride even on the worst city roads.
The total Nua Doppio build spec is rounded out with Shimano SLX hydraulic disc brakes, a Thomson X2 stem and Elite seatpost, Ergon GS1 grips and SMC4 saddle, a Crane Creek 40er headset, Exustar platform pedals, and Nua’s own Ti-Bar flat titanium handlebar.
The resulting bike sums up as a light and sporty ride to get around town, with the simple lines and durability of a singlespeed, and the rideability of a geared bike.