Fairwheel Bikes' Titus hardtail 29er boasts a trick sequential shifting custom Shimano Dura-Ace Di2 electronic transmission (Richard Hurst)

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In the absence of Shimano's still-anticipated release of an off-road version of their fantastic Dura-Ace Di2 electronic transmission, several companies and retailers have taken it upon themselves to create their own modifications.

Most of the ones we've seen have been very clever, if not downright brilliant. Arizona-based shop Fairwheel Bikes have crafted the best example yet. 

Sure, it's light and it's pretty with lots of anodised aluminium bits, but the key feature is Fairwheel's custom designed electronic 'brain' that turns the 2x10 setup into a trick sequential shifting system using just one shifter.

In terms of user interface it's as simple as could be when set in 'race' mode: simply tap one button for an upshift and the other one for a downshift.  According to Fairwheel's Jason Woznick, the custom brain calculates the gear inches and then shifts the front and/or rear derailleurs as needed to achieve the next logical ratio. 

Duplicate gears are ignored, and Woznick adds that the programming is designed to minimise cross-chaining and front derailleur shifts as well. "As the bike sits, it's completely linear: two shift buttons, one for up and one for down," he said.  "It can go from the 29/32T to the 42/11T, hitting all 13 equally spaced gears with only one front derailleur shift and without cross-chaining."

The single shifter and internal wiring make for an unusually clean looking cockpit

Alternatively, 'trail' mode allows for manual front and rear shifting as usual and full gear access across the entire range. "When in manual mode, the two shifter buttons control just the rear derailleur, shifting it up and down as a normal Di2 system," Woznick told us. "To shift the front derailleur, push both buttons at the same time.

"Since it's a double there's no need to tell it up or down, but just to shift.  [Trail mode] isn't really that practical but it's still something we wanted as a possibility." In fact, project software engineer Jeff Roberson says that, "really anything you can imagine is possible".  

The system is connected to a PC via a standard USB cable and from there, Roberson can load as many modes as he wants and can also program any button combination to swap in between them. The execution is well done, too, with mostly internal wiring, a custom battery pack that resides inside the frame, and the custom brain built right into the inside of an Enve Composites carbon stem. Luckily for Fairwheel, Shimano's latest satellite shifter is already appropriate for the application.

The custom brain is tucked right inside the Enve Composites carbon stem

The rest of the bike is nothing to sneeze at, either, comprising a custom Titus titanium 29er hardtail frame, a Cannondale Lefty fork, Enve Composites tubular rims and fat Dugast tyres, plus a wealth of lightweight goodies from Tune and KCNC. Claimed weight as pictured is just 7.3kg (16lb) and Woznick says it was built to be ridden, not just for show.

"After Interbike, I plan on switching to a set of Enve clinchers for daily riding and using this bike a lot," he said. "I think endurance events are a great place for something like this as you don't have to think about shifting when mental fatigue sets in. The other place we see this as a big step forward is for people who have the use of only one hand."

Potential buyers had better be prepared to write a hefty cheque. According to Woznick, the price for just the bike itself is estimated at between US$12,000-13,000 and the costs surrounding the custom brain are almost innumerable.

The tuned Di2 rear derailleur moves the KMC chain across a SRAM XX cassette

"I can't really answer the price on the brain as it doesn't have a real price," he said. "The fabrication part was the small cost – paying someone to engineer, design and write the software that controls it as well as how to wire it into the system would be the largest part of the brain expense.

"We don't really have any solid plans on making these available because it isn't just plug-and-play. There really is so much customisation that goes into something like this. Everything from figuring out how to wire it together without using the stock plugs from Shimano to setting up chainlines and building custom batteries that fit inside the frame. It's not something that could easily be put into a package and sold."

Fairwheel will have a number of other choice items on display at their Interbike booth this week (though we'll have to wait until then to shoot images first-hand), including a semi-wireless Di2 system, a 2.85kg (6.28lb) road bike and a custom three-speed internally geared fixie with Ashima hydraulic brakes. Vegas, here we come!

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